From: tan (tan@dia.janis.or.jp)
Date: Tue Feb 25 2003 - 22:41:48 GMT-3
David, do your instructions say you must have two routes on the southern
routers? Maybe load balancing will work. If using load balancing, two routes
could be best, but I don't know if this means two routes will be sent, but
sounds likely. Load balancing only works on ebgp, but if you use confed-ebgp
to those southern routers, and maximum paths command to raise default paths
from one to 2, maybe you can get both paths sent...
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> Peter van Oene
> Sent: Wednesday, February 26, 2003 6:58 AM
> To: ccielab@groupstudy.com
> Subject: Re: BGP Route Reflector
>
>
> At 02:47 PM 2/25/2003 -0500, David Buechner wrote:
> >To follow up to my question from yesterday:
> >
> >First, someone asked for relevant configuration information
> from R2 which
> >I have included below.
> >
> >Second, I've gotten a couple of responses like Annu Roopa's
> which said:
>
> A route reflector (or any bgp speaker for that matter) only
> advertises a
> single best path. Hence, in this case, R6 sends only one of
> the two paths
> received from r3 and r1 toward the southern routers in the
> network whereas
> with a full mesh, those other routers would receive both paths
> directly. Hence, the route reflector clients get a single
> best path from
> r6 and will use it, vs being able to see the paths directly
> and chose their
> own best path.
>
> Route Reflection is highly used and very useful. Proper
> design includes
> building hierarchies that will yield optimal/desired traffic
> flows. IGP
> topologies and metrics are useful to consider in these
> designs as they tend
> to be a popular tie breaker.
>
>
> >>I think in the first case when u do IBGP full mesh all
> >>the routers including R2,R5,R6 get two routes from R1
> >>and R3 and then they decide the best path (*>).
> >>
> >>But when u are doing the RR case Router R6 gets two
> >>paths as seen and decides the best path for the
> >>networks.R6 will advertise only the best path to its
> >>clients R2 and R5 and hence they have only 1 path the
> >>best path of R6. What do u think ? Am i correct in
> >>understanding ? someone care to comment.
> >
> >If this is true, then it seems like the Route Reflector is
> of much less
> >use that I would otherwise believe. Cisco doc and Doyle Vol
> 2 (among
> >other places) give me the idea that a route reflector
> cluster (properly
> >configured) is a functional replacement for the same group
> of routers with
> >full-mesh IBGP. So far I believe I've not gotten the "properly
> >configured" part of this right yet - although if I'm
> mis-understanding the
> >purpose of route reflectors here please tell me! Thanks to
> those who have
> >responded so far - my apologies if I'm being dense!
> >
> >Below is output from my R2 as well as yesterday's note for reference.
> >
> >Thanks!
> >
> >David
> >
> >R2#sh ip bgp 172.16.0.0
> >BGP routing table entry for 172.16.0.0/24, version 2
> >Paths: (1 available, best #1, table Default-IP-Routing-Table)
> > Not advertised to any peer
> > 254
> > 151.100.2.254 (metric 20) from 131.1.6.6 (131.1.6.6)
> > Origin IGP, metric 0, localpref 100, valid, internal, best
> > Originator: 131.1.3.3, Cluster list: 131.1.6.6
> >
> >R2#sh ip bgp
> >BGP table version is 9, local router ID is 131.1.2.2
> >Status codes: s suppressed, d damped, h history, * valid, >
> best, i - internal
> >Origin codes: i - IGP, e - EGP, ? - incomplete
> >
> > Network Next Hop Metric LocPrf Weight Path
> >*>i172.16.0.0/24 151.100.2.254 0 100 0 254 i
> >*>i172.16.1.0/24 151.100.2.254 0 100 0 254 i
> >*>i172.16.2.0/24 151.100.2.254 0 100 0 254 i
> >*>i172.16.3.0/24 151.100.2.254 0 100 0 254 i
> >*>i172.16.4.0/24 151.100.2.254 0 100 0 254 i
> >*>i172.16.5.0/24 151.100.2.254 0 100 0 254 i
> >*>i172.16.6.0/24 151.100.2.254 0 100 0 254 i
> >*>i172.16.7.0/24 151.100.2.254 0 100 0 254 i
> >
> >R2#sh running-config | begin router bgp
> >router bgp 400
> > no synchronization
> > bgp log-neighbor-changes
> > neighbor internal peer-group
> > neighbor internal remote-as 400
> > neighbor internal update-source Loopback0
> > neighbor 131.1.6.6 peer-group internal
> > no auto-summary
> >!
> >
> >
> >At 04:15 pm 2/24/2003 -0500, I wrote:
> >>Hi all!
