LDP Configuration Commands

LDP Configuration Commands

Generic Commands

ldp
Syntax [no] ldp

Context config>router

Default This command creates the context to configure an LDP parameters. LDP is not enabled by default and
must be explicitly enabled (no shutdown).

To suspend the LDP protocol, use the shutdown command. Configuration parameters are not
affected.

The no form of the command deletes the LDP protocol instance, removing all associated
configuration parameters. The LDP instance must first be disabled with the shutdown command
before being deleted.

Default none (LDP must be explicitly enabled)

ldp-shortcut
Syntax [no] ldp-shortcut

Context config>router

Description This command enables the resolution of IGP routes using LDP LSP across all network interfaces
participating in the IS-IS and OSPF routing protocol in the system.

When LDP shortcut is enabled, LDP populates the routing table with next-hop entries corresponding
to all prefixes for which it activated an LDP FEC. For a given prefix, two route entries are populated
in the system routing table. One corresponds to the LDP shortcut next-hop and has an owner of LDP.
The other one is the regular IP next-hop. The LDP shortcut next-hop always has preference over the
regular IP next-hop for forwarding user packets and specified control packets over a given outgoing
interface to the route next-hop.

All user and specified control packets for which the longest prefix match in RTM yields the FEC
prefix will be forwarded over the LDP LSP.

When an IPv4 packet is received on an ingress network interface, a subscriber IES interface, or a
regular IES interface, the lookup of the packet by the ingress forwarding engine will result in the
packet being sent labeled with the label stack corresponding to the NHLFE of the LDP LSP when the
preferred RTM entry corresponds to an LDP shortcut.

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 If the preferred RTM entry corresponds to an IP next-hop, the IPv4 packet is forwarded without a
label.

When ECMP is enabled and multiple equal-cost next-hops exit for the IGP route, the ingress
forwarding engine will spray the packets for this route based on hashing routine currently supported
for IPv4 packets. When the preferred RTM entry corresponds to an LDP shortcut route, spraying will
be performed across the multiple next-hops for the LDP FEC. The FEC next-hops can either be direct
link LDP neighbors or T-LDP neighbors reachable over RSVP LSPs in the case of LDP-over-RSVP
but not both.

When the preferred RTM entry corresponds to a regular IP route, spraying will be performed across
regular IP next-hops for the prefix.

The no form of this command disables the resolution of IGP routes using LDP shortcuts.

Default no ldp-shortcut

shutdown
Syntax [no] shutdown

Context config>router>ldp
config>router>ldp>if-params>interface
config>router>ldp>if-params>interface>ipv4
config>router>ldp>if-params>interface>ipv6
config>router>ldp>targ-session>peer
config>router>ldp>targeted-session>peer-template
config>router>ldp>egr-stats>fec-prefix
config>router>ldp>aggregate-prefix-match

Description This command administratively disables an entity. When disabled, an entity does not change, reset, or
remove any configuration settings or statistics.

The operational state of the entity is disabled as well as the operational state of any entities contained
within. Many objects must be shut down before they may be deleted. For an LDP interface, the
shutdown command exists under the main interface context and under each of the interface IPv4 and
IPv6 contexts.

• shutdown under the interface context brings down both IPv4 and IPv6 Hello
adjacencies and stops Hello transmission in both contexts.
• shutdown under the interface IPv4 or IPv6 contexts brings down the Hello
adjacency and stops Hello transmission in that context only.

The user can also delete the entire IPv4 or IPv6 context under the interface with the no ipv4 or no
ipv6 command which in addition to bringing down the Hello adjacency will delete the configuration

The no form of this command administratively enables an entity.

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Unlike other commands and parameters where the default state is not indicated in the configuration
file, the shutdown and no shutdown states are always indicated in system generated configuration
files.

Default no shutdown

aggregate-prefix-match
Syntax [no] aggregate-prefix-match

Context config>router>ldp

Description The command enables the use by LDP of the aggregate prefix match procedures.

When this option is enabled, LDP performs the following procedures for all prefixes. When an LSR
receives a FEC-label binding from an LDP neighbor for a given specific FEC1 element, it will install
the binding in the LDP FIB if:

• It is able to perform a successful longest IP match of the FEC prefix with an entry in the
routing table, and
• The advertising LDP neighbor is the next-hop to reach the FEC prefix.

When such a FEC-label binding has been installed in the LDP FIB, then LDP programs an NHLFE
entry in the egress data path to forward packets to FEC1. It also advertises a new FEC-label binding
for FEC1 to all its LDP neighbors.

When a new prefix appears in the routing table, LDP inspects the LDP FIB to determine if this prefix
is a better match (a more specific match) for any of the installed FEC elements. For any FEC for
which this is true, LDP may have to update the NHLFE entry for this FEC.

When a prefix is removed from the routing table, LDP inspects the LDP FIB for all FEC elements
which matched this prefix to determine if another match exists in the routing table. If so, it updates the
NHLFE entry accordingly. If not, it sends a label withdraw message to its LDP neighbors to remove
the binding.

When the next hop for a routing prefix changes, LDP updates the LDP FIB entry for the FEC
elements which matched this prefix. It also updates the NHLFE entry for these FEC elements
accordingly.

The no form of this command disables the use by LDP of the aggregate prefix procedures and deletes
the configuration. LDP resumes performing exact prefix match for FEC elements.

Default no aggregate-prefix-match

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prefix-exclude
Syntax prefix-exclude policy-name [policy-name...(up to 5 max)]
no prefix-exclude

Context config>router>ldp>aggregate-prefix-match

Description This command specifies the policy name containing the prefixes to be excluded from the aggregate
prefix match procedures. In this case, LDP will perform an exact match of a specific FEC element
prefix as opposed to a longest match of one or more LDP FEC element prefixes, against this prefix
when it receives a FEC-label binding or when a change to this prefix occurs in the routing table.

The no form of this command removes all policies from the configuration.

Default no prefix-exclude.

class-forwarding
Syntax class-forwarding
no class-forwarding

Context config>router>ldp

Description This command enables Class-Based Forwarding (CBF) capability. When this command is enabled,
LDP prefixes resolved to a set of ECMP tunnel next-hops will have their packets forwarded to the
LSP which is configured to carry the forwarding class the packet was classified to. As a pre-requisite
for that forwarding behavior to happen, the user must have enabled IGP shortcuts in the routing
instance, enabled ecmp in the global routing instance and have enabled the advertisement of unicast
prefix FECs on the Targeted LDP (T-LDP) session to the peer. The user must also have assigned
forwarding classes to LSPs (see config>router>mpls>lsp>class-forwarding).
Class based forwarding will occur when a set of ECMP tunnel next hops is considered consistent
from a CBF perspective. It is the case if at least one CBF configuration (fc or default-lsp) is assigned
to one or more LSPs. If no LSP of the set has the default-lsp option assigned, one LSP will
automatically be selected for that assignment by LDP (the one with the lowest tunnel-id within the set
of LSPs with one or more forwarding classes assigned). Multiple LSPs can have a same forwarding
class assigned. However, for each of these forwarding classes only a single LSP will be used to
forward packets classified into this forwarding class. That LSP is the one with the lowest tunnel-id
amongst those sharing a given forwarding class. Similarly, multiple LSPs can have the default-lsp
configuration assigned. Only a single one will be designated to be the Default LSP. That LSP is the
one with the lowest tunnel-id amongst those with the default-lsp configuration assigned.
Under normal conditions, LDP prefix packets will be sprayed over a set of ECMP tunnel next-hops
by selecting either the LSP to which is assigned the forwarding class of the packets, if one exists, or
the Default LSP, if one does not exist. However, If the IOM detects that the LSP to which is assigned
a forwarding class is not usable, it will switch the forwarding of packets classified to that forwarding
class into the Default LSP, and if the IOM detects that the Default LSP is not usable, then it will
revert to regular ECMP spraying across all tunnels in the set of ECMP tunnel next-hops. In other
words, the CBF is suspended until LDP downloads a new consistent set of tunnel next-hops for the
FEC.

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This command only applies to LSR forwarding LDP FEC prefix packets over a set of MPLS LSPs
using IGP shortcuts. It does not apply to LER forwarding of shortcut packets over LDP FEC, which is
resolved to a set of MPLS LSPs using IGP shortcuts, nor does it apply to LER forwarding of packets
of VPRN and Layer-2 services, which use auto-binding to LDP when the LDP FEC is resolved to a
set of MPLS LSPs using IGP shortcuts.
The no form of this command disables the class based forwarding capability. In that case, LDP
prefixes resolved to a set of ECMP tunnel next-hops will have their packets forwarded according to
ECMP spraying.

Default no class-forwarding

egress-statistics
Syntax egress-statistics

Context config>router>ldp

Description This command provides the context for the user to enter the LDP FEC prefix for the purpose of
enabling egress data path statistics at the ingress LER for this FEC.

Default none

fec-prefix
Syntax [no] fec-prefix ip-prefix[/mask]

Context config>router>ldp>egr-stats

Description This command configures statistics in the egress data path at the ingress LER or LSR for an LDP
FEC. The user must execute the no shutdown command for this command to effectively enable
statistics. The egress data path counters will be updated for both originating and transit packets.
Originating packets may be service packets or IP user and control packets forwarded over the LDP
LSP when used as an IGP shortcut. Transit packets of the FEC which are label switched on this node.

