218 Cisco LAN Switching Configuration Handbook
[interface type interface_number] source_mac_address
[interface type interface_number]
destination_mac_address [vlan vlan_id] [detail]
Layer 2 traces are performed from the source MAC address src-mac (in dash-sepa-
rated hexadecimal pairs) to the destination MAC address dest-mac. Both source and
destination must be present in the address table on the switch. As well, both source
and destination must be in the same VLAN. If the hosts belong to more than one
VLAN, you can specify the desired VLAN number as vlan. The detail keyword dis-
plays additional information about the switch port media at each hop along the path.
If the MAC addresses are not readily known, you can give the source and destina-
tion as IP addresses src-ip and dest-ip. However, both hosts must be present in the
switch’s ARP table so that their MAC addresses can be found.
Packet-Tracing Example
On a Catalyst 6500 switch, a Layer 2 trace is performed from source 00-b0-d0-40-01-d1
to destination 00-10-a4-c6-b4-b7. These two hosts are on the same VLAN and are both
present in the switch’s address table.
The source address is found on port 2/12 of the local switch. The first Layer 2 hop is at
IP address 192.168.1.16, where the destination address is found in the address table for
port 3/1 on that switch.
Notice that the second Layer 2 hop is the switch at 192.168.1.253, which was identified
via CDP. However, either the switch model or its OS does not support the l2trace proto-
col. As a result, the Layer 2 traces time out, and no response is returned from the neigh-
boring switch at 192.168.1.253:
Switch#traceroute mac 00b0.d040.01d1 0010.a4c6.b4b7 detail
Source 00b0.d040.01d1 found on WS-C6509 (192.168.1.16)
1 192.168.1.16 :
Gi2/12 [full, 1000M] => Gi3/1 [auto, auto]
2 no response from neighbor 192.168.1.253
3 no response from neighbor 192.168.1.253
4 Error in trace
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