Load Balancing across two wan links

[sw1]

Hi,

I'm due to connect a 2nd WAN link to the same destination. The routers are 1601's and have a spare WIC slot which I'll furnish with a WIC-1T. We wish to either bundle the two links together or run load sharing across the two. Does anyone have an idea on which way would be best and what the configuration would be.

Kind Regards

Steve

[Richard Burts · Accepted solution]

Steve

If you have 2 WAN links originating on the same router and terminating on the same router then there are several options which could work for you. You could consider configuring the links to use PPP encapsulation and configuring ppp multilink. This effectively combines the two physical links into one logical link and takes care of utilizing both links.

It is also possible to configure the 2 links separately. What you would do will depend somewhat on whether you are running a dynamic routing protocol on the existing link or not. If you are running a dynamic interior routing protocol (like EIGRP, or OSPF, or even RIP) you can run the routing protocol over both links and the routing protocol will recognize that there are two paths to the destinations and will handle it automatically. If you are not running a dynamic routing protocol then you are probably using static routes. In this case just condfigure additional static routes similar to the existing ones and point the new static routes at the new WAN link.

HTH

Rick

[sw1]

Hi Rick,

Thanks for your quick response. We will be using static routes. I'll configure additional statics as you suggested for the 2nd serial connection - will the router automatically load ballance between the two and if so how will I be able to test this??

Kind Regards

Steve

[Richard Burts]

Steve

If the WAN links are point to point serial connections just configure the additional static route (is it a default route, or is it a route for particular networks or subnets?) Then when you do a show ip route you should see that the router has 2 paths to those destinations. If you really want to test load balancing a very simple test is to do show interface and to look at the counters on the two WAN interfaces. You should see the output counters on both interfaces going up. If you want a more complete test of load balancing you could configure ip accounting on the interfaces and look at the traffic passing through both interfaces.

As a note, your static routes will load balance what you send out on the links. Load balancing of what you receive must be done on the other router.

HTH

Rick

[sw1]

Hi Rick,

Thanks for the info. I'll have to check regarding the static or default route. That's a good point actually as I'd imagine if it was a default route I'd have an issue - is my assumtion correct??

[Richard Burts]

Steve

I do not think that there is any particular issue if it was a default route. I frequently see implementations with 2 static default routes and they work quite well. I was just wondering about the traffic distribution and it probably would be spread better over default routes than it would be to specific networks or subnets (the greater distribution of potential destinations through a default route as compared to destinations within a network or subnet).

HTH

Rick

[sw1]

Much appreciated Rick.

Kind Regards

Steve