Computer Network Security

Set the telnet source IP address for a Cisco router

The default source IP address when telnetting from a Cisco router is that of the interface closest to the destination. Because some access lists may block traffic from the default IP address, or to help test access lists, it may be useful to temporarily or permanently set the telnet source IP address.To temporarily set the telnet source IP address for a single telnet session, use the/source-interface extension to the telnet command. For example, to telnet to 192.168.1.4 using the source IP address of the interface FastEthernet0telnet 192.168.1.4 /source-interface FastEthernet0To set this interface as the source IP address for all telnet sesions, use this command in configuration mode (conf t):ip source-interface fastethern...

Set the time on a Cisco router manually

To set the time, use this command in enable mode (not configuration mode):Router# clock set 22:55:05 June 19 2006The time is in 24 hour mode. To see the information about the clock settings, use:Router# show clock detail22:56:07.136 PDT Mon Jun 19 2006Time source is user configurationThis will show the current date and time and the source of the time configuration (in this case showing that the time was manually se...

Configure Cisco router to set time from NTP server

Using NTP to synchronize the date and time of multiple devices makes sense even in a small network. When performing forensic analyses or troubleshooting connection problems, having consistent logging timestamps from multiple devices can save your life. Well, at least help keep your hair attached to your head.To configure a router to use the NTP server 192.168.1.15, issue these commands from enable mode:Router# conf tRouter# ntp server 192.168.1.15Multiple ntp server lines can be used for redundancy. By default, the router will use UTC as the time zone. To set the time zone to PST and add a second ntp server at 172.32.10.55, use these commands instead:Router# conf tRouter# ntp server 192.168.1.15Router# ntp server 172.32.10.55Router# clock timezone PST...

Configure Cisco router as an NTP server

An NTP server can provide synchronized date and times for devices in a network. Since a router cannot be a Stratum 1 device (cannot connect to a Stratum 0 device such as a GPS clock), a router is not an accurate source of time information. If this is not important to you, then using a router as an NTP server may be acceptable.To configure the router to work as an NTP server, use the following command in configuration mode (following a conf t):ntp master 8The 8 specifies the stratum of this NTP server, essentially the number of hops away from a Stratum 0 device. The default value is...

Cisco Switch 2900/2950: Display VLAN information

Knowing the commands to display configuration information about Virtual LANs (VLANs) is as important as knowing the commands to configure them. The commands here display information about all VLANs or a single VLAN by number or name.All of these commands must be run from privileged mode. To view detailed information about all VLANs on the local switch, use:# show vlanTo shorten the output and just display the highlights about all of the VLANs:# show vlan briefTo display information about VLAN 3, use:# show vlan id 3This version of the command can be extended to look at multiple VLANs. For example, to view information about VLANs 1, 2, 3 and 10, use:# show vlan id 1-3,10For increased administratability, VLANs can be named. To view information about a VLAN by name, for instance the VLAN named...

Cisco 2950 switch password recovery

This documents the procedure for performing a password recovery on a Cisco 2950 switch (and probably other models, as well).1. Unplug the power cable2. Hold down the mode button while replugging the power cable3. Type flash_init over the console4. Type load_helper5. Type Dir flash ://make sure to type the semi-colons6. Type rename flash:config.txt flash:config.old//the password is contained in the config.txt file7. Type boot//this reboots the system8. Type n to skip the initial setup configuration9. Type enable//this takes you to the enable mode10. Type rename flash:config.old flash:config.txt11. Save config.txt to system#copy flash:config.txt system:running-config12. Enter config mode and change the password# config t# no enable secret//this applies only if the enable secret password was...

How to convert VMware virtual disks from thin to thick with the vSphere client

Have you ever provisioned a new virtual machine in vSphere, put it in production, and discovered belatedly that you mistakenly used “thin provisioned” virtual disks? This can often happen when deploying from a template which was thin provisioned since the default option is to use the same disk format as the source. Good news! It is quite easy to convert these to thick with the vSphere client and your mouse.No command line required, as was the case with previous versions of VMware Infrastructure. The only downside is that the virtual machine must be shut down prior to inflating its disk(s).1. Launch your vSphere client and log in to your vCenter server.2. Select the virtual machine which has mistakenly been thin provisioned.3. Select the option to “Shut Down Guest” under Commands. This is a...