Port channel with both layer 2 and layer 3??

[paulkilcoyne]

Hi guys,

recently I noticed on a customer's network they had port channels with mulitple layer 3 sub-interfaces. This got me thinking might it be possible to have both layer 2 and layer 3 sub-interfaces running on the same port-channel.

This would help in spanning/ trunking layer 2 vlans to remote areas of our campus network. At present when we want to do this we have to add a physical fibre connection and thus take up another SFP interface etc.

So is it possible and if so recommended?

Thanks,

Paul

[glen.grant]

  Not sure i understand the question but you have always been able to run multiple links across a trunked port channel .  Usually if the L3 function is in a L3 switch you use SVI's and just trunk the L2 vlans to the remote end. If the L3 end is a router then you usually use subinterfaces to trunk , myself i haven't done port channels on a router but I know it can be done on some of the newer routers or routers with a switchcard installed.

[Joseph W. Doherty]

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Posting

On a L3 switch, sure, as Glen describes with VLAN interfaces.  This can also be done on router hosting switchports, as also noted by Glen.

On a router's routed ports, sub-interfaces are also routed ports and they would terminate L2.  I.e. don't believe they could extend L2.

E.g.

http://www.cisco.com/en/US/prod/collateral/routers/ps5855/prod_white_paper0900aecd806f698a.pdf

[Edison Ortiz]

The subinterface approach allows you to create multiple subnets. These subnets are associated to an unique Vlan tag ID in the switch.

This Vlan tag ID can't not be reused as part of the internal Vlan list thus you can't extend your internal Vlans via the subinterface design.

[paulkilcoyne]

Hi Edison,

what I'd like to achieve via the same cable between two switches is the following:

1. a layer 3 ospf link between the switches using a /29 point to point.

2. a layer 2 trunk to temporarily extend vlans across the campus without having to run a separate cable.

I thought it might be possible to create one port channel with say 2 sub-interfaces, one sub-interface would support the l3 ospf link and the second sub-interface would support the l2 trunk allowing the desired vlans to trunk across the switches.

Is this possible?

I hope I've been clearer this time

Thanks,

Paul