I know we have lot of queries related with this command why it is not work for MAC some time it works, so below information will provide all queries to solve.
Traceroute is a tool for measuring the route path and
transit times of packets across an Internet Protocol (IP) network.
Traceroute sends a sequence of Internet Control Message
Protocol (ICMP) packets addressed to a destination host. Tracing the
intermediate routers traversed involves control of the time-to-live (TTL)
Internet Protocol parameter. Routers decrement this parameter and discard a
packet when the TTL value has reached zero, returning an ICMP error message
(ICMP Time Exceeded) to the sender.
In a Data Center, it is often required to find a host and
the layer2 path. To do it, Cisco has implemented a good tool: traceroute mac.
The traceroute mac command output shows
the Layer2 path when the specified source and destination addresses
belong to the same VLAN. If
you specify source and destination addresses that belong to different VLANs,
the Layer 2 path is not identified, and an error message appears.
See you the example to understand how this feature works.
Suppose to have two host (192.168.0.4, 192.168.0.6) and you would find the
layer2 path using the Ciscozine-SW1 Switch.
SW1#sh
mac-address-table dynamic
Mac
Address Table
-------------------------------------------
Vlan Mac Address Type Ports
---- ----------- -------- -----
1 000e.d7e3.0880 DYNAMIC
Fa0/1
1 000e.d7e3.0881 DYNAMIC
Fa0/1
1 0014.a968.f0b1 DYNAMIC
Fa0/48
1 0019.9955.0f60 DYNAMIC
Fa0/21
1 0026.22eb.3bef DYNAMIC
Fa0/1
1 00a0.6011.aa0b DYNAMIC
Fa0/1
Total
Mac Addresses for this criterion: 6
SW1#sh
ip arp
Protocol Address Age (min) Hardware Addr Type
Interface
Internet 192.168.0.1 65
0014.a968.f0b1 ARPA Vlan1
Internet 192.168.0.4 0
00a0.6011.aa0b ARPA Vlan1
Internet 192.168.0.5 1
0026.22eb.3bef ARPA Vlan1
Internet 192.168.0.6 1
0019.9955.0f60 ARPA Vlan1
Internet 192.168.0.253 -
000e.d7d0.cd80 ARPA Vlan1
Internet 192.168.0.254 69
000e.d7e3.0880 ARPA Vlan1
You have two options to find the path between two hosts:
1.
Trace using the MAC address
2.
Trace using the IP address
In the first case, use the command ‘traceroute mac 0019.9955.0f60 00a0.6011.aa0b’
SW1#traceroute
mac 0019.9955.0f60 00a0.6011.aa0b
Source
0019.9955.0f60 found on SW1
1
SW1 (192.168.0.253) : Fa0/21 => Fa0/1
2
SW2 (192.168.0.254) : Fa0/1 => Fa0/27
Destination
00a0.6011.aa0b found on SW2
Layer
2 trace completed
In the second case, use the command ‘traceroute mac ip 192.168.0.4 192.168.0.6’
SW1#traceroute
mac ip 192.168.0.4 192.168.0.6
Translating
IP to mac .....
192.168.0.4
=> 00a0.6011.aa0b
192.168.0.6
=> 0019.9955.0f60
Source
00a0.6011.aa0b found on SW2
1
SW2 (192.168.0.254) : Fa0/27 => Fa0/1
2
SW1 (192.168.0.253) : Fa0/1 => Fa0/21
Destination
0019.9955.0f60 found on SW1
Layer
2 trace completed
and to have more detail about the trace use the ‘detail’
option:
SW1#traceroute
mac ip 192.168.0.4 192.168.0.6 detail
Translating
IP to mac .....
192.168.0.4
=> 00a0.6011.aa0b
192.168.0.6
=> 0019.9955.0f60
Source
not directly connected, tracing source .....
Source
00a0.6011.aa0b found on SW2[WS-C3550-48] (192.168.0.254)
1
SW2 / WS-C3550-48 / 192.168.0.254 :
Fa0/27
[auto, auto] => Fa0/1 [auto, auto]
2
SW1 / WS-C3550-48 / 192.168.0.253 :
Fa0/1
[auto, auto] => Fa0/21 [auto, auto]
Destination
0019.9955.0f60 found on SW1[WS-C3550-48] (192.168.0.253)
Layer
2 trace completed.
Point to Remember:
·
For Layer 2 traceroute to function properly,
Cisco Discovery Protocol (CDP) must be enabled on all the switches in the
network. Do not disable CDP.
·
When the switch detects a device in the Layer 2
path that does not support Layer 2 traceroute, the switch continues to send
Layer 2 trace queries and lets them time out.
·
The maximum number of hops identified in the path is ten.
·
Layer 2 traceroute supports only unicast traffic.
·
The traceroute mac command output shows the
Layer 2 path when the specified source and destination addresses belong to the
same VLAN.
Trace Mac not supported:
·
The Layer 2 traceroute feature is not supported
when multiple devices are attached to one port through hubs (for example,
multiple CDP neighbors are detected on a port).
·
This feature is not supported in Token Ring
VLANs.
·
The traceroute mac ip command output shows the
Layer 2 path when the specified source and destination IP addresses are in the
same subnet. When you specify the IP addresses, the switch uses Address
Resolution Protocol (ARP) to associate the IP addresses with the corresponding
MAC addresses and the VLAN IDs.
# if an ARP entry exists for the specified IP address, the
switch uses the associated MAC address and identifies the physical path.
# if an ARP entry does not exist, the switch sends an ARP
query and tries to resolve the IP address. The IP addresses must be in the same
subnet. If the IP address is not resolved, the path is not identified, and an
error message appears.
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