From: Brown, Patrick (NSOC-OCF} (PBrown4@chartercom.com)
Date: Fri Feb 07 2003 - 10:57:30 GMT-3
I have done configuration with peer groups and router reflectors often. I was wondering why is this in the config guide, and is this how I should approach the situation on the lab test. This link to the CCO site must be an updated version: http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/ip_c/ipcprt2/1cdbgp.htm#1001965 (It doesn't have the NOTE: statement)
My CD-documentation config guide has the following statement: Note: If client-to-client reflection is enabled, the clients of a
route reflector cannot be members of a peer group. I guess I will upgrade to latest version.
Thanks for your replies
Patrick B
-----Original Message-----
From: Joe Martin [mailto:jmartin@capitalpremium.net]
Sent: Wednesday, February 05, 2003 1:30 PM
To: Peter van Oene; CCIE GroupStudy
Subject: RE: Route Reflectors and Peer Groups
Peter,
Perfect! Thank you very much! So to reiterate:
E is a route reflector. As the reflection server, it reflects routes between
the clients, and reflects extra-cluster routes to the clients.
However, if the clients are fully meshed, there is no need to reflect
between clients, but there is still the need to reflect extra-cluster routes
to the clients.
This way the clients need only peer with the reflector and all other clients
in the cluster, but no one outside the cluster, still reducing the total
number of peer relationships in the AS (which is the whole purpose of route
reflectors).
Can't believe I didn't see this sooner. Too narrow minded. I wasn't
thinking about the inter-cluster relationships within the AS.
Correct me if I'm wrong. And thanks again.
Joe Martin
-----Original Message-----
From: Peter van Oene [mailto:pvo@usermail.com]
Sent: Wednesday, February 05, 2003 11:51 AM
To: Joe Martin; CCIE GroupStudy
Subject: RE: Route Reflectors and Peer Groups
At 10:53 AM 2/5/2003 -0700, Joe Martin wrote:
>Peter,
>
>Thanks for the quick response. I understand the route reflection process
(or
>at least I think I do), I just don't see the point of the "no bgp
>client-to-client reflection" command. In your scenario, instead of
>configuring E with no reflect, couldn't you just remove the route reflector
>client command from the neighbor statements for G and H? If I am not
>reflecting routes between clients, I am not a route reflector.
Exactly, but since G and H only peer with E, they are no longer receiving
routes from the rest of the network. For example, all the EBGP learned
routes from the edge that E possesses cannot be advertised to G and H.
>When I configure E with the "route reflector client" command in the
neighbor
>statements for G and H, I am making E a reflection server. If I then issue
>the no bgp client-to-client reflection" command, because G and H have
>decided to directly peer, E is no longer acting as a reflection server. It
>is not reflecting routes between clients. What's the point? That's no
>different than just removing the "route reflector client" command from the
>neighbor statements
True, if the network only consisted of E G and H. The question remains,
how do G and H learn about routes from A, B, C and D for example? They
don't peer directly, and having them peer directly would create scalability
problems (n*n-1/2 issues) Adding no-client-reflect simply pulls out the G
and H routes from the set of routes that E reflects. However, E also
reflects all the IBGP learned routes from B C and F and since B and C
advertise routes for A and D respectively, A and D's routes are also in
the mix. So here is a summary.
Consider router G and what it learns from E.
With Reflection on E and G and H non peered, G learns routes from A, B, C,
D, E , F, H from E.
With Reflection on E and G and H do peer * E has no client reflect, G
learns A, B, C, D, E, F from E.
Without reflection and E, G and H peer directly, G learns E from E.
Does that help?
>Hope that explained my point well enough.
>
>TIA,
>
>Joe Martin
>
>-----Original Message-----
>From: Peter van Oene [mailto:pvo@usermail.com]
>Sent: Wednesday, February 05, 2003 10:29 AM
>To: Joe Martin; ccielab@groupstudy.com
>Subject: RE: Route Reflectors and Peer Groups
>
>
>At 10:16 AM 2/5/2003 -0700, Joe Martin wrote:
> >Peter,
> >
> >Could you please explain to me what the purpose of a route reflector is
if
>I
> >have configured the no bgp client-to-client reflection command. If the
> >reflection server isn't reflecting routes between clients, what's the
>point?
