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Connecting two t-1s to two different ISPs and have them load balance


Is there away to configure traffic to load balance/increase bandwith between two different ISPs without using BGP? Both routers are 2600's and I don't know that they have enought horsepower to support BGP.



Not applicable


One thought is Multi-link PPP, another is that which is mentioned in the notes below, although I don't personally have experience what they describe but I thought it was interesting.



MultiLink PPP won't work if the T1's connect to different ISP's. 2600 routers can run BGP as long as each ISP doesn't send you the full BGP routing table.

For outbound traffic, you can configure a static default route on each router pointing to the serial interface. You can then load balance traffic between each router using MHSRP, though I've never considered MHSRP to be particularly elegant. GLBP (a newer version of HSRP that better supports load balancing) is also an option if you have a recent enough software version that supports it.

Inbound load balancing is more difficult, and depends on the details of your situation. Do you have different address blocks from each ISP?


You could also just advertise an equal cost default from each of the 2600's into your intergior gateway protocol, if you're not directly connecting devices to the 2600's. If you are running through a pix, you could run bgp through the pix, passing just a default in from each of the 2600's, giving the inside routers two default routes through bgp, which they could then load share between using iBGP multipath.

So, to better answer your question, what does the network look like behind these two 2600's?




Well, you can also use ip policy based routing on your gateway (a router or a routed ports on a catalyst 35xx), I had a situation once when I used policy based routing to use one of the links for smtp traffic and the other link for web traffic on a web server, however those links where not connected to ISP's.

Good Luck



Yes it is possible to provide various modes of load balancing under the conditions you specify, and depending upon your application and its performance and availability needs, it can be fairly easy. Note however, that without BGP, you can have significant downtime when one of your ISPs fails.

For example, if you are hosting a web server and high availability is not a requirement: Configure two IP addresses in DNS, one serviced by each ISP and have your web server respond to both.

If your goal is non-stop surfing from inside clients out to the world wide web, there is an example configuration in Chapter 8 of my book. The listings are on my web site.

Other approaches are possible as well. For example, you don't need much router to support BGP over two T1's. I've done it with a 2501. There is no law which says you must accept full routes (nor much benefit in many situations). See the Multihoming white paper on my website for some alternatives.

Good luck and have fun!

Vincent C Jones


You can do bgp on a smaller router and set default routes to your isp, this will load balance, but may set up asymmetric routing because you can't control how traffic returns. Do you have an address space from each isp, or do you have your own address space. If you own your own address space, its much easier, because you can use different parameters to affect the way traffic returns like as path prepending. If you have two different address spaces is much more difficult, because first of, you need to get permission from each of the isp's to route the others address space and to advertise it out with a longer mask, this is getting harder and harder to do. Lets say I am isp1 and own, I give you, now to my peers, I have to advertise and, this is because if I have gotten isp2 to advertise out to the world, when I go to a site somewhere out of these 2 as's, and my traffic need to return, unless isp 1 advertises the route with a /24 mask, the return traffic will always take isp 2 because of longer mask. This unfortunately causes the size of internet routing table to increase dramatically which is why it is difficult to get carriers to do this any more.

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