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New Member

3550 Routing

We have two connections to the Internet with two ISPs. The inter-connection between our two segments is provided by one ISP with a 3550 L3 switch. Both ISPs have two different IP segments (example: = ISP#1 and = ISP#2). On the switch, one port goes to our network, one goes to ISP#1 router/network, and one goes to ISP#2 router/network. Currently, ALL outbound traffic goes out ISP#2 and inbound traffic comes in both connections (depending on the IP subnet). What I want is to segment traffic so that all ISP#1 subnet traffic goes in AND out ISP#1 connection and all ISP#2 subnet traffic goes in AND out ISP#2 connection. I have been told by the ISP who owns the 3550 that this cannot be done. Can it? If so, how?


  • Other Network Infrastructure Subjects
New Member

Re: 3550 Routing

That is an interesting question you pose and it is not that uncommon of a request. The simple answer is yes, anything can be done.....but do you really want to deal with that level of complexity? Is there a reason you need to do this, or just a desire?

Anyway, it sounds like the switch has a default route on it sending outbound traffic out to ISP #2. The closest you could come to your desired setup is to run BGP on both ISP routers and on the conserve memory, only accept partial routing tables....these tables will include all the subnets that each ISP is responsible for......anything else should get a default route. If you desire, you could have two default routes and round robin traffic out each ISP.


New Member

Re: 3550 Routing

We actually did want to run BGP, but one of our ISPs (ISP#1) owns our ASN and is not willing to run BGP in conjunction with ISP#2.

New Member

Re: 3550 Routing

without BGP, the best you can do is have 2 default routes (1 to each ISP) and do equal cost load really have no control over what goes where though.

Another option would be to apply for your own can do this from then you can take control of your own routing policy from your ISP. Who have you talked to at your ISP? Technical support may shut you down, but when you tell your sales rep you are switching providers because of their unwillingness to work with you....things can magically get done

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