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BGP Conditional Advertisement Exist-Map Issue

Hi,

 

I am using BGP advertise-map and exist-map to conditionally advertise a prefix 10.10.10.10/24 from R2 to R1, only when R2 can receive default-route from R3. I am using "prefix-list" to match on desired prefixes.

 

R1 --- R2 ------- R3

 

 

!!!! R2 config snippet

router bgp 2
  neighbor 192.168.1.1 remote-as 2
  neighbor 192.168.1.1 advertise-map bgp-adv exist-map bgp-exist

route-map bgp-adv permit 10
  match ip address prefix-list bgp-adv
route-map bgp-exist permit 10
  match ip address prefix-list bgp-exist

ip prefix-list bgp-adv seq 10 permit 10.10.10.10/24
ip prefix-list bgp-exist seq 20 permit 0.0.0.0/0

 

R2 always sets the exist-map condition successful, the status is set to Advertise on R2 and R1 receives the 10 route. This is true regardless R2 has received 0.0.0.0/0 from R3 or not.

 

Now for the sake of testing, If I base the conditional check on a normal prefix say 20.20.20.20/24 on R2 (received from R3), the check passes only when the 20 route exists in R2's bgp table. 

 

The BGP conditional check works with a normal prefix but not with a default-route. Is this expected?

 

I am Lab'ing this in GNS3 on 3745 router and IOS 12.4(15)T14.

 

Regards, 

Rick.

2 REPLIES 2
VIP Mentor

Re: BGP Conditional Advertisement Exist-Map Issue

Hello,

 

post the config you use with the default route...

 

Actually, post the full configs of R1 and R2 you use with the default route...

Highlighted
VIP Mentor

Re: BGP Conditional Advertisement Exist-Map Issue

Hello,

 

I tested in GNS3 with and without a default route, results are as desired. Compare your configs to mine.

 

With default route:

 

R3

 

router bgp 3
bgp router-id 3.3.3.3
bgp log-neighbor-changes
neighbor 192.168.13.1 remote-as 1
neighbor 192.168.13.1 default-originate
neighbor 192.168.13.1 soft-reconfiguration inbound
!
ip route 0.0.0.0 0.0.0.0 null 0

 

R1

 

router bgp 1
bgp router-id 1.1.1.1
bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255
network 10.10.10.10 mask 255.255.255.255
neighbor 192.168.1.2 remote-as 2
neighbor 192.168.1.2 soft-reconfiguration inbound
neighbor 192.168.1.2 advertise-map bgp-adv exist-map bgp-exist
neighbor 192.168.13.3 remote-as 3
neighbor 192.168.13.3 soft-reconfiguration inbound
!
ip prefix-list bgp-adv seq 10 permit 10.10.10.10/32
!
ip prefix-list bgp-exist seq 20 permit 0.0.0.0/0
!
route-map bgp-exist permit 10
match ip address prefix-list bgp-exist
!
route-map bgp-adv permit 10
match ip address prefix-list bgp-adv

 

R1#sh ip bgp

Network Next Hop Metric LocPrf Weight Path
*> 0.0.0.0 192.168.13.3 0 3 i
*> 1.1.1.1/32 0.0.0.0 0 32768 i
*> 2.2.2.2/32 192.168.1.2 0 0 2 i
*> 10.10.10.10/32 0.0.0.0 0 32768 i

 

R2

 

R2#sh ip bgp

Network Next Hop Metric LocPrf Weight Path
*> 0.0.0.0 192.168.1.1 0 1 3 i
*> 1.1.1.1/32 192.168.1.1 0 0 1 i
*> 2.2.2.2/32 0.0.0.0 0 32768 i
*> 10.10.10.10/32 192.168.1.1 0 0 1 i
R2#

-------------------------------------

No default route

 

R3

router bgp 3
bgp router-id 3.3.3.3
bgp log-neighbor-changes
neighbor 192.168.13.1 remote-as 1
neighbor 192.168.13.1 soft-reconfiguration inbound


R1

router bgp 1
bgp router-id 1.1.1.1
bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255
network 10.10.10.10 mask 255.255.255.255
neighbor 192.168.1.2 remote-as 2
neighbor 192.168.1.2 soft-reconfiguration inbound
neighbor 192.168.1.2 advertise-map bgp-adv exist-map bgp-exist
neighbor 192.168.13.3 remote-as 3
neighbor 192.168.13.3 soft-reconfiguration inbound
!
ip prefix-list bgp-adv seq 10 permit 10.10.10.10/32
!
ip prefix-list bgp-exist seq 20 permit 0.0.0.0/0
!
route-map bgp-exist permit 10
match ip address prefix-list bgp-exist
!
route-map bgp-adv permit 10
match ip address prefix-list bgp-adv

R1#sh ip bgp

Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 0.0.0.0 0 32768 i
*> 2.2.2.2/32 192.168.1.2 0 0 2 i
*> 10.10.10.10/32 0.0.0.0 0 32768 i

 

R2

 

R2#sh ip bgp

Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 192.168.1.1 0 0 1 i
*> 2.2.2.2/32 0.0.0.0 0 32768 i

 

 

 

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