Lab - Troubleshooting ACL Configuration and Placement
Topology
Addressing Table
IP Address Subnet Mask
Device Interface IPv6 Address / Prefix Default Gateway
Link Local Address
192.168.1.1 255.255.255.0
HQ G0/1 2001:DB8:ACAD:1::1/64 N/A
FE80::1
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Lab - Troubleshooting ACL Configuration and Placement
10.1.1.2 255.255.255.252
S0/0/1 2001:DB8:ACAD:A::2/64 N/A
FE80::2
192.168.4.1 255.255.255.0
Lo0 2001:DB8:ACAD:4::1/64 N/A
FE80::1
192.168.3.1 255.255.255.0
G0/1 2001:DB8:ACAD:3::1/64 N/A
FE80::1
ISP
10.1.1.1 255.255.255.252
S0/0/0 (DCE) 2001:DB8:ACAD:A::1/64 N/A
FE80::1
S1 VLAN 1 192.168.1.11 255.255.255.0 192.168.1.1
S3 VLAN 1 192.168.3.11 255.255.255.0 192.168.3.1
192.168.1.3 255.255.255.0 192.168.1.1
PC-A NIC 2001:DB8:ACAD:1::3/64
FE80::1
FE80::3
192.168.3.3 255.255.255.0 192.168.3.1
PC-C NIC 2001:DB8:ACAD:3::3/64
FE80::1
FE80::3
Objectives
Part 1: Build the Network and Configure Basic Device Settings
Part 2: Troubleshoot Internal Access
Part 3: Troubleshoot Remote Access
Background / Scenario
An access control list (ACL) is a series of IOS commands that provide basic traffic filtering on a Cisco router.
ACLs are used to select the types of traffic to be processed.
A single ACL statement is called an access control entry (ACE). The ACEs in the ACL are evaluated from top
to bottom with an implicit deny all ACE at the end of the list. ACLs can also control the types of traffic into or
out of a network by the source and destination hosts or network. To process the desired traffic correctly, the
placement of the ACLs is critical.
In this lab, a small company has just added a web server to the network to allow customers to access
confidential information. The company IPv4 and IPv6 network is divided into two zones: Corporate network
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Lab - Troubleshooting ACL Configuration and Placement
zone and Demilitarized Zone (DMZ). The corporate network zone houses private servers and internal clients.
The DMZ houses the externally accessible web server (simulated by Lo0 on HQ).
To secure access to the corporate and DMZ networks, several ACLs were configured on the HQ router.
However, there are problems with the configured ACLs. In this lab, you will examine what the ACLs are doing
and take corrective actions to implement them properly.
When troubleshooting ACLs, it is important that its purpose and desired outcome is well understood. For this
reason, the following describes the ACLs configured on HQ:
• ACL 101 is implemented to limit the traffic leaving the corporate network zone. This zone is often referred
to as the private or internal network because it houses the private servers and internal clients. In this
topology, this zone is assigned network address 192.168.1.0/24. Therefore, only traffic from that network
should be permitted to leave the internal network.
• ACL 102 is used to limit the traffic into the corporate network. Only responses to requests that originated
from within the corporate network are allowed back into that network. This includes TCP-based requests
from internal hosts such as Web and FTP. ICMP is allowed into the network for troubleshooting purposes
so that incoming ICMP messages generated in response to pings can be received by internal hosts. No
other network should be able to access the corporate zone.
• ACL 121 controls outside traffic to the DMZ and corporate network. Only HTTP traffic is allowed to the
DMZ web server (simulated by Lo0 on HQ). Other network related traffic, such as EIGRP, is allowed from
outside networks. Furthermore, valid internal private addresses, such as 192.168.1.0, loopback address
such as 127.0.0.1 and multicast addresses are denied entrance to the corporate network to prevent
malicious network attacks from outside users.
• IPv6 ACL named NO-ICMP denies ICMP traffic to the DMZ and corporate network originated from the
outside. ICMP response is allowed into the network that is responding to the requests from the internet
hosts. Other network related traffic, such as EIGRP, is allowed from outside networks. Furthermore, the
outside network is allowed to access the DMZ web server (simulated by Lo0 on HQ).
Note: The routers used with CCNA hands-on labs are Cisco 1941 Integrated Services Routers (ISRs) with
Cisco IOS Release 15.4(3) (universalk9 image). The switches used are Cisco Catalyst 2960s with Cisco IOS
Release 15.0(2) (lanbasek9 image). Other routers, switches and Cisco IOS versions can be used. Depending
on the model and Cisco IOS version, the commands available and output produced might vary from what is
shown in the labs. Refer to the Router Interface Summary Table at the end of the lab for the correct interface
identifiers.
