[c-nsp] BGP re-announcement question

Adam Greene maillist at webjogger.net
Mon Jul 29 18:53:15 EDT 2013



We are receiving a heavily prepended route announcement from a customer and
are trying to re-announce it to our upstream provider, without success. 


We learn the route on router A via eBGP. Router A announces the route to
Router B via iBGP. Router B is then supposed to announce it to Router C, our
upstream provider, via eBGP, but it is not. 


Here is what Router B is seeing:


7206VXR#sh ip bgp

BGP routing table entry for, version 262804866

Paths: (2 available, best #2, table Default-IP-Routing-Table)


  27241 27241 27241 27241 27241 27241, (received & used) (metric 1) from (

      Origin IGP, metric 300, localpref 100, valid, internal

  12271 7843 3356 46887 27241, (received & used) from (

      Origin IGP, localpref 100, valid, external, best

      Community: 7843:2161 7843:2303 7843:2313


As you can see, the eBGP route Router B is receiving from Router C
(upstream) is considered the best route. Is that why we are not reannouncing
it back upstream? 


Prefix-lists and route-maps have all been checked, including regular
expressions; we allow out ^27241(_27241)*$ and a "sh ip bgp regexp
^27241(_27241)*$" provides this output: 


   Network          Next Hop            Metric LocPrf Weight Path

* i198.11.15.0            300    100      0 27241 27241
27241 27241 27241 27241 i


I do wonder a bit about the "metric 300" (I think my customer might be
trying to weight things) but I'm not sure that's coming into play here or


This was working fine recently, with no changes on our end, but the customer
was announcing without any prepends, and I'm not sure if the origin was "?"
before, or "i" like it is now. 




More information about the cisco-nsp mailing list