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New Member

Load balancing over WAN circuits

Is there any way to load balance on a per packet basis if you have 2 DS3's going to two different routers? For instance at point A I have 2 - 7200's with 2-DS3's (one in each 7200)going to point B with the same at the point B end. Is per-packet load balancing possible or can I only hope for load sharing?

Thanks,

5 REPLIES
Hall of Fame Super Silver

Re: Load balancing over WAN circuits

Jeff

If I understand correctly that you have two routers each of which has a single outbound DS3, that the DS3s terminate on different routers, I believe that it may be possible to achieve per packet but I strongly believe that you should not really want to do this.

To do it would would have to configure each router with 2 static default routes: one default route would point over its DS3 and the other default route would point to the other router as the next hop. You would also want something like cef per packet configured. The downside of this is that the router would send packets over its default routes in alternation. One packet would go over the DS3 and the next packet would be lateraled to the partner router. So performance and latency are going to be quite variable. And the real down side is that when router A sends the packet to router B (because this is the one that it is lateraling) it is quite possible that router B will select this packet as the one to lateral to its partner - so the packet could go back to router A to be forwarded.

You are really better off to have each router forward over its own DS3. Is there some alternative for controlling (or alternating) to which router traffic is sent to be transmitted out?

HTH

Rick

Re: Load balancing over WAN circuits

Doesn't some of this depend on the routing protocol? If the costs are equal, EIGRP for example, will load balance right (assume proper config's)?

New Member

Re: Load balancing over WAN circuits

Hi

you can configure on your site interfaces for per-packet load balancing since they are in the same router, but i think it does not make sense since you can not do the same thing on the oer side, check this link might be useful

http://www.cisco.com/en/US/products/ps6628/products_ios_protocol_option_home.html

Regards,

Burim

New Member

Re: Load balancing over WAN circuits

OK, I'm running EIGRP so routing is dynamic. I have two routers at each end so I have 4 routers total with one DS3 connecting a pair of routers. It was done this way originally so there would be hardware redundancy and load sharing depending on how the clients traversed the LAN. So, I have equal costs paths from the distribution layer to the core. There are two distribution layer switches with two L3 equal cost paths to dual core switches. The 7200's have a single connection to a core switch via fast ethernet. So there is one 7200 connected to one 6500. If client A from the access layer takes his preffered path because of HSRP it may traverse the wan via Core1 to 7200 #1. Another clients traffic on that same access layer switch in another VLAN may end up going through Core2 and through 7200 #2 based on distribution layer HSRP. Everything works fine but I see one DS3 getting used more than the other. I don't want to start tweaking EIGRP on the LAN to get traffic flowing evenly as things really are working well. I just want to gt more use out of the circuits. So, I was thinking about giving up hardware redundancy and sticking both DS3's into a single router at site A and B so I could utilize both circuits using per-packet load balancing. Basically CEF per-packet.

I was just wondering if there was a way to do this without giving up the hardware redundancy.

Thanks

Re: Load balancing over WAN circuits

Hi Jeff, Is the issue with CEF or the way HSRP provides a gatweay from your network? If the latter then have a look at GLBP as a possable way of providing a more balanced traffic flow from your network. If the issue is more CEF based there is the option of altering the per-flow CEF config. Have a look at "ip cef load-sharing algorithm". I've never configure this but it sounds like it may help.

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