Cramsession for Cisco Certified Network Associate 2.

0
This study guide will help you to prepare for Cisco exam 640-507,
Cisco Certified Network Associate 2.0. Exam topics include Bridging,
Switching, Network and WAN Protocols, Reference Model and
Layered Communication, Routing, Network Management, LAN
Design, Physical Connectivity, Cisco Basics, IOS, and Network
Basics.

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Contents:
Contents: ....................................................................................................... 1
OSI Reference / Network Protocols .................................................................... 3
Steps of Data Encapsulation ............................................................................. 5
Data link addresses....................................................................................... 5
Network address........................................................................................... 5
Network Structure Defined by Hierarchy............................................................. 6
IPX ............................................................................................................. 6
LAN Switching................................................................................................. 7
Three Switch Functions.................................................................................. 7
Bridging Compared to LAN Switching .............................................................. 9
Transmitting Frames through a Switch ............................................................ 9
TCP/IP Layers ................................................................................................10
Application Layer .........................................................................................10
Transport Layer ...........................................................................................10
Port Numbers ..............................................................................................10
TCP .........................................................................................................10
UDP ........................................................................................................10
IP Address Classes.......................................................................................11
Subnetting Formulas ....................................................................................11
Routing .........................................................................................................11
Static (manual) ...........................................................................................11
Routing Protocols ...........................................................................................12
Exterior ......................................................................................................12
Counting to Infinity.........................................................................................13
IOS / Routing / Network Security .....................................................................13
Privileged Mode ...........................................................................................13
Banner .......................................................................................................13
Hostname ...................................................................................................13
Editing .......................................................................................................14
Help...........................................................................................................14
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Router Elements/Configuration ......................................................................14

Network Security / Access Lists ........................................................................15
Standard IP access list .................................................................................15
Extended IP access list .................................................................................15
IPX Access lists ...........................................................................................16
IPX SAP Filters ............................................................................................16
To Monitor Access Lists.................................................................................17
WAN .............................................................................................................17
Layer 1 Connection Types .............................................................................17
Wan Service Providers..................................................................................17
Layer 2 Encapsulation Protocols.....................................................................17
Frame Relay PVC Connection.........................................................................19
ISDN..........................................................................................................19
ISDN Terminal Equipment Types.................................................................19
ISDN Protocols .........................................................................................20

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OSI Reference / Network Protocols

Application The application layer provides services directly to applications. The

functions of the application layer can include identifying communication partners,
determining resource availability, and synchronizing communication . Some
examples of application layer implementations include TCP/IP and OSI applications
such as Telnet, FTP, and SMTP, File Transfer, Access, and Management (FTAM),
Virtual Terminal Protocol(VTP), and Common Management Information Protocol
(CMIP).
Presentation The presentation layer provides a variety of coding and conversion
functions that are applied to application layer data. These functions ensure that
information sent from the application layer of one system will be readable by the
application layer of another system. Examples of presentation layer coding and
conversion schemes include ASCII, EBCDIC, JPEG,GIF, TIFF, MPEG, QuickTime,
various encryption methods, and other similar coding formats.
Session The session layer establishes, manages, maintains, and terminates
communication sessions between applications. Communication sessions consist of
service requests and service responses that occur between applications located in
different network devices. Some examples of session layer implementations include
Remote Procedure Call (RPC), Zone Information Protocol (ZIP), and Session Control
Protocol (SCP).
Transport The transport layer segments and reassembles data into data streams.
It is also responsible for both reliable and unreliable end-to-end data transmission.
Transport layer functions typically include flow control, multiplexing, virtual circuit
management, and error checking and recovery. Some examples of transport layer

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implementations include Transmission Control Protocol (TCP), Name Binding Protocol

