From: Mingzhou Nie (mnie@yahoo.com)
Date: Mon Sep 09 2002 - 22:18:54 GMT-3
--- Becky Qiang <becky.qiang@wincomsystems.com> wrote:
> 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.
the config you used "aggregate-address 172.160.0.0 255.255.252.0" will
actually adv both aggregate route and more specific routes. The loss of
info only occurs for aggregate and more sepcific routes, of course,
will keep their attributes. To adv aggregate only, use
"aggregate-address 172.160.0.0 255.255.252.0 summary-only"
>
> 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.
The metric attribute will only be passed along to the neiborgh AS.
Routes originated in AS2 will pass their metric to AS1 in order to
affluent routes coming back to AS2. However, it doesn't make sense for
them to pass their metric to AS65300. Routes originated from AS1,
however, will pass theri metric to AS65300, except aggregates :)
>
> 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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