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Community Member

Laod balancing and fail over

Hello,

I am using 1 7200 router and 2 isp's. I am not able to use bgp (cause 1 isp won't allow it ...BS) so i need to do this another way. How can I do load balancing and fail over on a single router going to to different isp's ?

Thank you in advance.....

7 REPLIES
Community Member

Re: Laod balancing and fail over

The quick and simple way is to do 2 static routes.......1 out each ISP and either process switch (for per packet load balancing) or route cache (for flow based load balancing).

You could also do Policy routing to load balance.....something like traffic destined for xx.xx.xx.xx goes out ISP 1 and traffic for yy.yy.yy.yy goes to ISP 2, but this method takes more work to setup

Community Member

Re: Laod balancing and fail over

ok, but what about fail over. What if the wan int on 1 of the isp's router goes down. How can my router know that and send all traffic out the other isp ?

Thank you

Community Member

Re: Laod balancing and fail over

d

Community Member

Re: Laod balancing and fail over

1st you need the ISP's to PEER. otherwise there's no load balenceing.

2nd you can run EIGRP to load balence across equal cost routes.

this will automaticly failover to the existing route.

Community Member

Re: Laod balancing and fail over

If I use eigrp dose the isp's have to have eigrp configured on their routers ?

Silver

Re: Laod balancing and fail over

There are several approaches you might be able to use, depending upon the details of your situation and exactly what your are trying to accomplish. For example, if you are using NAT with both, its really tough, but I tend to doubt that is the case if you can afford a 7200. One approach is discussed in my book (see Listings 8-25 and 8-26 on my web site), a two router solution for two ISPs and no BGP with fairly specific assumptions on addressing and environment. If the environment is fairly close to yours, you could adapt it to a single router. Regardless, it will give you a better idea of what you are up against and some of the considerations you will need to take into account to develop a workable solution.

Keep in mind that no matter what you do, you only get load balancing and fail over for inside users going out, and they will see disruption when the path they are using fails and they have to reconnect via the other ISP (using another IP address from the view of the outside world). Note also that you will only failover if the router can detect link failure at the link level, which implies point-to-point links. With frame relay, cable or DSL you need a router which can "ping" to test link upness, such as a Nexland pro800 turbo or waiting for the rumored IOS enhancement.

Good luck and have fun.

VIncent C Jones

www.networkingunlimited.com

Community Member

Re: Laod balancing and fail over

The only CLEAN way to do this is to run BGP with both providers. If one of the ISP's refuses to run BGP with you, threaten to take your buisness elsewhere! You can try all sorts of things involving NAT, DHCP, etc but none of these solutions is going to provide clean failover and they are a nightmare to manage.

If ISP1 will not run BGP with you, find a different ISP! If you are in an area that only has 2 providers, you *may* be better off moving both connections to one of the ISPs (into 2 different routers, POPs, etc). While you will not be protected against failures within the ISP (or if the ISP loses connectivity), you will probably still have much better uptime / survivability. You will probably also be able to load-balance over your 2 connections.

(For this discussion, ISP1 is the one that won't speak BGP, ISP2 is the other (better?!) one!)

If you are determind to make everything work with these 2 ISPs (and you have space from ISP1), you could always see if ISP1 will let you anounce the space through ISP2. If so, set up BGP with ISP2 and announce the space. Your announcement will be more specific through ISP2 and so trafic will take that path. If ISP2 goes down (or you lose your connection to them!), traffic will follow the the aggregate to ISP1. (Make ISP2 send you a default, and have a high cost default static pointing at ISP1 for outbound). This is also not a perfect solution, as is leads to fragmentation of ISP1s space, but you will have clean, fast, transparent failover.

(Most of the above is assuming that you need reachability from the Internet (you have servers) and that you have a largish set of addresses (trying to annonce a /29 through ISP2 won't accomplish anything, you need a /24 or bigger.) If this is just for reachabilty for a small to medium enterprise, you may want to consider someting like differant NATs, etc.).

Good luck, but remember, you are the customer. You are paying ISP1 to provide you with ISP service. If they aren't willing to provide you with the service you require, find someone who will!

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