(NBP), and OSI transport protocols (SPX).
Network The network layer uses logical addressing to provide routing and related
functions that allow multiple data links to be combined into an internet work. The
network layer supports both connection-oriented and connectionless service from
higher-layer protocols. Network layer protocols are typically routing protocols.
However, other types of protocols, such as the Internet Protocol (IP), are
implemented at the network layer as well. Routers reside here at the network layer.
Some common routing protocols include Border Gateway Protocol (BGP), Open
Shortest Path First(OSPF), and Routing Information Protocol (RIP). Packets and data
grams are sent across this layer of the OSI model (IPX).
Data Link The data link layer provides reliable transmission of data across a
physical medium. The data link layer specifies different network and protocol
characteristics, including physical addressing, network topology, error notification,
sequencing of frames, and flow control. The Data link layer is composed of two
sublayers known as the Media Access Control (MAC) Layer and the Logical Link
Control (LLC) layer.This can be seen in the following diagram:

The LLC sublayer manages communications between devices over a single link of a
network. LLC supports both connectionless and connection-oriented services used by
higher-layer protocols. The MAC sublayer manages protocol access to the physical
network medium. The IEEE MAC specification defines MAC addresses, which allow
multiple devices to uniquely identify one another at the data link layer. Data link
layer implementations can be categorized as either LAN or WAN specifications. The
most common LAN data link layer implementations include Ethernet/IEEE 802.3, Fast
Ethernet, FDDI, and Token Ring/IEEE 802.5. The most common WAN data link layer
implementations include Frame Relay, Link Access Procedure, Balanced (LAPB),
Synchronous Data Link Control (SDLC), Point-to-Point Protocol (PPP), and SMDS
Interface Protocol (SIP).

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Physical The physical layer defines the electrical, mechanical, procedural, and
functional specifications for activating, maintaining, and deactivating the physical link
between communicating network systems.
Physical layer specifications define such characteristics as voltage levels, timing of
voltage changes, physical data rates, maximum transmission distances, and the
physical connectors to be used. Physical layer implementations can be categorized as
either LAN or WAN specifications. Some common LAN physical layer implementations
include Ethernet/IEEE 802.3, Fast Ethernet, FDDI, and Token Ring/IEEE 802.5. Some
common WAN physical layer implementations include High-Speed Serial Interface
(HSSI),SMDS Interface Protocol (SIP), and X.21bis.

Steps of Data Encapsulation

1.
2.
3.
4.
5.

User information is converted to data

Data converted to segments
Segments converted to packets or data grams
Packets and data grams are converted to frames
Frames are converted to bits
Application
Presentation
Upper Layer Data

Session

PDU

TCP Header

Upper Layer Data

Transport

Segment

IP Header

Data

Network

Packet

LLC Header

Data

FCS

Data Link

Frame

Mac Header Data

FCS

Physical

Bits

010110101101010101

Data link addresses

Physical address. Flat addressing scheme where the physical address is burned into a
network card (MAC address)

Network address
Logical address. IP or IPX hierarchical scheme. The address is assigned to a
machine manually or dynamically.
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Physical through Transport layers are the Data Flow Layers

Session through Application layers are the Application (Upper) Layers

Hubs work on the Physical layer (Layer 1 device)

Switches and Bridges work on the Data Link Layer (Layer 2device)

Routers work on the Network layer (Layer 3 device)

Network Structure Defined by Hierarchy

Core Layer = Multi-layer switch

Purpose is to switch traffic as fast as possible

Characteristics:
o

Fast transport to enterprise services (e-mail, internet access, video

conferencing)

No packet manipulation

Distribution Layer = Routers

Primary function: perform potentially expensive packet manipulations such as
routing, filtering, and WAN access. Characteristics include:

Access Layer Aggregation Point

Routing traffic

Broadcast/Multicast Domains

Media Translation

Security

Possible point for remote access

Access Layer = Switches and Routers

End station entry point to the network

IPX
To turn on:

<>

ipx routing

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Then, on interface:

ipx network {#} encapsulation {sap, arpa, snap, hdlc,novell-ether} {sec}

ipx network 3100 encapsulation sap sec

To monitor:

<>

sh ipx traffic

sh ipx int e0

Frame Types:

802.3 novell-ether default

802.2 sap

Ethernet_II arpa

Ethernet_snap snap

LAN Switching
Switching examines MAC address. Same as multi portbridge

Three Switch Functions

Address learning

Forward/filter decision

Loop avoidance

Address Learning: maintains MAC address table used to track the location of
devices connected to the switch.
Forward/filter decision: when a frame arrives with a known destination address, it
is forwarded only on the specific port connected to that station.

