Friday, February 29, 2008

Network Tip No. 12: Configuring an Ethernet/Fast Ethernet Interface

Configuring an Ethernet/Fast Ethernet Interface

Router(config)#int fa0/0

Moves to Fast Ethernet 0/0 interface mode

Router(config-if)#description Sales LAN

Optional descriptor of the link is locally significant

Router(config-if)#ip address

Assigns address and subnet mask to interface

Thursday, February 28, 2008

Network Tip No. 11: Configuring a Serial Interface

Configuring a Serial Interface

Router(config)#int s0/0

Moves to interface Serial 0/0 mode

Router(config-if)#description Link to ISP

Optional descriptor of the link is locally significant

Router(config-if)#ip address

Assigns address and subnet mask to interface

Router(config-if)#clock rate 56000

Assigns a clock rate for the interface

Router(config-if)#no shut

Turns interface on

Network Tip No. 10: Moving Between Interfaces

Moving Between Interfaces

Router(config)#int s0

Router(config)#int s0

Moves to interface S0 mode


Router(config-if)#int e0

In int S0, move to E0

Router(config)#int e0


In E0 mode now


Prompt does not change; be careful

Wednesday, February 27, 2008

Network Tip No. 9: show Commands

show Commands

Router#show ?

Lists all show commands available

Router#show interfaces

Displays statistics for all interfaces

Router#show interface serial 0

Displays statistics for a specific interface, in this case Serial 0

Router#show ip interface brief

Displays a summary of all interfaces, including status and IP address assigned

Router#show controllers serial 0

Displays statistics for interface hardware. Statistics display if the clock rate is set and if the cable is DCE, DTE, or not attached

Router#show clock

Displays time set on device

Router#show hosts

Displays local host-to-IP address cache. These are the names and addresses of hosts on the network to which you can connect

Router#show users

Displays all users connected to device

Router#show history

Displays history of commands used at this edit level

Router#show flash

Displays info about Flash memory

Router#show version

Displays info about loaded software version

Router#show arp

Displays the ARP table

Router#show protocols

Displays status of configured Layer 3 protocols

Router#show startup-config

Displays configuration saved in NVRAM

Router#show running-config

Displays configuration currently running in RAM

Tuesday, February 26, 2008

Network Tip No. 8: Password Encryption

Password Encryption
Router(config)#service password-encryption
Applies a weak encryption to passwords

Router(config)#enable password cisco
Sets enable password to cisco

Router(config)#line con 0

Router(config-line)#password Cisco
Continue setting passwords as above


Router(config)#no service password-encryption
Turns off password encryption

Network Tip No. 7: Configuring your Passwords

Configuring Passwords
Works on both routers and switches.

Router(config)#enable password jepoy
Sets enable password

Router(config)#enable secret secret-jepoy
Sets enable secret password

Router(config)#line con 0

Router(config-line)#password console

Enters console-line mode

Sets console-line mode password to console

Enables password checking at login

Router(config)#line vty 0 4

Router(config-line)#password telnet

Enters vty line mode for all five vty lines

Sets vty password to telnet

Enables password checking at login

Router(config)#line aux 0

Router(config-line)#password backdoor

Enters auxiliary line mode

Sets auxiliary line mode password to backdoor

Enables password checking at login

Monday, February 25, 2008

Network Tip No. 6: Configuring a Router Name

Configuring a Router Name

This command works on both routers and switches.

Router(config)#hostname jepoy

Name can be any word you choose


Friday, February 22, 2008

Network Tip No. 5: disable Command

disable Command


Moves you from privileged mode back to user mode

Thursday, February 21, 2008

Network Tip No. 4: exit Command

exit Command

Router#exit or Router>exit

Logs a user off

Router (config)#

Moves you back one level


Moves you back one level

Network Tip No.3: Global Configuration Mode


Limited viewing of config cannot make changes in this mode.


