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Any one can answer the BGP Synchronization question ?

Posted on 2012-12-29
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Last Modified: 2012-12-31
Any one can answer the BGP Synchronization question ?

The topology is very simple. Router2---Router1--interface e1/1(ip address 111.1.1.1/24)

R1
router bgp 12
network 111.1.1.0 mask 255.255.255.0
 neighbor 2.2.2.2 remote-as 12
 neighbor 2.2.2.2 update-source Loopback0
router ospf 1
network 0.0.0.0 255.255.255.255 area 0

R2
router bgp 12
 synchronization
neighbor 1.1.1.1 remote-as 12
neighbor 1.1.1.1 update-source Loopback0
router ospf 1
network 0.0.0.0 255.255.255.255 area 0

R2#show ip bgp
   Network          Next Hop            Metric LocPrf Weight Path
* i111.1.1.0/24     1.1.1.1                  0    100      0 i

After R2 enabled synchronization, the network 111.1.1.0/24 in bgp table lost marker “>” in the bgp table.

Question:
In the case, synchronization rule means network 111.1.1.0/24 is inactive (meaning losing marker “>” ) in R2’ BGP table until this network goes into R2 via IGP. Now the network 111.1.1.0/24 already has gone into R2 via IGP. Why does the network 111.1.1.0/24 is still inactive in R2 BGP table after enabling synchronization in R2 ?
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Question by:davidy2001
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4 Comments
 
LVL 3

Expert Comment

by:Teeshirt
ID: 38730694
Your topology isn't desirable to enable synchronization.

You can disable synchronization if one of the following conditions is true:

- Your AS does not pass traffic from one AS to another AS.
- All the transit routers in your AS run BGP.
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Author Comment

by:davidy2001
ID: 38730966
Thanks. No matter whether I connect other additional iBGP or EBGP router to Router2, or not, the effect should be the same. The network 111.1.1.0/24 must be active ( with marker ">") , and then it can travel to next EBGP. what i am concerned is why the network 111.1.1.0/24 is not active after enabling synchronization
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Accepted Solution

by:
Phyo HTET AUNG earned 500 total points
ID: 38732162
You are speaking ibgp and ospf between R1 and R2.
What is result of "R2#show ip bgp x.x.x.x". It's "not synchronized"?


I got troubleshooting guide from iphelp



Refer Cisco Case Studies

Hope this help.
Regards
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Author Comment

by:davidy2001
ID: 38733598
Great, thanks, phyohtetaung
If eBGP connect with R2, there two ways to let 111.1.1.0/24 reach the eBGP: 1, turn off synchronization at R2, 2, redistribute the route or publish it by igp though the route is marked with "r" in bgp table.
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