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Broadcast and Multicast frames: may be of interest to all stations. The switch
normally floods to all ports other than the origination port. A switch never learns a
broadcast or multicast address because broadcast and multicast addresses never
appear as the source address of a frame.

All nodes on an Ethernet network can transmit at the same time, so the more
nodes you have the greater the possibility of collisions happening. This can
slow the network down.

Redundant Topology eliminates single points of failure. Causes broadcast

storms, multiple frame copies, and MAC address table instability problems.
Multiple Frame Copies when a new switch is added, the other switches may not
have learned its correct MAC address. The host may send a unicast frame to the new
switch. The frame is sent through several path sat the same time. The new switch
will receive several copies of the frame. This causes MAC Database Instability.
MAC Database Instability results when multiple copies of a frame arrive on
different ports of a switch.
Multiple Loop Problems complex topology can cause multiple loops to occur.
Layer 2 has no mechanism to stop the loop. This is the main reason for Spanning
Tree Protocol.
Spanning-Tree Protocol (STP) IEEE 802.1d. developed to prevent routing loops.
STA (Spanning-Tree Algorithm) is implemented by STP to calculate a loop-free
network topology. In most switches, BPDU (Configuration Bridge Protocol Data Unit),
are sent and received by all switches, and processed to determine the spanning-tree
topology. (STP is on by default).

A port is in either a forwarding or blocking state. Forwarding ports provide the

lowest cost path to the root bridge. All ports start in the blocking state to
prevent bridge loops. The port stays in a blocked state if the spanning tree
determines that there is another path to the root bridge that has a better
cost. Blocking ports can still receive BPDUs.

Spanning-Tree operation Selects one root bridge. All the ports are designated
ports (forwarding). For non-root bridge, there will be one root port. This offers the
lowest cost path from non-root bridge to the root bridge. On each segment, there is
one designated part. This port also has the lowest cost to the root bridge.

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Time to Convergence
The time for all the switches and bridges ports transition to either the forwarding or
blocking state. When network topology changes, switches and bridges must recompute the Spanning-Tree Protocol, which disrupts traffic.

Bridging Compared to LAN Switching

Bridging: primarily software based. One spanning-tree instance per bridge. Usually
up to 16 ports per bridge.
LAN Switching: primarily hardware based. Many spanning-tree instances per
switch. More ports per switch, (up to 100). Faster than a Bridge.

Transmitting Frames through a Switch

Store-and-Forward copies entire frame into buffer, checks for CRC errors.
Higher latency.

Cut-Through reads only the destination address into buffer, and forwards
immediately. Low latency.

Fragment free (modified cut-through). Switch will read into the first 64
bytes before forwarding the frame. Collisions will usually occur within the first
64 bytes. (default for 1900 series).

Full-Duplex Ethernet can provide double the bandwidth of traditional

Ethernet, but requires a single workstation on a single switch port, and NIC
must support it. Collision free because there are separate send and receive
wires, and only one workstation is on the segment. Half-Duplex must provide
for collision detection, therefore can only use 50% of bandwidth available. It
sends and receives on the same set of wires.

LAN Segmentation: breaking up the collision domains by decreasing the number of

workstations per segment.
Fast Ethernet (100bt) provides 10 times the bandwidth of older 10bastT
Ethernet. Must have Cat5 cable, no longer than 100meters, and Fast Ethernet NICs
and Hubs/Switches.
Bridges examines MAC address, and forwards frames unless the address was
local. Forwards to all other segments it is attached to. Forwards multicast packets, so
broadcast storms can occur.

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Routers examines network address, and forwards using the best available route
to destination network. Can have multiple active paths.
Virtual LANs sets different ports on a switch to be part of different sub-networks.
Some benefits: simplify moves, adds, changes; reduce administrative costs; have
better control of broadcasts; tighten security; and distribute load. Relocate the
server into a secured location.

