These are snippets and codes we use a lot in our projects


Codes frequently used for routers

Config Mode

There are multiple modes in routers, including Normal Mode and Config Mode.

You can switch to config mode with config terminal or simply conf t command and get back to normal mode with exit:

R1# conf t
R1(config)# exit


Pay attention to what mode you are in.


You can simply ping a destination with ping command in Normal Mode. If you are in Config mode, use do ping command.

Mode Command Example
Normal ping x.x.x.x ping
Config do ping x.x.x.x do ping

Save or Show configs

If you are in Normal mode, simply type show running-config to show the current config, and copy running-config startup-config to save the configs for next start.

If you are in Config mode, put a do prefix before those commands:

R1# ping
R1# show running-config
R1# copy running-config startup-config

R1(config)# do ping
R1(config)# do show running-config
R1(config)# do copy running-config startup-config

Config interfaces

You can config interfaces of the router in config mode. You may have multiple interfaces on your router such as FastEthernet or GigabitEthernet, etc. Simply use int <interface_id> to config the interface. The interface_id parameter should be in any forms of the interface type, for example all of these are accepted: FastEthernet0/0, fa0/0 or f0/0.

R1#conf t
R1(config)#int fa0/0
R1(config-if)#ip addr
R1(config-if)#no shut

Here we first switched to interface config mode with int fa0/0 command and then changed the IP address and subnet mask of the interface. The shutdown command disables the interface. Putting a no (no shutdown or simply no shut) before this command (re)enables the interface.

Notice that the exit command only changes the mode one level upper and does not directly switch to the Normal mode.


Interfaces of the same router can not be in the same network. For example you can not have two interfaces in a router with IPs and

Show interface configs

You can see the IP and status of the interfaces with show ip interface brief in Normal mode. The shortened version sh ip int br also works.

R1#show ip interface brief

Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0       YES manual up                    up
GigabitEthernet1/0     YES manual up                    up

Add item to route table

A router must know on which interface it should to forward a packet, based on the network address of it. You can manually add items to the routing table of a router using ip route x.x.x.x y.y.y.y <interface_id> command where the x.x.x.x is the network address and y.y.y.y is the subnet mask.

R1(config)#ip route fa0/0

The example above simply forwards every packet with destination of 192.168.1.x to its FastEthernet0/0 port.


Codes frequently used for VPCs

Short Codes

Command Description Example
ping x.x.x.x Pings an IP address ping
save Saves the configs of the VPC save
ip x.x.x.x/y z.z.z.z Sets IP, Subnet mask and Gateway ip
ip dhcp Gets the IP from DHCP server ip dhcp