load balancing and failover

Unanswered Question
May 22nd, 2007


I have internet connection(lease line) form two different ISP.

How can i load balance the internet access between two ISP's and also configure failover if one of the intenet link goes down.

I have this problem too.
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Overall Rating: 4 (1 ratings)
spremkumar Tue, 05/22/2007 - 00:51


Do you own ur public ip address block ?

if yes you can think of load balancing with different ISPs.

But if you are being currently using Provident Assigned which is unique to individual providers then you can configure redundancy/failover.


la-technologies Tue, 05/22/2007 - 01:04


Different ISP vendor has provided different IP Blocks.

Kindly let me know the steps and procedure required.

A configuration example will help a lot.


Amit Singh Tue, 05/22/2007 - 04:20


If I were you, I would have thought of using NAT and PBR (policy based routing).I would first look at the kind of traffic, users, applications that I have to go the outisde world. Once the traffic is determined I would see the traffic distribution of the users over the two links. I would use my application, mail traffic to go thorough one link and internet and other traffic to use another link.I will make both the links as back up of each other.In case of one of the link goes my all the traffic will use the other link. I would suggest to implement proper QOS and rate limiting to drop the unwanted traffic.



Policy Based Routing:





HTH,Please rate if it does.

-amit singh

bjornarsb Tue, 05/22/2007 - 05:20


I would recomend that you apply for your own Public IP addresses. PI = Provider Independent Addresse. This is the only way that you can achieve full redundancy and load balancing based on prefix.

When you are using two different ISP's you will also get your own AS number.

For configuration on your side have a look at this example:





Paolo Bevilacqua Tue, 06/26/2007 - 07:56

Asingh2's reply is more realistic and applicable. In these days, requests for provider-independent address space are routinely turned down because most organizations do not have or can't prove the requirements. Same for AS number applications.

Try to believe.

Pavel Bykov Tue, 06/26/2007 - 08:11

I agree with Bjornar.

After that you can advertise one part of your PI prefix to first provider, and another part of your PI prefix to the second provider.

Also, you will advertise your whole prefix to both providers, but because it is not the longest match, it will be used only in case if one of ISPs fail.

That's for communication coming inside your AS.

As for communication coming outside your AS, that's easier configuration of your internals. You can use either multihop, or other balancing methods if you don't want asymetric routing and are using NAT.


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