Port-Channel Groups

[dmccluskey1970]

Whom It May Concern,

Simple question but cannot seem to find the answer. Have a CISCO switch that includes two separate port-channel groups (6 (0/15-0/16) & 7 (0/17-0/18)), each of which go to different switches (6 goes to switch 1 and 7 goes to switch 2). Can we somehow prioritize so that all traffic is destined for switch 2?

Any help would be greatly appreciated.

Thanks,

Doug

[Jon Marshall]

Doug

Difficult to answer without more details eg.

are switch 1 and switch 2 interconnected ?

are the etherchannels L2 or L3 ?

when you say you want to prioritize the traffic to switch 2 is the traffic to end devices on switch 2 or is it being routed on that switch to other subnets ?

The more details you can provide the easier to help.

Jon

[dmccluskey1970]

Hi Jon,

Yes, you are correct, switch 1 and 2 are interconnected. Unfortunately, they are both HP. We had recently moved all physical cables over to switch 2 in an attempt to troubleshoot an issue with switch 1 but decided to leave the Port-Channel connections alive on both for redundancy purposes. Both these switches are actually our core routers for the network with some connected servers. Our CISCO gear is actually part of our IBM Blade infrastructure. We have two CISCO switch modules each consisting of two Port-Channel Groups. One port group goes to core switch 1 and the other to core switch 2. We are noticing that most of our traffic coming from the Blade Infrastructure is going to core switch 1 and then to core switch 2 over our ISL trunk (HP equivalent to Port Group). We would like the traffic to go directly to switch 2 as everything is connected to it.

Hope this helps.

Thanks,

Doug

[Jon Marshall]

Doug

If the HP switches are interconnected is this with a L2 trunk or a L3 connection ?

If it is a trunk then I would have thought that one of the links from the Cisco switch would be blocking because of STP ?

If this is the case this may explain why most of the traffic is going via a particular core switch.

How many vlans are there from the Cisco switch and what version of STP are you using ?

Jon

[dmccluskey1970]

Hi Jon,

Thanks for all your help. Yes, STP is probably the culprit and I kick myself for not checking that first! We will investigate STP, make switch 2 the root (if that is the case) and let you know how it worked out. This will have to wait a bit as we want to avoid any re-convergence during business hours :)

Thanks,

Doug

[Jon Marshall]

Doug

Apologies, I was in a bit of a rush when I posted my last response.

Basically I think STP may well be blocking one of the uplinks. If you are running a variant of PVST+ then it will be blocking per vlan so some vlans may be using the link you want where the majority are using the "wrong" link.

You can influence STP but first you need to work out which switch is the root bridge for each vlan  and then you can decide where and how you are going to change the configuration so that STP blocks the link you want.

You can do this on a per vlan basis but it may be easier to simply do it at the port level although this would mean all vlans would use only one of the links. Unless it fails obviously in which case it would use the other link.

Edit - note that core switch 1 may be the root for all vlans in which case the simplest solution would be to make core switch 2 the root and then that link would be favoured.

However that is just a guess and even if it is correct be aware if you decide to do this there will be an outage while STP reconverges.

Please feel free to come back with more queries or if I have misunderstood your setup.

Jon

[dmccluskey1970]

Hi Jon,

Sorry, the etherchannels are L2.

Thanks,

Doug

[Joseph W. Doherty]

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Posting

Your prioritization options should be mostly the same as if you were using single links rather than port-channels (the reason I say "mostly", there might be some "exotic" features supported on single links but not on the port-channels).