Filters on packet lenght on ASR9k 4.2

[MATTHIAS SCHAERER]

In the Access List manual of version 4.2

http://www.cisco.com/en/US/docs/routers/asr9000/software/asr9k_r4.2/addr_serv/command/reference/b_ipaddr_cr42asr9k_chapter_01.html#wp1019212976

I read that there is a possiblity to filter packets according to packet-length. Has anybody been able to use this feature? Is it just for specific protocols? I have tried it in various contexts but have not been successful so far.

[Florian Frotzler]

Hi Matthias,

Reading through your referenced link I find no mentioning of this feature.

Regards,

Florian

[Bryan Garland]

Matthias,

I haven't heard of that capability with regards to straight ACLs.  You can capture so many bytes with regards to SPAN which can be used from an ACL.  It's referred to as partial packet mirroring.  Maybe that is what you are referring to?

RP/0/RP0/CPU0:ASR9922-A(config)#ipv4 access-list blah permit ipv4 any any ?

  capture     Capture matched packet

  default     Use specified default nexthop on match against this entry

  dscp        Match packets with given DSCP value(s)

  fragments   Check non-initial fragments

  log         Log matches against this entry

  log-input   Log matches against this entry, including input interface

  nexthop1    Forward to specified nexthop on match against this entry

  precedence  Match packets with given precedence

  ttl         match against ttl

Info regarding SPAN, use this link:

https://supportforums.cisco.com/docs/DOC-15772

Thanks,

Bryan