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Chapter 6
Troubleshooting TCP/IP Connectivity
If, after analyzing the access list, you can't see any problems but the prob-
lem is still occurring, you can temporarily remove the access list from the
interface to see what effect this has on the problem. If the problem disap-
pears after the access list is removed, something is wrong with the access list
and it needs to be fixed. If the problem does not go away with the removal
of the access list from the interface, you can eliminate it as a possible cause.
The commands used to view IP access lists are simply show running-
config
, show startup-config, or show ip access-list <access-list
number>
. These commands provide the information regarding each line of
the access list. In addition to these commands, you can issue the show ip
interface
command, which provides you with information regarding
which access lists are applied to the interface. Here is a sample output from
the show ip interface command:
Router_B>show ip interface
Ethernet0 is up, line protocol is up
Internet address is 172.16.50.1/24
Broadcast address is 255.255.255.255
Address determined by non-volatile memory
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 not set
Inbound access list is not set
Proxy ARP is enabled
Security level is default
Split horizon is enabled
ICMP redirects are always sent
ICMP unreachables are always sent
ICMP mask replies are never sent
IP fast switching is enabled
IP fast switching on the same interface is disabled
IP multicast fast switching is disabled
Router Discovery is disabled
IP output packet accounting is disabled
IP access violation accounting is disabled
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