L3 Switch to Router Connection Options

Unanswered Question
Jun 11th, 2007

If I want to connect a Layer 3 switch (Cat4500 w/SupIV, running EIGRP) to a WAN router (7206 w NPE300, running EIGRP), I see that it can be accomplished using two different methods:

1) Create a routed ethernet port on the L3 switch, assign an IP address, and connect it to a routed ethernet port on the router, in the same IP subnet. All non-local packets will be routed between the L3 switch and the WAN router.


2) Utilize an existing VLAN and VLAN interface on the L3 switch, and connect a switchport in this VLAN to the routed port on the router, where the router's IP address is in the same IP subnet as the VLAN interface of the switch. In this model, the L3 switch is the default gateway for hosts on the subnet, and it switches non-local packets to the WAN router at Layer 2.

I see both ways done in our network, and I tend to support method 1 as the best method, but both seem to work.

What is the recommended way to connect these two devices?



I have this problem too.
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Richard Burts Mon, 06/11/2007 - 17:32


As you mention both methods will work and it becomes a choice with few clearly defined parameters. I share your opinion that a layer 3 routed link is attractive, in part because now convergence in the event of a network failure is a function of the routing protocol and not of Spanning Tree. But other people may have different opinions - and they are welcome to share them.




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