From: Pavel Bykov (slidersv@gmail.com)
Date: Sun Jan 11 2009 - 21:00:42 ARST
RR is not a status that router hold globally. It could be RR to one of the
routers (client) and no to others (non-client). Only relatively to those who
are clients, the split-horizon rules is overcome.
If RR receives information from ibgp non-client, it will not forward it to
ibgp non-client (i.e. normal split horizon).
P.S.: when talking about split horizon in BGP, don't forget to think on
Layer 4 of OSI model. I.E. instead of ethernet/serial/loopback think about
neighbor relationships as interfaces and ports. Then it won't matter if
there are 100 hops on layer 3 or 1, and it will be clear.
On Sun, Jan 11, 2009 at 8:21 AM, Mujeeb Sarwar <mujeebsarwar@gmail.com>wrote:
> 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
> >
> > Internetwork Expert, Inc.
> > http://www.InternetworkExpert.com <http://www.internetworkexpert.com/>
> > Toll Free: 877-224-8987
> > Outside US: 775-826-4344
> >
> >
> > 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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