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Cisco 3750 and Nortel switch trunk help


Not sure were to start here, but any useful Cisco commands/ideas would be great.

On our LAN we have 2 gigabit Cisco 3750's on our network that are just for our Exchange 2007 servers, from each Cisco switch we have 2 trunk cables going to one core Nortel 8600 switch and the other 2 trunk cables fromt he 3750 to our other Nortel 8600.

(THe was all setup by an external Nortel engineer and a Cisco engineer).

Now any users on the LAN which are on the Nortel edge switches and any server on the core Nortel switch can ping all the Exchange servers and virtual cluster IP's.

Now the Exchange 2007 consultants have created a NLB cluster (Microsoft Network Load Balancing cluster) with the Exchange servers on the Cisco switches. All look great and you can ping the NLB virtual IP's from the Exchange servers and any PC connected into the Cisco switches.

Now the issue, some users and servers on the Nortel's can ping the NLB and some can't, they sometimes they can, seems to be no common reason or maybe a trunk/routing issue. Thing is everyone can ping the server IP's all the time which are in the same VLAN (id 1028).

I have attached the configs of the 2 3750's maybe someone can add anything so I can speak to the Nortel and Cisco guys?

Ports 12 and 24 are the trunk ports to the Nortel.

The Exchange guys say the NBL is setup fine as anything on the Cisco devices have no issues, plus the Nortel guy says they set the Nortel trunks up fine as they can ping the servers...etc :)

Also the Nortel guy said it might be worth setting the Cisco switches to load balance on the Ether channel using the source mac address only - mean anything to you?



Re: Cisco 3750 and Nortel switch trunk help

The way you explain it, this realy looks like a routing issue.

Can you try to ping the NLB ip from each of the nortel switch.

To change the load-balancing behavior on the channel, use this command:

port-channel load-balance {dst-ip | dst-mac | src-dst-ip | src-dst-mac | src-ip | src-mac}

In your case, since the source IP will always be the NLB IP, and the destination MAC always your gateway. You should use dst-ip or src-mac. You need to chose the one that changes the most to optimise the load balancing.

Community Member

Re: Cisco 3750 and Nortel switch trunk help

Sounds to me like it could possibly be an ARP or MAC-address table issue.

You might want to see if the NLB ARP address is showing up on the Nortel switch when the problem occurs.

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