When ECMP is enabled and multiple paths exist for a FEC, the same set of counters are updated for
each packet forwarded over any of the NHLFEs associated with this FEC and for as long as this FEC
is active.

The statistics can be enabled on prefix FECs imported from both LDP neighbors and T-LDP
neighbors (LDP over RSVP).Only /32 FEC prefixes are accepted. Service FECs, i.e., FEC 128 and
FEC 129 are not valid. LDP FEC egress statistics are not collected at the Penultimate-Popping Hop
(PHP) node for a LDP FEC using an implicit null label.

The no form of this command disables the statistics in the egress data path and removes the
accounting policy association from the LDP FEC.

Default none

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accounting-policy
Syntax accounting-policy acct-policy-id
no accounting-policy

Context config>router>ldp>egr-stats

Description This command associates an accounting policy to the MPLS instance.

An accounting policy must be defined before it can be associated else an error message is generated.

The no form of this command removes the accounting policy association.

Default none

Parameters acct-policy-id — Enter the accounting policy-id as configured in the config>log>accounting-policy

context.
Values 1 — 99

collect-stats
Syntax [no] collect-stats

Context config>router>ldp>egr-stats

Description This command enables accounting and statistical data collection. When applying accounting policies
the data, by default, is collected in the appropriate records and written to the designated billing file.

When the no collect-stats command is issued the statistics are still accumulated by the forwarding
engine. However, the CPU will not obtain the results and write them to the billing file. If a
subsequent collect-stats command is issued then the counters written to the billing file include all the
traffic while the no collect-stats command was in effect.

Default collect-stats

export
Syntax export policy-name [policy-name upto 5 max]
no export

Context config>router>ldp

Description This command specifies the export route policies used to determine which routes are exported to
LDP. Policies are configured in the config>router>policy-options context.

If no export policy is specified, non-LDP routes will not be exported from the routing table manager
to LDP. LDP-learned routes will be exported to LDP neighbors. Present implementation of export
policy (outbound filtering) can be used “only” to add FECs for label propagation. The export policy
does not control propagation of FECs that an LSR receives from its neighbors.

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If multiple policy names are specified, the policies are evaluated in the order they are specified. The
first policy that matches is applied. If multiple export commands are issued, the last command entered
will override the previous command. A maximum of 5 policy names can be specified.

The no form of the command removes all policies from the configuration.

Default no export — No export route policies specified.

Parameters policy-name — The export route policy name. Allowed values are any string up to 32 characters long
composed of printable, 7-bit ASCII characters. If the string contains special characters (#, $,
spaces, etc.), the entire string must be enclosed within double quotes.
The specified name(s) must already be defined.

fast-reroute
Syntax [no] fast-reroute

Context config>router>ldp

Description This command enables LDP Fast-Reroute (FRR) procedures. When enabled, LDP uses both the
primary next-hop and LFA next-hop, when available, for resolving the next-hop of an LDP FEC
against the corresponding prefix in the routing table. This will result in LDP programming a primary
NHLFE and a backup NHLFE into the forwarding engine for each next-hop of a FEC prefix for the
purpose of forwarding packets over the LDP FEC.

When any of the following events occurs, LDP instructs in the fast path the forwarding engines to
enable the backup NHLFE for each FEC next-hop impacted by this event:

• An LDP interface goes operationally down, or is admin shutdown.

• An LDP session to a peer went down as the result of the Hello or Keep-Alive timer
expiring.
• The TCP connection used by a link LDP session to a peer went down, due say to
next-hop tracking of the LDP transport address in RTM, which brings down the
LDP session.
• A BFD session, enabled on a T-LDP session to a peer, times-out and as a result the
link LDP session to the same peer and which uses the same TCP connection as the
T-LDP session goes also down.
• A BFD session enabled on the LDP interface to a directly connected peer, times out
and brings down the link LDP session to this peer.

The tunnel-down-dump-time option or the label-withdrawal-delay option, when enabled, does not
cause the corresponding timer to be activated for a FEC as long as a backup NHLFE is still available.

Note that because LDP can detect the loss of a neighbor/next-hop independently, it is possible that it
switches to the LFA next-hop while IGP is still using the primary next-hop. Also, when the interface
for the previous primary next-hop is restored, IGP may re-converge before LDP completed the FEC
exchange with it neighbor over that interface. This may cause LDP to de-program the LFA next-hop

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 from the FEC and blackhole traffic. In order to avoid this situation, it is recommended to enable IGP-
LDP synchronization on the LDP interface.

When the SPF computation determines there is more than one primary next-hop for a prefix, it will
not program any LFA next-hop in RTM. Thus, the LDP FEC will resolve to the multiple primary
next-hops that provide the required protection.

The no form of this command disables LDP FRR.

Default no fast-reroute

export-tunnel-table
Syntax [no] export-tunnel-table policy-name

Context config>router>ldp

Description This command applies a tunnel table export policy to LDP for the purpose of learning BGP labeled
routes from the CPM tunnel table and stitching them to LDP FEC for the same prefix.

The user enables the stitching of routes between LDP and BGP by configuring separately tunnel table
route export policies in both protocols and enabling the advertising of RFC 3107, Carrying Label
Information in BGP-4, formatted labeled routes for prefixes learned from LDP FECs.

The route export policy in BGP instructs BGP to listen to LDP route entries in the CPM Tunnel
Table. If a /32 LDP FEC prefix matches an entry in the export policy, BGP originates a BGP labeled
route, stitches it to the LDP FEC, and re-distributes the BGP labeled route to its iBGP neighbors.

The user adds LDP FEC prefixes with the statement ‘from protocol ldp’ in the configuration of the
existing BGP export policy at the global level, the peer-group level, or at the peer level using the
commands:

• configure>router>bgp>export policy-name
• configure>router>bgp>group>export policy-name
• configure>router>bgp>group>neighbour>export policy-name

To indicate to BGP to evaluate the entries with the from protocol ldp statement in the export policy
when applied to a specific BGP neighbor, a new argument is added to the existing advertise-label
command:

configure>router>bgp>group>neighbour>advertise-label ipv4 include-ldp-prefix

Without the include-ldp-prefix argument, only core IPv4 routes learned from RTM are advertised as
BGP labeled routes to the neighbor. No stitching of LDP FEC to the BGP labeled route will be
performed for this neighbor even if the same prefix was learned from LDP.

The tunnel table route export policy in LDP instructs LDP to listen to BGP route entries in the CPM
Tunnel Table. If a /32 BGP labeled route matches a prefix entry in the export policy, LDP originates
an LDP FEC for the prefix, stitches it to the BGP labeled route, and re-distributes the LDP FEC to its
iBGP neighbors.

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The user can add BGP labeled route prefixes with the statement ‘from protocol bgp’ in the
configuration of the LDP tunnel table export policy. Note that the ‘from protocol’ statement has an
effect only when the protocol value is ldp. Policy entries with protocol values of rsvp, bgp, or any
value other than ldp are ignored at the time the policy is applied to LDP.

The no form of the command removes the policy from the configuration.

Default no export-tunnel-table — no tunnel table export route policy is specified.

Parameters policy-name — The export-tunnel-table route policy name. Allowed values are any string up to 32
characters long composed of printable, 7-bit ASCII characters excluding double quotes. If the
string contains spaces, use double quotes to delimit the start and end of the string. The specified
name(s) must already be defined.

fec-originate
Syntax fec-originate ip-prefix/mask [advertised-label in-label] [swap-label out-label] interface
interface-name
fec-originate ip-prefix/mask [advertised-label in-label] next-hop ip-address [swap-label
out-label]
fec-originate ip-prefix/mask [advertised-label in-label] next-hop ip-address [swap-label
out-label] interface interface-name
fec-originate ip-prefix/mask [advertised-label in-label] pop
no fec-originate ip-prefix/mask interface interface-name
no fec-originate ip-prefix/mask next-hop ip-address
no fec-originate ip-prefix/mask next-hop ip-address interface interface-name
no fec-originate ip-prefix/mask pop

Context config>router>ldp

Description This command defines a way to originate a FEC (with a swap action) for which the LSR is not egress,
or to originate a FEC (with a pop action) for which the LSR is egress.

Parameters ip-prefix/mask — Specify information for the specified IP prefix and mask length.
Values <ip-address/mask> ipv4-prefix - a.b.c.d
ipv4-prefix-le - [0..32]
ipv6-prefix x:x:x:x:x:x:x:x (eight 16-bit pieces)
x:x:x:x:x:x:d.d.d.d
x - [0..FFFF]H
d - [0..255]D
ipv6-prefix-le - [0..128]
next-hop — Specify the IP address of the next hop of the prefix.
advertised-label — Specify the label advertised to the upstream peer. If not configured, then the
label advertised should be from the label pool. If the configured static label is not available then
the IP prefix is not advertised.
out-label — Specify the LSR to swap the label. If configured, then the LSR should swap the label
with the configured swap-label. If not configured, then the default action is pop if the next-hop
parameter is not defined.

