Cisco 3750 Stackwise Question

A) If you have one cable go from stack port 1 to stack port 2.  I strongly suggest you obtain two cables or else you will only have 50% of the back plane throughput.

B) Once you power on the switches the stack master election with occur. (decide with switch IOS takes over) You can influence this by typing:  set 15 new-priority-value on the switch you want to be the master.

If you get an SDM mismatch error let me know.  

Do not think of SFP ports for uplinking only.  Think of them as regular swith ports EXCEPT that they have priority access to the full back plane of he switch.  In the case of the 3750 the truth is the ports are rated at wired speed so it matters little other than media type.











 

Connecting both on a stack of just two switches is recommended.  You're not doing anything else with the stack port, and it provides redundancy and bandwidth capacity.

In larger stacks, it would look like this:

One little trick for not having to re-order your switches.  If you have 5 in a stack and you want them ordered top down 1 - 5.  Cable them up and then power the switch #1, then wait 30 secs, power switch #2, wait a bit and power switch #3, etc..  The first time powered on the switches go in the boot order in which they were added to the stack.  If you do this the first time you won't have to re-order them.

Aleghart has the correct stacking sequence.

Doing it like this means that if any one stacking calbe fails the whole stack stays up,

and if any one switch fails only that switch will go down, and the rest will still have a root back to the master switch (or indeed any other switch in the stack.

And just to be clear the TOTAL bandwidth of the stacking ports is 64gbs on a 3750. connecting up 2 stacking cables does not give you 2 X 64gbs.... So any switch in the stack can only communicate with the rest of the stack at a max of 64gbs. not the 128gbs ass suggested.

Also 48 X1gbs ports has a bandwith of 96gbs (Ports are full duplex).

However for 90% of insulations backplane bandwidth, and inter stack bandwidths are not to much of an issue with 3750-E series switchs.

As for the SFP's, As Every1 said they do have a direct connection back to the Backplane (normal switch ports are usually groped together to reduce costs) but the benefits of this are in most cases quite small.

More usefully they allow you to insert modules with various types of connectors. Ie. Single mode fibre, Multimode fibre, and on top of this depending what module you insert the length the fibre can be will vary between 500meters and up to 50KM or more.  You can also have a simple Ethernet converter if you so wish.

This is purely to make it cheaper to produce. If CISCO built these modules in to there switches each series of switches would have to have hundrads of models for each different type of connector. It also mean companies can say upgrade from multi mode to single mode fibre. they only need to buy new modules where the fibers attach, rather than a whole new switch.

IF you only use Ethernet they are not so usefully. (although you can get a 10gbs module for say uplinking a switch back to the core over ethernet) But in a network that uses lots of fibre they become a very useful feature.