reg:serial failover

Unanswered Question
Dec 3rd, 2007

Dear sir,

Iam having 2620 router and iam having 2 serial connectivity terminated on this router now we want if one serial fails automatically second serial will up and we want loadbalance also on single fastethernet .for this setup 2621 will supoort and plz give me the samle config for this.

Regards

srini

I have this problem too.
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vasuramnet Mon, 12/03/2007 - 21:33

Dear sir,

Thanks for ur reply .The 2 serial iam connecting 2different isps i.e(v.35)now my doubt is can take these 2 isps on single ethernet and we want serial failover and load balance.plz give me some examples.

Regards

srini

9246571397

bvsnarayana03 Mon, 12/03/2007 - 05:17

The question is not very clear. Where are the links terminating, are these to 2 different ISP's & used for internet or pt 2 pt for intranet connectivity.

What protocol are you using ? revert with required details.

vasuramnet Mon, 12/03/2007 - 21:35

Dear sir,

Thanks for ur reply .The 2 serial iam connecting 2different isps i.e(v.35)now my doubt is can take these 2 isps on single ethernet and we want serial failover and load balance.plz give me some examples.This is for internet only

Regards

srini

9246571397

paul.matthews Tue, 12/04/2007 - 06:24

Just so I am clear, you have a single router, that wouter has two WAN interfaces (V35) and you wish to connect to two different ISPs?

Depending upon what you want to actually acheive, this can be done in a number of ways. The "accepted" way will mean you need your own AS number and your own chunk of publically routable addressing, and you simply configure BGP to both ISPs. You will need route maps outbound to permit only your own address space to be advertised (missing that means you could end up being a transit AS between the ISPs!).

That will get your connectivity up. You then need to adjust it how you want. If you want a primary link and a backup, simply set a preferred weight (or if you want to be ready to scale your internet connectivity local preference) on the BGP peer for the ISP you wish to prefer. That will send all outbound traffic that way, with the other peer only taking over on a fail, or for routes not learnt via the primary peer.

You can use as_path prepending to make the backup ISP less preferred for inbound traffic.

If you want to load balance, then just set it up and go, and see what load distribution you get. You may be lucky and get a reasonable distribution as default. If you don't, you can use access lists and route maps to set either weight or local preference for selected inbound routes until you get an acceptable balance on outbound traffic.

Inbound traffic is less easy to balance - when talking to two ISPs the only parameter you have any control over is the as_path length and as_path prepending can be a bit of a blunt instrument.

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