[j-nsp] remove-private for iBGP session

[Cydon Satyr]

Cisco removes private AS numbers from updates sent to eBGP peers. So this
is something you would have configured on PE router which is sending
updates to your upstream ISP, for example.

I don't recall ever trying this on iBGP sessions, which is why I'm confused
by Juniper implementation.

Adam, as a side note, I tried modifying MED inside iBGP session, and that
works as well.

So is this a bug or a feature ?

BR



On Sun, Sep 27, 2015 at 10:05 PM, Karsten Thomann <karsten_thomann at linfre.de
> wrote:

> Hello,
>
>
>
> the point should be that the remove-private isn't a standard RFC based
> path modification.
>
> How would you configure the remove-private when it isn't done by the
> ingress PE Router before sending the route to the RR?
>
> How should the RR/Egress PE know from which routes it should remove the
> private AS and from which it shouldn't? There is no secret flag afaik to
> the route to tell the egress PE's to remove the private as number.
>
>
>
> I'm a bit curious how Cisco is doing it, or where you expect that the AS
> is removed from the AS path.
>
>
>
> Regards,
>
> Karsten
>
>
>
> Am Sonntag, 27. September 2015, 19:23:18 schrieb Cydon Satyr:
>
> > Hello,
>
> >
>
> > I'm very well aware of that which is why I'm confused.
>
> > Here, PE is removing private AS before sending update to RR.
>
> >
>
> > Could anyone explain what are we missing here?
>
> >
>
> > Regards
>
> >
>
> > On Sun, Sep 27, 2015 at 6:09 PM, Adam Vitkovsky <
> Adam.Vitkovsky at gamma.co.uk>
>
> > wrote:
>
> > > 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
>
> > > W: www.gamma.co.uk
>
> > >
>
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