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 NOTE: The next-hop, advertised-label, swap-label parameters are all optional. If next-hop is
configured but no swap label specified, then it will be a swap with label 3, such as, pop and
forward to the next-hop. If the next-hop and swap-label are configured, then it is a regular swap.
If no parameters are specified, then a pop and route is performed.
Values 16 — 1048575
in-label — Specifies the number of labels to send to the peer associated with this FEC.
Values 32 — 1023
pop — Specifies to pop the label and transmit without the label.
interface interface-name — Specifies the name of the interface the label for the originated FEC is
swapped to. For an unnumbered interface, this parameter is mandatory since there is no address
for the next-hop. For a numbered interface, it is optional.

graceful-restart
Syntax [no] graceful-restart

Context config>router>ldp

Description This command enables graceful restart helper.

The no form of the command disables graceful restart. Note that graceful restart helper configuration
changes, enable/disable or change of a parameter, will cause the LDP session to bounce.

Default no graceful-restart (disabled) — Graceful-restart must be explicitly enabled.

implicit-null-label
Syntax [no] implicit-null-label

Context config>router>ldp

Description This command enables the use of the implicit null label. Use this command to signal the IMPLICIT
NULL option for all LDP FECs for which this node is the egress LER.

The no form of this command disables the signaling of the implicit null label.

Default no implicit-null-label

maximum-recovery-time
Syntax maximum-recovery-time interval
no maximum-recovery-time

Context config>router>ldp>graceful-restart

Description This command configures the local maximum recovery time.

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The no form of the command returns the default value.

Default 120

Parameters interval — Specifies the length of time in seconds.

Values 15 — 1800

neighbor-liveness-time
Syntax neighbor-liveness-time interval
no neighbor-liveness-time

Context config>router>ldp>graceful-restart

Description This command configures the neighbor liveness time.

The no form of the command returns the default value.

Default 120

Parameters interval — Specifies the length of time in seconds.

Values 5 — 300

import
Syntax import policy-name [policy-name up to 5 max]
no import

Context config>router>ldp

Description This command configures import route policies to determine which label bindings (FECs) are
accepted from LDP neighbors. Policies are configured in the config>router>policy-options context.

If no import policy is specified, LDP accepts all label bindings from configured LDP neighbors.
Import policies can be used to limit or modify the routes accepted and their corresponding parameters
and metrics.

If multiple policy names are specified, the policies are evaluated in the order they are specified. The
first policy that matches is applied. If multiple import commands are issued, the last command
entered will override the previous command. A maximum of five policy names can be specified.

The no form of the command removes all policies from the configuration.

Default no import — No import route policies specified.

Parameters policy-name — The import route policy name. Allowed values are any string up to 32 characters long
composed of printable, 7-bit ASCII characters. If the string contains special characters (#, $,
spaces, etc.), the entire string must be enclosed within double quotes.
The specified name(s) must already be defined.

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label-withdrawal-delay
Syntax label-withdrawal-delay seconds
no label-withdrawal-delay

Context config>router>ldp

Description This command specifies configures the time interval, in seconds, LDP will delay for the withdrawal
of FEC-label binding it distributed to its neighbors when FEC is de-activated. When the timer
expires, LDP then sends a label withdrawal for the FEC to all its neighbors. This is applicable only to
LDP IPv4 prefix FECs and is not applicable to pseudowires (service FECs).

When there is an upper layer (user of LDP) which depends of LDP control plane for failover
detection then label withdrawal delay and tunnel-down-damp-time options must be set to 0.

An example is PW redundancy where the primary PW doesn’t have its own fast failover detection
mechanism and the node depends on LDP tunnel down event to activate the standby PW.

Default no label-withdrawal-delay

Parameters seconds — Specifies the time that LDP delays the withdrawal of FEC-label binding it distributed to
its neighbors when FEC is de-activated.
Values 3 — 120

mcast-upstream-frr
Syntax [no] mcast-upstream-frr

Context config>router>ldp

Description When LDP programs the primary ILM record in the data path, it provides the IOM with the This
command enables the mLDP fast upstream switchover feature.

When this command is enabled and LDP is resolving a mLDP FEC received from a downstream
LSR, it checks if an ECMP next-hop or a LFA next-hop exist to the root LSR node. If LDP finds one,
it programs a primary ILM on the interface corresponding to the primary next-hop and a backup ILM
on the interface corresponding to the ECMP or LFA next-hop. LDP then sends the corresponding
labels to both upstream LSR nodes. In normal operation, the primary ILM accepts packets while the
backup ILM drops them. If the interface or the upstream LSR of the primary ILM goes down causing
the LDP session to go down, the backup ILM will then start accepting packets.

In order to make use of the ECMP next-hop, the user must configure the ecmp value in the system to
at least 2 using the following command:

configure>router>ecmp

In order to make use of the LFA next-hop, the user must enable LFA using the following commands:

config>router>isis>loopfree-alternate

config>router>ospf>loopfree-alternate

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Enabling IP FRR or LDP FRR features is not strictly required since LDP only needs to know where
the alternate next-hop to the root LSR is to be able to send the Label Mapping message to program the
backup ILM at the initial signaling of the tree. Thus enabling the LFA option is sufficient. If however,
unicast IP and LDP prefixes need to be protected, then these features and the mLDP fast upstream
switchover can be enabled concurrently.

Note that mLDP FRR fast switchover relies on the fast detection of loss of **LDP session** to the
upstream peer to which primary ILM label had been advertised. As a result it is strongly
recommended to perform the following:

• Enable BFD on all LDP interfaces to upstream LSR nodes. When BFD detects the
loss of the last adjacency to the upstream LSR, it will bring down immediately the
LDP session which will cause the IOM to activate the backup ILM.
• If there is a concurrent TLDP adjacency to the same upstream LSR node, enable
BFD on the T-LDP peer in addition to enabling it on the interface.
• Enable the ldp-sync-timer option on all interfaces to the upstream LSR nodes. If an
LDP session to the upstream LSR to which the primary ILM is resolved goes down
for any other reason than a failure of the interface or of the upstream LSR, routing
and LDP will go out of sync. This means the backup ILM will remain activated until
the next time SPF is rerun by IGP. By enabling IGP-LDP synchronization feature,
the advertised link metric will be changed to max value as soon as the LDP session
goes down. This in turn will trigger an SPF and LDP will likely download a new set
of primary and backup ILMs.

The no form of this command disables the fast upstream switchover for mLDP FECs.

Default no mcast-upstream-frr

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tunnel-down-damp-time
Syntax tunnel-down-damp-time seconds
no tunnel-down-damp-time

Context config>router>ldp

Description This command specifies the time interval, in seconds, that LDP waits before posting a tunnel down
event to the Tunnel Table Manager (TTM).

When LDP can no longer resolve a FEC and de-activates it, it de-programs the NHLFE in the data
path. It will however delay deleting the LDP tunnel entry in the TTM until the tunnel-down-damp-
time timer expires. This means users of the LDP tunnel, such as SDPs (all services) and BGP (L3
VPN), will not be notified immediately. Traffic is still blackholed because the forwarding engine
NHLFE has been de-programmed.

If the FEC gets resolved before the tunnel-down-damp-time timer expires, then LDP programs the
forwarding engine with the new NHLFE and performs a tunnel modify event in TTM updating the
dampened entry in TTM with the new NHLFE information. If the FEC does not get resolved and the
tunnel-down-damp-time timer expires, LDP posts a tunnel down event to TTM which deletes the
LDP tunnel.

When there is an upper layer (user of LDP) which depends of LDP control plane for failover
detection then label withdrawal delay and tunnel-down-damp-time options must be set to 0.

An example is pseudowire redundancy where the primary PW doesn’t have its own fast failover
detection mechanism and the node depends on LDP tunnel down event to activate the standby PW.

The no form of this command then tunnel down events are not damped.

Parameters seconds — Specifies the time interval, in seconds, that LDP waits before posting a tunnel down event
to the Tunnel Table Manager.

keepalive
Syntax keepalive timeout factor
no keepalive

Context config>router>ldp>if-params>interface>ipv4
config>router>ldp>if-params>interface>ipv6
config>router>ldp>if-params>ipv4
config>router>ldp>if-params>ipv6
config>router>ldp>targeted-session>ipv4
config>router>ldp>targeted-session>ipv6
config>router>ldp>targ-session>peer
config>router>ldp>targ-session>peer-template

Description This command configures the time interval, in seconds, that LDP waits before tearing down the
session. The factor parameter derives the keepalive interval.

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 Generic Commands

If no LDP messages are exchanged for the configured time interval, the LDP session is torn down.
Keepalive timeout is usually three times the keepalive interval. To maintain the session permanently,
regardless of the activity, set the value to zero.

When LDP session is being set up, the keepalive timeout is negotiated to the lower of the two peers.
Once a operational value is agreed upon, the keepalive factor is used to derive the value of the
keepalive interval.

The no form of the command at the interface-parameters and targeted-session levels sets the
keepalive timeout and the keepalive factor to the default value.

The no form of the command, at the interface level, sets the keepalive timeout and the keepalive
factor to the value defined under the interface-parameters level.

The no form of the command, at the peer level, will set the keepalive timeout and the keepalive
factor to the value defined under the targeted-session level.

Note that the session needs to be flapped for the new args to operate.

