Problem with BGP

[murali_k_meda]

Plz help on BGP, I am working for the ISP. I have Many Backbones, and few Block of Class C ( 195.X.X.X )IPs. Here i am advetising the each block to separate backbones throu rote-maps In BGP How can we split the one Block. For Ex: 195.X.X.0 255.255.255.240 has to come throu one Backbone and Remaining has to come with some other backbone. How this can be achive.

Thanks

Murali Krishna

[mheusinger]

Hello,

you could advertise a partial block in BGP

router bgp 65000

no synchronization

no auto-summary

network 192.168.1.128 mask 255.255.255.128

network 192.168.1.0 mask 255.255.255.128

network 192.168.1.0

neighbor 10.1.1.1 remote-as 65001

neighbor 10.1.1.1 prefix-list 101 out

neighbor 10.2.2.2 remote-as 65002

neighbor 10.2.2.2 prefix-list 102 out

ip route 192.168.1.0 255.255.255.128 Null0 250

ip route 192.168.1.128 mask 255.255.255.128 Null0 250

ip route 192.168.1.0 mask 255.255.255.0 Null0 250

ip prefix-list 101 seq 5 deny 192.168.1.128/25

ip prefix-list 101 seq 10 permit 0.0.0.0/0 le 32

ip prefix-list 102 seq 5 deny 192.168.1.0/25

ip prefix-list 102 seq 10 permit 0.0.0.0/0 le 32

This would announce 192.168.1.0/25 to AS 65001 and 192.168.1.128/25 to AS 65002. Additionally both ASes get the full address block (plus all other routes) to ensure connectivity for the full address block if one neighbor goes down.

Be aware however, that in the internet it is highly unlikely to get updates announced smaller than /24. Most large ISPs will block anything smaller than /24.

Hope this helps! please rate all posts.

Regards, Martin

[murali_k_meda]

Thanx Martin i will configure and i will test that

[vickyp183]

Thx Martin for the crisp explaination

[khaderbasha]

Hello Murali,

Have tried using med.

1.Tag a higher med to all the routes which you do not want to be reached from one backbone and announce it.

You can follow this procedure to all backbone routers and influence backbone to follow what you want. Again it depends on what attributes your ISP is checking or considering on their end.

You can use route-map to achieve this.

Khader