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Community Member

Dual ISP Feeds

Is ther any way to have Dual ISP feeds (2 x DSL) into a Router and load balance?

Cisco1721, 2 x WIC-1ENET. Two ISP feeds.

I can't see how without BGP?

Thanks,

Bob

6 REPLIES
Silver

Re: Dual ISP Feeds

Bob,

This would depend on your specific needs. BGP is not needed, again depending on what you need. Simply two equal cost static routes to 0.0.0.0 pointing at each of your Service providers might do what you need for outbound load sharing. Inbound would have a lot to do with how your providers advertise your address space out to the internet core.

Hope this helps you,

Don

Community Member

Re: Dual ISP Feeds

Don,

When you put equal cost default routes, doesn't the router send one packet out the first route, one out the second router and then rotate thru?

You then only get half your packets thru?

This would be two interfaces to two different ISP's.

Bob

Silver

Re: Dual ISP Feeds

Bob,

Depending on your load balancing methods (Fast Switching / Cef / Cef per packet, etc) you may vary how you send your packets. Per destination (with Fast Switching for example) will go per destination. So you'd not go per packet. Process switching and cef per-packet allows for per packet load sharing. The biggest down fall to not getting specific routes in through your ISP's is sub-optimal routing or asymetric routing. Neither of which will cause failure. Can cause out of order packets which can cause problems with some applications. All your packets should be able to make it to your destination even if you did per-packet, but out of order packets can occur.

Hope this helps you,

Don

Community Member

Re: Dual ISP Feeds

Don,

Thanks for the input. Fast Switching seems to be the answer.

This is really a Dual VPN scenario for redundancy. I will use GRE./PSEC with EIGRP to allow redundancy to remote offices. If one ISP goes down, the traffic

should go to the other GRE/IPSEC Tunnel due to EIGRP. I can manipulate the EIGRP for Primary Tunnel.

I should be able to use EIGRP Load Balancing across these GRE/IPSEC

Tunnels I presume?

Thanks,

Bob

Community Member

Re: Dual ISP Feeds

I tried to do this with 2 T1's using Route Maps, My problem is I didn't want to use BGP, although I wanted to have 1-1 static nat translations with 2 nat pools.

Meaning you could come in from the outside hitting my 192.168.1.1 via 2 different 2 providers, 2 different IP's. I could not get that to work, that beeing said, if you are just worried about traffic going out and not worried about it comming in.

You can create 2 nat pools and use route maps and weighted routes, and I even managed to get it work. The only catch, is its a pool, not a 1-1 translation.

If you a do a search on the subject "Complicated Nat" you should see a few posts on it in this news group.

Gold

Re: Dual ISP Feeds

The problem you're most likely having is that you're getting into issues with assymetrical routing going out. If you have two exit points, say one with the translation from your 192.168.1.1 address to 10.1.1.1, and the other translating your 192.168.1.1 to 10.2.2.2, what's going to happen is this: Someone outside starts a session to 10.1.1.1. Suppose the loadsharing is such that the outbound side of this connection goes through the other connection, which means the source address of the outbound packets gets translated to 10.2.2.2. The session will fail.

BGP isn't really going to help in this situation, since optimum routing isn't the problem symmetrical routing is. There's no way to know which inbound connection traffic from any given source is going to come in on, no matter what your local routing tables say, so you can always have assymterical routing.

Russ

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