Default
Context timeout factor

config>router>ldp>if-params 30 3

config>router>ldp>targ-session 40 4

config>router>ldp>if-params>if Inherits values from interface-parameters context.

config>router>ldp>targ-session>peer Inherits values from targeted-session context.

Parameters timeout — Configures the time interval, expressed in seconds, that LDP waits before tearing down the
session.
Values 1 — 65535
factor — Specifies the number of keepalive messages, expressed as a decimal integer, that should be
sent on an idle LDP session in the keepalive timeout interval.
Values 1 — 255

local-lsr-id
Syntax local-lsr-id {system | interface | interface-name interface-name}
no local-lsr-id

Context config>router>ldp>interface-parameters>interface>ipv4/
config>router>ldp>interface-parameters>interface>ipv6
config>router>ldp>targeted-session>peer
config>router>ldp>targeted-session>peer-template

Description This command enables the use of the address of the local LDP interface, or any other network
interface configured on the system, as the LSR-ID to establish link LDP Hello adjacency and LDP
session with directly connected LDP peers. The network interface can be a loopback or not.

7950 XRS MPLS Guide Page 687

 Link LDP sessions to all peers discovered over a given LDP interface share the same local LSR-ID.
However, LDP sessions on different LDP interfaces can use different network interface addresses as
their local LSR-ID.

By default, the LDP session to a peer uses the system interface address as the LSR-ID unless
explicitly configured using the above command. Note, however, that the system interface must
always be configured on the router, or the LDP protocol will not come up on the node. There is no
requirement to include it in any routing protocol.

At initial configuration, the LDP session to a peer will remain down while the network interface used
as LSR-ID is down. LDP will not try to bring it up using the system interface.

At any time the network IP interface used as LSR-ID goes down, the LDP sessions to all discovered
peers using this LSR-ID go down.

If the user changes the LSR-ID value on the fly between system, interface, and interface-name while
the LDP session is up, LDP will immediately tear down all sessions using this LSR-ID and will
attempt to re-establish them using the new LSR-ID.

Note that when an interface other than system is used as the LSR-ID, the transport connection (TCP)
for the link LDP session will also use the address of that interface as the transport address. If system
or interface value is configured in the configure>router>ldp>interface-
parameters>interface>ipv4/ipv6>transport-address context, it will be overridden.

The no form of the command returns to the default behavior in which case the system interface
address is used as the LSR-ID.

Default no local-lsr-id

Parameters interface-name — Specifies the name, up to 32 character in length, of the network IP interface. AN
interface name cannot be in the form of an IP address. If the string contains special characters (#,
$, spaces, etc.), the entire string must be enclosed within double quotes.

tunneling
Syntax [no] tunneling

Context config>router>ldp>targ-session>peer
config>router>ldp>targ-session>peer-template

Description This command enables LDP over tunnels.

The no form of the command disables tunneling.

Default no tunneling

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 Generic Commands

lsp
Syntax [no] lsp lsp-name

Context config>router>ldp>targ-session>tunneling

Description This command configures a specific LSP destined to this peer and to be used for tunneling of LDP
FEC over RSVP. A maximum of 4 RSVP LSPs can be explicitly used for tunneling LDP FECs to the
T-LDP peer.

It is not necessary to specify any RSVP LSP in this context unless there is a need to restrict the
tunneling to selected LSPs. All RSVP LSPs with a to address matching that of the T-LDP peer are
eligible by default. The user can also exclude specific LSP names by using the ldp-over-rsvp exclude
command in the configure->router->mpls->lsp lsp-name context.

7950 XRS MPLS Guide Page 689

Interface Parameters Commands

interface-parameters
Syntax interface-parameters

Context config>router>ldp

Description This command enables the context to configure LDP interfaces and parameters applied to LDP
interfaces. The user can configure different default parameters for IPv4 and IPv6 LDP interfaces by
entering ipv4 or ipv6 as the next command.

ipv4
Syntax ipv4

Context config>router>ldp>interface parameters

This command enables the context to configure LDP interfaces and parameters applied to an IPv4
LDP interface.

ipv6
Syntax ipv6

Context config>router>ldp>interface parameters

Description This command enables the context to configure LDP interfaces and parameters applied to an IPv6
LDP interface.

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 Interface Parameters Commands

hello
Syntax hello timeout factor
no hello

Context config>router>ldp>if-params>interface>ipv4
config>router>ldp>if-params>interface>ipv6
config>router>ldp>if-params>ipv4
config>router>ldp>if-params>ipv6
config>router>ldp>targ-session>ipv4
config>router>ldp>targ-session>ipv6
config>router>ldp>targ-session>peer
config>router>ldp>targ-session>peer-template

Description This command configures the time interval to wait before declaring a neighbor down. The factor
parameter derives the hello interval.

Hold time is local to the system and sent in the hello messages to the neighbor. Hold time cannot be
less than three times the hello interval. The hold time can be configured globally (applies to all LDP
interfaces) or per interface. The most specific value is used.

When LDP session is being set up, the holddown time is negotiated to the lower of the two peers.
Once a operational value is agreed upon, the hello factor is used to derive the value of the hello
interval.

The no form of the command at the interface-parameters and targeted-session level sets the hello
timeout and the hello factor to the default values.

The no form of the command, at the interface level, will set the hello timeout and the hello factor to
the value defined under the interface-parameters level.

The no form of the command, at the peer level, will set the hello timeout and the hello factor to the
value defined under the targeted-session level.

Note that the session needs to be flapped for the new args to operate.

Default
Context Timeout Factor

config>router>ldp>if-params 15 3

config>router>ldp>targ-session 45 3

config>router>ldp>if-params>if Inherits values from interface-parameters context.

config>router>ldp>targ-session>peer Inherits values from targeted-session context.

Parameters timeout — Configures the time interval, in seconds, that LDP waits before a neighbor down.
Values 1 — 65535

7950 XRS MPLS Guide Page 691

 factor — Specifies the number of keepalive messages that should be sent on an idle LDP session in
the hello timeout interval.
Values 1 — 255

hello-reduction
Syntax hello-reduction {enable factor | disable}
no hello-reduction

Context config>router>ldp>targeted-session>ipv4
config>router>ldp>targeted-session>ipv6
config>router>ldp>targeted-session>peer
config>router>ldp>targ-session>peer-template

Description This command enables the suppression of periodic targeted Hello messages between LDP peers once
the targeted LDP session is brought up.

When this feature is enabled, the target Hello adjacency is brought up by advertising the Hold-Time
value the user configured in the “hello timeout” parameter for the targeted session. The LSR node
will then start advertising an exponentially increasing Hold-Time value in the Hello message as soon
as the targeted LDP session to the peer is up. Each new incremented Hold-Time value is sent in a
number of Hello messages equal to the value of the argument factor, which represents the dampening
factor, before the next exponential value is advertised. This provides time for the two peers to settle
on the new value. When the Hold-Time reaches the maximum value of 0xffff (binary 65535), the two
peers will send Hello messages at a frequency of every [(65535-1)/local helloFactor] seconds for the
lifetime of the targeted-LDP session (for example, if the local Hello Factor is three (3), then Hello
messages will be sent every 21844 seconds.

The LSR node continues to compute the frequency of sending the Hello messages based on the
minimum of its local Hold-time value and the one advertised by its peer as in RFC 5036. Thus for the
targeted LDP session to suppress the periodic Hello messages, both peers must bring their advertised
Hold-Time to the maximum value. If one of the LDP peers does not, the frequency of the Hello
messages sent by both peers will continue to be governed by the smaller of the two Hold-Time
values.

When the user enables the hello reduction option on the LSR node while the targeted LDP session to
the peer is operationally up, the change will take effect immediately. In other words, the LSR node
will start advertising an exponentially increasing Hold-Time value in the Hello message, starting with
the current configured Hold-Time value.

When the user disables the hello reduction option while the targeted LDP session to the peer is
operationally up, the change in the Hold-Time from 0xffff (binary 65535) to the user configured
value for this peer will take effect immediately. The local LSR will immediately advertise the value
of the user configured Hold-Time value and will not wait until the next scheduled time to send a
Hello to make sure the peer adjusts its local hold timeout value immediately.

In general, any configuration change to the parameters of the T-LDP Hello adjacency (modifying the
hello adjacency Hello Timeout or factor, enabling/disabling hello reduction, or modifying hello
reduction factor) will cause the LSR node to trigger immediately an updated Hello message with the
updated Hold Time value without waiting for the next scheduled time to send a Hello.

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 Interface Parameters Commands

The no form of this command disables the hello reduction feature.

Default no hello-reduction

Parameters factor — Specifies the integer that specifies the Hello reduction dampening factor.
Values 3 —20

interface
Syntax [no] interface ip-int-name [dual-stack]

Context config>router>ldp>interface-parameters

Description This command enables LDP on the specified IP interface.

The no form of the command deletes the LDP interface and all configuration information associated
with the LDP interface.

The LDP interface must be disabled using the shutdown command before it can be deleted.

The user can configure different parameters for IPv4 and IPv6 LDP interfaces by entering ipv4 or
ipv6 as the next command.

