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07-19-2021 08:02 AM
Hello,
My question is about route redistribution from OSPF to BGP.
Below is my topology.
eBGP is configured between R1 and R2. OSPF is configured in R2-R4.
On R2-R4, prefix-suppression is added in router ospf context.
Redistribution is configured on R2 to inject OSPF route to BGP.
In BGP, I can see not only /32 route but also /24 route which is between R2 and R3 has been redistributed in BGP.
Router(config-router)#do sh ip route
Codes: L - local, C - connected, S - static, 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
i - IS-IS, su - IS-IS summary, 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, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override
Gateway of last resort is not set
10.0.0.0/8 is variably subnetted, 7 subnets, 2 masks
C 10.0.12.0/24 is directly connected, Ethernet0/0
L 10.0.12.1/32 is directly connected, Ethernet0/0
B 10.0.23.0/24 [20/0] via 10.0.12.2, 00:04:31
C 10.255.255.1/32 is directly connected, Loopback0
B 10.255.255.2/32 [20/0] via 10.0.12.2, 00:04:31
B 10.255.255.3/32 [20/11] via 10.0.12.2, 00:01:37
B 10.255.255.4/32 [20/21] via 10.0.12.2, 00:00:12
May I ask why and how to avoid it?
Thanks a lot.
BR,
Dan
------------------------------------
Below the R2 config for reference.
R2:
interface Loopback0
ip address 10.255.255.2 255.255.255.255
ip ospf 1 area 0
!
interface Ethernet0/0
ip address 10.0.12.2 255.255.255.0
!
interface Ethernet0/1
ip address 10.0.23.2 255.255.255.0
ip ospf 1 area 0
!
router ospf 1
prefix-suppression
!
router bgp 10001
bgp router-id 10.255.255.2
bgp log-neighbor-changes
redistribute ospf 1
neighbor 10.0.12.1 remote-as 10000
Solved! Go to Solution.
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07-19-2021 09:21 AM
Hi @Dan22 ,
This is due to the fact that this prefix (192.168.23.0/24) is local and attached to an interface that is owned by OSPF. If you may want to use a route-map when you redistribute OSPF in BGP to only include host routes (/32).
route-map ospf2bgp permit 10
match IP address prefix-list host-routes
!
ip prefix-list host-routes seq 5 permit 0.0.0.0/0 ge 32
!
router bgp 10001
redistribute ospf 1 route-map ospf2bgp
Regards,
Harold Ritter, CCIE #4168 (EI, SP)
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07-19-2021 08:38 AM
You need to post more information - what IP address each segment configured, what where is this output taken from what Router ?
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07-19-2021 09:21 AM
Hi @Dan22 ,
This is due to the fact that this prefix (192.168.23.0/24) is local and attached to an interface that is owned by OSPF. If you may want to use a route-map when you redistribute OSPF in BGP to only include host routes (/32).
route-map ospf2bgp permit 10
match IP address prefix-list host-routes
!
ip prefix-list host-routes seq 5 permit 0.0.0.0/0 ge 32
!
router bgp 10001
redistribute ospf 1 route-map ospf2bgp
Regards,
Harold Ritter, CCIE #4168 (EI, SP)
