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Community Member

EtherChannel - L3 & L2 Connection

Hello,

When a L2 trunk and L3 connection must be setup between L3 switches over etherchannel, should they run over the same channel? In other words, should the IP address for L3 be configured on the Port Channel or on vlan interface? If it is best to configure a L3 portchannel, then I would need another connection between the switches for the L2 trunk. If it is best to setup L3 on the vlan interface, then I can have all traffic flow over the same trunk. Any ideas?

Thanks!!

- Lee

6 REPLIES
Silver

Re: EtherChannel - L3 & L2 Connection

Put L3 on the Vlan-interface and let the port-channel be just L2 as this gives you the most flexibility.

Did it help?

Community Member

Re: EtherChannel - L3 & L2 Connection

Thanks for your reply.

I know it will provide for more flexibility, but is there any downside for running a routing protocol, ie ospf, with the vlan interface as compared to the L3 portchannel? ie convergence, ospf costs...?

Thanks!

Re: EtherChannel - L3 & L2 Connection

There shouldn't be any issues with running it on the VLAN interface. I have several clients running ospf on 3550's and 3750's and don't have any problems with it.

Community Member

Re: EtherChannel - L3 & L2 Connection

Hello friends,

I am facing this issue right now and have not quite figured out what I should do.

My question is if this config provides more flexibility with no negitive impacts on performace/loadbalance/etc, why not program all port-channels in this fashion? It would allow you to route with a dynamic protocol with the added option to "add-in" trunk traffic in the furture if required.

Is there really now downfall on combining the two over the same etherchannel?

Am I gaining anything by making a new connection for just bridged/trunk traffic?

I did find this artical http://tinyurl.com/7rate addressing how to manage the OSPF aspect of a L2+L3 combined etherchannel.

thank you,

DJ

Community Member

Re: EtherChannel - L3 & L2 Connection

any inputs?

Thanks.

Community Member

Re: EtherChannel - L3 & L2 Connection

If I understand you correctly, are you suggesting to run 1*L3 etherchannel and 1*L2 etherchannel between two switches?

I agree with previous responses that you don't need to do that. It will complicate matters, make your configuration more expensive (more GigEth ports if using high end switches) with no real benefit. Ok OSPF can potentially be notified faster if a L-3 port was to fail as opposed to a L-2 port, but you also have to look at your topology as a whole and take into account HSRP/VRRP convergence times, STP timers etc that may have impact on traffic being dropped even if OSPF converges faster. In any case you can reduce the ospf hello/dead timers if you want ospf to converge faster...

I have worked with a number of clients where running SVIs for ospf has never been a problem.

HTH

E.

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