TCP/IP Layers
Application Layer
File transfer, E-Mail, Remote Login, Network Management, Name Management.

Transport Layer
TCP (connection oriented), UDP(Connectionless).
Flow control provided by sliding windows. Reliability provided by sequence numbers
and acknowledgements.

Port Numbers
Used to pass information to the upper layers.

TCP

FTP 21

Telnet 23

SMTP 25

DNS 53

UDP

DNS 53

TFTP 69

SNMP 161

RIP 520

Numbers below 1024 are well known ports. Dynamically assigned ports are above
1024. Registered ports are for vendor specific applications: usually above 1024.

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Internet Layer Corresponds with OSI Network layer

IP provides connectionless, best-effort delivery routing of datagrams

ICMP provides control and messaging capabilities

ARP determines the data link layer address for known IP address

RARP determines network address when data link layer addresses are known

IP Address Classes
Class Net.Node.Node.Node 0
A

1
127

127 networks,
16M nodes

Class Net.Net.Node.Node
B

10

128 16K networks

191
65K nodes

Class Net.Net.Net.Node
C

110 192223

2M networks
254 nodes

Subnetting Formulas
(Count the bits only from the Node portion of the address. Therefore, for a Class B
address, the total masked bits+ unmasked bits = 16):

Max # of Subnets: 2(masked bits)-2

Max # of Hosts (per subnet): 2(unmasked bits)-2

Routing
Routers must learn destinations that are not directly connected.

Static (manual)
Uses a route that the network administrator enters manually. (Must be setup bidirectional)

Enter the IP Route command in global configuration mode

ip route {destination network} {mask} {port, on remote side, to get there}

ip route 172.16.10.0 255.255.255.0 172.16.40.1

Dynamic: Uses a route that a network routing protocol adjusts automatically

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router rip

network 172.16.0.0

router igrp {autonomous system #}

network 172.16.0.0

< use monitor, To>sh ip route {rip / igrp)

Routing Protocols
Interior - (within an autonomous system AS group of routers under the same
administrative authority)
Distance Vector understands the direction and distance to any network
connection on the internet work. Knows how many hops (the metric) to get there. All
routers w/in the internet work listen for messages from other routers, which are sent
every 30 to 90 seconds. They pass their entire routing tables. Possible problems:
Slow convergence, Routing Loops, Counting to Infinity (this is solved by maximum
hop count). Solutions: Split Horizon(cannot send information back in the direction it
was received);Hold-Downs(prevent regular update messages from reinstating a
route thats gone down). Uses hop count for measurement.

RIP 15 hop count max

IGRP 255 hop count max, uses reliability factor (255 optimal), and
bandwidth

Link State understands the entire network, and does not use secondhand
information. Routers exchange LSPs (hello packets). Each router builds a
topographical view of the network, then uses SPF (shortest path first) algorithm to
determine the best route. Changes in topology can be sent out immediately, so
convergence can be quicker. Uses Bandwidth for measurement.

OSPF decisions based on cost of route (metric limit of 65,535)

EIGRP hybrid protocol (has features of Distance Vector and Link State
protocols), Cisco proprietary

Exterior

EGP (Exterior Gateway Protocol)

BGP (Border Gateway Protocol)

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Counting to Infinity

Define a limit on the number of hops to prevent infinite loops

Split Horizon (never sends information about a route back the same direction
in which it was received)
Route Poisoning (Routers set the distance of routes that have gone down to
infinity. Used with hold-down timers)
Hold-Down Timers (Router keeps an entry for the network possibly down
state, allowing time for other routers to re-compute for this topology change)
Poison Reverse(overrides split horizon. Informs the sending router that the
destination is inaccessible)
Triggered Updates (Sends updates when a change in its routing table occurs.
Does not wait for the prescribe time to expire

IOS / Routing / Network Security

Cisco IOS (operating system) is stored in flash memory (EEPROM)

