Which BGP show command for internal prefix count?

[jwbensley]

I have two routers (R1 and R2); R1 has the full BGP table and some local connections to. They are all being advertise to it's iBGP neighour R2. I can't find a command that I can run on R2 that will show the number of prefixes learnt from R1 that are internal to the local AS only. It just says 425~k which is all the Internet routes and the local ones.

What command can I use for this?

[Giuseppe Larosa · Accepted solution]

Hello Jwbensley,

the local AS originated networks has AS path attribute empty.

So you could define an ip as-path acl matching an empty string

ip as-path access-list 1 permit ^$
then you can invoke the as-path access-list as a filter action on show ip bgp on R2

show ip bgp filter-list 1

see

BGP command reference

http://www.cisco.com/en/US/docs/ios-xml/ios/iproute_bgp/command/bgp-s1.html#GUID-2618748E-42ED-495A-875C-D398A02D79F9

At this point it is enough to count the lines in show ip bgp filter-list 1 output to count the routes that are originated in the local AS at R1 and received on R2 and installed on R2.

Hope to help

Giuseppe

[cadet alain]

Hi Giuseppe,

clever way of doing it  (  + 5, +4 because my fingers messed with the stars)  so a sh ip bgp regexp looking for empty AS_PATH would also do the trick, aint't it  ?

Regards.

Alain.

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[Giuseppe Larosa]

Hello Alain,

yes of course a show ip bgp regexp could be used instead

it would be

show ip bgp regexp ^$

http://www.cisco.com/en/US/docs/ios-xml/ios/iproute_bgp/command/bgp-s1.html#GUID-DC1E5812-83AF-4465-8F77-86CD5B7D043F

Best Regards

Giuseppe

[milan.kulik]

Hi Giuseppe,

but this would show all the iBGP prefixes received from all neighbors, wouldn't that?

As the original request was "...command that I can run on R2 that will show the number of prefixes learnt from R1 that are internal to the local AS only", wouldn't

sh ip bgp nei R1_IP_address paths ^$

give a better result?

See http://www.cisco.com/en/US/docs/ios/iproute_bgp/command/reference/irg_bgp5.html#wp1160809

for details.

BR,

Milan

[Giuseppe Larosa]

Hello Milan,

you are right I have assumed that R2 is a sort of stub with only an iBGP session to R1 from what the original poster has said.

Thanks for your note

Best Regards

Giuseppe

[cadet alain]

Hi Milan,

didn't know about this command, thanks a lot for mentioning it.

Regards.

Alain

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[jwbensley]

Thank you for showing me this command.

That is pretty much what I wanted, and I like the shortened version! Although, I do have to dump this to a text file every time and run a small script against it to get a count of the actual routes, as this just prints out all the routing entries.

Thank you!