From: Becky Qiang (becky.qiang@wincomsystems.com)
Date: Mon Sep 09 2002 - 22:11:41 GMT-3
As I thought your explanantion was clear, I ran into a deeper (this time three
routers) senario and got more confused.
Please pay special attention to the bottom of my reply - 'routerC#show ip
bgp'.
1) Notice that the more specific routes and the aggregate routes are
configured in two different AS. Yet, when all of them get passed along to
routerC, the show ip bgp still shows the full AS path information. This is
different from your previous explanation-"The reason show ip bgp still shows
"2 i" is because the more specific routes are originated in the same AS is
aggregated route." --- Please further explain.
2) From routerB to routerA, the Metric value for more specific routes is all
ZERO. Then, from routerA to routerC, the Metric values become NULL. --- Why is
that? This is a new question.
3) From routerB to routerA, the Metric value for the aggregate route is NULL,
this is due to the 'atomic-aggregate' which means part of the AS path
information is lost. (This is consistent with your previous context)
routerC -----routerA ------routerB
routerC: AS 65530
routerA: AS1
routerB: AS2
Config:
routerA#
router bgp 1
aggregate-address 172.160.0.0 255.255.252.0
neighbor <routerB ip> remote-as 2
neighbor <routerC ip> remote-as 65530
routerB#
Lo0~lo3 -- IP: 172.16.0.1/24 ~172.16.3.1/24
router bgp 2
network lo0~lo3 mask /24
neighbor <routerA ip> remote-as 1
routerC#
router bgp 65530
neighbor <routerA ip> remote-as 1
routerA# show ip bgp
...
*>172.16.0.0~172.16.3.0/24 NextHop: routerB, Metric: 0 LocPrf: Null; Weight:
0, Path: 2 i
*>172.16.0.0/22 NextHop: 0.0.0.0 Metric: Null LocPrf: Null; Weight: 32768,
Path: i
routerC#show ip bgp
*>172.16.0.0~172.16.3.0/24 NextHop: routerA, Metric: Null, LocPrf: Null;
Weight: 0, Path: 1 2 i
*>172.16.0.0/22 NextHop: 0.0.0.0 Metric: Null LocPrf: Null; Weight: 0, Path: 1
i
----- Original Message -----
From: "Mingzhou Nie" <mnie@yahoo.com>
To: "Becky Qiang" <becky.qiang@wincomsystems.com>; <ccielab@groupstudy.com>
Sent: Monday, September 09, 2002 4:59 PM
Subject: Re: BGP atomic-aggregate
> Becky,
>
> Aggregate means loss of information and metric is part of them. The
> reason show ip bgp still shows "2 i" is because the more specific
> routes are originated in the same AS is aggregated route. In your case,
> they happen in same router.
>
> Ming
>
> --- Becky Qiang <becky.qiang@wincomsystems.com> wrote:
> > I have an aggregated route (172.16.0.0/22) advertised from routerB to
> > routerA.
> > A brief config as follows.
> >
> > Question:
> > 1) In 'show ip bgp' on routerB and routerA, the aggregate route
> > 172.16.0.0/22
> > has no Metric value, why is that?
> > 2) The 'show ip bgp 172.16.0.0 255.255.252.0 ' on routerA shows
> > 'atomic-aggregate', yet, 'show ip bgp' on routerA still shows path '2
> > i' for
> > this route. I thought the 'atomic-aggregate' means AS information for
> > the
> > aggregate has been lost?
> >
> > RouterB#
> > router bgp 2
> > network 172.16.0.0 mask 255.255.255.0
> > network 172.16.1.0 mask 255.255.255.0
> > network 172.16.2.0 mask 255.255.255.0
> > network 172.16.3.0 mask 255.255.255.0
> > aggregate-address 172.16.0.0 255.255.252.0
> > neighbor 10.1.1.1 remote-as 1
> >
> > RouterA#
> > router bgp 1
> > neighbor 10.1.1.2 remote-as 2
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This archive was generated by hypermail 2.1.4 : Mon Oct 07 2002 - 07:43:47 GMT-3