Dual homing solutions

[Mastek]

I am making my LAN redundant by adding a 128KB circuit to connect to the WAN. I am currently running a T1 to the WAN. I am using Cisco 2621’s for both circuits. I would like to use the second circuit (128KB) to help optimize my network instead of just having it on standby as a back up. I was told that due to the difference in circuit speed load balancing would be a bad idea and traffic sharing may actually slow the network down. Thoughts, suggestions?

[thisisshanky]

You can do load balancing over both the links but there are some things to be considered...

1. As you said, since link speeds are different, load balancing might cause latency problems, but this also depends on the upstream provider.

2. By doing a load balancing, you ll be able to do an outbound LB, but achieving true inbound LB, is possible only if you run BGP.

3. if the upstream isp is the same for both the links, and if they both terminate on same router, you can configure ppp multilink, which will increase the total bandwidth of the link (sum of two links). You will need to talk to your ISP about configuring PPP multilink at their end.

You can also try using CEF for load balancing additionally, after considering the current CPU utilsation and memory resource availability.

HTH

[Mastek]

I will be running BGP and I'll be using 2 different upstream provides (at different node locations) in order to achieve true redundancy. This is why I am worried about the latency problem. I'll look into the CEF solution, thanks.

[vcjones]

Link 1 = 1544 Kbps, Link 2 = 128 Kbps, so the best you could possibly do with perfect load balancing is 1672 Kbps, less than a 10% improvement. Plus the time to send a single frame on Link 2 will be over ten times longer than over link 1 (94 ms for a 1500byte frame versus 8 ms on the T1).

Bottom line, you really don't want to use the backup link for anything other than backup (and watchout for performance when you do use it). But you do want to keep using it for something (such as BGP) to ensure that when it breaks, it gets fixed immediately. Otherwise, it will die and you won't know about the failure until you need to use the link, at which point it is too late!

Good luck and have fun!

Vincent C Jones

www.networkingunlimited.com