> >>
> >>I have a BGP route reflector issue on the following network:
> >>
> >>
> >>--- (E1) --- R7 (AS 254) --- (E0) ---
> >>| |
> >>| |
> >>R3 (AS 400) R1 (AS 400)
> >>| |
> >>| |
> >>------------ R6 (AS 400) ------------
> >> | \
> >> | \-- R5 (AS 400)
> >> |
> >> R2 (AS 400)
> >>
> >>R7 is simulating a "backbone" router which is advertising several
> >>networks to R1 and R3. If I set up a full mesh between all
> of the AS 400
> >>routers (i.e. R1, R2, R3, R5, R6) then I get the results I
> would expect -
> >>each router has two entries in the BGP table for each advertised
> >>network. The route with the "closest" next-hop is then
> entered in the
> >>main IP routing table (where distance to the next-hop is
> determined by
> >>the IGP - OSPF in this case). If I try to set this up as a Route
> >>Reflector cluster with all routers peering with R6 I do NOT get the
> >>results I expect. Instead, what I get is that R2 and R5
> only have one
> >>entry for each network in their BGP table which corresponds
> to the "best"
> >>one chosen by R6.
> >>
> >>Any ideas what I'm missing here? Thanks!
> >>
> >>David
> >>
> >>
> >>R6#sh ip bgp 172.16.0.0
> >>BGP routing table entry for 172.16.0.0/24, version 2
> >>Paths: (2 available, best #2, table Default-IP-Routing-Table)
> >> Advertised to non peer-group peers:
> >> 131.1.1.1 131.1.2.2 131.1.5.5
> >> 254, (Received from a RR-client)
> >> 10.0.1.207 (metric 20) from 131.1.1.1 (150.100.35.1)
> >> Origin IGP, metric 0, localpref 100, valid, internal
> >> 254, (Received from a RR-client)
> >> 151.100.2.254 (metric 20) from 131.1.3.3 (131.1.3.3)
> >> Origin IGP, metric 0, localpref 100, valid, internal, best
> >>R6#sh ip bgp
> >>BGP table version is 9, local router ID is 131.1.6.6
> >>Status codes: s suppressed, d damped, h history, * valid, >
> best, i -
> >>internal
> >>Origin codes: i - IGP, e - EGP, ? - incomplete
> >>
> >> Network Next Hop Metric LocPrf Weight Path
> >>* i172.16.0.0/24 10.0.1.207 0 100 0 254 i
> >>*>i 151.100.2.254 0 100 0 254 i
> >>* i172.16.1.0/24 10.0.1.207 0 100 0 254 i
> >>*>i 151.100.2.254 0 100 0 254 i
> >>* i172.16.2.0/24 10.0.1.207 0 100 0 254 i
> >>*>i 151.100.2.254 0 100 0 254 i
> >>* i172.16.3.0/24 10.0.1.207 0 100 0 254 i
> >>*>i 151.100.2.254 0 100 0 254 i
> >>* i172.16.4.0/24 10.0.1.207 0 100 0 254 i
> >>*>i 151.100.2.254 0 100 0 254 i
> >>* i172.16.5.0/24 10.0.1.207 0 100 0 254 i
> >>*>i 151.100.2.254 0 100 0 254 i
> >>* i172.16.6.0/24 10.0.1.207 0 100 0 254 i
> >>*>i 151.100.2.254 0 100 0 254 i
> >>* i172.16.7.0/24 10.0.1.207 0 100 0 254 i
> >>*>i 151.100.2.254 0 100 0 254 i
> >>R6#sh running-config
> >>Building configuration...
> >>
> >>router bgp 400
> >> no synchronization
> >> bgp always-compare-med
> >> bgp log-neighbor-changes
> >> neighbor 131.1.1.1 remote-as 400
> >> neighbor 131.1.1.1 update-source Loopback0
> >> neighbor 131.1.1.1 route-reflector-client
> >> neighbor 131.1.2.2 remote-as 400
> >> neighbor 131.1.2.2 route-reflector-client
> >> neighbor 131.1.3.3 remote-as 400
> >> neighbor 131.1.3.3 update-source Loopback0
> >> neighbor 131.1.3.3 route-reflector-client
> >> neighbor 131.1.5.5 remote-as 400
> >> neighbor 131.1.5.5 update-source Loopback0
> >> neighbor 131.1.5.5 route-reflector-client
> >> maximum-paths 2
> >> no auto-summary
> >>!
This archive was generated by hypermail 2.1.4 : Sat Mar 01 2003 - 11:06:35 GMT-3