Adding a Cisco 3750 Switch to an Existing Stack

Another simple task that Cisco doesn't quite make 100% clear.

Let's say you have an existing Cisco 3750 Switch Stack and you have had a bit of an office redesign and you now need to add another member to the stack to add additional port capacity for the new users moving in.

This is mostly simple to do, but there are several checks to make along your journey, and hopefully I can point them out clearly.

1. First, check the stacking status of your existing stack using the below command. It should say that the stack ring speed is "full". If it doesn't you need to ensure you have a complete stack "ring" thereby having redundant stacking paths on each switch.
   
   

   ZZStack#show switch stack-ring speed
   
   Stack Ring Speed        : 32G
   Stack Ring Configuration: Full
   Stack Ring Protocol     : StackWise

   
   
   See this publication for stack-wiring help:
   http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/hardware/quick/guide/3750GSG3.html#wp49279
   
   
2. Once you know your stack is a complete ring("full") you can safely break this ring to insert your new switch. ENSURE YOUR NEW SWITCH IS POWERED OFF. Rack this new switch adjacent to your existing switches. "Break" the ring in one place so you can wire your new switch so it fits nice and neat in this new stack, following the wiring schema linked above. Once everything is wiring in place, you may NOW power on your new switch.
   
   
3. After a few minutes your switch will have booted and the existing stack should recognize it as joining the stack. You can verify its status with:
   
   

   ZZStack#show switch stack-ring speed
   
   Stack Ring Speed        : 32G
   Stack Ring Configuration: Full
   Stack Ring Protocol     : StackWise

   
   
   

   ZZStack#show switch
   Switch/Stack Mac Address : 0024.9803.8e80
                                              H/W   Current
   Switch#  Role   Mac Address     Priority Version  State
   ----------------------------------------------------------
   *1       Master 0024.9803.8e80     15     0       Ready
    2       Member 0023.ac0f.7880     1      0       Ready
    3       Member 001a.e267.0080     1      0       Version Mismatch

   
   
   In this example switch 3 was added to the stack, the stack ring looks good, but on the switch status output, instead of saying "Ready" it says "Version Mismatch." You now need to ensure your switch gets the same IOS version as its stack-mates and reboots for this to take effect(see below).
   
   If your stack says your new switch is in the "Ready" state, you are in luck and you are done! (except for configuring your new user ports)
   
   
4. Automatic Upgrade is a great thing in theory, but I've not had the best of luck with it. From what I can tell if your existing stack and this new member you are adding are running different IOS featuresets, the automatic upgrade will NOT WORK.
   
   To check to see if its working or not, check the log. If you see log entries resembling any of the below, it appears automatic upgrade is working as it should.
   

   ZZStack#show log
   ---snip---
   Nov 24 16:58:36.388 EST: %IMAGEMGR-6-AUTO_COPY_SW_INITIATED: Auto-copy-software process initiated for switch number(s) 3

   
   This shows that it has started the auto upgrade process. You can check the status with the "show archive status" command or by continually checking the log.
   
   If you see the below it was successful and is now rebooting this member switch so the correct IOS loads and it can finally join the stack as it should(and you should be done):
   

   ---snip---
   Nov 24 17:06:04.453 EST: %IMAGEMGR-6-AUTO_COPY_SW: Software successfully copied to
   Nov 24 17:06:04.453 EST: %IMAGEMGR-6-AUTO_COPY_SW: system(s) 3
   Nov 24 17:06:04.453 EST: %IMAGEMGR-6-AUTO_COPY_SW: Done copying software
   Nov 24 17:06:04.453 EST: %IMAGEMGR-6-AUTO_COPY_SW: Reloading system(s) 3

   
   
   If you don't see any of the above log entries, go on to the next step.
   
   
5. This is the step they don't really explain well. Thankfully, the "Version Mismatch" state, while not activating any of its ports, does allow you to manipulate the flash filesystem of the inconsistent member so you can stage it from the main stack interface.
   
   If you made it to this step, it probably means there is a featureset mismatch(or some other problem) and you need to force this new member to take the IOS version that the stack is currently running. In this scenario, even the "archive copy-sw" command does not work, so you must either load the IOS bin file manually or use use the appropriate "archive download-sw" command with the "/allow-feature-upgrade" switch to load the IOS to the ENTIRE STACK again, including this new member(but you only need to reboot the new member). I prefer to use the archive command, its slow but its so easy!
   
   Here's the link to the software upgrade caveats/howtos for stack configurations(if it seems like I breezed through this last step):
   http://www.cisco.com/en/US/products/hw/switches/ps5023/products_configuration_example09186a00804799d7.shtml

Renumbering a Cisco 3750 Stack

For those of you familiar with the Cisco 3750 switches, their killer feature is their ability to "stack". Stacking sets one switch as the "master" and utilizing stack cables out of the back of the switch, each switch in the stack appears as one. This allows for expandability, and ease of management.

Anywho, one annoyance of stacking 3750s is that an engineer building or adding to a stack can often install switches "out of order" meaning their stack ID does not match their order as-racked. Basically, most English(or any other Western language) speaking peoples. would assume that a group of 5 switches in a rack would be numbered 1-5, top to bottom. If this isnt the case, ASSumptions can lead to some mistakes and mistakes lead to fussy customers. Yes, this can be checked by pressing the mode button on the front of any stack member, but isnt it better to not worry with that and have it right from the beginning?

Anyway, as a best practice, I always set the order as racked to match the stack order. Its not as simple as issuing the renumber subcommand as it won't move your switch port configurations with the move, you have to do some trickery to move the configurations(it even warns you of this when you hit the commands). If you want to renumber switches in a stack, here is a little HOWTO, since Cisco really doesn't go over this scenario, and I've done it a few times.

