- Alcatel Internetworking, Inc. Switch Troubleshooting Guide

ARP Protocol Failure Troubleshooting ARP
page 11-2 OmniSwitch Troubleshooting Guide September 2005
ARP Protocol Failure
If device A is not able to communicate with device B, it could be a result of ARP resolution failure. To
troubleshoot ARP the first reference point is to make sure that the MAC address of device A and device B
are learned on the right port and in correct VLAN.
Use the following command syntax:
show mac-address-table slot number
In our case we have a device connected in slot 16, so the command to verify the MAC address is as
follows:
-> show mac-address-table slot 16
Legend: Mac Address: * = address not valid
Vlan Mac Address Type Protocol Operation Interface
------+-------------------+--------------+-----------+------------+-----------
10 08:00:20:a8:f0:8a learned 10800 bridging 16/2
Total number of Valid MAC addresses above = 1
This command displays that MAC Address 08:00:20:a8:f0:8a, belonging to Device A, is learned on port
16/2 and in VLAN 10.
A more comprehensive look for all the MAC addresses learned by the switch can be done by using the
show mac-address-table command. For example:
-> show mac-address-table
Now, verify that the gateway defined in device A points towards the correct IP address. In our case, the
gateway of device A is defined as 10.10.42.1.
Workstation: A Workstation: B
08:00:20:a8:f0:8a 00:C0:4F:04:6C:2A
Gatewa
y
Gatewa
y
Se
g
ment: A Se
g
ment: B
00:d0:95:79:62:d1
00:d0:95:79:62:8b