Load balancing question with Cisco 2620

[BGC316]

We currently have 2 T1's in a Cisco 2600 router and load balance through multiple default routes. However, the utilization on one T1 is always at 90+% while the other is only 20+%. Both T1's are from the same upstream provider. We are also adding a 3rd T1 and another router to the mix shortly. My question is, would multilink PPP (and Multichassis MLPPP when we add an additional router) be a better solution to optimize our bandwidth? Is there any additonal configuration needed on the upstream providers routers for us to use MLPPP?

Thanks in advance for your help!!!

Brent

 

[Rucus1]

If you are useing standard routeing methods to load balance and have route-cache on then the lines will be load balancend on a per connection basis. If you want to per packet load balance you must turn off route-cache. Keep in mind that this only controlls traffic leaving your org. In order to configure the return path you must contact your provider and have them configure it.

Matt Newsom

 

[Guest_imported]

the way to balnce accros multiple t's with multiple isp's is to use bgp. otherwise the return - outbound, packet will use the default gw.

 

[Rucus1]

There is really no reason to run BGP because you have stated that both T1's are comeing from the same provider. The reason that one T1 shows up as 90 percent ut and the other as only 20 percent is because the traffic is being loadbalanced on a connection basis. After the first packet of a connection is established the route-cache is updated with the path. All aditional packets with the same address as simlpy forwarded between the interfaces. If you want them to be load balanced on a per packet basis you must turn off the route-cache. You can also upgrade your IOS to 12.2 and turn off fast switching and enable CEF, or cisco express forwarding. This is a new kind of route cacheing that is more intelligent and does support per packet load balanceing. These articles further explain it.

http://www.cisco.com/warp/public/105/loadbal_cef.html

http://www.cisco.com/warp/public/cc/pd/ifaa/pa/much/tech/althb_wp.htm

Matt Newsom

 

[BGC316]

Thanks for the responses guys! Turning off route-cache seems to have helped things considerably and I will look into using CEF. What configuration changes do I need my upstream provider to make (if any) to optimize these connections?

Thanks,

Brent

 

[NewToo]

Try this

interface Serial0/0
ip address xxx.xxx.xxx.xxx 255.xxx.xxx.xxx
no ip route-cache
no ip mroute-cache
load-interval 30
no fair-queue
!
interface Serial0/1
ip address xxx.xxx.xxx.xxx 255.xxx.xxx.xxx
ip load-sharing per-packet
no ip route-cache
no ip mroute-cache
load-interval 30

ip route 0.0.0.0 0.0.0.0 Serial0/0
ip route 0.0.0.0 0.0.0.0 Serial0/1


it should work if not tell him

 

[Rucus1]

Yes that will work. Looks good Newtoo. Loadbalanceing in this method will give you max utilization by spliting traffic between the two links. I would suggest looking into an IOS upgrade. With the newer 12.2 you can use Cisco Express Forwarding and load balance on a per packet basis. This will give you a faster switching path. By turning off the route cache you are forceing the router to use the CPU to make routeing decisions for each packet. In your case its not a bad thing since you have a small routeing table and only two T1 interfaces. You must also keep in mind that this method will only controll traffic leaveing your org. Your provider determines how it comes back into your org. They will most likely return the traffic on a per connection basis.

 

[pmcouto]

Hi there,

I have a question more or less the same as BGC316, but with a different approach:

- I have two links, each one to a different provider.
* I want to be able to share the load between both.

What would you guys advise:
- Using CEF? if yes how?
- Using NAT? if yes how?
- Would it be better to use OSPF?

Thanks,

 

[tschouten]

PMCOUTO, You should create your own thread for that question. But as .nap said in a post earlier.
BGP is the best method to load balance between different ISP's and their t1 connections. For the single ISP with multiple t1's CEF (cisco express forwarding) and an upgrade to 12.2 is truely the most effective method for load balancing anything leaving your org.

 

[pmcouto]

tschouten,

thanks for the info, i think my next problem will be having my two providers announcing my networks (via bgp), otherwise will be no good.

Thanks once more.