LAG and trunks

[Garfank00]

I've recently began building a couple of switches up to replace some Dell switches that have been in my environment and been fairly troublesome.  I wish I had the funds to really build a good L2 network, but I don't, so the layer 2 of my network is going to look like the attached PDF.  Some day my network will move to a three tier hierarchical internetworking model, but for now I need to work with what I have available.  I have two C3750E switches, and a bunch of Dell switches that my end users will be plugged into. I've got 4 VLANs that are going to be set up to segregate traffic between my corporate network, SAN network, DMZ network, and a Vmotion network for the VMware ESX boxes.  Most of my servers have been virtualized, but any remaining physical servers will probably be plugged into the basement access switch.

I've been working on setting up if-core1-sw and if-core2-sw.  I've set up their VLANs and am now looking at setting up the trunks.  I've dedicated two ports per switch as trunking ports for the VLANs.  Tossed up a sample network in my Boson network simulator just to make sure STP would work with the trunks as I envisioned it would and it does.  One of the trunks will forward, and one is set in a blocking state.  What I'm wondering, is if I should add more trunks between the two switches and try to set up some link aggregation.  It's something I can play around with on my network simulator and work on more, just looking to see if anyone is doing trunks in LAGs and how it's working out for them.  Haven't really dug into LAGs, so not even sure if you can add trunk ports to link aggregation groups.

[Roman Rodichev · Accepted solution]

Are the two 3750E's stacked? If not, you should stack them. Then create a L2 trunk LAG to each access switch. This will increase your bandwidth to the access switches and reduce spanning-tree change effects.

[Garfank00]

I don't have them stacked right now.  It's something I can try, but the access switches are only going to be in one VLAN, they won't have access to the other three.  However, your response does imply that I can have L2 trunks in a LAG configuration which is good news.  I hadn't really looked into stacking the switches, but it's something that I should probably dig into.  Think I'm probably going to have to do some more planning.  It would be nice to have a LAG out to each of the access switches.

[Roman Rodichev]

You can build a LAG from two stacked 3750's to each access layer switch, configure them as layer 2 trunks, and allow only VLANs that you want to allow for access layer switch to have.

In regards to stacking, it's a sin not to stack two 3750's if you have them close to each other stack gives you 64gbps connection between two 3750e's, it allows you to manage one device instead of two, you can do cross-stack LAGs, those are great advantages!