[c-nsp] erspan for just one IP

Phil Mayers p.mayers at imperial.ac.uk
Thu Jan 12 05:34:55 EST 2012

On 01/12/2012 02:44 AM, Robert Hass wrote:
> Hi
> Is any way to have ERSPAN (on Cat6500) where traffic is copied only
> for one IP within VLAN.
> Eg. VLAN400, IP (where VLAN consist /16 subnet and 2k active hosts)

Sadly not, on sup720.

Nexus 7k has this, and since it's using EARL8 as well I assume it's 
possible in hardware on sup2T, but as I recall no sign of the feature in 

If it suits your needs, the "capture" SPAN type can apply an IP ACL in 

mon sess X capture
   filter access-group ...

...but since it captures to a memory buffer, and you have to TFTP the 
packets off for any detailed analysis, this only works for relatively 
low-bandwidth captures.

No IPv6 either :o(

Also: beware of "capture" SPAN sessions. We've seen some bugs, which 
seem to have reared their head again in the SXJ train, where enabling a 
"capture" SPAN causes all existing and future ERSPAN sessions to 
malfunction - specifically, ERSPAN packet generation no longer obeys the 
routing table, and packets always flow to This usually 
results in a routing loop...

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