Parameters ip-int-name — The name of an existing interface. If the string contains special characters (#, $,
spaces, etc.), the entire string must be enclosed within double quotes.
dual-stack — This optional keyword allows the user to distinguish between configuration execs prior
to SR OS Release 13.0 from those in Release 13.0, as the interface node implementation has
changed in Release 13.0 to include new IPv4 and IPv6 contexts. The following are some of the
key points for this keyword:
• If the keyword is provided, then IPv4 interface context will not be created. If it is not
provided, the IPv4 interface context will be created. This will take care of execs of prior to
Release 13.0 configurations on a router running SR OS Release 13.0.
• This new keyword will always show in a Release 13.0 configuration.
• When entering an already configured interface, there is no need to provide the keyword, but
it will be ignored if provided.
• When deleting a configured interface, the keyword will not be accepted in the no version of
the interface command.

ipv4
Syntax [no] ipv4

Context config>router>ldp>interface parameters>interface

This command enables the context to configure IPv4 LDP parameters applied to the interface.

7950 XRS MPLS Guide Page 693

ipv6
Syntax [no] ipv6

Context config>router>ldp>interface parameters>interface

Description This command enables the context to configure IPv6 LDP parameters applied to the interface.

bfd-enable
Syntax bfd-enable [ipv4][ipv6]
no bfd-enable

Context config>router>ldp>if-params>if

Description This command enables tracking of the Hello adjacency to an LDP peer using BFD.

When this command is enabled on an LDP interface, LDP registers with BFD and starts tracking the
LSR-id of all peers it formed Hello adjacencies with over that LDP interface. The LDP hello
mechanism is used to determine the remote address to be used for the BFD session. The parameters
used for the BFD session, that is, transmit-interval, receive-interval, and multiplier are those
configured under the IP interface in existing implementation: config>router>interface>bfd

The operation of BFD over an LDP interface tracks the next-hop of the IPv4 and IPv6 prefixes in
addition to tracking the LDP peer address of the Hello adjacency over that link. This is required since
LDP can resolve both IPv4 and IPv6 prefix FECs over a single IPv4 or IPv6 LDP session and as such
the next-hop of a prefix will not necessarily match the LDP peer source address of the Hello
adjacency.

The failure of either or both of the BFD session tracking the FEC next-hop and the one tracking the
Hello adjacency will cause the LFA backup NHLFE for the FEC to be activated or the FEC to be re-
resolved if there is no FRR backup.

When multiple links exist to the same LDP peer, a Hello adjacency is established over each link and
a separate BFD session is enabled on each LDP interface. If a BFD session times out on a specific
link, LDP will immediately associate the LDP session with one of the remaining Hello adjacencies
and trigger the LDP FRR procedures. As soon as the last Hello adjacency goes down due to BFD
timing out, the LDP session goes down and the LDP FRR procedures will be triggered.

The no form of this command disables BFD on the LDP interface.

Default no bfd-enable

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 Interface Parameters Commands

transport-address
Syntax transport-address {interface | system}
no transport-address

Context config>router>ldp>interface-parameters>interface>ipv4
config>router>ldp>interface-parameters>interface>ipv6
config>router>ldp>interface-parameters>ipv4
config>router>ldp>interface-parameters>ipv6

Description This command configures the transport address to be used when setting up the LDP TCP sessions.
The transport address can be configured as interface or system. The transport address can be
configured globally (applies to all LDP interfaces) or per interface. The most specific value is used.

With the transport-address command, you can set up the LDP interface to the connection which can
be set to the interface address or the system address. However, there can be an issue of which address
to use when there are parallel adjacencies. This situation can not only happen with parallel links, it
could be a link and a targeted adjacency since targeted adjacencies request the session to be set up
only to the system IP address.

Note that the transport-address value should not be interface if multiple interfaces exist between
two LDP neighbors. Depending on the first adjacency to be formed, the TCP endpoint is chosen. In
other words, if one LDP interface is set up as transport-address interface and another for
transport-address system, then, depending on which adjacency was set up first, the TCP endpoint
addresses are determined. After that, because the hello contains the LSR ID, the LDP session can be
checked to verify that it is set up and then match the adjacency to the session.

Note that for any given ILDP interface, as the local-lsr-id parameters is changed to interface, the
transport-address configuration loses effectiveness. Since it will be ignored and the ILDP session
will always use the relevant interface IP address as transport-address even though system is chosen.

The no form of the command, at the global level, sets the transport address to the default value.
The no form of the command, at the interface level, sets the transport address to the value defined
under the global level.

Default system — The system IP address is used.

Parameters interface — The IP interface address is used to set up the LDP session between neighbors. The
transport address interface cannot be used if multiple interfaces exist between two neighbors,
since only one LDP session is set up between two neighbors.
system — The system IP address is used to set up the LDP session between neighbors.

multicast-traffic
Syntax [no] multicast-traffic

Context config>router>ldp>interface-parameters>interface

Description This command enables P2MP multicast traffic forwarding on the interface.

7950 XRS MPLS Guide Page 695

 The no form of command disables P2MP LDP multicast traffic on the interface. P2MP tree branching
out on the interface would not withdraw label map from the peer session on interface shutdown or
multicast traffic is disabled. Session may exist on multiple parallel interfaces. Only forwarding entry
is changed when interface is shutdown or multicast traffic support is disabled.

Note that LDP may choose to egress the mLDP tree over this interface, but if multicast-traff is
disabled, the dataplane will not forward traffic on this branch.

Default multicast-traffic enable

mp-mbb-time
Syntax [no] mp-mbb-time

Context config>router>ldp

Description This command configures the maximum time a P2MP transit/bud node must wait before switching
over to the new path if the new node does not send MBB TLV to inform of the availability of data
plane.

The no form of command should configure the default timer of 3 seconds.

Default 3 seconds

Parameters interval — seconds.

Values 1 — 10 seconds

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 Session Parameters Commands

Session Parameters Commands

session-parameters
Syntax session-parameters

Context config>router>ldp

Description This command enables the context to configure peer specific parameters.

peer
Syntax [no] peer ip-address

Context config>router>ldp>session-parameters

Description This command configures parameters for an LDP peer.

Default none

Parameters ip-addr — The IPv4 or IPv6 address of the LDP peer in dotted decimal notation.

adv-adj-addr-only
Syntax [no] adv-adj-addr-only

Context config>router>ldp>session-parameters>peer

Description This command provides a means for an LDP router to advertise only the local IPv4 or IPv6 interfaces
it uses to establish hello adjacencies with an LDP peer. By default, when a router establishes an LDP
session with a peer, it advertises in an LDP Address message the addresses of all local interfaces to
allow the peer to resolve LDP FECs distributed by this router. Similarly, a router sends a Withdraw
Address message to of all its peers to withdraw a local address if the corresponding interface went
down or was deleted.

This new option reduces CPU processing when a large number of LDP neighbors come up or go
down. The new CLI option is strongly recommended in mobile backhaul networks where the number
of LDP peers can be very large.

The no form of this command reverts LDP to the default behavior of advertising all local interfaces.

7950 XRS MPLS Guide Page 697

dod-label-distribution
Syntax [no] dod-label-distribution

Context config>router>ldp>session-parameters>peer

Description This command enables the use of the LDP Downstream-on-Demand (DoD) label distribution
procedures.

When this option is enabled, LDP will set the A-bit in the Label Initialization message when the LDP
session to the peer is established. When both peers set the A-bit, they will both use the DoD label
distribution method over the LDP session (RFC 5036).

This feature can only be enabled on a link-level LDP session and therefore will apply to prefix labels
only, not service labels.

As soon as the link LDP session comes up, the 7x50 will send a label request to its DoD peer for the
FEC prefix corresponding to the peer’s LSR-id. The DoD peer LSR-id is found in the basic Hello
discovery messages the peer used to establish the Hello adjacency with the 7x50.

Similarly if the 7x50 and the directly attached DoD peer entered into extended discovery and
established a targeted LDP session, the 7x50 will immediately send a label request for the FEC prefix
corresponding to the peer’s LSR-id found in the extended discovery messages.

However, the 7x50 node will not advertise any <FEC, label> bindings, including the FEC of its own
LSR-id, unless the DoD peer requested it using a Label Request Message.

When the DoD peer sends a label request for any FEC prefix, the 7x50 will reply with a <FEC, label>
binding for that prefix if the FEC was already activated on the 7x50. If not, the 7x50 replies with a
notification message containing the status code of “no route.” The 7x50 will not attempt in the latter
case to send a label request to the next-hop for the FEC prefix when the LDP session to this next-hop
uses the DoD label distribution mode. Hence the reference to single-hop LDP DoD procedures.

As soon as the link LDP session comes up, the 7x50 will send a label request to its DoD peer for the
FEC prefix corresponding to the peer’s LSR-id. The DoD peer LSR-id is found in the basic Hello
discovery messages the peer used to establish the Hello adjacency with the 7x50.

Similarly if the 7x50 and the directly attached DoD peer entered into extended discovery and
established a targeted LDP session, the 7x50 will immediately send a label request for the FEC prefix
corresponding to the peer’s LSR-id found in the extended discovery messages. Peer address has to be
the peer LSR-ID address.

The no form of this command disables the DoD label distribution with an LDP neighbor.

Default no dod-label-distribution

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 Session Parameters Commands

export-addresses
Syntax export-addresses policy-name [policy-name...(up to 5 max)]
no export-addresses

Context config>router>ldp>session-parameters>peer

Description This command specifies the export prefix policy to local addresses advertised to this peer.

