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New Member

2 T1s one router (load sharing)


I have a router with one Ethernet to our private network and a serial to our ISP (Full T1 line). Our ISP is giving us a new deal (2 full T1 lines for the price of one), so we bought a new serial interface to put in our router (2620 w/ IOS 12.0). I am wondering how I should configure the secondary interface to make sure that there is load sharing and in case one of our T1 goes down half of the packets will not be going to the dead T1. Currently I did not enable any routing protocol on this router; everything is directly connected as far as the routing is converned; should I enable a routing protocol? A guy at AT&T suggested BGP with per packet load sharing.

What do you think is the best setup for this case?

Do you know any example that I can follow for the configuration?

I appreciate any advices or pointers you could provide.



Re: 2 T1s one router (load sharing)

Depending on the way that your ISP has set things up I think that the simplest solution is the following:

Create a loopback (X) interface with IP & mask from your existing serial.

Make both links IP unnumbered loopback (X)

Your router will now load-balance the traffic between the T1s. When one link goes physically down all traffic will be redirected to the other link.

When you are utilizing a static route to an interface, you should make it point to loopback(X) or the remote IP.


Re: 2 T1s one router (load sharing)

You can simply define two default static routes with same metrics in your router. This will either session balance or packet balance. When one of the links physically goes down, that route will be automatically removed.

You cant run any routing protocol unilaterally. Ask your ISP.


New Member

Re: 2 T1s one router (load sharing)

I agree with all the solutions .See There can be two ways either you can go for routing protocols load balacing or you can use PPP multilink feature and do load balacing.(BY configuring rotary pool and Dialer interface).The another way round if you are using frame-relay then Cisco IOS itself in new ios images have included support for frame-relay load balacing.No need to rely on ppp encap multilink feature. or use can also go for CEF but i have never implemented that part.

New Member

Re: 2 T1s one router (load sharing)

Can you use the PPP Multilink feature to combine the 2 T1 interfaces together for a 3.08mb link? Also will this work with the router runnig NAT? And if all is YES then how?

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