From: Mujeeb Sarwar (mujeebsarwar@gmail.com)
Date: Sun Jan 11 2009 - 05:21:48 ARST
Hi,
As Nit mentioned in his first email that SW1 is a RR so if it recieves
prefixes from CLIENT or NON CLIENT then it will forward those prefixes to
its clients means 'Split-Horizon' type behavior will not come into play.
Correct me if I am mis understanding.
On Sat, Jan 10, 2009 at 5:15 AM, Anthony Sequeira <
asequeira@internetworkexpert.com> wrote:
> Yeah - there is something commonly referred to as "BGP Split-Horizon" but
> that specifically references a BGP speaker taking an iBGP update and not
> passing it to another iBGP peer by default (using any interface). It is not
> the typical use of the term split horizon that we are used to with Distance
> Vector routing protocols.
>
> Anthony J. Sequeira, CCIE #15626, CCSI #23251
> Senior CCIE Instructor
>
> asequeira@internetworkexpert.com
>
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>
> On Jan 9, 2009, at 7:47 PM, Huan Pham wrote:
>
> Bgp does not use the concept of split horizon. Bgp can peer over more than
>> one hop away, so it does not really care how (I.e. via what interface)
>> routes are exchanged.
>>
>> I cannot read your topology properly so I cannot tell exactly where
>> problem is. Few general suggestions you can check:
>>
>> - make sure bgp peerings are up
>> - double check RR config
>> - check what is next hop advertized via bgp. You have to have reachability
>> to the next hop or bgp route is not installed. Use next hop self on the
>> "edge" router for the iBGP session to change next hop advertised to iBGP
>> peer if required
>> - check bgp community attributes. No-advertise may stop RR from advertise
>> routes received from one client to others
>>
>> - post full bgp config , I will have a look at it when I have access to my
>> pc
>>
>>
>> Sent from my iPhone
>>
>> On 10/01/2009, at 10:03 AM, Nitro Drops <nitrodrops@hotmail.com> wrote:
>>
>> Hi Guys,
>>
>> Can BGP prefixes be learned from a IBGP peer neighbor and resend out to
>> another IBGP peer neighbor from the SAME interface, with route-reflector
>> client configured?
>>
>> Understand BGP doesnt use 'split-horizon', for IBGP, it uses loop
>> prevention
>> via route suppression which requires the use of RR, Confederation, Full
>> Mesh.
>>
>> R3 F0/0 (AS3) > EBGP > (AS1) F0/0 R4 F0/1 > F0/0 R6 F0/1 > Vlan30 SW1
>> Vlan 30
>> F0/0 R5
>> AS3 advertising BGP prefixes to AS1, and full L3 reachability
>> R3 - AS3
>> R4, R6, SW1, R5 - AS1
>> R4 - RR client of R6
>> R5 - RR client of SW1
>>
>> In the above setup, SW1 is learning the the BGP prefixes from IBGP
>> neighbor
>> R6, which is non-RR-client of SW1, SW1 being a RR should reflect the BGP
>> prefixes to R5, learning and sending via SVI Vlan 30.
>>
>> What i noticed, R5 cant learn the BGP prefixes at all, even though R5 has
>> an
>> underlying L3 routes to R3.
>>
>> I even made both SW1 a RR-client of R6, and R6 a RR-client of SW1, still
>> R5
>> cant learn the prefixes.
>>
>> Next, i created another new SVI Vlan 20 for the subnet between SW1 and R5
>>
>> R3 F0/0 (AS3) > EBGP > (AS1) F0/0 R4 F0/1 > F0/0 R6 F0/1 > Vlan30 SW1
>> Vlan 20
>> F0/0 R5
>>
>> Only, then R5 is able to learn the BGP prefixes.
>>
>> So my question is, can a single SAME interface be used for learning BGP
>> prefixes from one IBGP neighbor and sending them to another IBGP neighbor?
>> Some kind of split-horizon concept here even though BGP doesnt use that.
>> Anyway BGP commands to disable this?
>>
>> Cheers
>> Nit
>>
>>
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