[j-nsp] remove-private for iBGP session

[Adam Vitkovsky]

Hello Cydon,

> Of Cydon Satyr
> Sent: Saturday, September 26, 2015 12:35 PM
>
> Hello,
>
> I was under the impression that remove-private works for eBGP sessions, as
> it does on Cisco routers (if my memory serves me right).
>
> But I notices that remove-private on a PE router would remove private AS
> (from customer's vrf bgp session) before sending it to a route reflector.
>
> Is this normal behavior, or I'm missing something?
>
> Regards

It's not normal according to the RFC4271 section 5.1.2.a

5.1.2.  AS_PATH

>snip

   When a BGP speaker propagates a route it learned from another BGP
   speaker's UPDATE message, it modifies the route's AS_PATH attribute
   based on the location of the BGP speaker to which the route will be
   sent:

      a) When a given BGP speaker advertises the route to an internal
         peer, the advertising speaker SHALL NOT modify the AS_PATH
         attribute associated with the route.

      b) When a given BGP speaker advertises the route to an external
         peer, the advertising speaker updates the AS_PATH attribute as
         follows:

>snip

There are other attributes (e.g. MED springs to mind) that can't be modified or set on iBGP sessions.


For iBGP to iBGP (on a RR)
On XR you can modify all attributes only when cmd "ibgp policy out enforce-modifications"
Because by default:
In addition, when a RR reflects a route, it SHOULD NOT modify the
   following path attributes: NEXT_HOP, AS_PATH, LOCAL_PREF, and MED.
   Their modification could potentially result in routing loops.


adam


        Adam Vitkovsky
        IP Engineer

T:      0333 006 5936
E:      Adam.Vitkovsky at gamma.co.uk
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