From: Jung-I Lin (easyman.lin@gmail.com)
Date: Mon Sep 25 2006 - 10:18:21 ART
Hi,
I've never saw such kind of requirement.
Even if you enable bgp load balancing on R1 & R6, I believe it still not
able to have both routes as the best routes.
Because one route is ebgp(leaned from AS254), the other routes is ibgp(from
AS3, R5 in this case).
IMHO I think it is impossible except peering R5 to BB1&BB3 directly.
On 9/25/06, Daniel Fredrick <dfredrick@gmail.com> wrote:
>
> But if the requirement is to have the routes from BB1 and BB2 in the BGP
> table in all 3 routers (R1, R5, and R6)... how would this me achieved?
>
> On 9/24/06, Ivan <ivan@iip.net> wrote:
> >
> > 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
>
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-- Thanks Best Regards,Jung-I Lin
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