Policies are configured in the config>router>policy-options context. A maximum of five policy

names can be specified.

The no form of the command removes the policy from the configuration.

Parameters policy-name — The export-prefix route policy name. Allowed values are any string up to 32
characters long composed of printable, 7-bit ASCII characters excluding double quotes. If the
string contains spaces, use double quotes to delimit the start and end of the string. The specified
name(s) must already be defined.

export-prefixes
Syntax [no] export-prefixes policy-name

Context config>router>ldp>session-parameters>peer

Description This command specifies the export route policy used to determine which prefixes received from other
LDP and T-LDP peers are re-distributed to this LDP peer via the LDP/T-LDP session to this peer. A
prefix that is filtered out (deny) will not be exported. A prefix that is filtered in (accept) will be
exported.

If no export policy is specified, all FEC prefixes learned will be exported to this LDP peer. This
policy is applied in addition to the global LDP policy and targeted session policy.

Policies are configured in the config>router>policy-options context. A maximum of five policy

names can be specified. Peer address has to be the peer LSR-ID address.

The no form of the command removes the policy from the configuration.

Default no export-prefixes - no export route policy is specified

Parameters policy-name — The export-prefix route policy name. Allowed values are any string up to 32
characters long composed of printable, 7-bit ASCII characters excluding double quotes. If the
string contains spaces, use double quotes to delimit the start and end of the string. The specified
name(s) must already be defined.

7950 XRS MPLS Guide Page 699

fec-limit
Syntax fec-limit limit [log-only] [threshold percentage]
no fec-limit

Context config>router>ldp>session-parameters>peer

Description This command configures a limit on the number of FECs which an LSR will accept from a given peer
and add into the LDP label database. The limit applies to the aggregate count of all FEC types
including service FEC. Once the limit is reached, any FEC received will be released back to the peer.
This behavior is different from the per-peer import policy which will still accept the FEC into the
label database but will not resolve it.

When the FEC limit for a peer is reached, the LSR performs the following actions:

1. Generates a trap and a syslog message.

2. Generates a LDP notification message with the LSR overload status TLV, for each
LDP FEC type including service FEC, to this peer only if this peer advertised
support for the LSR overload sub-TLV via the LSR Overload Protection Capability
TLV at session initialization.
3. Releases, with LDP Status Code of "No_Label_Resources", any new FEC,
including service FEC, from this peer which exceeds the limit.

Note that if a legitimate FEC is released back to a peer, while the FEC limit was exceeded, the user
must have a means to replay that FEC back to the 7x50 LSR once the condition clears. This is done
automatically if the peer is a 7x50 and supports the LDP overload status TLV (SROS 11.0R5 and
higher). Third party peer implementations would need to support the LDP overload status TLV or
provide a manual command to replay the FEC.

The threshold percent option allows to set a threshold value when a trap and an syslog message are
generated as a warning to the user in addition to when the limit is reached. The default value for the
threshold when not configured is 90%.

The log-only option causes a trap and syslog message to be generated when reaching the threshold
and limit. However, LDP labels are not released back to the peer.

If the user decreases the limit value such that it is lower than the current number of FECs accepted
from the peer, the LDP LSR raises the trap for exceeding the limit. In addition, it will set overload for
peers which signaled support for LDP overload protection capability TLV. However, no existing
resolved FECs from the peer which does not support the overload protection capability TLV should
be de-programmed or released.

A different trap is released when crossing the threshold in the upward direction, when reaching the
FEC limit, and when crossing the threshold in the downward direction. However the same trap will
not be generated more often than 2 minutes apart if the number of FECs oscillates around the
threshold or the FEC limit.

Default no fec-limit

Parameters limit — Specify the aggregate count of FECs of all types which can be accepted from this LDP peer.

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 Session Parameters Commands

log-only — Specify only a trap and syslog message are generated when reaching the threshold and
limit. However, LDP labels are not released back to the peer.
threshold percent — Specify the threshold value (as a percentage) that triggers a warning syslog
message and trap to be sent.

fec129-cisco-interop
Syntax [no] fec129-cisco-interop

Context config>router>ldp>session-parameters>peer

Description This command specifies whether LDP will provide translation between non-compliant FEC 129
formats of Cisco. Peer LDP sessions must be manually configured towards the non-compliant Cisco
PEs.

When enabled, Cisco non-compliant format will be used to send and interpret received label release
messages i.e. the FEC129 SAII and TAII fields will be reversed.

When the disabled, Cisco non-compliant format will not be used or supported. Peer address has to be
the peer LSR-ID address.

The no form of the command returns the default.

Default no fec129-cisco-interop

fec-type-capability
Syntax fec-type-capability

Context config>router>ldp>session-parameters>peer
config>router>ldp>interface-parameters>interface>ipv4
config>router>ldp>interface-parameters>interface>ipv6

Description This command enables or disables the advertisement of a FEC type on a given LDP session or Hello
adjacency to a peer.

p2mp
Syntax p2mp {enable | disable}

Context config>router>ldp>session-parameters>peer>fec-type-capability

Description This command enables or disables P2MP FEC capability for the session.

7950 XRS MPLS Guide Page 701

p2mp-ipv4
Syntax p2mp {enable | disable}

Context config>router>ldp>interface-parameters>interface>>ipv4>fec-type-capability
config>router>ldp>interface-parameters>interface>>ipv6>fec-type-capability
config>router>ldp>session-parameters>peer>fec-type-capability

Description This command enables or disables IPv4 P2MP FEC capability on the interface.

p2mp-ipv6
Syntax p2mp {enable | disable}

Context config>router>ldp>interface-parameters>interface>>ipv4>fec-type-capability
config>router>ldp>interface-parameters>interface>>ipv6>fec-type-capability
config>router>ldp>session-parameters>peer>fec-type-capability

Description This command enables or disables IPv6 P2MP FEC capability on the interface.

prefix-ipv4
Syntax prefix-ipv4 {enable | disable}

Context config>router>ldp>interface-parameters>interface>ipv4>fec-type-capability
config>router>ldp>interface-parameters>interface>ipv6>fec-type-capability
config>router>ldp>session-parameters>peer>fec-type-capability

Description This command enables or disables IPv4 prefix FEC capability on the session or interface.

prefix-ipv6
Syntax prefix-ipv6 {enable | disable}

Context config>router>ldp>interface-parameters>interface>ipv4>fec-type-capability
config>router>ldp>interface-parameters>interface>ipv6>fec-type-capability
config>router>ldp>session-parameters>peer>fec-type-capability

Description This command enables or disables IPv6 prefix FEC capability on the session or interface.

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import-prefixes
Syntax [no] import-prefixes policy-name

Context config>router>ldp>session-parameters>peer

Description This command configures the import FEC prefix policy to determine which prefixes received from
this LDP peer are imported and installed by LDP on this node. If resolved these FEC prefixes are then
re-distributed to other LDP and T-LDP peers. A FEC prefix that is filtered out (deny) will not be
imported. A FEC prefix that is filtered in (accept) will be imported.

If no import policy is specified, the node will import all prefixes received from this LDP/T-LDP peer.
This policy is applied in addition to the global LDP policy and targeted session policy.

Policies are configured in the config>router>policy-options context. A maximum of five policy

names can be specified. Peer address has to be the peer LSR-ID address.

The no form of the command removes the policy from the configuration.

Default no import-prefixes - no import route policy is specified

Parameters policy-name — The import-prefix route policy name. Allowed values are any string up to 32
characters long composed of printable, 7-bit ASCII characters excluding double quotes. If the
string contains spaces, use double quotes to delimit the start and end of the string. The specified
name(s) must already be defined.

path-mtu-discovery
Syntax path-mtu-discovery
no path-mtu-discovery

Context config>router>ldp>tcp-session-parameters>peer-transport

Description This command enables Path MTU discovery for the associated TCP connections. When enabled, the
MTU for the associated TCP session is initially set to the egress interface MTU. The DF bit is also set
so that if a router along the path of the TCP connection cannot handle a packet of a particular size
without fragmenting, it sends back and ICMP message to set the path MTU for the given session to a
lower value that can be forwarded without fragmenting. Note that if one or more transport addresses
used in the Hello adjacencies to the same peer LSR are different from the LSR-ID value, the user
must add each of the transport addresses to the path MTU discovery configuration as a separate peer.
This means when the TCP connection is bootstrapped by a given Hello adjacency, the path MTU
discovery can operate over that specific TCP connection by using its specific transport address.

Default no path-mtu-discovery

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pe-id-mac-flush-interop
Syntax [no] pe-id-mac-flush-interop

Context config>router>ldp>session-parameters>peer

Description This command enables the addition of the PE-ID TLV in the LDP MAC withdrawal (mac-flush)
message, under certain conditions, and modifies the mac-flush behavior for interoperability with
other vendors that do not support the flush-all-from-me vendor-specific TLV. This flag can be
enabled on a per LDP peer basis and allows the flush-all-from-me interoperability with other
vendors. When the pe-id-mac-flush-interop flag is enabled for a given peer, the current mac-flush
behavior is modified in terms of mac-flush generation, mac-flush propagation and behavior upon
receiving a mac-flush.

