Load sharing

[mgandara]

Can anybody explain me about the implementacin of the cisco express forwarding( CEF)?? I need to configure a load sharing in my cisco 7513 router. I have 2 E1 connections, and my proposite is to have an equal load sharing with the 2 connections. We don't have an autononous system AS to advertise the route, how I can do that??

[aretana]

Manuel:

Assuming that you have two equal cost routes (most likely a default) pointing out the 2 E1s, then CEF has two modes it can operate in:

1. Per Flow Load Sharing -- in this case the traffic is assigned to each link on a per-flow basis: the algorithm takes the source and destination IP addresses into account. Note that even if the number of existing flows gets evenly split between the two links, there's no guarantee that you will achieve "equal load sharing" because the ammount of traffic on each flow is not considered.

2. Per Packet Load Sharing -- in this case packets (regardless of the flow) are assigned one after the other to the first link, then the second, then back to the first, and so on. This mechanism gets you the closest to "equal load sharing"...but, because the packets for a specific flow, are routed through different paths to the destination, then it may result in our of order packets. Some applications may be more sensitive than others to this behavior...and using two parallel links between the same two routers pretty much eliminates the effect...

Hope this helps!

Saludos.

Alvaro.

[mgandara]

Thanks, for the info Alvaro. I will explain more what I need in order to obtain a better help. I have one cisco 7507 that function as our Core. We have around 30 clients, wich have internet and transmision data service. Up to now, we rent 2 E1 to have a internet connection with the Nap with diffents carriers, one E1 with Equant and the other E1 with Internexa. The ip address given by these operator are 206.49.x.x and 65.199.x.x . In our router config, we use eigrp as our routing protocol.We don't use bgp to implement mpls.

The deal is that we have around 5 clients with one connection and 25 with Equant. When something happen with the Equant connection, we are really in problem, because we must wait until the service is up again. The ideal idea will to automatic redistribute these traffic to the other connection, when one E1 is down, all the traffic will be routed to the up connection and vice-versa.

I hope you can give me a hand.

Ciao, Manuel