AS Override query

[Vinayaka Raman]

{10.46.0.254/32 is advertised on R1 (AS 65457)} ••>AS (3549) -->AS (4058) ---->AS (17776) ••>R2 (local AS 65458) ••>R3 (local AS 65457) ••>AS 65000 ••>{ R4 (AS 65457) advertises 100.9.254.0/24}

Scenario 1:                                                                                                                                                                                                                                                                                                                                                                                         

R2 and R3 are eBGP peers on LAN..

R1#show ip bgp neighbors 10.117.36.89 adv

BGP table version is 72, local router ID is 10.46.0.254

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

             r RIB-failure, S Stale, m multipath, b backup-path, x best-externa

l, f RT-Filter

Origin codes: i - IGP, e - EGP, ? - incomplete

   Network         Next Hop           Metric LocPrf Weight Path

*> 10.46.0.254/32   0.0.0.0                 0         32768 i

Total number of prefixes 1

R2#show ip bgp 10.46.0.254

BGP routing table entry for 10.46.0.254/32, version 1143

Paths: (1 available, best #1, table Default-IP-Routing-Table)

Advertised to update-groups:

       2

17776 4058 3549 65457

   10.117.37.161 from 10.117.37.161 (10.117.37.25)

     Origin IGP, localpref 100, valid, external, best

     Extended Community: RT:4058:43983000

R3#show ip bgp 10.46.0.254

% Network not in table

This is an expected behavior.

Scenario 2:

R3#show ip bgp 100.9.254.0

BGP routing table entry for 100.9.254.0/24, version 12297

Paths: (1 available, best #1, table default)

Advertised to update-groups:

     7

65000 65000

   152.161.238.37 from 152.161.238.37 (159.24.198.60)

     Origin incomplete, localpref 100, valid, external, best

R2#show ip bgp 100.9.254.0

BGP routing table entry for 100.9.254.0/24, version 496

Paths: (1 available, best #1, table Default-IP-Routing-Table)

Advertised to update-groups:

       1

65457 65000 65000

   10.66.0.59 from 10.66.0.59 (10.66.0.253)

     Origin incomplete, localpref 100, valid, external, best

R1#show ip bgp 100.9.254.0

BGP routing table entry for 100.9.254.0/24, version 0

Paths: (1 available, no best path)

Not advertised to any peer

3549 4058 17776 65458 3549 65000 65000, (received-only)

[skarthic]

Hi Vinayak,

can you explain your query a bit.

Thanks.

[Vinayaka Raman]

I am sorry for not pasting my query..copy paste error

I wanted R3 to learn the route(10.45.0.254)- that is advertised by R1. As you see R3 is rejecting this route due to as loop behaviour..

Also, I would not prefer doing allowas-in command on R3..

on 3549, we have an as-override enabled for 65457..This is the config the provider had made:

group XXXXXX-2005099058 {

    type external;

    log-updown;

    import BGP-import;

    family inet {

        any {

            prefix-limit {

                maximum 2000;

            }

        }

    }

    export [ BGP-export 15884-1-Toledo-2005099058-export ];

    peer-as 65457;

    as-override;

    neighbor 10.117.36.90;

}

10.117.36.90 is the CPE address managed by us..

Even after applying this we still see 65457 unaltered at R2 (refer aboev outputs)..we did clear bgp also..

Now the provider is asking me to apply an as-overried at R2 towards 65457..

I am little confused because i thought the above as-override config must suffice my requirement..

[skarthic]

Do you have any policies configured at your end on R1? You are right. AS3549 should replace AS 65467 which is not happening which means the as-override functionality is not working. Did you check with the provider on this?

[Vinayaka Raman]

yes i do have an inbound route-map at R 1 that denies certain prefexies coming with community tags..

by the way, i tag it at R2..

that's why we see it as received-routes at R1..i have enabled soft reconfiguration inbound at R1 for viewing this prefixes while debugging.

I am checking with the provider and they want me to do one more as-override at R2..I am reluctant to do this..

One question:

Do we need to reset the BGP neighbhorship on the PE router for this changes to take effect?

It is a juniper box...

[Vinayaka Raman]

{10.46.0.254/32 is advertised on R1 (AS 65457)} ••>AS (3549) -->AS (4058) ---->AS (17776) ••>R2 (local AS 65458) ••>R3 (local AS 65457) ••>AS 65000 ••>{ R4 (AS 65457) advertises 100.9.254.0/24}

In my scenario where all as-overide has to be enabled?

All i wanted is at R3  should be able to learn the prefix 10.46.0.254.