Are you referring to connecting two 3750G's together via copper or fiber and trunking them together? I see little to no benefit to setting the two switches up this way. Using the stackwise cable will give you 32Gb/s vs 1Gb/s link between the two switches. Stacking them will also let you manage the stack with one management IP vs having two, and most importantly you can always add more switches for future expansion to the stack and not waste user ports.
Stackwise has several advantages in terms of performance and management. As others have mentioned, speeds of 32 Gbits/s inter-switch are possible. In addition, a single session can be used to configure and administer all switches in the stack.
The limitation of Stackwise is that all switches in the stack must be in close physical proximity, as the longest Stackwise cable is about 10 feet (3m).
Trunking, either 802.1q (IEEE standard) or ISL (Cisco-proprietary) allows a single Ethernet cable to carry traffic for multiple virtual LANs. It can be used among switches of any distance that the Ethernet medium permits, several miles with fiber.
Trunking doesn't offer the increased throughput or single-stack-management of Stackwise. It is used instead to allow multiple VLANs to ride on a single Ethernet connection.
A third technology which may enter into your decision is Etherchannel (PAGP/LACP) which allows multiple Ethernet links to load-balance traffic.
Which technology or combination to use is dependent on the problem that you are trying to solve.
Thanks everyone for their response. I should have provided a little more detail to explain the request. So here goes...
We are implementing VMWare servers in a new dedicated cluster. This cluster (3 racks) contains two dedicated 3750G-48TS switches with Stackwise and an 4GB Etherchannel (2GB per switch) to a 4507R switch via fiber. Each VMWare server has 6 NICS with 1 dedicated to VMotion, 1 dedicated to VM Console, and 4 dedicated to data with 2 data NICS going to each 3750G switch.
The VMWare implementation team is requesting we implement ISL trunking between the two 3750G switches before connecting to the core switch.
"The VMWare implementation team is requesting we implement ISL trunking between the two 3750G switches before connecting to the core switch.
Am I missing something?"
Don't think so, but they may be missing something. My guess is they don't realize with the 3750Gs all ready connected with stack cables, there's no reason to define a channel (or trunk) between them. Since stacked 3750s operate as a single virtual switch, trying to interconnect them would loop the two switches.
If they're asking for ISL between the 3750 stack and the VMWare servers, or between the 3750 stack and the 4507R, then the request might makes more sense, but why not use the newer channel standard vs. ISL?
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...