From: Victor Cappuccio (vcappuccio@ccbootcamp.com)
Date: Tue Jul 31 2007 - 16:31:27 ART
Hi Nitin,
For a quick example of how synchronization can cause problems
having this topology
(R2 in AS 2) --- (R5 in AS 1)
Take a look at the output of show ip bgp.
R2#show ip bgp
BGP table version is 7, local router ID is 192.168.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
* i200.200.1.0 192.168.1.1 0 100 0 i
*> 200.200.2.0 0.0.0.0 0 32768 i
*> 200.200.3.0 192.168.5.5 0 1 i
*> 200.200.4.0 192.168.5.5 0 1 i
*> 200.200.5.0 192.168.5.5 0 0 1 i
*> 200.200.6.0 192.168.5.5 0 1 i
Looking at the output of show ip bgp 200.200.1.0, we see the following:
BGP routing table entry for 200.200.1.0/24, version 0
Paths: (1 available, no best path)
Not advertised to any peer
Local
192.168.1.1 (metric 2713600) from 192.168.1.1 (192.168.1.1)
Origin IGP, metric 0, localpref 100, valid, internal, not synchronized
R2#
the route is know as not synchronized. Since R2 does not have an IGP route
for the network, it will not synchronize. Synchronization will only affect
routes learned from IBGP peers. The networks from R3, R4, R5, and R6 are
fine, because they were learned from an EBGP peer (R5). If there is only one
router in the AS, synchronization will never be a problem for a BGP route.
We will disable synchronization on R2. Now the routes all show as best in the
output of show ip bgp.
R2(config)#router bgp 2
R2(config-router)#no sync
R2#show ip bgp
BGP table version is 8, local router ID is 192.168.2.2
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
*>i200.200.1.0 192.168.1.1 0 100 0 i
*> 200.200.2.0 0.0.0.0 0 32768 i
*> 200.200.3.0 192.168.5.5 0 1 i
*> 200.200.4.0 192.168.5.5 0 1 i
*> 200.200.5.0 192.168.5.5 0 0 1 i
*> 200.200.6.0 192.168.5.5 0 1 i
*>i200.200.35.0 192.168.35.35 0 100 0 3 i
R2#
The routes now show as best.
Here, we are adding additional loopbacks to BGP. Configuration for this task
is not quite as simple as it looks. First, we will configure the two networks
for BGP and watch what happens.
R5#conf ter
Enter configuration commands, one per line. End with CNTL/Z.
R5(config)#router bgp 1
R5(config-router)#network 192.168.5.0
R5(config-router)#
R2#
R2#conf ter
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#router bgp 2
R2(config-router)#network 192.168.2.0
R2(config-router)#^Z
R2#
Take a look at the BGP table.
R2#show ip bgp 192.168.5.0
BGP routing table entry for 192.168.5.0/24, version 49
Paths: (1 available, best #1, table Default-IP-Routing-Table)
Flag: 0x820
Advertised to update-groups:
1
1
192.168.5.5 (metric 2) from 192.168.5.5 (100.5.5.5)
Origin IGP, metric 0, localpref 100, valid, external, best
Our routes are no longer showing as best. If we look at the output for one
particular route, we can see why.
R2#show ip bgp 192.168.5.0
BGP routing table entry for 192.168.5.0/24, version 49
Paths: (1 available, best #1, table Default-IP-Routing-Table)
Flag: 0x820
Advertised to update-groups:
1
1
192.168.5.5 (metric 2) from 192.168.5.5 (100.5.5.5)
Origin IGP, metric 0, localpref 100, valid, external, best
R2#
An example of a RIB failure that could originate problems even with your bgp
peering
R2#show ip bgp summ
BGP router identifier 100.2.2.2, local AS number 2
BGP table version is 10, main routing table version 10
8 network entries using 936 bytes of memory
8 path entries using 416 bytes of memory
5/4 BGP path/bestpath attribute entries using 620 bytes of memory
1 BGP AS-PATH entries using 24 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 1996 total bytes of memory
BGP activity 8/0 prefixes, 8/0 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down
State/PfxRcd
192.168.1.1 4 2 389 391 10 0 0 06:24:34 1
192.168.5.5 4 1 393 392 10 0 0 06:26:17 5
We are learning the route to 192.168.5.0 via 192.168.5.5. If we look at the
output of debug ip routing, we see the following:
R2#debug ip routing
IP routing debugging is on
R2#
*Jul 31 04:50:20.711: RT: recursion error routing 192.168.5.5 - probable
routing loop
R2#u all
All possible debugging has been turned off
Debug IP routing is a very useful tool. If your topology is stable, you will
see almost nothing. If you have flapping routes, however, you will see very
quickly. For lab purposes, it is recommended to turn on debug ip routing on
your redistribution routers, and clear the routing table. After the routes
are re-learned, you will usually know very quickly if you have a problem with
your redistribution.
The underlying issue here is administrative distance. We are learning the
route for our peering address from two sources, OSPF and BGP. Because BGP is
learning the network via an external BGP peering, the administrative distance
is 20, which is preferred over the administrative distance of 110 for OSPF.
