Re: BGP advertise non best routes?

I think everyone is misunderstanding what he is actually trying to
accomplish. Changing the BGP best-path selection process, lowering the
AD to induce rib-failure, or using multipath to install multiple
routes into the rib, will not affect the behavior he is trying to
circumvent. BGP will always select a "best path" no matter what, even
if you're doing equal-cost load-balancing or bgp dmzlink. Whichever
single route is selected as best, will be advertised to its neighbors.

BGP will not advertise two of the same prefixes with different NLRI,
unless these are vpnv4 routes which will have route distinguishers
associated with them. One way you may be able to accomplish this would
be with VRFs, tunnels, and multiple BGP sessions. ( So that your
downstream peers could get both distinct copies of the BGP table).

-Yuri

On Sun, May 13, 2012 at 2:03 PM, Jay McMickle <jay.mcmickle_at_yahoo.com> wrote:
> Hey Marc-
> What you may be looking for is multipath, using the maxium-path
> statement.
>
> http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094431.
> shtml
>
>
> Regards,
> Jay McMickle- CCIE #35355
>
>
> From: marc abel
> <marcabel_at_gmail.com>
> To: john matijevic <john.matijevic_at_gmail.com>
> Cc: Group
> Study <ccielab_at_groupstudy.com>
> Sent: Sunday, May 13, 2012 2:07 PM
> Subject:
> Re: BGP advertise non best routes?
>
> 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.
>> >
>> >
>> > Blogs and organic groups at http://www.ccie.net
>> >
>> >
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Received on Sun May 13 2012 - 14:52:42 ART