[c-nsp] BGP re-announcement question

[Adam Greene]

Thanks to all who replied! 

The customer reduced their prepends, and now we're advertising the route
upstream.

I appreciate the help.

Thanks,
Adam

-----Original Message-----
From: Scott Granados [mailto:scott at granados-llc.net] 
Sent: Monday, July 29, 2013 10:43 PM
To: Adam Greene
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] BGP re-announcement question

This is correct, in your set up, the customer learned route is not the best
route.  If you want to preserve the prepends I would increase the pref of
your learned customers so you install them as the most preferred.

Thanks
Scott

On Jul 29, 2013, at 6:53 PM, Adam Greene <maillist at webjogger.net> wrote:

> Hi!
> 
> 
> 
> 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 198.11.15.0
> 
> BGP routing table entry for 198.11.15.0/24, version 262804866
> 
> Paths: (2 available, best #2, table Default-IP-Routing-Table)
> 
> 
> 
>  27241 27241 27241 27241 27241 27241, (received & used)
> 
>    204.8.83.14 (metric 1) from 172.18.18.20 (172.18.18.20)
> 
>      Origin IGP, metric 300, localpref 100, valid, internal
> 
>  12271 7843 3356 46887 27241, (received & used)
> 
>    24.29.112.25 from 24.29.112.25 (69.193.224.79)
> 
>      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      204.8.83.14            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 not.
> 
> 
> 
> 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. 
> 
> 
> 
> Thanks,
> 
> Adam
> 
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