From: Jack Heney (jheneyccie@xxxxxxxxxxx)
Date: Wed Oct 25 2000 - 17:29:42 GMT-3
I just set it up...here's the config:
10.2.1.0 10.2.2.0 10.12.1.0 10.1.2.0 10.1.1.0
---------R1----------R2-----------R3----------R4----------
BGP stuff:
R1 - BGP AS 1
R2 and R4 - BGP AS 2
R1 has a neighbor relation ship with R2
R1 has a "network 10.2.1.0 mask 255.255.255.0" statement
R2 has neighbor relationships with R1 and R4
R4 has a neighbor relationship with R2
OSPF stuff:
R2, R3, R4 area running OSPF in area 0 for networks 10.12.1.0, 10.1.2.0, and
10.1.1.0
R2 has redstribute connected in OSPF so R4 doesn't have next-hop problems
with IBGP
Sync stuff:
All BGP routers have synchronization on
As configured above, R4 learns about the 10.2.1.0 network in its BGP table,
but the route is not in the routing table...Here is the BGP table:
BGP table version is 2, local router ID is 10.1.2.254
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
* i10.2.1.0/24 10.2.2.254 0 100 0 1 i
If BGP is redistributed into OSPF on R2, both R3 and R4 learn an external
OSPF route to the 10.2.1.0 network. Also, the BGP table on R4 now looks
like this:
BGP table version is 2, local router ID is 10.1.2.254
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
*>i10.2.1.0/24 10.2.2.254 0 100 0 1 i
R4 has the OSPF route in the routing table (lower administrative distance
than IBGP), but R4 is now advertising the 10.2.1.0 network in BGP (I added
another router, R5, to the network and established an EBGP connection with
R4 and the route was learned). Thus, since R4 heard about the 10.2.1.0
network through both BGP and OSPF, it was free to advertise the route via
BGP with synchronization on.
hth,
Jack
>From: mark salmon <masalmon@cisco.com>
>Reply-To: mark salmon <masalmon@cisco.com>
>To: ccielab@groupstudy.com
>Subject: Re: BGP sync/no sync (loosing marks for extra commands)
>Date: Wed, 25 Oct 2000 14:47:06 -0700
>
>It is my understanding that BGP will not put BGP derived routes in the
>routing table until either it is synced with IGP or no sync is enables.
>Has anyone have sync enabled with an IGP running as seen the BGP routes
>in the routing table?
>
>Jack Heney wrote:
> >
> > Hang on a second...
> >
> >
> > Are you sure about this? I thought the point of synchronization was
>that in
> > an environment where transit service is being provided and some of the
> > transit router are not running BGP, we need to make sure that the
>transit
> > routers are not dropping traffic because they don't have as much
>information
> > as the BGP routers. This would seem to indicate that BGP needs to be
> > redistributed into the IGP....Maybe I'm completely wrong, or maybe I'm
>
>--
>
>
>
>Mark Salmon
>Network Support Engineer - SBC OP HQ
>Cisco Systems Inc
>8735 W. Higgins Road Suite 300
>Chicago IL 60631
>Phone:773-695-8235
>Pager:800-365-4578
>email: masalmon@cisco.com
>Empowering The Internet Generation.
>
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