3750 Stack Wise

[paul.carlos]

We are very close to putting together a stack of 7 3750 PoE switches, but would like to understand the Stacking process a bit better:

I plan on connecting the devices so that there is redundant connectivity.

With this configuration, will the all the VLAN information be bassed along the cable or is there still the need for trunking?

[Georg Pauwen · Accepted solution]

Hello Paul,

all VTP (and VLAN) information is carried across the stack. Basically, the stack is seen as one switch. There is no need for additional trunking. Watch out though that when you change the VTP mode on one of the stack member switches, the VTP mode of all the other members changes as well.

This is what CCO says:

VTP and Switch Stacks

VTP configuration is the same in all members of a switch stack. When the switch stack is in VTP server or client mode, all switches in the stack carry the same VTP configuration. When VTP mode is transparent, the stack is not taking part in VTP.

•When a switch joins the stack, it inherits the VTP and VLAN properties of the stack master.

•All VTP updates are carried across the stack.

•When VTP mode is changed in a switch in the stack, the other switches in the stack also change VTP mode, and the switch VLAN database remains consistent.

HTH,

GP

http://www.solutionfinders.nl

[Craig Norborg · Accepted solution]

I'm not sure if you can stress how these switches act like a single switch enough. When the switches are stacked, you couldn't tell remotely that they were separate switches unless you knew about that model specifically.

There is a single configuration.

There is a single spanning tree instance.

Because of the single configuration, there is only one VTP configuration/instance.

Same for VLAN configuration, only one.

In the configuration the switchports show up like:

interface FastEthernet1/0/1

...

interface FastEthernet1/0/48

interface FastEthernet2/0/1

...

interface FastEthernet7/0/1

...

interface FastEthernet7/0/48

...

Since you don't configure them separately and only one switch CPU acts as the master, they are one single switch for all that matters...

[sdang]

In regards to the statement above. Would it be safe to say that since there is one spantree instance with one vtp instance we cound consider the stack as a whole similar to a 65XX without an MSFC? Kinda like a poormans 65XX?

[Craig Norborg]

Well, that depends on what you mean by that. It is a little like a 6500 in that you can add more ports and its expandable like a 6500. You can even do L3 switching if you get the enterprise image, kinda like adding a MSFC to a 6500. Single spanning-tree yes, its one big switch when stacked.

I'm sure there are many ways in which it differs though also. We are using them in places where a 6500 or something similar might have been used in the past, they are quite powerful switches by Cisco's specs...

[harizanovg]

Even with the standard image the 3750 is L3 capable.

RIP routing protocol and HSRP are available with the standard image. The enhanced image adds support for the other routing protocols - OSPF, BGP, EIGRP, etc.