Limitations, conflicts, or exclusions

The following limitations, conflicts, or exclusions apply when configuring multiple mirroring sessions on a switch:

  • CPU generated packets egressing on a routed L3 interface will not be mirrored to the destination port.

  • Untagged egress packets that get mirrored will have the native VLAN tag in the mirrored packet. These extra bytes can cause traffic loss at the mirror destination when running line rate traffic.

  • A mirroring session can either be rx, tx, or both. When a user configures a mirroring session with both rx and tx enabled, two mirroring sessions are created in hardware. A mirroring session with only rx or tx counts as one mirroring session in hardware. Up to 4 such rx/tx sessions in total are supported. Any additional configured mirroring sessions will not work. The number of mirroring sessions created does not depend upon the number of source interfaces being mirrored, but on whether the traffic being mirrored in the session isrx, tx, or both. An rx mirroring session with multiple source ports will create one hardware mirroring session (refer to configuration 3). A mirroring session mirroring both rx and tx traffic on different source ports will create two hardware mirroring sessions (refer to configuration 1).

  • True egress mirroring is not supported on 8325 platforms. Egress mirroring takes place at the ingress. The packets that may get dropped at the egress might also have been mirrored at ingress. The mirrored traffic will also be mirrored before the policy actions are processed at the egress.

The following configurations each create two mirroring sessions in the hardware:

Configuration 1 
mirror session 1
          source interface 1/1/1 rx
          source interface 1/1/2 tx
          destination interface 1/1/3
          enable
Configuration 2 
mirror session 1
          source interface 1/1/1 both
          destination interface 1/1/3
          enable

If configuration 1 and configuration 2 are applied on the switch, no more mirroring sessions can be configured as the limit of four mirroring sessions is reached.

The following configurations each create one mirroring session:

Config 3 
mirror session 1
          source interface 1/1/1 rx
          source interface 1/1/2 rx
          destination interface 1/1/3
          enable
Config 4 
mirror session 1
          source interface 1/1/1 tx
          source interface 1/1/2 tx
          destination interface 1/1/3
          enable

Configuration 3 and configuration 4 each create one hardware mirroring session. If configuration 3 and configuration 4 are applied on the switch, two more hardware mirroring sessions can be created.

Activation of a fifth hardware mirroring session will result in an error Operation Status field: 'platform_session_limit_reached' in the Status field. 
8320# show mirror 3
       Mirror Session: 3
       Admin Status: enable
       Operation Status: platform_session_limit_reached
       Source: interface 1/1/5 both
       Destination: interface 1/1/6
       Output Packets: 0
       Output Bytes: 0