There are a few methods that we can use to get around this problem. We can
adjust the administrative distance for OSPF or BGP using the distance command
under the routing process, or we can tell BGP to prefer the IGP route using a
network statement with the backdoor keyword. On R2, we will adjust the
administrative distance for BGP, and on R5, we will use the network command
with the backdoor keyword.
R2(config)#router bgp 2
R2(config-router)#distance bgp 200 200 200
R5(config)#router bgp 1
network 192.168.2.0 backdoor
Note: With the network backdoor command, you specify the route that you want
to have a higher administrative distance. The ONLY route that we need to
change is the route for the network to which we are peering.
R5#show ip bgp rib-failure
Network Next Hop RIB-failure RIB-NH Matches
192.168.2.0 192.168.2.2 Higher admin distance n/a
HTH
thanks,
Victor Cappuccio.-
- CCSI# 31452
Network Learning Inc - A Cisco Sponsored Organization (SO)
YES! We take Cisco Learning credits!
vcappuccio@ccbootcamp.com
http://www.ccbootcamp.com (Training, Workbooks, Remote Racks)
Toll Free: 877-654-2243
Intl: 702-968-5100
FAX: 702-446-8012
-----Original Message-----
From: nobody@groupstudy.com on behalf of NITIN NITIN
Sent: Tue 31-Jul-07 11:19 AM
To: ccielab@groupstudy.com
Subject: BGP route not showing synchronize
HI Experts,
I have a problem -----
113.0.0.0/8 is learnt via ospf still in bgp not showing rib failure
and due to which my synchronisation rule failing
Rack1R6#sh ip bgp
BGP table version is 11, local router ID is 150.1.6.6
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 28.119.16.0/24 54.1.2.254 0 54 i
*> 28.119.17.0/24 54.1.2.254 0 54 i
*> 112.0.0.0 54.1.2.254 0 0 54 50 60 i
* i113.0.0.0 150.1.4.4 0 100 0 54 50 60 i
*> 114.0.0.0 54.1.2.254 0 0 54 i
* i115.0.0.0 150.1.4.4 0 100 0 54 i
*> 116.0.0.0 54.1.2.254 0 0 54 i
* i117.0.0.0 150.1.4.4 0 100 0 54 i
*> 118.0.0.0 54.1.2.254 0 0 54 i
* i119.0.0.0 150.1.4.4 0 100 0 54 i
r> 139.1.0.0 0.0.0.0 32768 i
r i 150.1.4.4 0 100 0 i
s> 139.1.6.0/24 0.0.0.0 0 32768 ?
Rack1R6#sh ip route | i 113.0.0.0
O E2 113.0.0.0/8 [110/20] via 139.1.0.3, 00:00:43, FastEthernet1/0
Rack1R6#sh ip route | i B
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
B 118.0.0.0/8 [20/0] via 54.1.2.254, 00:00:49
B 116.0.0.0/8 [20/0] via 54.1.2.254, 00:00:49
B 114.0.0.0/8 [20/0] via 54.1.2.254, 00:00:49
B 112.0.0.0/8 [20/0] via 54.1.2.254, 00:00:49
B 28.119.17.0 [20/0] via 54.1.2.254, 00:00:49
B 28.119.16.0 [20/0] via 54.1.2.254, 00:00:49
Rack1R6#sh ip bgp rib-failure
Network Next Hop RIB-failure RIB-NH Matches
139.1.0.0 0.0.0.0 Admin distance >= 255 n/a
Rack1R6#sh ip bgp 113.0.0.0
BGP routing table entry for 113.0.0.0/8, version 0
Paths: (1 available, no best path)
Not advertised to any peer
54 50 60
150.1.4.4 (metric 20) from 150.1.4.4 (150.1.4.4)
Origin IGP, metric 0, localpref 100, valid, internal, not
synchronized<<<<<<<<<<<<<<
router ospf 1
router-id 150.1.6.6
log-adjacency-changes
redistribute bgp 100 subnets route-map EVEN
network 139.1.0.6 0.0.0.0 area 0
network 139.1.6.6 0.0.0.0 area 0
network 150.1.6.6 0.0.0.0 area 1
!
router bgp 100
synchronization
bgp router-id 150.1.6.6
bgp log-neighbor-changes
aggregate-address 139.1.0.0 255.255.0.0 summary-only
redistribute ospf 1 route-map VLAN-5
neighbor 54.1.2.254 remote-as 54
neighbor 54.1.2.254 prefix-list EVEN in
neighbor 54.1.2.254 maximum-prefix 150000 90
neighbor 150.1.4.4 remote-as 100
neighbor 150.1.4.4 update-source Loopback0
neighbor 150.1.4.4 next-hop-self
distance bgp 20 200 255
no auto-summary
Regards
---------------------------------
Need a vacation? Get great deals to amazing places on Yahoo! Travel.
---------------------------------
Yahoo! oneSearch: Finally, mobile search that gives answers, not web links.
This archive was generated by hypermail 2.1.4 : Sat Aug 18 2007 - 08:17:42 ART