The below details how to recover a Cisco router if you have forgotten the password of there is a problem with the configuration.

WARNING: By doing this you may loose any configuration on the router.

1. You will need to be physically connected to the console port
2. Turn the router off
3. Turn the router on while holding down CTRL and repeatedly pressing BREAK. If this goes well then you should get a message saying *** System received abort due to Break Key ***

I have recently had some issues connecting to one of our remote Hitahci AMS Storage Array's using Storage Navigator Modular which by default uses port 2000.

I was getting messages such as the below;

Failed to connect with the subsystem. Confirm the subsystem status and the LAN environment, and try again.

The physical connection was as below;

If when you run show logging or try to view the debug logs on a Cisco IOS device the date and time is not displayed and instead you get something like the below, here is the solution.

6w4d: %ETHCNTR-3-LOOP_BACK_DETECTED: Loop-back detected on FastEthernet2/0/8.

Get into configure terminal mode and enter the below

service timestamps log datetime localtime
service timestamps debug datetime localtime

Recently I noticed that my 100Mb link between my ASA and my 2801 router always ran very slow, after doing a show interface X on my routers interface I noticed a large number of CRC errors. CRC errors add a performance hit so I thought that would be a good place to start.

In my case the cause of the CRC errors was a mismatch in the duplex settings, the ASA was set to auto and router was set to full.

The ARP table on a Cisco device is a list of learned IP address and what MAC addresses they resolve to, this is required as generally switches work at layer 2 with MAC addresses not IP Address’s.

Problem:

If you replace a device with another device that is still using the same IP address as the original device but has a different MAC address you find that you are unable to connect to it due to the ARP record on your Cisco device is still pointing to the original devices MAC address.

Recently I upgraded our Cisco 4402 Wireless LAN Controller to a later release and soon after the upgrade I started noticing the below messages, I am not sure if this started happing because of the upgrade or if I had never noticed it before.

SNMP Trap Log:
WPA MIC Error counter measure activated on Radio with MAC XX:XX:XX:XX:XX:XX and Slot ID 1. Station MAC Address is XX:XX:XX:XX:XX:XX and WLAN ID is 1.

If like me you what to see the output of a dubug command via a telnet connection, follow the below steps

1) Enable Virtual Terminal Logging

Telnet into the router and get yourself into privileged (Enable) mode and enter the command

terminal monitor

2) Enable Debugging on Virtual Terminal

In order to enable debugging messages on your virtutal terminal, enter the following commands:

Before you can remove a directory on a Cisco devices the directory must be empty, the below steps will show you how to delete all of the files and folders the directory contains.

Most modern Catalyst switches store their IOS in a folder due them being bundled with HTML files, so this may come in useful when you want to remove your current IOS pre / post an update.

The Problem:
I recently had a situation where hosts on my internal LAN needed to communicate with a servers on our DMZ using its public IP address however the packets where being sent to the outside world and where being lost.

So Hosts on the LAN where unable to communicate with servers on the DMZ using their public IP address’s.

If you find yourself in ROMMON mode having done something silly like wiping the flash or if there was a problem updating the IOS then the below steps will go though how to copy a replacement image from tftp to the routers flash.

What you will need

- A tftp server, I tend to use tftpd32
- A compatible IOS image in the base directory of your tftp server
- The router need to be pluged into your network
- You need to be connected to the router via a console cable

The Commands

Enter the below commands one by one