Can see config and move to make changes

Router#(config) t

Moves to global config mode. This prompt indicates that you can start making changes

Wednesday, February 20, 2008

Network Tip No.2: Enable Command

enable Command


Moves user from user mode to privileged mode

Tuesday, February 19, 2008

Linux Tip No. 20: Change your Default Gateway

How to Change Your Default Gateway

[root@jepoy /]# route add default gw eth0


Config file: /etc/sysconfig/network


Monday, February 18, 2008

Linux Tip No. 19: View your routing table

[root@proxy ~]# netstat -nr
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface U 0 0 0 eth0 U 0 0 0 eth1 U 0 0 0 eth1 UG 0 0 0 eth0

Sunday, February 17, 2008

Linux Tip No. 18: Restart Network Service

[root@proxy docadmin]# /sbin/service network restart
Shutting down interface eth0: [ OK ]
Shutting down interface eth1: [ OK ]
Shutting down loopback interface: [ OK ]
Disabling IPv4 packet forwarding: net.ipv4.ip_forward = 0
[ OK ]
Bringing up loopback interface: [ OK ]
Bringing up interface eth0: [ OK ]
Bringing up interface eth1: [ OK ]

Thursday, February 14, 2008

Linux Tip No. 17: Enable/Disable interface

[root@jepoy]# ifdown eth0
[root@jepoy]# ifup eth0

Wednesday, February 13, 2008

Linux Tip No. 16 IP Address Aliasing - Permanent

IP Address Aliasing - Permanent

Edit you config file

Config file: /etc/sysconfig/network-scripts/ifcfg-eth0:0


Tuesday, February 12, 2008

Linux Tip No.15: IP Address Aliasing - Temporary

Network IP aliasing

ifconfig eth0 XXX.XXX.XXX.XXX netmask broadcast XXX.XXX.XXX.255

route add -host XXX.XXX.XXX.XXX dev eth0

ifconfig eth0:0 netmask broadcast
ifconfig eth0:1 netmask broadcast

route add -host dev eth0
route add -host dev eth0

Monday, February 11, 2008

Linux Tip No.14: Locally resolve hosts

Locally resolve hosts

File: /etc/hosts

[root@proxy etc]# more hosts

# Do not remove the following line, or various programs

# that require network functionality will fail. localhost.localdomain localhost proxy winxp

[root@proxy etc]# ping winxp

PING winxp ( 56(84) bytes of data.

[root@proxy etc]# ping proxy

PING proxy ( 56(84) bytes of data.

64 bytes from proxy ( icmp_seq=0 ttl=64 time=0.092 ms

Sunday, February 10, 2008

Linux Tip No.13: Setting your resolver

Setting your resolver – DNS Entries

File: /etc/resolv.conf

search - Name of your domain or ISP's domain if using their name server

nameserver XXX.XXX.XXX.XXX - IP address of primary name server

nameserver XXX.XXX.XXX.XXX - IP address of secondary name server





Thursday, February 7, 2008

Linux Tip No. 12: DHCP client configuration

DHCP client configuration



Tuesday, February 5, 2008

Linux Tip No. 11: Changing your IP Address - Permanent

Changing your IP Address – Permanent

Files: /etc/sysconfig/network-scripts/

[root@proxy network-scripts]# ls -l

total 360

-rw-r--r-- 3 root root 190 Feb 28 2007 ifcfg-eth0

-rw-r--r-- 3 root root 191 Nov 8 2005 ifcfg-eth1

-rw-r--r-- 1 root root 254 Jun 21 2001 ifcfg-lo

Edit ifcfg-eth0:

Monday, February 4, 2008

Linux Tip No. 10: Changing your IP Address - Temporary

Changing your IP Address - Temporary


Ifconfig netmask

[root@bigboy tmp]# ifconfig eth0 netmask up

The ifconfig command does NOT store this information permanently. Upon reboot this information is lost. (Manually add the commands to the end of the file /etc/rc.d/rc.local to execute them upon boot.)