SVI & EtherChannel versus Layer 3 EtherChannel

[david-washington]

Hi, I'm trying to understand the difference between using SVI and EtherChannel versus Layer 3 EtherChannel. I am proposing connecting two stacks of 3750 (using StackWise) connected together with cross-stack EtherChannel but I'm unsure what's the best method for routing across this link. Dave

[srue]

I would say it depends on how you're currently using your 3750 stacks. If they're being used as only layer 2 switches at this point, it may make sense to just use a layer 2 etherchannel...same goes for layer 3.

[david-washington]

The stacks will be used to terminate two LES links between two buildings. I need to route between these two buildings.

[Edison Ortiz]

If each building have independent L2 structure (separate VTP domain and such), I recommend going with L3 etherchanneling.

[Jon Marshall]

Hi David

If you use SVI and etherchannel you are connecting your 2 sites via a layer 2 link and Spanning-tree will now have to extend between the 2 sites.

If you use a Layer 3 etherchannel then spanning-tree stays isolated within each buildiing. If you have no need to extend teh same vlan across your two sites then i agree with Edison and would go with the Layer 3 etherchannel solution.

HTH

Jon

[Amit Singh]

David,

There is a difference the way both the connection works. Although they will have the same purpose but there is the difference the way the switch ports will work.

In case of a SVI you will have eventually a Layer-2 link between the switches. This will run your normal STP and other control traffic between the switches.This will extend your STP domain from a switch to the other switch.The ports will go thorugh the normal STP states and in case of a link flap or link going dowm/coming back the recovery time will be a little high.

In case of a routed port between the switches,you will have a layer 3 link between the switches and will work as a normal router port. There will no STP running on the ports and the STP domain will not be extended beyond the downstream switches.Applring layer3 features like ACL's,PBR's will be a ltille easy in this case.

The Disadvantage of running routed ports is that each port will be a separate network and you will have to manage a large number of IP subnets on the network. Running a routing protocol will be a good idea in this case.

My suggestion for running a point-point link between 2 layer3 device would always be a layer-3 link. But this also depends on the kind of network topology you have.

HTH,Please rate if it does.

-amit singh

[david-washington]

Thanks for the answer Amit although I deliberately left routed ports out of the question unless I'm missing the point and there is no difference between routed routes and Layer 3 EtherChannel (where the Layer 3 address is assigned to the port-channel logical interface and not to the physical ports in the channel.)

[Jon Marshall · Accepted solution]

Hi David

There is no difference between a routed port and a layer 3 etherchannel other than you have aggregated multiple links.

Both are treated as one logical layer 3 link with an IP address on either end.

HTH

Jon