[j-nsp] Prepending customer AS results in AS23456

[philxor at gmail.com]

23456 was reserved as a compatibility ASN to sort of make things compatible with 2-byte implementations.   There is a lot of information on the interweb so I wont go into detail here. 


Phil






From: Markus
Sent: ‎Wednesday‎, ‎May‎ ‎21‎, ‎2014 ‎5‎:‎33‎ ‎PM
To: juniper-nsp at puck.nether.net List





PS: On a second thought, of course as-path-prepend will make the session 
get dropped by the remote router, because my AS is not first in the path 
anymore. My mistake, so please ignore that.

I checked some more looking glasses in the meantime and I can see 
my-upstream my-asn 222222 at some of them. Only one looking glass showed 
me my-upsteam my-asn 23456, so I'm thinking maybe everything is fine and 
only this particular LG cannot display 4-byte ASN and uses 23456 instead?

Sorry for the noise in that case. :)


Am 21.05.2014 23:20, schrieb Markus:
> Hi list!
>
> I'm trying to prepend a customers 4-byte ASN to their prefixes. JunOS
> 12.3R2.5 on M7i. This is my config, simplified:
>
> [routing-options static]
> route a.a.a.a/22 {
>      next-hop b.b.b.b;
>      readvertise;
> }
>
> [policy-options]
> policy-statement UPSTREAM-OUT {
>      term 1 {
>          from {
>              route-filter a.a.a.a/22 exact;
>          }
>          then {
>              as-path-expand 222222;
>          }
>      }
>
> UPSTREAM-OUT is applied as export to my upstream's BGP peer. So far so
> good:
>
> admin at router# run show route advertising-protocol bgp my-upstream-ip
>
> Prefix           Nexthop           MED   Lclpref    AS path
> * a.a.a.a/22     Self              10               222222 I
>
> But when I check a public looking glass I can see that 222222 becomes
> 23456:
>
> 3257 1299 my-upstream my-asn 23456
>
> I changed "as-path-expand" to "as-path-prepend" and this resulted in the
> BGP session to drop and I can see this in my log:
>
> router rpd[1567]: bgp_read_v4_message:10289: NOTIFICATION received from
> my-upstream-ip (External AS my-upstream): code 3 (Update Message Error)
> subcode 11 (AS path attribute problem), Data:  40 02 0a 02 02 00
>
> Does this maybe mean that my upstream routers software does not yet
> support 4-byte ASNs?
>
> I'm also doing the same to various peers and there it works fine. I can
> see the path "my-asn 222222" in my peers looking glasses.
>
> Thanks!
> Markus
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