Note: Make sure that the routers and switches have been erased and have no startup configurations. If you
are unsure, contact your instructor.
Required Resources
• 2 Routers (Cisco 1941 with Cisco IOS Release 15.4(3) universal image or comparable)
• 2 Switches (Cisco 2960 with Cisco IOS Release 15.0(2) lanbasek9 image or comparable)
• 2 PCs (Windows with terminal emulation program, such as Tera Term)
• Console cables to configure the Cisco IOS devices via the console ports
• Ethernet and serial cables as shown in the topology
Part 1: Build the Network and Configure Basic Device Settings
In Part 1, you will set up the network topology and configure the routers and switches with basic settings such
as passwords and IP addresses. Preset configurations are also provided for you for the initial router configurations.
You will also configure the IP settings for the PCs in the topology. Step 1: Cable the network as shown in
the topology.
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Lab - Troubleshooting ACL Configuration and Placement
Step 2: Configure PC hosts according to the Addressing Table Step
3: Initialize and reload the routers and switches as necessary.
Step 4: (Optional) Configure basic settings for each switch.
a. Disable DNS lookup.
b. Configure host names as shown in the Topology.
c. Configure IP addresses and default gateways as shown in the Addressing Table.
d. Assign cisco as the console and vty passwords.
e. Assign class as the privileged EXEC password.
f. Configure logging synchronous to prevent console messages from interrupting command entry.
Step 5: Configure basic settings for each router.
a. Disable DNS lookup.
b. Configure host names as shown in the topology.
c. Assign class as the privileged EXEC password.
d. Assign cisco as the console and vty passwords.
e. Configure logging synchronous to prevent console messages from interrupting command entry.
Step 6: Configure HTTP access and user credentials on HQ router. Local user
credentials are configured to access the simulated web server (192.168.4.1).
HQ(config)# ip http server
HQ(config)# username admin privilege 15 secret adminpass HQ(config)#
ip http authentication local
Step 7: Load router configurations.
The configurations for the routers ISP and HQ are provided for you. There are errors within these
configurations, and it is your task to correct them.
Router ISP hostname ISP
ipv6 unicast-routing
ipv6 router eigrp 1
eigrp router-id
10.1.1.1 no
shutdown interface
GigabitEthernet0/1
ip address
192.168.3.1
255.255.255.0 ipv6
address FE80::1
link-local ipv6
address
2001:DB8:ACAD:3::1/6
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Lab - Troubleshooting ACL Configuration and Placement
4 ipv6 eigrp 1 no
shutdown interface
Serial0/0/0 ip
address 10.1.1.1
255.255.255.252
clock rate 128000
ipv6 address FE80::1
link-local ipv6
address
2001:DB8:ACAD:A::1/6
4 ipv6 eigrp 1 no
shutdown router
eigrp 1 network
10.1.1.0 0.0.0.3
network 192.168.3.0
no auto-summary end
Router HQ hostname HQ
ipv6 unicast-routing
ipv6 router eigrp 1
eigrp router-id
10.1.1.2 no
shutdown interface
Loopback0 ip
address 192.168.4.1
255.255.255.0 ipv6
address FE80::1
link-local ipv6
address
2001:DB8:ACAD:4::1/6
4 ipv6 eigrp 1
interface
GigabitEthernet0/1
ip address
192.168.1.1
255.255.255.0 ipv6
address FE80::1
link-local ipv6
address
2001:DB8:ACAD:1::1/6
4 ip access-group
101 out ip access-
group 102 in ipv6
eigrp 1 no shutdown
interface
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Lab - Troubleshooting ACL Configuration and Placement
Serial0/0/1 ip
address 10.1.1.2
255.255.255.252 ip
access-group 121 in
ipv6 address FE80::2
link-local ipv6
address
2001:DB8:ACAD:A::2/6
4 ipv6 eigrp 1 ipv6
traffic-filter NO-
ICMP out no shutdown
router eigrp 1
network 10.1.1.0 0.0.0.3
network 192.168.1.0
network 192.168.4.0 no
auto-summary ip http
server
access-list 101 permit ip 192.168.11.0 0.0.0.255 any
access-list 101 deny ip any any
access-list 102 permit tcp any any established
access-list 102 permit icmp any any echo-reply
access-list 102 permit icmp any any unreachable
access-list 102 deny ip any any
access-list 121 permit tcp any host 192.168.4.1 eq 89
access-list 121 deny icmp any host 192.168.4.11
access-list 121 deny ip 192.168.1.0 0.0.0.255 any
access-list 121 deny ip 127.0.0.0 0.255.255.255 any
access-list 121 deny ip 224.0.0.0 31.255.255.255 any
access-list 121 permit ip any any access-list 121
deny ip any any ipv6 access-list NO-ICMP deny icmp
any any echo-request permit ipv6 any any end
Part 2: Troubleshoot Internal Access
In Part 2, the ACLs on router HQ are examined to determine if they are configured correctly.
