Preserving encapsulation across SPAN
By stretch | Thursday, May 1, 2008 at 2:02 a.m. UTC
The other day I was attempting to analyze traffic traversing an 802.1Q trunk via SPAN, and I noticed the trunk headers were missing. I also noticed I wasn't seeing the typical background traffic like STP and CDP. A bit of poking around suggested I needed to configure SPAN to replicate the source 802.1Q encapsulation.
Switch(config)# monitor session 1 source interface g0/1 Switch(config)# monitor session 1 destination interface g0/2 encapsulation replicate
Alternatively, the encapsulation can be explicitly configured as either 802.1q or ISL. After modifying the SPAN session I was seeing all traffic as expected. Seems strange that this isn't done by default.
Posted in Switching
May 1, 2008 at 2:56 a.m. UTC
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