Stacking

[Novelluser]

Hi Guys,

I currently have two cisco switches (3750) and would like to add a 3rd to the stack, will doing this require downtime of the other two or switches?

 

[vipergg]

No it won't. Make sure the code on the new one is the same as the other 2 . Rack the switch connect the stack cables and then power on the switch , don't power on the switch before powering everything up.

 

[Novelluser]

Hey thanks for the reply, how do I make sure the code is the same?

 

[jgunkel]

If you are stacking 3750's, at least make sure that the firmware on the switch you are adding is not _newer_ than the rest of the stack. It's not a big deal if it's a little bit older though, as when a new stack member is joined, the unit with the newest firmware will update the firmware on the rest of the stack.

As far as checking the firmware, you would need to power the new switch up by itself, so you are in a catch-22 situation between "check the firmware" and "don't power on the switch."

Reason being, if you power on the switch, it will automagically provision itself into a "stack" with one member.

This can, as you might imagine, cause some muttering and head scratching as to "why won't this %$^$ing thing join the stack, as it had for me when I assembled our stack in our lab for the first time.

Then I read the instructions :/

IIRC, what I did to join the new member to the stack was powered the new one up in recovery mode, blew away the startup-config and powered it off. I then joined the switch to the stack, pwered the whole mess on, and promptly watched it grind to a halt as the other three members of the stack grabbed the latest firmware from the new switch, and elected it master. (hence the warning about versions above)

To make a long story short, after a firmware reload through the serial port because of a shoe-powerbar interface error in the middle of all this, we got the whole stack joined together.

But yeah, as long as the firmware of the new switch is the same or OLDER you are fine to connect it without downtime.

Or at least we didn't have downtime when we added our last switch.

Cheers!

 

[burtsbees]

sh ver
I myself recommend against stacking, because it introduces a single point of failure. Just my 2 cents

Burt

 

[vipergg]

Burts not sure what you mean by a single point of failure .That is the point with 3750 stacking , all members in the stack know the complete config so it will continue to run if you lose 1 switch . If you are stacking it would be smart to have 2 uplinks on different switches which then gives you redundancy even if you lose one switch. The whole stacking scenario can be tricky with the code versions and upgrading procedure. Make sure you elect the switch you want as master by using the "switch 1 priority 15 " command which would make switch 1 the master . Use this command on each member in the stack making each one lower than the previous , the priority statement determines which switch will be elected master.

 

[burtsbees]

I should not have posted that...I didn't know that, I had just heard that it was a sigle point of failure, which lead me to believe the entire point was to make one big switch. The lead network dude where I work told me that, and he was the network guru for a A.G. Edwards for 15 years. Then again, it took him a bit to realize that IGRP does not support VLSM (we had an arguement)...I'll be careful to whom I pay attention...sorry.

Burt

 

[eliotB]

It wasn't until I checked out the docs on switch stacking that I realized how redundant it really is. Even if one switch goes down; due to the stack connections, it should always find a way to the uplink switch. If the uplink switch goes down nothing gets out(unless you had that 2nd uplink like Vegg suggested) - that would be no different from a normal network anyways.

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3750/12240se/scg1/swstack.htm

p.s. Burt, do you work out of the St Louis area?

 

[eliotB]

Just to add, the OP may want to read this section of the doc:

Switch Stack Offline Configuration

You can use the offline configuration feature to provision (to supply a configuration to) a new switch before it joins the switch stack. You can configure in advance the stack member number, the switch type, and the interfaces associated with a switch that is not currently part of the stack. The configuration that you create on the switch stack is called the provisioned configuration. The switch that will be added to the switch stack and that receives this configuration is called the provisioned switch.

You manually create the provisioned configuration through the switch stack-member-number provision type global configuration command. The provisioned configuration also is automatically created when a switch is added to a switch stack that is running Cisco IOS Release 12.2(20)SE or later and when no provisioned configuration exists.

When you configure the interfaces associated with a provisioned switch (for example, as part of a VLAN), the switch stack accepts the configuration, and the information appears in the running configuration. The interface associated with the provisioned switch is not active, operates as if it is administratively shut down, and the no shutdown interface configuration command does not return it to active service. The interface associated with the provisioned switch does not appear in the display of the specific feature; for example, it does not appear in the show vlan user EXEC command output.