Step 1: Troubleshoot ACL 101
ACL 101 is implemented to limit the traffic leaving the corporate network zone. This zone houses only internal
clients and private servers. Only 192.168.1.0/24 network can exit this corporate network zone. a. Can PC-A
ping its default gateway?
b. After verifying that PC-A was configured correctly, examine the HQ router to find possible configuration
errors by viewing the summary of ACL 101. Enter the command show access-lists 101. HQ# show
access-lists 101
Extended IP access list 101
10 permit ip 192.168.11.0 0.0.0.255 any
20 deny ip any any
c. Are there any problems with ACL 101? Yes must support ip 192.168.1.0 an not 192.168.11.0
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Lab - Troubleshooting ACL Configuration and Placement
d. Correct ACL 101. Record the commands used to correct the errors.
HQ# show ip interface g0/1
GigabitEthernet0/1 is up, line protocol is up
Internet address is 192.168.1.1/24
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1500 bytes
Helper address is not set
Directed broadcast forwarding is disabled
Multicast reserved groups joined: 224.0.0.10
Outgoing access list is 101
Inbound access list is 102
e. Can PC-A ping its default gateway?
f. PC-A still cannot ping its default gateway, therefore verify that ACL 101 is applied in the correct direction
on the G0/1 interface. Enter the show ip interface g0/1 command.
HQ# show ip interface g0/1
GigabitEthernet0/1 is up, line protocol is up
Internet address is 192.168.1.1/24
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1500 bytes
Helper address is not set
Directed broadcast forwarding is disabled
Multicast reserved groups joined: 224.0.0.10
Outgoing access list is 101
Inbound access list is 102
Is the direction for interface G0/1 configured correctly for ACL 101?
g. Correct the direction of ACL 101 on the G0/1 interface. Record the commands used to correct the errors.
h. Verify the traffic from network 192.168.1.0 /24 can exit the corporate network. PC-A should now be able
to ping its default gateway interface.
Step 2: Troubleshoot ACL 102
ACL 102 is implemented to limit traffic going into the corporate network. Traffic originating from the outside
network is not allowed onto the corporate network. Remote traffic is allowed into the corporate network if the
established traffic originated from the internal network. ICMP reply messages are allowed for troubleshooting
purposes.
a. Can PC-A ping PC-C? No
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Lab - Troubleshooting ACL Configuration and Placement
b. Examine the HQ router to find possible configuration errors by viewing the summary of ACL 102. Enter
the command show access-lists 102. HQ# show access-lists 102
Extended IP access list 102
10 permit tcp any any established
20 permit icmp any any echo-reply
30 permit icmp any any unreachable
40 deny ip any any (57 matches)
c. Are there any problems with ACL 102?
d. Verify that the ACL 102 is applied in the correct direction on G0/1 interface. Enter the show ip interface
g0/1 command.
HQ# show ip interface g0/1
GigabitEthernet0/1 is up, line protocol is up
Internet address is 192.168.1.1/24
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1500 bytes
Helper address is not set
Directed broadcast forwarding is disabled
Multicast reserved groups joined: 224.0.0.10
Outgoing access list is 101
Inbound access list is 101
e. Are there any problems with the application of ACL 102 to interface G0/1?
f. Correct any errors found regarding ACL 102. Record the commands used to correct the errors.
g. Can PC-A ping PC-C now? Yes
Part 3: Troubleshoot Remote Access
In Part 3, ACL 121 is configured to prevent spoofing attacks from the outside networks and allow only remote
HTTP access to the web server (192.168.4.1) in the DMZ.
a. Verify ACL 121 has been configured correctly. Enter the show ip access-list 121 command.
HQ# show ip access-lists 121
Extended IP access list 121
10 permit tcp any host 192.168.4.1 eq 89
20 deny icmp any host 192.168.4.11
30 deny ip 192.168.1.0 0.0.0.255 any
40 deny ip 127.0.0.0 0.255.255.255 any
50 deny ip 224.0.0.0 31.255.255.255 any
60 permit ip any any (354 matches)
70 deny ip any any
Are there any problems with this ACL?
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Lab - Troubleshooting ACL Configuration and Placement
b. Make and record the necessary configuration changes to ACL 121.
HQ# show ip interface s0/0/1
Serial0/0/1 is up, line protocol is up
Internet address is 10.1.1.2/30
Broadcast address is 255.255.255.255
<Output Omitted>
Multicast reserved groups joined: 224.0.0.10
Outgoing access list is not set
Inbound access list is 121
c. Verify that the ACL 121 is applied in the correct direction on the HQ S0/0/1 interface. Enter the show ip
interface s0/0/1 command.
