Monitoring and Analyzing Switch Operation

Traffic Mirroring

Effect of Downstream VLAN Tagging on Untagged,Mirrored Traffic

In a remote mirroring application, if mirrored traffic leaves the switch without 802.1Q VLAN tagging, but is forwarded through a downstream device that adds 802.1Q VLAN tags, the MTU for untagged mirrored frames leaving the source switch is reduced below the values shown in Table B-2.

For example, if the MTU on the path to the destination is 1522 bytes, then untagged mirrored frames leaving the source switch cannot exceed 1518 bytes. Likewise, if the MTU on the path to the destination is 9220 bytes, then untagged mirrored frames leaving the source switch cannot exceed 9216 bytes.

Tagged 10 Gbps VLAN link.

Adds 4 bytes to each frame.

 

 

 

 

 

 

6200yl

 

Router in the

 

8212zl

Aggregator

 

Mirror Path

1Gbps

Remote

 

 

 

 

 

Mirror

 

 

 

 

 

 

 

 

 

 

Destination

Untagged 1 Gbps

VLAN Links

 

 

 

 

Traffic

3500yl

 

3500yl

 

Analyzer

Mirror Source

 

Mirror Source

 

 

 

 

Due to VLAN tagging on the 10 Gbps link, untagged traffic from the mirror sources must be at least 4 bytes smaller than the MTU for the path to the mirror destination.

Figure B-57. Effect of Downstream VLAN Tagging on the MTU for Mirrored Traffic
B-94