Ip prefix-list - Page 2

kumarpmt83 · ‎02-22-2012

Hi,

i have cisco 2800 router with the following config:

we have two service provider.

Lan IP : 10.10.70.0/23

Bsnl wan : 192.168.24.56/30

Tata wan : 10.70.56.36/30

router bgp 95001

no synchronization

bgp log-neighbor-changes

network 10.10.70.0 mask 255.255.254.0

network 10.10.70.0 mask 255.255.255.0

network 172.16.0.3 mask 255.255.255.255

neighbor 10.70.56.35 remote-as 6855

neighbor 10.70.56.35 route-map EBGP-TATAWAN out

neighbor 192.168.24.57 remote-as 7839

neighbor 192.168.24.57 description ***EBGP Peer to BSNL***

neighbor 192.168.24.57 soft-reconfiguration inbound

neighbor 192.168.24.57 weight 100

neighbor 192.168.24.57 route-map EBGP-BSNLWAN out

ip prefix-list BSNL-LANROUTES seq 10 permit 10.10.70.0/24

ip prefix-list BSNL-LANROUTES seq 20 permit 10.10.70.0/23

!

ip prefix-list TATA-LANROUTES seq 10 permit 10.10.71.0/24

ip prefix-list TATA-LANROUTES seq 20 permit 10.10.70.0/23

route-map EBGP-TATAWAN permit 10

match ip address prefix-list TATA-LANROUTES

route-map EBGP-BSNLWAN permit 10

match ip address prefix-list BSNL-LANROUTES

what does mean the above configuration.

what is prefix-list??what is the purpose we use it??

i have confused with the configuration.

Can anyone tell me...

milan.kulik · ‎02-24-2012

Hi,

are you still advertising 10.10.71.0/24 to Tata only from the client site?

Remeber the "longest match wins!" routing rule.

So the BSNL router in your HQ might be receiving the 10.10.71.0/24 route via Tata somehow.

Are you abel to check?

sh ip bgp 10.10.70.0/23 longer

issued on the BSNL router should show you all prefixes necessary if received via BGP.

sh ip route static | in 10.10.71.

sh ip route static | in 10.10.70.

issued for sure should show any possible static configured for the client site.

HTH,

Milan

kumarpmt83 · ‎02-24-2012

Now i removed 10.10.71.0/24 prefix to Tata in client side and it is working.

But in the Bsnl prefix 10.10.70.0/24 & 10.10.70.0/23 not removed in the client side.

It is ok or not.

Thank u very much guys for all the valuable post.

it is very helpful for me.

milan.kulik · ‎02-24-2012

Hi,

as we discussed with Kishore here, there are different possibilities how to make one provider connection preferred for incoming traffic.

You can advertise 10.10.70.0/24 and 10.10.71.0/24 to BSNL and (only) 10.10.70.0/23 to Tata in your case, e.g.

Or you can advertise 10.10.70.0/23 (only) to both providers and prepend the client site AS number several times when advertising to Tata.

Or you can use communities agreed with your providers.

But it's your decision based on the detailed knowledge of your network, we can give you just general recommendations here.

BR,

Milan

Kishore Chennupati · ‎02-23-2012

Dinesh,

you need to use local-pref on your primary link and AS-PATH prepend on your backup link if you are going to advertise 10.10.70.0/23 on both links. . This will ensure that the routing is optimal and not asymetrical.

HTH

Please free to ask further

Kishore

milan.kulik · ‎02-23-2012

Hi,

local-pref has no sense if weight is set alreday and only a single CE router is on the site.

AS-PATH prepend on the backup link might not be enough if each line is provided by a different provider.

BR,

Milan

Kishore Chennupati · ‎02-23-2012

Hi Milan,

Didn't notice he was talking about one CE.

I just read his last post and thought it was dual routers multihomed

Cheers, Kishore