*************
Example:
*************
Stack of 2 switches in a rack, Switch 2 is on top, switch 1 is on the bottom.

Step 1: Prime the switches by setting their new stack numbers
We want 2 to become 1 and 2 to become 2, right?

In config mode:

switch 1 renumber 2
switch 2 renumber 1

Then write your config...simple enough.

Step 2:
Copy the startup config to your favorite text editor via screen scrape or file transfer. Do a find replace on all 2/0/ and replace with X/0/ and then find replace 1/0/ with 2/0/, and finally X/0/ with 1/0/. Basically you have flip-flopped all the port configs between the two switches using the power of find/replace.

Step 3:
Upload the file you edited above and have it overwrite the startup config of the stack. Reload the stack

Step 4:
Test. (of course).

Testing Copper Cables with Cisco Switches (TDR)

You can quickly detect any cable problems from your test with any 3560G/3750G/4500(with Gig Ports)/6500(with Gig Ports) by using the built-in IOS TDR. It will tell you the length of the cable and if there are any open pairs(and if so, where in the line they occur). This is better than running up to the location with a Fluke in hand to test cable problems.

First, you must run the test(its intrusive on the interface its being run on, so only run it on something that is OK to be unreachable for about a minute):

test cable-diagnostics tdr interface <InterfaceName>

After it completes, all you have to do is view the result:

show cable-diagnostics tdr interface <InterfaceName>

See the link below for the full scoop from Cisco:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_46_se/configuration/guide/swtrbl.html#wp1400280

How to Sort IP Addresses in Microsoft Excel

A strange combination of Excel tools will yield a method to sort a long list of IP Addresses. I'll start from copying a list from a Cisco Router ARP Table.

Here's how:

1. Paste the ARP Table into Excel, it will be a long line of text all in one column.


2. Select the column by clicking the letter at the top and run the "text to columns" tool.


3. Run through the short wizard using a space deliminator, should yeild you with 5 or so columns, one for IP, one for MAC, and the others.


4. Now, select the new column where the IP Addresses are, and run the same text to columns tool again, this time using a period as the deliminator.(you may want to first insert 3 blank columns to the right of the IP Address to make room for this new columnized data)


5. Now, sort by lowest to highest using first octet, then by second octet, then by third octet, and then by fourth octet.


6. Insert yet another column anywhere, and on line one use the CONCATENATE function as such(a1=first octet of first address, B1 as second of first, etc):



=CONCATENATE(A1,".",B1,".",C1,".",D1)



7. This should yield a cell with the address formatted properly. Select it and click the dot in the lower right hand corner of the selection and drag all the way down every row in your table, thereby copying the formula with relative cell modifications in your formula.


8. Now, select all these addresses in this column, and copy them.


9. By default, pasting them in another column will only paste formula data, so under Edit->Paste Special(or if you have 2007, click the arrow underneath the paste button) and select Paste Values.


10. Tada! You can now delete all 5 of you intermediary columns.

Native VLANs - ISL vs 802.1q, CatOS vs IOS

When configuring trunking, the discussion of Native VLANs may be a little confusing, especially when comparing ISL trunking vs 802.1q, and IOS vs CatOS.

Here's a breakdown:

First, the concept of Native VLAN is only understood by 802.1q. So, for ISL trunking, do not worry about setting it, as ISL encapsulates EVERY FRAME going through that trunk(more below).

A Native VLAN is merely a single VLAN ID already allowed on a trunk that will be used for all untagged frames sent/received. In other words, if the switch receives a frame on this trunk with no VLAN ID tagged on it, it will assume that this frame is in the Native VLAN, and inversely, if it sends a frame on this trunk that is in the Native VLAN, it will not bother tagging the frame.

As stated above, this does not apply to ISL because it encapsulates packets(instead of tagging them, like 802.1q), and every packet must be encapsulated, therefore, ISL does not bother with the concept.

Typically, you have a dedicated "switch management" VLAN on your network, and all your switches' management addresses are in this VLAN, and this VLAN is set as native on every trunk link between these switches. A lot of times setting the Native VLAN does not matter on newer switches, but I have found that some Cisco Autonomous APs and very old switches require it set, so I feel it is best to keep it consistent, YMMV.

To check the current Native VLAN on IOS:

sh int trunk InterfaceX/Y

To check the current Native VLAN on CatOS:

sh trunk X/Y

On IOS, its pretty easy to set the native VLAN, just enter the following command under the interface(where Z is the VLAN ID):

switchport trunk native vlan Z

On CatOS, its not as obvious, but just as easy, you just merely set the vlan of the trunk port as if it were an access port:

set vlan Z X/Y

As I said before its not terribly necessary nowadays, but for consistency I recommend setting it to the same VLAN as the management interface of your end-user switches. No matter what you do, you must ensure that the Native VLAN matches on both sides of your 802.1q trunk, because otherwise two Cisco switches will detect the mismatch via CDP and will block the port, until its fixed. The following IOS command will show you a list of any such blocked ports:

show spanning-tree inconsistentports

Cisco "Setup Express"

Newer Cisco "pizza box" switches (3560/3750 and others) have a MODE button on the front of them that is used for both the password-recovery feature, as well as the "setup express" feature.

Reference:
http://cciepursuit.wordpress.com/2007/06/29/completely-clearing-a-cisco-switchkinda/


I would recommend disabling the setup express feature(no setup express in configure mode) as it really provides NO benefit in my eyes. It does not affect the password recovery feature(unless you are super paranoid, disabling password recovery can be disastrous).

My argument is that while a switch is powered on, there should not be this easy to essentially reboot the switch with a blank config, with the only way to remedy is renaming files via console cable. This can have one nosy user/janitor take down your switch until you can run out there with a laptop.