From: Bob Sinclair (bsinclair@netmasterclass.net)
Date: Thu May 19 2005 - 18:10:25 GMT-3
SAN,
Right! The RIDs are relevant only when sync is enabled and you are
redistributing BGP into OSPF. You set the RID for the entire process:
router ospf 1
router-id 172.16.103.1
router bgp 1
bgp router-id 172.16.103.1
You can see the RIDs on the receiving router as shown in the ouput below.
R1#sh ip bgp 157.10.1.208
BGP routing table entry for 157.10.1.208/28, version 4
Paths: (1 available, best #1, table Default-IP-Routing-Table,
RIB-failure(17))
Advertised to non peer-group peers:
172.16.123.2
500
172.16.43.3 (metric 65) from 172.16.43.3 (172.16.103.1)
Origin IGP, metric 0, localpref 100, valid, internal, synchronized,
best
SHOW IP BGP 157.10.1.208 shows the RID of the BGP source <172.16.103.1>
R1#sh ip route 157.10.1.208
Routing entry for 157.10.1.208/28
Known via "ospf 1", distance 110, metric 1
Tag 500, type extern 2, forward metric 65
Last update from 172.16.14.4 on Serial0/0.14, 00:34:54 ago
Routing Descriptor Blocks:
* 172.16.14.4, from 172.16.103.1, 00:34:54 ago, via Serial0/0.14
Route metric is 1, traffic share count is 1
SHOW IP ROUTE 157.10.1.208 command shows the RID of the ASBR <172.16.103.1>
HTH,
Bob Sinclair
CCIE #10427, CCSI 30427, CISSP
www.netmasterclass.net
----- Original Message -----
From: san
To: Bob Sinclair ; Cisco certification
Sent: Thursday, May 19, 2005 4:26 PM
Subject: Re: BGP basic router-id understanding
Bob,
Thanks Bob.
Can you check if i am correct.
This problem happens if sync is enabled & Rtr is redistributing BGP to
ospf & that Rtr is not a ASBR
route-maps does not have a "set router-id" option..how can i change
the router-id of adversiting routes ?
Do you have a link to this solution?
/SAN
On 5/19/05, Bob Sinclair <bsinclair@netmasterclass.net> wrote:
>
> San,
>
>
> RFC 1745 says that when synchronization is enabled and you are
> redistributing BGP into OSPF, then the BGP source must also be OSPF ASBR.
> If they differ, BGP considers the route un-synchronized.
>
> The basic problem can be satisfied by making sure that the redistribution
is
> done on the BGP border router, and by assuring that the OSPF RID on that
> router is the same as the BGP RID on that router. (which they would be
by
> default).
>
> The document you reference points out that it is very difficult, if not
> impossible, to satisfy the RFC 1745 requirement when you use
> route-reflectors. This is because the route-reflector changes the BGP
> source to the RID of the route-reflector. If the RR is not the ASBR, you
> have problems.
>
> As a hack, you can tweak the RIDs so that the OSPF ASBR RID is the same
as
> the RR RID, even if they are different routers.
>
> HTH,
>
>
> Bob Sinclair
> CCIE #10427, CCSI 30427, CISSP
> www.netmasterclass.net
>
>
> ----- Original Message -----
> From: san
> To: Cisco certification
> Sent: Thursday, May 19, 2005 12:37 PM
> Subject: BGP basic router-id understanding
>
> Hello Group,
>
> I am trying to understand BGP Notes from 911networks.com. I did not
> understand the below points or how to do it . If possible, can you
> explain me how to solve it ?
>
>
> Statement 1:
> ---------------
> The ospf router-id must be the same as the bgp router-id for
> redistributing the routes from ospf to bgp. It needs to be done
> manually if a route-reflector is involved or it won't work.
>
> Question 1:
> ----------------
> ex: R1---------R2 (RR)------R3
> Should i change the router-id of incoming ospf updates on R3 ? or
> should i change Bgp router-id on R3 ? Any examples.
>
> Closest i found from searching is below, but could not benefit.
> http://www.groupstudy.com/form/read.php?f=7&i=30353&t=30126
>
>
> Statement 2:
> --------------
> The BGP Router-id is used with the synchronization and in iBGP the BGP
> Router-id is used as tie breaker for the BGP path selection
>
> * Just because the next hop is pingable, it does not mean it's a
> valid next hop.
> * Next hop addresses that are reachable only via a default route
> aren't valid.
> * Next hop addresses that are reachable only via another BGP route
> are also not valid.
> Question 2:
> ---------------
> I thought, if there is a problem with nexthop, route will not be
> available in BGP routing table right ?
>
>
>
> /SAN
>
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