The switch stack retains the provisioned configuration in the running configuration whether or not the provisioned switch is part of the stack. You can save the provisioned configuration to the startup configuration file by entering the copy running-config startup-config privileged EXEC command. The startup configuration file ensures that the switch stack can reload and can use the saved information whether or not the provisioned switch is part of the switch stack.

 

[burtsbees]

Uh oh...

Burt

 

[burtsbees]

That means yes, St. Louis...who be you, sir?

Burt

 

[jgunkel]

Re: redundancy...

yup. The 3750's stacking is not the old-school style spoke and hub. It's a full loop around all the switches, and control of the stack is not permanently tied to any one particular switch. That is, if the current master dies, one of the surviving switches will be elected as the master, and you can replace the failed switch without bringing the rest of the stack down. I guess the closest way to describe it is to say that the stack actually functions as more of a cluster of switches, but still provides the same symantics as a single switch. (ie: you can provision an etherchannel between another device from two different phyisical devices in the stack)

On another note, has anybody experienced a failure where the stack goes "split brain"? (to borrow a term from pc clustering)

 

[eliotB]

Burt - I live in the St Louis area too. I'm looking for a job

It's hard trying to find an entry-level networking job when you only have 2 years of experience, yet a whole lot of knowledge ;/

anyways, ya I saw AG Edwards and thought you may live around here. That's cool.

-E

 

[burtsbees]

oh...*whew*...thought you may have been the guy I accidentally flamed...
I know how it is here, bro---I'm probably the only CCNP alive with no experience, and it kinda shows...lol
I get contractor offers all the time...I remember right after I got my CCNA a few years ago that I interviewed for this network technician job, and I was A+ and a CCNA---she said the company required a Network+ cert for the job, so I was to call her when I got the Network+! I almost aced it the next day, called her, and she never called me back!
Do you know anything about servers? I think our office will need to hire another person or two in the very near future...

Burt (not my real name, by the way)
(ps...who do you work for now, or what do you do?)

 

[eliotB]

Add me to your list of CCNPs without much experience.

I as well have my CCNP and I am currently studying for my CCIE. Talk about being overqualified and under-experienced! ;/

I'm currently not working. I graduated college about a year ago and have taken an extended break. Since I have all this time off, I thought, might as well start studying for the CCIE My plan is to attempt the lab by the end of next year.

In the last few months, however, I've been actively looking for a job.

I know enough about servers. If it's windows stuff, I started studying for my MCSA a few months ago, so I have an idea as to what's going on. I've used VMware to mess around w/W2k3 server.

My 2 years of experience was from working at my university for the network department when I was going to school.

 

[burtsbees]

We're a server hardware support company, working on Alpha servers, VAX, DEC, Dell, Hp/Compaq, Sun, etc. We support tape libraries/drives as well, and mess around with OS's such as Solaris, OpenVMS, AIX, Tru64 UNIX, Windows, Linux (mostly Red Hat and Open BSD), and HP-UX. We have also been known to do printers (WHY ME?!?!?!?!?!), and have recently been supporting and offering SmartNet with Cisco and spot services/professional services on Cisco devices (routers, switches and PIX firewalls), as well as hardware support on them.

Burt

 

[eliotB]

lol, in that case, I would say I know very little about "servers".I think the only place I could be of help is w/the Cisco stuff, Windows, and some Linux boxes.

Hopefully sooner or later I'll find something...

 

[burtsbees]

When they hired me, I had very little idea of even what RAID was, much less anything about servers---they hired me because I was a CCNA then...

Burt

 

[drewdown]

This thread is too funny. Burt making a mis-informed statement like that then coming back and saying he is a CCNP? Then eliotB chiming in and saying he doesnt know anything either but is also a CCNP studying for his CCIE.

lol.

 

[burtsbees]

A CCNP with no experience. They did not cover stacking in the CCNP cirriculum. Just thought that since networking jobs are scarce around here, I'd study and get my CCNP to help get my foot in the door. Is that good enough for you? Does that appease you? Don't call Cisco and tell them I don't know much about stacking 3750's...they might take my CCNP away...good thing I know OpenVMS and UNIX...

Burt