reg:isp faiover

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Oct 9th, 2007
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Iam having 3 links with 2 different ISP for the internet traffic. i want to achieve the 3 links active at the same time for internet traffic & the same time i need failover for this links.

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vasuramnet Wed, 10/10/2007 - 03:59
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Yes sir,

3 links on the same router




bvsnarayana03 Wed, 10/10/2007 - 04:22
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Default route pointing to the 3 interfaces could be a solution for outgoing traffic, but incoming traffic would be a concern.

There are 2 methods to solve this: either use BGP with the ISP's, or use a hardware link load-balancer. Choice is entirely with admin based on his expertise over BGP.

guruprasadr Wed, 10/10/2007 - 05:10
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Verify the possibility of Bundling the 3 Links for further usage.

As i know, Bundling will provide the Load Balancing as well as Fail over requirement.

Pls Rate if Helps

Best Regards,

Guru Prasad R

vasuramnet Wed, 10/10/2007 - 21:21
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Dear guruprasad,

Thanks for ur valuble reply and if u dont mind can u explain clearly what is ment by bundling.plz give any exampls for this.




If you are using multiple ISPs you will not be able to bundle the circuits. This typically only works when all links terminate in a single device... on both ends of the links.

As for a hardware load balancer, that will only work for outbound traffic, not inbound.

IMHO BGP is going to be your only real option when doing multi-carrier bidirectional load balancing...

paolo bevilacqua Thu, 10/11/2007 - 18:03
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Actually, "hardware" load balancers can also balance inbound traffic. By virtue of NAT, they do so by allocating more TCP outgoing requests to circuits where more incoming traffic is wanted at any give time.

Since for most installations incoming is more than outgoing, the resulting unbalance on outgoing traffic is not a concern.

BGP is simply not possible for most installations. So what is done, is NAT to multiple ISP, with multiple static routes and multiple NAT statements. This works reasonably well. For the case in question, it wold be advantageous if the ISP providing two links, was to bundle them using Multilink PPP.

Hope this helps, please rate post if it does!

guruprasadr Thu, 10/11/2007 - 20:28
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HI Srinivas, [Pls Rate if HElps]

Sorry for the late reply.

Bundling should be possible by using Multilink PPP but Bundling has to be done end-to-end (ie., at your customer end and at service provider end).

If not means, the Outbound traffic can be load balanced to various link but the inbound traffic from ISP cannot be assured.

Its better to speak to your ISP reg this requirement.

Note: 3 Links from 2 different ISP's and with this Scenario the Bundling Concept will not work in Normal.

Whereas the 1" Link from a different ISP can be kept as Failover purpose and 2" Link from an ISP can be Bundled with the help of Service provider. So you have Failover + Load Balancing facility availaible.


Best Regards,

Guru Prasad R


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