The mac-flush generation will be changed depending on the type of event and according to the
following rules:

• Any all-from-me mac-flush event will trigger a mac-flush all-but-mine message

(RFC 4762 compliant format) with the addition of a PE-ID TLV. The PE-ID TLV
contains the IP address of the sending PE.
• Any all-but-mine mac-flush event will trigger a mac-flush all-but-mine message
WITHOUT the addition of the PE-ID TLV, as long as the source spoke-sdp is not
part of an end-point.
• Any all-but-mine mac-flush event will trigger a mac-flush all-but-mine message
WITH the addition of the PE-ID TLV, if the source spoke-sdp is part of an end-point
and the spoke-sdp goes from down/standby state to active state. In this case, the PE-
ID TLV will contain the IP address of the PE to which the previous active spoke-sdp
was connected to.

Any other case will follow the existing mac-flush procedures.

When the pe-id-mac-flush-interop flag is enabled for a given LDP peer, the mac-flush ingress
processing is modified according to the following rules:

• Any received all-from-me mac-flush will follow the existing mac-flush all-from-me
rules regardless of the existence of the PE-ID.
• Any received all-but-mine mac-flush will take into account the received PE-ID, i.e.
all the mac addresses associated to the PE-ID will be flushed. If the PE-ID is not
included, the mac addresses associated to the sending PE will be flushed.
• Any other case will follow the existing mac-flush procedures.

When a mac-flush message has to be propagated (for an ingress sdp-binding to an egress sdp-
binding) and the pe-id-mac-flush-interop flag is enabled for the ingress and egress TLDP peers, the
following behavior is observed:

• If the ingress and egress bindings are spoke-sdp, the PE will propagate the mac-
flush message with its own PE-ID.

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 Session Parameters Commands

• If the ingress binding is an spoke-sdp and the egress binding a mesh-sdp, the PE will
propagate the mac-flush message without modifying the PE-ID included in the PE-
ID TLV.
• If the ingress binding is a mesh-sdp and the egress binding an spoke-sdp, the PE will
propagate the mac-flush message with its own PE-ID.
• When ingress and egress bindings are mesh-sdp, the mac-flush message is never
propagated. This is the behavior regardless of the pe-id-mac-flush-interop flag
configuration.

Note that the PE-ID TLV is never added when generating a mac-flush message on a B-VPLS if the
send-bvpls-flush command is enabled in the I-VPLS. In the same way, no PE-ID is added when
propagating mac-flush from a B-VPLS to a I-VPLS when the propagate-mac-flush-from-bvpls
command is enabled. Mac-flush messages for peers within the same I-VPLS or within the same B-
VPLS domain follow the procedures described above.

Default no pe-id-mac-flush-interop

prefer-tunnel-in-tunnel
Syntax [no] prefer-tunnel-in-tunnel

Context config>router>ldp

Description This command specifies to use tunnel-in-tunnel over a simple LDP tunnel. Specifically, the user
packets for LDP FECs learned over this targeted LDP session can be sent inside an RSVP LSP which
terminates on the same egress router as the destination of the targeted LDP session. The user can
specify an explicit list of RSVP LSP tunnels under the Targeted LDP session or LDP will perform a
lookup in the Tunnel Table Manager (TTM) for the best RSVP LSP. In the former case, only the
specified LSPs will be considered to tunnel LDP user packets. In the latter case, all LSPs available to
the TTM and which terminate on the same egress router as this target ed LDP session will be
considered. In both cases, the metric specified under the LSP configuration is used to control this
selection.

Note that the lookup in the TTM will prefer a LDP tunnel over an LDP-over-RSVP tunnel if both are
available. Also note that the tunneling operates on the dataplane only. Control packets of this targeted
LDP session are sent over the IGP path.

shortcut-transit-ttl-propagate
Syntax [no] shortcut-transit-ttl-propagate

Context config>router>ldp
config>router>mpls

Description This command configures the TTL handling of transit packets for all LSP shortcuts originating on this
ingress LER. It applies to all LDP or RSVP LSPs that are used to resolve static routes, BGP routes,
and IGP routes.

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 The user can enable or disable the propagation of the TTL from the header of an IP packet into the
header of the resulting MPLS packet independently for local and transit packets forwarded over an
LSP shortcut.

By default, the feature propagates the TTL from the header of transit IP packets into the label stack of
the resulting MPLS packets forwarded over the LSP shortcut. This is referred to as Uniform mode.

When the no form of the command is enabled, TTL propagation is disabled on all transit IP packets
received on any IES interface and destined to a route that is resolved to the LSP shortcut. In this case,
a TTL of 255 is programmed onto the pushed label stack. This is referred to as Pipe mode.

Default shortcut-transit-ttl-propagate

shortcut-local-ttl-propagate
Syntax [no] shortcut-local-ttl-propagate

Context config>router>ldp
config>router>mpls

Description This command configures the TTL handling of locally generated packets for all LSP shortcuts
originating on this ingress LER. It applies to all LDP or RSVP LSPs that are used to resolve static
routes, BGP routes, and IGP routes.

The user can enable or disable the propagation of the TTL from the header of an IP packet into the
header of the resulting MPLS packet independently for local and transit packets forwarded over an
LSP shortcut.

Local IP packets include ICMP Ping, traceroute, and OAM packets, that are destined to a route that is
resolved to the LSP shortcut. Transit IP packets are all IP packets received on any IES interface and
destined to a route that is resolved to the LSP shortcut

By default, the feature propagates the TTL from the header of locally generated IP packets into the
label stack of the resulting MPLS packets forwarded over the LSP shortcut. This is referred to as
Uniform mode.

When the no form of the above command is enabled, TTL propagation is disabled on all locally
generated IP packets, including ICMP Ping, traceroute, and OAM packets, that are destined to a route
that is resolved to the LSP shortcut. In this case, a TTL of 255 is programmed onto the pushed label
stack. This is referred to as Pipe mode.

Default shortcut-local-ttl-propagate

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 Targeted Session Commands

Targeted Session Commands

targeted-session
Syntax targeted-session

Context config>router>ldp

Description This command configures targeted LDP sessions. Targeted sessions are LDP sessions between non-
directly connected peers. Hello messages are sent directly to the peer platform instead of to all the
routers on this subnet multicast address. The user can configure different default parameters for IPv4
and IPv6 LDP targeted hello adjacencies.

The discovery messages for an indirect LDP session are addressed to the specified peer and not to the
multicast address.

Default none

bfd-enable
Syntax [no] bfd-enable

Context config>router>ldp>targ-session>peer
config>router>ldp>targeted-session>peer-template

Description This command enables the bidirectional forwarding detection (BFD) session for the selected TLDP
session. By enabling BFD for a selected targeted session, the state of that session is tied to the state of
the underneath BFD session between the two nodes.

The parameters used for the BFD are set via the BFD command under the IP interface.

The no form of this command removes the TLDP session operational state binding to the central BFD
session one.

Default no bfd-enable

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disable-targeted-session
Syntax [no] disable-targeted-session

Context config>router>ldp>targ-session

Description This command disables support for SDP triggered automatic generated targeted sessions. Targeted
sessions are LDP sessions between non-directly connected peers. The discovery messages for an
indirect LDP session are addressed to the specified peer and not to the multicast address.

The no form of the command enables the set up of any targeted sessions.

Default no disable-targeted-session

peer
Syntax [no] peer ip-address

Context config>router>ldp>targeted-session

Description This command configures parameters for an LDP peer.no

Default none

Parameters ip-address — The IPv4 or IPv6 address of the LDP peer in dotted decimal notation.

peer-template-map
Syntax peer-template-map template-name policy peer-prefix-policy1 [peer-prefix-policy2..up to 5]
no peer-template-map peer-template template-name

Context config>router>ldp>targeted-session

Description This command enables the automatic creation of a targeted Hello adjacency and LDP session to a
discovered peer. The user configures a targeted session peer parameter template and binds it to a peer
prefix policy.

Each application of a targeted session template to a given prefix in the prefix list will result in the
establishment of a targeted Hello adjacency to an LDP peer using the template parameters as long as
the prefix corresponds to a router-id for a node in the TE database. As a result of this, the user must
enable the traffic-engineering option in ISIS or OSPF. The targeted Hello adjacency will either
trigger a new LDP session or will be associated with an existing LDP session to that peer.

Up to 5 peer prefix policies can be associated with a single peer template at all times. Also, the user
can associate multiple templates with the same or different peer prefix policies. Thus multiple
templates can match with a given peer prefix. In all cases, the targeted session parameters applied to
a given peer prefix are taken from the first created template by the user. This provides a more
deterministic behavior regardless of the order in which the templates are associated with the prefix
policies.

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 Targeted Session Commands

Each time the user executes the above command, with the same or different prefix policy associations,
or the user changes a prefix policy associated with a targeted peer template, the system re-evaluates
the prefix policy. The outcome of the re-evaluation will tell LDP if an existing targeted Hello
adjacency needs to be torn down or if an existing targeted Hello adjacency needs to have its
parameters updated on the fly.

If a /32 prefix is added to (removed from) or if a prefix range is expanded (shrunk) in a prefix list
associated with a targeted peer template, the same prefix policy re-evaluation described above is
performed.