IOS configuration is stored in NVRAM

User Mode ordinary tasks checking status, etc. Need password depending on
how youre entering (Virtual Terminal pw for telnet session, Auxiliary pw for aux
port, Console pw for console port)

conf t

line vty 0 {line aux 0} {line con 0}

login

password letmein

Privileged Mode

conf t

enable password letmein

Banner

conf t

banner motd #

Hostname

conf t
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hostname MyRouter

Editing

CTRL+A beginning of line

CTRL+E end of line

<>show history
TAB completes command

Help

Press ? after any command for a list of what comes next

Router Elements/Configuration

<>show startup-config

<>show running-config

<>copy running-conifg startup-config

erase startup-config

setup

reload

boot system {flash / tftp}

copy flash tftp< to OR server) tftp software IOS(backup>

<>copy tftp flash

copy run tftp < configuration to tftp OR server)(backup>

copy tftp run

<>show proc

show mem

show buff

show flash

show cdp

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Network Security / Access Lists

Standard IP access list
Check the source address of packets that could be routed. Permits or denies output
for an entire protocol suite.

Filters based on source

Permit or deny entire TCP/IP protocol suite

Range is 1 through 99

Place close to the destination

access-list {number} {permit / deny} {source address}

access-list 10 permit 172.16.30.2

Extended IP access list

Check for both source and destination packet address. Can also check for specific
protocols, port numbers, and other parameters, which allows administrators more
flexibility in describing what checking the access list will do.

Filter based on Source and destination

Specifies a particular IP protocol and port number

Range is 100 though 199

Place lists close to the source

access-list {number} {permit / deny} {protocol}{source} {destination}

{port}

access-list 110 permit tcp host 172.16.50.2 host 172.16.10.2 eq8080

Access lists may be applied to:

o

Inbound access lists. Saves overhead of routing lookups if the packet

is to be discarded because it is denied by the filtering tests.

Outbound access lists. Packets are routed to the outbound interface

and then processed through the outbound access lists.

An access list can be applied to multiple interfaces. However, there can

be only one access list per protocol, per direction, per interface.

Wildcard masks use masks to identify insignificant bits, eg

access-list 11 permit 172.16.30.0 0.0.0.255

(permits anybody with 172.16.30.x)

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Note: you can use 0.0.0.0 as the mask to limit to that specific host, or prefix
it with host

Applying the list to an interface (use access-group on the interface):

o

<>

int e0

ip access-group 110 out

IPX Access lists

Standard: access-list {number} {permit/deny} {source}{destination}

Extended: access-list {number} {permit/deny} {protocol} {source}{socket}

{destination} {socket}

access-list 810 permit 30 10

int e0

ipx access-group 810 out

IPX SAP Filters

access-list {number} {permit/deny} {source} {service type}

To apply on interface: ixp input-sap-filter {number}

access-list 1010 permit 11.0000.0000.0001 0

int e0

ipx input-sap-filter 1010

Access list Numbers allowed:

1-99

IP
Standard

100199

IP
Extended

800899

IPX
Standard

900999

IPX
Extended

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10001099

IPX SAP

To Monitor Access Lists

<>

Show access-list

WAN
Layer 1 Connection Types

Leased Lines point-to-point or dedicated connection. Pre-established

WAN path from customer through ISP to remote network.

Circuit Switching Dedicated circuit path must exist between sender and
receiver for the duration of the call. Used with ISDN. Used when customer
doesnt need a 24/7 connection, but needs a reliable connection

Packet Switching Network devices share a single point-to-point link to

transport packets from a source to a destination across a carrier network.
They use virtual circuits that provide end-to-end connectivity.

Wan Service Providers

Customer premises equipment (CPE) - Devices physically located at

subscribers location.

Demarcation (or demarc) - The place where the CPE ends and the local
loop portion of the service begins. (Usually in the phonecloset).

Local loop - Cabling from the demarc into the WAN service providers central
office.

Central Office switch (CO) - Switching facility that provides the nearest
point of presence for the providers WAN service.

Toll network The switches and facilities,(trunks), inside the WAN

providers cloud.

