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RE: BGP sync posted 10/27/2002
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Without knowing your exact topology, it is difficult to give an accurate answer BUT -
when using OSPF as the underlying IGP you can have BGP sync issues.
The reason is that the OSPF Router-ID for the IGP route must be the same as the BGP router-ID.
If they are different they are considered out of sync.
This is a common problem when using Route reflectors for example.

Look at the following doc
If you do a search on the archieves, you will find this a common issue that many people have come across.

You have the following options to fix this problem (based upon you using Route reflectors for example)

1) Turn off BGP sync
2) Use confederations
3) Change the OSPF router-ID and BGP router-id's on the appropriate routers so that they match.   
4) Use another IGP instead, eg EIGRP

I have reseached and documented this issue. If you would like an example pls email me directly and I will forward the word doc I have created.


-----Original Message-----
From: Richard Davidson [mailto:rich@xxxxxxxxxxxxxx]
Sent: 27 October 2002 06:00
To: groupstudy
Subject: BGP sync

This is the rull of bgp sync as I know it.  If the IGP
knows the network that BGP has than bgp will be in
sync.  In the show ip route and sho ip bgp I have a
route to each of the bgp networks but they are not all
in sync.  Am I missing something.  Shouldn't they (bgp
routes) all be in sync.


r2#sho ip bgp
BGP table version is 3162, local router ID is
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
*>i137.20.10.0/24             20    100 
    0 ?
*>i137.20.20.0/24             84    100 
    0 ?
* i137.20.25.0/24             11    100 
    0 ?
* i137.20.33.0/26             75    100 
    0 ?
* i137.20.48.0/20             12    100 
    0 ?
* i137.20.64.0/20             11    100 
    0 ?
* i137.20.100.34/32             10    100 
    0 ?
* i137.20.100.35/32             74    100 
    0 ?
* i137.20.240.0/20             11    100 
    0 ?
*>i172.168.70.0/24           170    100 
    0 3 i
* i172.168.80.0/24              0    100 
    0 1 i
*>i200.200.100.0             75    100 
    0 ?
* i200.200.200.0              0    100 
    0 ?

r2#sho ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M
- mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA -
OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA
external type 2
       E1 - OSPF external type 1, E2 - OSPF external
type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS
level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static
route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is to network

C is directly connected, Loopback223
O IA [110/66] via,
00:18:09, Serial0 is variably subnetted, 14 subnets,
6 masks
O E1 [110/164] via,
00:18:10, Serial0
O [110/65] via,
00:18:20, Serial0
O [110/1626] via,
00:18:20, Serial0
O IA [110/65] via,
00:18:10, Serial0
C is directly connected,
O E2 [110/20] via,
00:18:11, Serial0
O E1 [110/164] via,
00:18:11, Serial0
O [110/66] via,
00:18:21, Serial0
O IA [110/129] via,
00:18:11, Serial0
O E2 [110/20] via,
00:18:12, Serial0
C is directly connected,
O [110/128] via,
1d02h, Serial0
O [110/64] via,
1d02h, Serial0
O [110/65] via,
00:18:22, Serial0
C is directly connected, Loopback0 is subnetted, 2 subnets
O E2 [110/500] via,
00:18:12, Serial0
O E2 [110/500] via,
00:18:12, Serial0
S* is directly connected, Ethernet0

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