Redundancy + Loadsharing

Unanswered Question
Jan 27th, 2010

Dear All,

I have 2 cisco 2821 routers with internet connections from differents isp, they are connected to a cisco switch on which 2 ASA 5510 are also connected.Behind the firewall, there is another switch for lan users.I can achieve redundancy by configuring reliable static routing on the routers or firewalls.How could i configure loadbalancing with redundancy in this case.I would like internet traffic to be load shared accross the 2 links and at the same time they should be able to failover(every host redirected to the first link) if one of the other fails.

Thank you.

I have this problem too.
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sachinraja Wed, 01/27/2010 - 12:20

Normally load balancing output traffic is straight forward.. static entries will do, but the complexity increases with the traffic coming back to your network (incoming).. each service provider supports only their routable public IP addresses , to which traffic forwarding is enabled..

if you have a single Public IP pool and need to route it over two different service providers, then E-BGP is the way to go.. you can either use a private AS or a public AS and configure the service providers to route this traffic. BGP will take care of redundancy between these links...

with manual configuration of BGP policies, you can route subnet - 1 through ISP 1 and subnet - 2 through ISP - 2.. easiest way is to implement as-path prepending on these subnets to prefer appropriate ISP's.. or  you can use third party devices which can do automatic load sharing and multihoming, but cant be sure of their reliability...

What is your business model ? how many subnets do you have ? Do you plan to own an Autonomous system number or do you have your own public IP addresses obtained ?

Hope this helps.. all the best


kolawole1 Thu, 01/28/2010 - 00:03

Dear Sir,

I have 15 subnets to load balance and provide redundan

cy for.The service provider is not running BGP and i do not have control over service provider network, i do not own an AS, i have 2 different public IP pools one for each service provider.Is it possible for me to run BGP although the service provider is not running BGP ?

I want to run load balancing and redundancy at the same time.



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