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Community Member

FEC and Load Balancing with Compaq Servers

I’m setting up a new building. I have two 6509s with RSMs running full IOS 12.1(8b)EX5 set up as a pair using hsrp. There are 8 floors in the building, two cat 4000s per floor, and 1 vlan per cat 4000. The servers are on their own Vlan.

My server team are installing Compaq DL580s with two minimum 1000BSX interfaces and we’re trying to set up FEC and Load balancing. My questions are:

If I want to set up a pair of 1000BSX interfaces from a server with FEC, do both ports have to connect to the same 6500, or can I have one on 6500 A and the other on 6500 B.

What’s the best way to load balance in this case? Source destination mac? IP? L4 port?




Re: FEC and Load Balancing with Compaq Servers

All port in a Fast Etherchannel have to reside on the same module. Configuring a FEC that spans two switches is therefore not possible.

When you are using Gigabit to connect the servers it will not be possible to fully load the link due to bus limitations on the server. I would go for a simple failover configuration with a link to each switch. The only requirement for that from the switch is that the ports reside in the same vlan.

In my opinion one Gigabit link will be sufficient for your servertraffic and in that way you will have a higher redundancy.

Community Member

Re: FEC and Load Balancing with Compaq Servers

Good point on the server bus limitation. However, all ports in a fast etherchannel do not any longer have to reside in the same module. I've just done it, and have been running it across different modules in 4000s and 6500s for a while. (Unless I'm very much deluded).

I'm following a company template on the config so my hands are somehwat tied. Having spent some time on this now, I think turning on load balancing for destination IP address would be optimum. Given my understanding of how it works, since there is always going to be one IP address at the server side of the link, the way the link gets divvied up would be skewed if I used it as a parameter. Hence use the dest_ip.

Re: FEC and Load Balancing with Compaq Servers

Might very well be true that todays FECs work on different modules within the same device. When it was first introduced, it only worked on neigbouring ports in the same switch. Later this was relaxed a bit and it became possible to use FEC on any combination of ports on the same module. Appearently possibilites have increased even further. But still, I would not expect a FEC to span multiple devices as I thought was your question. I would not know how to specify two interfaces on different switches to belong to the same port-channel interface. When you are using very fast links you might not notice it when an interface on your channel fails.

To check the proper functioning of the channel you can use the following:

>sh int port-channel 1

Port-channel1 is up, line protocol is up

Hardware is EtherChannel, address is 0001.c96d.96cc (bia 0001.c96d.96cc)

Description: Channel between 6509's

MTU 1500 bytes, BW 2000000 Kbit, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Full-duplex, 1000Mb/s

Members in this channel: Gi1/1 Gi1/2

-output discarded-

So my point is that for optimum redundancy you should not use FEC but some failover system.



Community Member

Re: FEC and Load Balancing with Compaq Servers

Yep you have an excellent point. Thanks for the input.

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