Cisco's Interface Config Cache

Ever notice that doing a show run on a large 3750 Stack or a 6513 can take a (relatively) long time? Enter Cisco's Interface Config Cache:

http://www.cisco.com/en/US/docs/ios/12_3t/12_3t7/feature/guide/gtinvgen.html

Basically, what it does is cache the config in memory, so that your "show run"s execute a LOT faster. Normally, everytime you do show run, it has to query EVERY interface in the system to determine the config for each, and then displays it.

This command tells the IOS to cache it the first time "show run" is executed, so every subsequent "show run" is loading a cache'd copy. Every time a config change is made, the cache is cleared, to keep itself fresh.

In other words, this command won't make a difference the first time you do a "show run" after a config change, but every "show run" thereafter(until the next interface change) will be loaded from the cache and be SUPER speedy.

For the impatient, the command is:

parser config cache interface

Sun JRE Native 64-bit Plugin support in Firefox

Finally, 64-bit Linux computing is becoming usable for the masses, I'm sure the major distros will pick up on this and make this even easier for those without patience.

Anyway, Sun's JRE 6.0 Update 12 added 64-bit support. I recommend downloading Update 14 build 03 to get the latest and greatest. (as of this writing of course)

http://download.java.net/jdk6/index.html

I've not tried this in Vista 64 or XP 64bit.

Under Linux, download the 64-bit bin file, chmod it to run(I recommend the /opt directory), and it will extract and install itself. Then you only need to add a symbolic link in your firefox plugin directory to the libnpjp2.so file in the /lib/amd64 subdirectory of the newly installed JRE.

Here is what I did under Ubuntu 8.10:

cd /opt
sudo mv ~/Desktop/jre-6u14-ea-bin-b03-linux-amd64-10_mar_2009.bin ./
sudo chmod 777 jre-6u14-ea-bin-b03-linux-amd64-10_mar_2009.bin
sudo ./jre-6u14-ea-bin-b03-linux-amd64-10_mar_2009.bin
cd /usr/lib/mozilla/plugins
sudo ln -s /opt/jre1.6.0_14/lib/amd64/libnpjp2.so

Taken from:

http://ubuntuforums.org/showthread.php?t=1011899

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.

Gartner Blogger: Interesting IT Trends '09

Good read to see whats coming in '09:

http://blogs.gartner.com/david_cearley/2008/10/14/gartner%E2%80%99s-top-10-strategic-technologies-for-2009/