The template comes up in the no shutdown state and as such it takes effect immediately. Once a
template is in use, the user can change any of the parameters on the fly without shutting down the
template. In this case, all targeted Hello adjacencies are updated.

The SR OS supports multiple ways of establishing a targeted Hello adjacency to a peer LSR:

• User configuration of the peer with the targeted session parameters inherited from
the config>router>ldp>targeted-session in the top level context or explicitly
configured for this peer in the config>router>ldp>targeted-session>peer context
and which overrides the top level parameters shared by all targeted peers. Let us
refer to the top level configuration context as the global context. Note that some
parameters only exist in the global context and as such their value will always be
inherited by all targeted peers regardless of which event triggered it.
• User configuration of an SDP of any type to a peer with the signaling tldp option
enabled (default configuration). In this case the targeted session parameter values
are taken from the global context.
• User configuration of a (FEC 129) PW template binding in a BGP-VPLS service. In
this case the targeted session parameter values are taken from the global context.
• User configuration of a (FEC 129 type II) PW template binding in a VLL service
(dynamic multi-segment PW). In this case the target session parameter values are
taken from the global context
• User configuration of a mapping of a targeted session peer parameter template to a
prefix policy when the peer address exists in the TE database (this feature). In this
case, the targeted session parameter values are taken from the template.

Since the above triggering events can occur simultaneously or in any arbitrary order, the LDP code
implements a priority handling mechanism in order to decide which event overrides the active
targeted session parameters. The overriding trigger will become the owner of the targeted adjacency
to a given peer. The following is the priority order:

• Priority 1: manual configuration of session parameters

• Priority 2: mapping of targeted session template to prefix policy.
• Priority 3: manual configuration of SDP, PW template binding in BGP-AD VPLS
and in FEC 129 VLL.

Note that any parameter value change to an active targeted Hello adjacency caused by any of the
above triggering events is performed on the fly by having LDP immediately send a Hello message

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 with the new parameters to the peer without waiting for the next scheduled time for the Hello
message. This allows the peer to adjust its local state machine immediately and maintains both the
Hello adjacency and the LDP session in UP state. The only exceptions are the following:

• The triggering event caused a change to the local-lsr-id parameter value. In this
case, the Hello adjacency is brought down which will also cause the LDP session to
be brought down if this is the last Hello adjacency associated with the session. A
new Hello adjacency and LDP session will then get established to the peer using the
new value of the local LSR ID.
• The triggering event caused the targeted peer shutdown option to be enabled. In this
case, the Hello adjacency is brought down which will also cause the LDP session to
be brought down if this is the last Hello adjacency associated with the session.

Finally, the value of any LDP parameter which is specific to the LDP/TCP session to a peer is
inherited from the config>router>ldp>session-parameters>peer context. This includes MD5
authentication, LDP prefix per-peer policies, label distribution mode (DU or DOD), etc.

The no form of this command deletes the binding of the template to the peer prefix list and brings
down all Hello adjacencies to the discovered LDP peers.

peer-template
Syntax [no] peer-template template-name

Context config>router>ldp>targeted-session

Description This command creates a targeted session peer parameter template that can be referenced in the
automatic creation of targeted Hello adjacency and LDP session to a discovered peer.

The no form of command deletes the peer template. A peer template cannot be deleted if it is bound
to a peer prefix list.

Parameters template-name — Specifies the template name to identify targeted peer template. It must be 32
characters maximum.

export-prefixes
Syntax export-prefixes policy-name [policy-name...(up to 5 max)]
no export-prefixes

Context config>router>ldp>targeted-session

Description This command specifies the export route policy used to determine which FEC prefix label bindings
are exported from a targeted LDP session. A route that is filtered out (deny) will not be exported. A
route that is filtered in (accept) will be exported.

If no export policy is specified, all bindings learned through a targeted LDP session will be exported
to all targeted LDP peers. This policy is applied in addition to the global LDP policy.

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Policies are configured in the config>router>policy-options context. A maximum of five policy

names can be specified.

The no form of the command removes the policy from the configuration.

Parameters policy-name — The export policy name. Allowed values are any string up to 32 characters long
composed of printable, 7-bit ASCII characters. If the string contains special characters (#, $,
spaces, etc.), the entire string must be enclosed within double quotes.

import-prefixes
Syntax import-prefixes policy-name [policy-name...(up to 5 max)]
no import-prefixes

Context config>router>ldp>targeted-session

Description This command configures the import route policy to determine which FEC prefix label bindings are
accepted from targeted LDP neighbors into this node. A label binding that is filtered out (deny) will
not be imported. A route that is filtered in (accept) will be imported.

If no import policy is specified, this node session will accept all bindings from configured targeted
LDP neighbors. This policy is applied in addition to the global LDP policy.

Policies are configured in the config>router>policy-options context. A maximum of five policy

names can be specified.

The no form of the command removes the policy from the configuration.

Parameters policy-name — The import policy name. Allowed values are any string up to 32 characters long
composed of printable, 7-bit ASCII characters. If the string contains special characters (#, $,
spaces, etc.), the entire string must be enclosed within double quotes.

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ipv4
Syntax ipv4

Context config>router>ldp>targeted-session

Description This command enables the context to configure parameters applied to targeted sessions to
all IPv4 LDP peers.

ipv6
Syntax ipv4

Context config>router>ldp>targeted-session

Description This command enables the context to configure parameters applied to targeted sessions to
all IPv6 LDP peers.

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 TCP Session Parameters Commands

TCP Session Parameters Commands

tcp-session-parameters
Syntax tcp-session-parameters

Context config>router>ldp

Description This command enables the context to configure parameters applicable to TCP transport session of an
LDP session to remote peer.

peer-transport
Syntax peer-transport ip-address
no peer transport

Context config>router>ldp>tcp-session-parameters

Description This command configures the peer transport address, that is, the destination address of the TCP
connection, and not the address corresponding to the LDP LSR-ID of the peer.

Parameters ip-address — The IPv4 or IPv6 address of the TCP connection to the LDP peer in dotted dec-
imal notation.

auth-keychain
Syntax auth-keychain name

Context config>router>ldp>tcp-session-parameters>peer-transport

Description This command configures TCP authentication keychain to use for the session.

Parameters name — Specifies the name of the keychain to use for the specified TCP session or sessions. This
keychain allows the rollover of authentication keys during the lifetime of a session up to 32
characters in length. Peer address has to be the TCP session transport address.

authentication-key
Syntax authentication-key [authentication-key | hash-key] [hash | hash2]
no authentication-key

Context config>router>ldp>tcp-session-parameters>peer-transport

Description This command specifies the authentication key to be used between LDP peers before establishing
sessions. Authentication uses the MD-5 message-based digest. Peer address has to be the TCP session
transport address. Note that if one or more transport addresses used in the Hello adjacencies to the

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 same peer LSR are different from the LSR-ID value, the user must add each of the transport
addresses to the authentication-key configuration as a separate peer. This means when the TCP
connection is bootstrapped by a given Hello adjacency, the authentication can operate over that
specific TCP connection by using its specific transport address.

The no form of this command disables authentication.

Default none

Parameters authentication-key — The authentication key. The key can be any combination of ASCII characters
up to 16 characters in length (unencrypted). If spaces are used in the string, enclose the entire
string in quotation marks (“ ”).
hash-key — The hash key. The key can be any combination of up 33 alphanumeric characters. If
spaces are used in the string, enclose the entire string in quotation marks (“ ”).
This is useful when a user must configure the parameter, but, for security purposes, the actual
unencrypted key value is not provided.
hash — Specifies the key is entered in an encrypted form. If the hash keyword is not used, the key is
assumed to be in a non-encrypted, clear text form. For security, all keys are stored in encrypted
form in the configuration file with the hash parameter specified.
hash2 — Specifies the key is entered in a more complex encrypted form. If the hash2 parameter is
not used, the less encrypted hash form is assumed.

path-mtu-discovery
Syntax path-mtu-discovery
no path-mtu-discovery

Context config>router>ldp>tcp-session-parameters>peer-transport

Description This command enables Path MTU discovery for the associated TCP connections. When enabled, the
MTU for the associated TCP session is initially set to the egress interface MTU. The DF bit is also set
so that if a router along the path of the TCP connection cannot handle a packet of a particular size
without fragmenting, it sends back and ICMP message to set the path MTU for the given session to a
lower value that can be forwarded without fragmenting.

Note that if one or more transport addresses used in the Hello adjacencies to the same peer LSR are
different from the LSR-ID value, the user must add each of the transport addresses to the path MTU
discovery configuration as a separate peer. This means when the TCP connection is bootstrapped by a
given Hello adjacency, the path MTU discovery can operate over that specific TCP connection by
using its specific transport address.

Default no path-mtu-discovery

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 TCP Session Parameters Commands

ttl-security
Syntax ttl-security min-ttl-value
no ttl-security

Context config>router>ldp>tcp-session-parameters>peer-transport

Description This command configures TTL security parameters for incoming packets. When the feature is
enabled, BGP/LDP will accept incoming IP packets from a peer only if the TTL value in the packet is
greater than or equal to the minimum TTL value configured for that peer. Peer address has to be the
TCP session transport address.

The no form of the command disables TTL security.

Default no ttl-security

Parameters min-ttl-value — Specify the minimum TTL value for an incoming packet.
Values 1 — 255

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