Basics¶
These are snippets and codes we use a lot in our projects
Routers¶
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#
R1# conf t
R1(config)#
R1(config)# exit
R1#
Note
Pay attention to what mode you are in.
Ping¶
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 192.168.1.23 |
| Config | do ping x.x.x.x | do ping 192.168.1.23 |
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 192.168.1.1
R1# show running-config
R1# copy running-config startup-config
R1(config)# do ping 192.168.1.1
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 192.198.1.1 255.255.255.0
R1(config-if)#no shut
R1(config-if)#exit
R1(config)#
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.
Warning
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 192.168.1.1/24 and 192.168.1.2/24.
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
FastEthernet0/0 192.168.1.1 YES manual up up
GigabitEthernet1/0 192.168.2.1 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 192.168.1.0 255.255.255.0 fa0/0
The example above simply forwards every packet with destination of 192.168.1.x to its FastEthernet0/0 port.