Layer 2 Trace Route Utility

The Layer 2 trace route utility traces the traffic path through a specified device in a VLAN. It can also be used to probe all reachable paths to all devices in the VLAN. The utility can do the following:

  • Trace a specific IP, MAC, or hostname in a VLAN
  • Probe the entire Layer 2 topology

The command output shows the following information:

  • Input or output ports of each hop in the path
  • Round trip travel time of each hop
  • Hops in the VLAN that form a loop
  • Each hop's Layer 2 protocol such as STP, RSTP, IEEE 802.1w, SSTP, metro ring, or route-only
  • Hostname for each hop

The probed Layer 2 information is discarded when a new trace-l2 command is issued.

Layer 2 Trace Path Example

device# trace-l2 vlan 1
device# trace-l2 show

*** Warning! The following 4 hops form a loop in vlan 1

hop   input  output IP and/or MAC address       microsec comment    hostname

  1                    d4c1.9e18.7ca8

  2   e2/1/35          609c.9f52.19b2

  3   e1/1/23          d4c1.9e18.8b19

  4   e1/1/11          0000.0000.00bb

Vlan 1 L2 topology was probed 6 sec ago, # of paths: 2

path 1 from e1/1/27, 3 hops:

  hop   input  output IP and/or MAC address       microsec comment    hostname

  1   e2/1/35 e2/1/23  10.0.0.6  609c.9f52.19b2     65611

  2   e1/1/23 e1/1/36  10.0.0.7  d4c1.9e18.8b19     64415

  3   e1/1/11          10.0.0.8  0000.0000.00bb     62042

path 2 from e1/1/1, 3 hops:

  hop   input  output IP and/or MAC address       microsec comment    hostname

  1   e1/1/10 e1/1/11  10.0.0.8  0000.0000.00bb     67943

  2   e1/1/36 e1/1/23  10.0.0.7  d4c1.9e18.8b19     6044

  3   e2/1/23          10.0.0.6  609c.9f52.19b2     1262

path 3 from e1/1/15, 1 hops:

  hop   input  output IP and/or MAC address       microsec comment    hostname

  1    e2/1/15         10.0.0.9  0000.6e13.00aa     67943

device#

Considerations and Limitations

  • The Layer 2 trace route utility supports only Unicast destination MAC addresses.
  • The results of this command are stored for no more than 10 minutes on a device and are replaced when a new trace-l2 command is issued again.
  • The Layer 2 trace route utility detects the IP as the IP of the virtual Ethernet (VE) interface, if available; else it will try to detect the IP of the Loopback interface.
  • On a topology where loops are avoided by a loop avoidance protocol, the traced path will honor the loop-free network path.
  • Devices and interfaces that do not support the Layer 2 trace route utility will act as transparent bridges and will be invisible to the trace-l2 result.
  • The destination for trace-l2 operation must be another ICX device and not an end host.
  • At any point in time only one trace-l2 operation can be running in a network.
  • The Layer 2 trace route utility is not supported on breakout ports.
  • The Layer 2 trace route utility results can discover up to 8 hops in a single path.
  • The Layer 2 trace route utility operation takes at most one second to complete.
  • To use the Layer 2 trace route utility with a hostname, a DNS mapping with the hostname must be present in the DNS server.
Parent topic: VLANs