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Please Help! BGP load sharing configuration

Please see the attached picture. Basically I have been assigned a /28. I have (2) 2800 routers that each have a connection to the same ISP. I would like to split the /28 and advertise a /29 out one pipe, and a /29 out the other. The problem I am having is that nothing gets advertised unless I just have the network statement 172.16.100.0 mask 255.255.255.240. See below for how I would like it to work..

2800-1

fa0/0 ip add 10.10.10.1/30 (goes to ISP)

fa0/1 ip add 172.16.100.2/28 (goes to ASA)

ip route 172.16.100.0 255.255.255.248 172.16.100.1 10 (ASA) To get in routing table

router bgp 65123

network 172.16.100.0 mask 255.255.255.248

neigh 10.10.10.2 remote 200

neigh 172.16.100.3 remote 65123

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

2800-2

fa0/0 ip add 20.20.20.1/30 (goes to ISP)

fa0/1 ip add 172.16.100.3/28 (goes to ASA)

ip route 172.16.100.8 255.255.255.248 172.16.100.1 10 (ASA) To get in routing table

router bgp 65123

network 172.16.100.8 mask 255.255.255.248

neigh 20.20.20.2 remote 200

neigh 172.16.100.2 remote 65123

1 ACCEPTED SOLUTION

Accepted Solutions

Re: Please Help! BGP load sharing configuration

Hi Scott,

The reason your are not able to advertise the /29 subnet may be because the route is not in your IGP routing table.

Can you see the /29 routes when you do a sh ip bgp

To make sure the networks fallback you should advertise one /29 subnet from router1 with a higher metric (use ASs prepending) to your ISP and the reverse on router2.

But this may not work as your ISP will be filtering your private AS

If your ISP can accept MEDs then instead of AS prepend advertise MEDs to him with suitable manipulation

2800-1

router bgp 65123

network 172.16.100.0 mask 255.255.255.248

network 172.16.100.8 mask 255.255.255.248

neigh 10.10.10.2 remote 200

neigh 10.10.10.2 route-map Map1 out

neigh 172.16.100.3 remote 65123

ip route 172.16.100.0 255.255.255.248 172.16.100.1

ip route 172.16.100.8 255.255.255.248 172.16.100.1

access-list 1 permit 172.16.100.0 0.0.0.7

access-list 2 permit 172.16.100.8 0.0.0.7

route-map Map1 permit 10

match ip address 1

set as-path prepend 65123 65123 65123

route-map Map1 permit 20

match ip address 2

2800-2

router bgp 65123

network 172.16.100.0 mask 255.255.255.248

network 172.16.100.8 mask 255.255.255.248

neigh 20.20.20.2 remote 200

neigh 20.20.20.2 route-map Map1 out

neigh 172.16.100.2 remote 65123

ip route 172.16.100.0 255.255.255.248 172.16.100.1

ip route 172.16.100.8 255.255.255.248 172.16.100.1

access-list 1 permit 172.16.100.0 0.0.0.7

access-list 2 permit 172.16.100.8 0.0.0.7

route-map Map1 permit 10

match ip address 2

set as-path prepend 65123 65123 65123

route-map Map1 permit 20

match ip address 1

HTH, rate if it does

Narayan

3 REPLIES

Re: Please Help! BGP load sharing configuration

Hi,

Can you give us the output of the":

show ip bgp 172.16.100.0 255.255.255.248

show ip bgp 172.16.100.8 255.255.255.248

show ip bgp neighbor 172.16.100.2 adve

show ip bgp neighbor 20.20.20.2 adve

Vlad

Re: Please Help! BGP load sharing configuration

Hi Scott,

The reason your are not able to advertise the /29 subnet may be because the route is not in your IGP routing table.

Can you see the /29 routes when you do a sh ip bgp

To make sure the networks fallback you should advertise one /29 subnet from router1 with a higher metric (use ASs prepending) to your ISP and the reverse on router2.

But this may not work as your ISP will be filtering your private AS

If your ISP can accept MEDs then instead of AS prepend advertise MEDs to him with suitable manipulation

2800-1

router bgp 65123

network 172.16.100.0 mask 255.255.255.248

network 172.16.100.8 mask 255.255.255.248

neigh 10.10.10.2 remote 200

neigh 10.10.10.2 route-map Map1 out

neigh 172.16.100.3 remote 65123

ip route 172.16.100.0 255.255.255.248 172.16.100.1

ip route 172.16.100.8 255.255.255.248 172.16.100.1

access-list 1 permit 172.16.100.0 0.0.0.7

access-list 2 permit 172.16.100.8 0.0.0.7

route-map Map1 permit 10

match ip address 1

set as-path prepend 65123 65123 65123

route-map Map1 permit 20

match ip address 2

2800-2

router bgp 65123

network 172.16.100.0 mask 255.255.255.248

network 172.16.100.8 mask 255.255.255.248

neigh 20.20.20.2 remote 200

neigh 20.20.20.2 route-map Map1 out

neigh 172.16.100.2 remote 65123

ip route 172.16.100.0 255.255.255.248 172.16.100.1

ip route 172.16.100.8 255.255.255.248 172.16.100.1

access-list 1 permit 172.16.100.0 0.0.0.7

access-list 2 permit 172.16.100.8 0.0.0.7

route-map Map1 permit 10

match ip address 2

set as-path prepend 65123 65123 65123

route-map Map1 permit 20

match ip address 1

HTH, rate if it does

Narayan

Re: Please Help! BGP load sharing configuration

You need a matching route in the RIB for the network to be advertised. Remove the existing static route(s) and add the following. Then, issue the command 'clear ip bgp soft * out' for the change to take effect.

2800-1:

ip route 172.16.100.0 255.255.255.248 f0/1

2800-2:

ip route 172.16.100.8 255.255.255.248 f0/1

HTH

Sundar

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