Benefits of using L3 VLAN for Point to point links

[James Matthews]

Can anyone tell me what the benefit (if there is one) of configuring a L3 VLAN on a switch and assigning a switchport to the vlan for a single point to point connection with another switch? Would it not be a whole lot easier just to configure an IP address on the switchports at both ends and be done with it?

We have several instances of this configuration in our organisation and I cannot fathom out why the links have been set up this way.

[Jon Marshall · Accepted solution]

James

Main reason to do it would be if one of the switches was running CatOS such as the 6500 in hybrid mode. Then you can only setup a P2P link with a L3 vlan interface because CatOS does not support L3 routed ports.

Interestingly a thread i was recently involved with also used this solution because the poster wanted a L3 link but needed to pass one vlan at L2 so you simply make the link a L2 trunk, have 2 vlans, 1 vlan for L3 peering, the other vlan to be L2 switched.

Other than that i would always go with L3 routed ports and have the IP assigned to the ports. This stops all L2 control protocols, especially STP, having to go across the link.

Jon

[James Matthews]

Thanks for that Jon. This makes perfect sense.