>
>Most medium to large BGP networks employ a hierarchy of route
>reflection. In these cases, it is normal and indeed necessary to maintain
>multiple route reflection clusters. Therefore, without the route
>reflector, members of a cluster would only learn intra cluster routes. It
>is the route reflectors role to bring extra cluster routes into the cluster
>and to similar export cluster routes to those routes beyond the cluster.
>
>Since that test is pretty confusing sounding and heavy on the cluster,
>consider the below network.
>
>--ebgp-A-------B--------C-------D-ebgp
> | |
> E--------F
> / \ / \
> G H I J
>
>In the above, B,C,E,F represent the IBGP core of this simple network. A and
>D represent two peering routers in network while G to J are regional market
>routers. In this case, you would have BCEF IBGP directly, and have E
>reflect to G and H, and F reflect to I and J. Also, B would likely reflect
>to A and C similarly to D. If G and H chose to peer directly, you would
>enable no client reflect on E, but you will still need E to advertise G and
>H's routes to the rest of the network, and to import routes from the rest
>of the network for G and H.
>
>The above isn't meant to be a best practise network and only an example ;-)
>
>Pete
>
>
> >Is this just used as a migration tool away from or into a route reflector
> >design?
> >
> >TIA,
> >
> >Joe Martin
> >
> >-----Original Message-----
> >From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> >Peter van Oene
> >Sent: Wednesday, February 05, 2003 8:44 AM
> >To: Brown, Patrick (NSOC-OCF}; ccielab@groupstudy.com
> >Subject: RE: Route Reflectors and Peer Groups
> >
> >
> >At 09:31 AM 2/5/2003 -0600, Brown, Patrick (NSOC-OCF} wrote:
> > >This is what is was talking about from the 12.1 config guide
>documentation
> > >under BGP.
> > >
> > >By default, the clients of a route reflector are not required to be
fully
> > >meshed and the routes from a client are reflected to other clients.
> > >However, if the clients are fully meshed, the route reflector does not
> > >need to reflect routes to clients. To disable client-to-client route
> > >reflection, use the no bgp client-to-client reflection command,
beginning
> > >in router configuration mode:
> >
> >This is accurate
> >
> > >Note: If client-to-client reflection is enabled, the clients of a
route
> > >reflector cannot be members of a peer group.
> >
> >This is odd, but may be an ios limitation. In Juniper, one applies
> >no-client-reflect to the peer group. It is quite normal to have all
> >members of a reflection cluster in the same peer group.
> >
> > >What I interpret from this statment,is that RR can't have clients that
>are
> > >in a peer group they configured(logical).
> >
> >I would tend to agree with your interpretation, though I'm not sure what
> >the technical limitation is.
> >
> > >Tx,
> > >
> > >Patrick B
> > >-----Original Message-----
> > >From: Peter van Oene [mailto:pvo@usermail.com]
> > >Sent: Wednesday, February 05, 2003 7:29 AM
> > >To: ccielab@groupstudy.com
> > >Subject: Re: Route Reflectors and Peer Groups
> > >
> > >
> > >At 10:03 PM 2/4/2003 -0600, Brown, Patrick (NSOC-OCF} wrote:
> > > >Question
> > > >
> > > >Is it true that you can not have neighbors in a peer-group and be
> > > >their route reflector at the same time?
> > > >If this is true, should the "no bgp client-to-client reflection"
>command
> > > >take card of this.
> > > >I have seen labs were this configuration happened.
> > >
> > >Are you asking if clients in a reflection cluster can be neighbors
> > >themselves? peer-groups are just a configuration tool and don't
actually
> > >affect the performance of BGP external to the router. If this is that
> > >case, then yes is the answer, and no client-to-client-reflection will
>stop
> > >the reflection server from reflecting intra cluster routes back to
>clients
> > >(since they will be learning these directly)
> > >
> > >Pete
> > >
> > >
> > >
> > >
> > > >Tx,
> > > >
> > > >Patrick B
> > > >.
> > >.
> >.
.
.
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