Re: BGP advertise non best routes?

Suppose you have this topology

R1------R3--------R2
              --------R4

R3 is learning the same route from both R2 and R4. R3 will go through the
BGP selection process and install the best route into the RIB. R3 will only
advertise this preferred route to R1. What I am looking for is a way for R3
to prefer one path, but R1 to prefer a different path without peering
between R1 and any other router than R3, and without using PBR.

On Sun, May 13, 2012 at 2:48 PM, john matijevic <john.matijevic_at_gmail.com>wrote:

> Network Next Hop Metric LocPrf Weight Path
> * i100.100.1.0 10.1.2.254 0 100 0 500 i
> *>i 10.1.1.254 0 100 0 500 200 i
>
>
> "Your router will only advertise out the route it considers best to
> its BGP peer. So in this case it would only advertise the route
> through 10.1.1.254."
>
> Actually 10.1.1.254 is the next hop, the network is 100.100.1.0, in
> this case it is learning the same network from two different peers.
> The networks that BGP advertise is different than what the best route
> network that BGP learns from the peers.
>
>
>
> "What I want is to be able to send both options to the next router in
> the line and then let it choose based on weight or as path or
> something."
>
> Im not sure what you mean by being able so send both options. Can you
> rephrase or be more specfic?
>
>
>
> Regards,
> John
>
>
>
>
> On 5/13/12, Tony Singh <mothafungla_at_gmail.com> wrote:
> > Would as path ignore not cause loops and black holes?
> >
> > I understand what you want but I'm sure bgp will only offer the best
> route
> > to that prefix to the routing table, it might be worth experimenting with
> > the as's and see if primary link goes down does your ping get through on
> the
> > other path?
> >
> >
> > BR
> >
> > Tiny
> >
> > Sent from my iPhone on 3
> >
> > On 13 May 2012, at 20:07, marc abel <marcabel_at_gmail.com> wrote:
> >
> >> Thank you for your response john. I may not have explained what I am
> >> trying
> >> to do well enough.
> >>
> >>
> >> what I am talking about is if you have two paths in the bgp table such
> as
> >> this:
> >>
> >> R3(config-if)#do show ip bgp
> >> BGP table version is 21, local router ID is 1.1.3.3
> >> Status codes: s suppressed, d damped, h history, * valid, > best, i -
> >> internal,
> >> r RIB-failure, S Stale
> >> Origin codes: i - IGP, e - EGP, ? - incomplete
> >>
> >> Network Next Hop Metric LocPrf Weight Path
> >> * i100.100.1.0 10.1.2.254 0 100 0 500 i
> >> *>i 10.1.1.254 0 100 0 500 200
> >> i
> >>
> >> Your router will only advertise out the route it considers best to its
> >> BGP
> >> peer. So in this case it would only advertise the route through
> >> 10.1.1.254.
> >> What I want is to be able to send both options to the next router in the
> >> line and then let it choose based on weight or as path or something.
> >>
> >> *note I have applied "bgp bestpath as-path ignore" that is why this one
> >> isn't preferring the shorter AS path.
> >>
> >>
> >>
> >>
> >> On Sun, May 13, 2012 at 1:49 PM, john matijevic
> >> <john.matijevic_at_gmail.com>wrote:
> >>
> >>> Good Afternoon Marc,
> >>>
> >>> "Is there any way to force BGP to advertise all of it's routes, even
> >>> ones
> >>> it
> >>> doesn't consider best? "
> >>>
> >>> You can use the network statement under the BGP process to advertise
> >>> the connected networks. For routes learned via another protocol, you
> >>> can use the redistribute command.
> >>>
> >>> Once you have all the routes that you want advertised you can use
> >>> different filter techniques to advertise or bgp attributes command to
> >>> prefer one path over another.
> >>>
> >>> Hope this helps.
> >>>
> >>> Regards,
> >>> John
> >>>
> >>>
> >>> On 5/13/12, marc abel <marcabel_at_gmail.com> wrote:
> >>>> Is there any way to force BGP to advertise all of it's routes, even
> >>>> ones
> >>> it
> >>>> doesn't consider best? Particularly looking for a way to make an iBGP
> >>> peer
> >>>> prefer a different route than it's route reflector.
> >>>>
> >>>>
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> >>>>
> >>>>
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Received on Sun May 13 2012 - 14:53:56 ART