From: Ivan (ivan@iip.net)
Date: Sun Sep 24 2006 - 17:59:12 ART
All of the BGP-routers advertise their best path to BGP-peers. In my
understading all condition is equal except AS-path length. As-path length is
determine condition for path choosing.
To overlay this you can try ignore as-path length and to decide BGP-path on
router ID or metric.
bgp bestpath as-path ignore
On Sunday 24 September 2006 19:51, Daniel Fredrick wrote:
> OK... that makes sense, but is there a way to get all of them to have two
> routes in the bgp table? Only thing I could think of is that prepending the
> as on R6.
>
> Thanks,
> Dan
>
> On 9/24/06, Marvin Greenlee <marvingreenlee@yahoo.com> wrote:
> > Is the issue that R5 and R6 are removing them or that
> > R1 isn't advertising them? Debug your BGP updates. I
> > would guess that R1 isn't advertising them to R5,
> > because his best path for the networks is the route
> > learned via R5. R1 is only going to advertise his
> > best path. When the other link drops, R1's best path
> > is via AS254 directly, and he will advertise that to
> > R5 and R6.
> >
> > Thanks,
> > Marvin
> >
> > --- Daniel Fredrick <dfredrick@gmail.com> wrote:
> > > Here's the BGP topology...
> > >
> > > AS254 AS254
> > > (BB1) (BB2)
> > >
> > > | RR |
> > >
> > > (R1)---------(R5)-----------(R6)
> > > AS3 AS3 AS3
> > >
> > > R5 is the route reflector.
> > >
> > > OK... now BB1 and BB2 are sending the same BGP
> > > routes. The only difference
> > > is BB1 is sending the same routes is an aspath of
> > > "254 253". BB2 is sending
> > > the same routes, but with an aspath of just "254"
> > >
> > > OK... so here's my problem. When I do a "show ip
> > > bgp" all of the routers
> > > don't show both routes from BB1 and BB2.
> > >
> > > R1 shows both routes from BB1 and BB2, with BB2
> > > routes preferred... since it
> > > has a shorter BGP path.
> > >
> > > R5 only shows only BB2 routes.
> > >
> > > R6 only shows BB2 routes.
> > >
> > > So... here comes the confusing part...
> > >
> > > When R5 loses R6 as a bgp neighbor and it is down,
> > > the routes from BB2
> > > disappear in "show ip bgp" and the routes from BB1
> > > show up in "show ip bgp"
> > >
> > > So what could cause R5 and R6 to remove the routes
> > > from the bgp table? It
> > > should keep them in there... but just not use them
> > > as a preferred route.
> > >
> > > Thanks,
> > > Dan
> >
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-- Ivan
This archive was generated by hypermail 2.1.4 : Sun Oct 01 2006 - 16:55:41 ART