Load Balancing w/ Cisco

Answered Question
Jan 30th, 2008

We have one service provider that we use the full T1 on a regular basis. We would like to go with another service provider to double our bandwidth and load balance the 2 internet connections. We contacted a consultant, and he keeps pushing the Radware Linkproof device (http://www.radware.com/content/products/lp/default.asp)

We currently have a Cisco2811 series router unused. Could this achieve our desired function?

Also, how difficult would this be to do?

Many Thanks,

Shaun

I have this problem too.
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Correct Answer by Rick Morris about 8 years 10 months ago

There are several ways to accomplish this.

1. If you use 2 separate providers you will want to have your own IP space to simplify things, unless the IP space you have the provider will allow you to route that space through their network. Other wise you will need your own. The best scenario for this is to run BGP with both providers. In order to do this you will need your own ASN since you will be multi-homed. Now traffic will never balance, no one can ever guarentee that, but it will share traffic. Based on many different route selections in the BGP rules, you can do a search for BGP route selection if you want to know them all. Once you get this you can then begin to do some traffic shaping if it is not giving you exactly what you want, but with BGP you have that ability since you advertise the routing, your peers just send it to their peers.

2. Another way is to have another link from the same provider from the same POP, then run equal weight static routes, this will give you more of a 50/50 split, but again not always.

3. You can used different providers and different IP space and route outbound traffic out one line and all inbound traffic in the other.

4. You can subnet your block's. If you own a /24 route the lower half of the /25 block out one connection and the higher /25 out the other connection then have a metric on the opposite block when routing in case one link goes down the other will pickup the load for all traffic.

Bottom line it comes down to requirement.

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jproos Thu, 01/31/2008 - 00:16

It really depends on your requirements. Are you using these lines only for Internet-access, or are you also providing servers (www, mail, etc.) over these lines, if so, would you also like to loadbalance these?

smleeper1 Thu, 01/31/2008 - 05:14

We would want to use the lines for remote desktop, Citrix, some web accessed client applications, internet. I was hoping it would be as simple as providing 2 service provider lines and having the router disperse the packets as evenly as possible. The question you posed makes me think each application/access method will need to be individually configured?

jproos Thu, 01/31/2008 - 07:56

For outgoing traffic (+ return traffic) it should not be so hard, although you will probably need some fiddling to get a somewhat even loadbalancing over the lines.

For incoming traffic (such as a hosted website or hosted applications), it is quite different. You'd need a block of public IP addresses and you'd probably need to talk BGP to both providers, if you want to use both lines for this traffic.

smleeper1 Thu, 01/31/2008 - 10:28

So if the Cisco 2811 were set up the way you say with BGP, would it be able to do Dynamic load balancing and failover automatically?

Thanks!

Paolo Bevilacqua Thu, 01/31/2008 - 10:45

Yes, but BGP require applying for a public AS number, this can be lengthy and expensive.

For simple office usage where you do not have hosted server that must be 100% accessible, I suggest you simple connect the ISP and use NAT to both of them. This is a simple configuration that most customers use with satisfaction.

Hope this helps, please rate post if it does!

Correct Answer
Rick Morris Fri, 02/01/2008 - 07:38

There are several ways to accomplish this.

1. If you use 2 separate providers you will want to have your own IP space to simplify things, unless the IP space you have the provider will allow you to route that space through their network. Other wise you will need your own. The best scenario for this is to run BGP with both providers. In order to do this you will need your own ASN since you will be multi-homed. Now traffic will never balance, no one can ever guarentee that, but it will share traffic. Based on many different route selections in the BGP rules, you can do a search for BGP route selection if you want to know them all. Once you get this you can then begin to do some traffic shaping if it is not giving you exactly what you want, but with BGP you have that ability since you advertise the routing, your peers just send it to their peers.

2. Another way is to have another link from the same provider from the same POP, then run equal weight static routes, this will give you more of a 50/50 split, but again not always.

3. You can used different providers and different IP space and route outbound traffic out one line and all inbound traffic in the other.

4. You can subnet your block's. If you own a /24 route the lower half of the /25 block out one connection and the higher /25 out the other connection then have a metric on the opposite block when routing in case one link goes down the other will pickup the load for all traffic.

Bottom line it comes down to requirement.

smleeper1 Fri, 02/01/2008 - 07:59

Thanks, All of your posts definitely helped me get pointed in the right direction.

-Shaun

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