HQ# show ip interface s0/0/1
Serial0/0/1 is up, line protocol is up
Internet address is 10.1.1.2/30
Broadcast address is 255.255.255.255
<output omitted>
Multicast reserved groups joined: 224.0.0.10
Outgoing access list is not set
Inbound access list is 121
Are there any problems with the application of this ACL?
d. Verify that PC-C can only access the simulated web server on HQ by using the web browser. Provide the
username admin and password adminpass to access the web server (192.168.4.1).
Part 4: Troubleshoot IPv6 ACL
In Part 4, an IPv6 ACL named NO-ICMP denies ICMP traffic to the DMZ and corporate network originating
from the outside. ICMP response to the internal hosts, EIGRP packets, and network related traffic are
allowed from outside networks. Furthermore, the outside network is allowed to access the DMZ web server
(simulated by Lo0 on HQ).
a. Verify ACL NO-ICMP has been configured correctly. Enter the show ipv6 access-list NO-ICMP
command.
HQ# show ipv6 access-list NO-ICMP IPv6
access list NO-ICMP
deny icmp any any echo-request sequence 10
permit ipv6 any any sequence 20
Are there any problems with this ACL?
b. Verify that the ACL NO-ICMP is applied in the correct direction on the HQ S0/0/1 interface. Enter the
show ipv6 interface s0/0/1 command.
HQ# show ipv6 interface s0/0/1
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Lab - Troubleshooting ACL Configuration and Placement
Serial0/0/1 is up, line protocol is up
IPv6 is enabled, link-local address is FE80::2
No Virtual link-local address(es):
Global unicast address(es):
2001:DB8:ACAD:A::1, subnet is 2001:DB8:ACAD:A::/64
Joined group address(es): FF02::1 FF02::2
FF02::A
FF02::1:FF00:1
FF02::1:FF00:2
MTU is 1500 bytes
ICMP error messages limited to one every 100 milliseconds
ICMP redirects are enabled
ICMP unreachables are sent
Output features: Access List
Outgoing access list NO-ICMP
ND DAD is enabled, number of DAD attempts: 1
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Lab - Troubleshooting ACL Configuration and Placement
ND reachable time is 30000 milliseconds (using 30000)
ND RAs are suppressed (periodic)
Hosts use stateless autoconfig for addresses. Are
there any problems with the application of this ACL?
c. Make and record the necessary configuration changes to ACL NO-ICMP.
Reflection
1. How should the ACL statement be ordered? From general to specific or vice versa?
The order should be specific to general, given that the ACL is executed from top to bottom, in sequential
order. When a condition is true, the processing in the list stops and no other comparison is made.
2. If you delete an ACL by using the no access-list command and the ACL is still applied to the interface,
what happens How should the ACL statement be ordered? From general to specific or vice versa?
A default deny any statement would apply. Care must be taken when removing an ACL applied to an active
interface.
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Lab - Troubleshooting ACL Configuration and Placement
Router Interface Summary Table
Router Interface Summary
Router Model Ethernet Interface #1 Ethernet Interface #2 Serial Interface #1 Serial Interface #2
1800 Fast Ethernet 0/0 Fast Ethernet 0/1 Serial 0/0/0 (S0/0/0) Serial 0/0/1 (S0/0/1)
(F0/0) (F0/1)
1900 Gigabit Ethernet 0/0 Gigabit Ethernet 0/1 Serial 0/0/0 (S0/0/0) Serial 0/0/1 (S0/0/1)
(G0/0) (G0/1)
2801 Fast Ethernet 0/0 Fast Ethernet 0/1 Serial 0/1/0 (S0/1/0) Serial 0/1/1 (S0/1/1)
(F0/0) (F0/1)
2811 Fast Ethernet 0/0 Fast Ethernet 0/1 Serial 0/0/0 (S0/0/0) Serial 0/0/1 (S0/0/1)
(F0/0) (F0/1)
2900 Gigabit Ethernet 0/0 Gigabit Ethernet 0/1 Serial 0/0/0 (S0/0/0) Serial 0/0/1 (S0/0/1)
(G0/0) (G0/1)
Note: To find out how the router is configured, look at the interfaces to identify the type of router and how many
interfaces the router has. There is no way to effectively list all the combinations of configurations for each router
class. This table includes identifiers for the possible combinations of Ethernet and Serial interfaces in the device.
The table does not include any other type of interface, even though a specific router may contain one. An
example of this might be an ISDN BRI interface. The string in parenthesis is the legal abbreviation that can be
used in Cisco IOS commands to represent the interface.
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