From: Omer Ansari (omer@xxxxxxxxxx)
Date: Thu Aug 29 2002 - 17:31:21 GMT-3
Brian,
thanks that makes sense.
however, my question was targetting more the bgp best path selection than
the eventual routing of the packets.
say we have a bgp route 12.1.2.0/24, and we are also learning a 12.0.0.0/8
network from a neighbor.
we also have "aggregate-address 12.0.0.0 255.0.0.0" command on the
router.
if local_pref of both the local and learnt aggregate are the same and no
weights have been applied on routes, the bgp best path algo should put
the [local] aggregate address going to Null0 in the route table instead
of the "learnt 12.0.0.0/8" route.
this entry ofcourse was never competing with the 12.1.2/24 entry in the
best path algo.
..
if the above is true, my question was if the aggregate address was used
with as-set, does this drop the aggregate address further down in the best
path algo selection?
e.g if the "learnt 12.0.0.0/8" route has a low bgp metric, and that turns
out to be the next criteria for path selection would that route be put in
the table or the aggregate-address for 12.0.0.0/8 with as-set..
regards,
Omer
On Thu, 29 Aug 2002, Brian McGahan wrote:
> Omer,
>
> You will never route traffic to a locally generated aggregate,
> since the outgoing interface is null. Besides, if the local router is
> doing the aggregation, it should always have a longer match to the
> destination network in the first place. This is the reason the null
> route is used, to in fact prevent the local router from routing traffic
> for which the longest match is your locally generated aggregate.
>
> HTH
>
> Brian McGahan, CCIE #8593
> Director of Design and Implementation
> brian@cyscoexpert.com
>
> CyscoExpert Corporation
> Internetwork Consulting & Training
> http://www.cyscoexpert.com
> Voice: 847.674.3392
> Fax: 847.674.2625
>
>
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > Omer Ansari
> > Sent: Thursday, August 29, 2002 3:39 AM
> > To: ccielab@groupstudy.com
> > Subject: how does as-set change the bgp best path selection?
> >
> > All,
> >
> > we know that local routes from the bgp router are 3rd in the selection
> > list:
> > http://www.cisco.com/warp/public/459/25.shtml
> >
> > this includes bgp routes generated using the aggregrate-address
> command.
> >
> > however if the as-set option is used, does that route still qualify as
> a
> > locally generated route and if not, does that drop this route further
> down
> > in the bgp path selection list?
> >
> > thanks
> > Omer
This archive was generated by hypermail 2.1.4 : Sat Sep 07 2002 - 19:48:42 GMT-3