Layer 2 Encapsulation Protocols

High-Level Data Link Control (HDLC) Default encapsulation type on

point-to-point, dedicated links, and circuit switched connections. Used for
communications between two Cisco devices.

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Point-to-Point Protocol (PPP) Provides router-to-router and host-to-network

connections over synchronous and asynchronous circuits.

Uses PAP or CHAP authentication.

Int s0, encapsulation PPP

Serial Line Internet Protocol (SLIP) Standard protocol for use with
TCP/IP. It has, for the most part, been replaced by PPP.

X.25/Link Access Procedure, Balanced (LAPB) Standard that defines

how connections between DTE and DCE are maintained.

Frame Relay Industry standard, switched data linklayer protocol that

handles multiple virtual circuits. (Replaces X.25). Shared bandwidth over
public network. Virtual circuits are identified by DLCIs.

DLCI - (Data Link Connection identifiers). LMI(Local Management Interface),

co-developed in 1990 by Cisco, provides message information about current
DLCI values (global or local significance), and the status of virtual circuits.
Subinterfaces allow you to have multiple virtual circuits on a single serial
interface. You must map an IP device to the DLCI (using the frame-relay map
command or the Inverse-ARP function)
o

int s0

encapsulation frame-relay {ietf}

Note: if you dont specify ietf, it uses cisco bydefault

frame-relay interface-dlci {#}

frame-relay lmi-type {cisco, ansi, q933a}

Subinterfaces:

int s0.x {multipoint / point-to-point}

Mapping:

int s0

inverse-arp or

frame-relay map ip x.x.x.x #

Monitoring:

show frame {pvc / ip / lmi / traffic / etc.}

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Asynchronous Transfer Mode (ATM) International standard for cell relay while
using multiple services (voice, video, data)

Frame Relay PVC Connection

Uses the Data Link and Physical Layer of OSI model.

Local access Rate Clock speed of the connection to the Frame Relay cloud
Virtual Circuit (VC) Logical circuit created to ensure communication between
two devices.
PVC Virtual circuit that is permanent. Saves bandwidth by not having to
establish circuits each time it is used.
SVC Virtual circuit that is established on-demand and is disconnected when
no longer needed.
Data-link connection identifier (DLCI) -A number which identifies the logical
circuit between the router and the Frame Relay Switch.
Committed Information Rate (CIR) The rate that the Frame relay switch
agrees to transfer data (in bits per second).
Inverse Address resolution Protocol (Inverse ARP) Method of dynamically
associating a network layer address with a DLCI.
Local Management Interface(LMI) Signaling standard between the router
device and the Frame Relay Switch.
Backward Explicit Congestion Notification (BECN) When congestion occurs,
a BECN is sent from the receiving Frame Relay switch to reduce the rate of
sending date.

ISDN
ISDN - digital service that runs over existing telephone networks
Normally used to support applications requiring high-speed voice, video, and data
communications for home users, remote offices, etc.

ISDN Terminal Equipment Types

TE1 understand ISDN standards

TE2 predate ISDN standards, require a TA (terminal adaptor)

NT1 Converts BRI signals into a form used by the ISDN digital line.

NT2 ISDN PBX

TA Terminal Adapter, converts V.35, and other signals into BRI signals.

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TM

Cramsession: CCNA 2.0

Reference Points describe the point between

R non-ISDN and TA

S user terminals and NT2

T NT1 and NT2 devices

U NT1 and line termination

ISDN Protocols

E on existing telephone network

I concepts, terminology, and services

Q switching and signaling

ISDN BRI (Basic Rate Interface): 2 64K B channels, plus 1 16K D channel

ISDN PRI (Primary Rate Interface):

23 64K B channels, plus 164K D channel (North America & Japan)
30 64K B channels, plus 1 64K D channel (Europe & Australia)

Configuration example:
o

config t

isdn switch-type basic-dms100

int bri0

encap ppp

isdn spid1 775154572

isdn spid1 455145664

Special thanks to
Dale Long
for contributing this
Cramsession.

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