[c-nsp] re-advertising eBGP learned prefixes

[Andrey Koklin]

Thanks, Gert, for your reply.

On 10/20/2011 16:25, Gert Doering wrote:

> On Thu, Oct 20, 2011 at 03:27:53PM +0400, Andrey Koklin wrote:

>> I need to re-advertise some eBGP-learned routes to another eBGP peer:

>> ClientA---> ASX---R3-AS2---> R1-AS1--(ibgp)--R2-AS1---> R4-AS3

>> BGP advertises only prefixes originating in the same AS.
>> But we need to propagate some prefixes further to another eBGP-peer.

>> Do there exist a solution for such a thing?

> Maybe.  Like, get a router, which has a BGP config.  And then *show*
> that to us.

> BGP has no problem in redistribution eBGP-iBGP-eBGP - actually, this is
> the normal behaviour, unless you have filters in place to prevent that.

> BGP will never(*) do redistribution eBGP-iBGP-iBGP, though, so depending
> if your setup has multiple iBGP links in sequence, this will prevent
> prefix propagation.

There is no direct iBGP peers connection, indeed,
but the routers get updates through route reflector.

It seems, I found the problem now, but not solution yet.

The scheme is a bit more complicated, in fact, something like:

               --- R4-AS2 ---
ClientA---> AS4              R1-AS1--(ibgp)--R2-AS1---> R3-AS3
               --- R5-AS3 ---

We use the same operator (AS3) to organize 2 independent VPN's
for magistral and regional services.

The problem here looks that AS3 is present already in the path,
so the prefixes are not advertised into another VPN.

Here AS3 = 21017. And what I see on R2:

spring#sh ip bgp 10.36.72.32
BGP routing table entry for 10.36.72.32/27, version 505812
Paths: (1 available, best #1, table Default-IP-Routing-Table)
  Not advertised to any peer
  21017 44237 30835, (received & used)
    10.36.2.22 (metric 3072) from 213.129.126.1 (10.36.1.1)
      Origin incomplete, metric 0, localpref 100, valid, internal, best
      Originator: 10.36.1.4, Cluster list: 10.36.1.1


Could you suggest a proper way to handle it?


PS: No, it seems, my guess was wrong.
I've just changed weight for incoming prefixes to prefer another AS path.
The AS 2107 is disappeared, but still the routes are not advertised:

spring#sh ip bgp 10.36.72.32                                   
BGP routing table entry for 10.36.72.32/27, version 506076
Paths: (1 available, best #1, table Default-IP-Routing-Table)
  Not advertised to any peer
  20485 30835, (received & used)
    10.36.2.22 (metric 3072) from 213.129.126.1 (10.36.1.1)
      Origin incomplete, metric 0, localpref 100, valid, internal, best
      Originator: 10.36.1.4, Cluster list: 10.36.1.1

spring#sh ip bgp 10.36.72.32 255.255.255.224 longer-prefixes   
BGP table version is 506076, local router ID is 10.36.33.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*>i10.36.72.32/27   10.36.2.22               0    100      0 20485 30835 ?