PVRSTP+ on Etherchannel and L3 Etherchannel

Unanswered Question
Aug 19th, 2008


I need you quick help on two of my small queries:

1). Can we run PVRSTP+ on cross-stack Etherchannel trunks? I have got 3 fibre pairs coming from the access layer stack to the two core and looking best solution for connectivity. I was thinking to use Etherchannel and run PVRSTP+ towards core and enable MHSRP for multiple VLANS.

2). Also, I am planning to connect two core switches via 1*10GBps link and 4*1Gbps links, just wondering what is the best way to implement this. Congigure them as L3 routed links or bind them as L3 Etherchannels with OSPF? If L3 Etherchannels,is there any supporting documentation available that explains the scenerio how to configure it?

Thanks a lot in advance.


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lamav Tue, 08/19/2008 - 16:56

You are deploying a collapsed core, correct?

If so, is it feasible to deploy a routed accesss layer and utilize L3 uplinks to the collapsed core? Between the 2 routed access layer switches, you can have an L2 trunk, which will allow you to span the vlans across both switches to support the HSRP design. If you do that, your worries about a bridging loop will be all but non-existent. All you'll need is to deploy pvst+ and not worry about the rapid STP with backbone fast and uplink fast.

As for the second question, you can either have the 10-G link or the 4-G etherchannel, as you cannot bundle unlike ports to create a 14-G links. In other words, all ports in an etherchannel must have the same port capabilities, including speed, of course.



csco11142276 Wed, 08/20/2008 - 00:06

Thanks for the reply mate.Yes, Indeed its a collapsed core/distribution design.

I agree with your option but the problem is we have all layer 2 between access and core and wouldnt be a good idea for 1 or 2 stacks to have L3 routed links between core and access thats why I am after Etherchannel. You are spot on HSRP design side which I was thinking but not with 802.1q trunks with etherchannel links. I am aware that you can creat etherchannel with 3 links in my scenerio, but can I run PVSTP+ on them with HSRP on core switches as 802.1q trunks.

I am aware that I cant bundle 10Gb and 1Gb links togeather unless I make 10GB as primary and 4GB Etherchannel as secondary. I just want to know instead of wasting 4GB bandwidth in backup mode, can I not use them as active/active scenerio by any chance. If there is any way of doing it please tell me as this would be a great help.

Thanks again mate.


lamav Wed, 08/20/2008 - 00:35

but can I run PVSTP+ on them with HSRP on core switches as 802.1q trunks.

Im sorry, but Im not sure I understand the question. "HSRP as dot1q trunks"? If I understand you correctly, you have 3 fiber ports available on each access switch and you want to bundle them in a dot1q etherchannel up to the core. And then you want to run pvst+. Correct? So, whats the problem?

As for active/active on the routed cross links, it depends on the routing protocol youre using and how they determine best path. EIGRP and OSPF use BW as a metric, so they will not see the 10G link and the 4G etherchannel links as equal cost paths, unless you manipulate the bandwidths on the ports or configure EIGRP variance.



csco11142276 Wed, 08/20/2008 - 02:46

Not HSRP as Dot1q trunks. You have got my question in your answer i.e. dot1q Etherchannel with PVSTP+. Can we do that? If yes, have you got any supported document that explain how you do this?

I am planning OSPF between two core switches which doesnt doesnt support unequal ECMP as EIGRP does. So is there any option available with OSPF to do the active/active loadbalancing between 10GB link and 4G Etherchannel?

Thanks again mate for all input.



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