Editing Routing table (section)

==Contents==
The routing table consists of at least three information fields:
#''network identifier'': The destination subnet and netmask
#''metric'': The [[routing metric]] of the path through which the packet is to be sent. The route will go in the direction of the gateway with the lowest metric.
#''next hop'': The next hop, or gateway, is the address of the next station to which the packet is to be sent on the way to its final destination

Depending on the application and implementation, it can also contain additional values that refine path selection: 
#''quality of service'' associated with the route. For example, the U flag indicates that an IP route is up.
#''filtering criteria'': [[Access-control list]]s associated with the route
#''interface'': Such as eth0 for the first Ethernet card, eth1 for the second Ethernet card, etc.

Shown below is an example of what the table above could look like on a computer connected to the internet via a [[home router]]:

{| class="wikitable"
|+Example routing table contents
|-
! Network destination
! Netmask
! Gateway
! Interface
! Metric
|-
| 0.0.0.0
| 0.0.0.0
| 192.168.0.1
| 192.168.0.100
| 10
|-
| 127.0.0.0
| 255.0.0.0
| 127.0.0.1
| 127.0.0.1
| 1
|-
| 192.168.0.0
| 255.255.255.0
| 192.168.0.100
| 192.168.0.100
| 10
|-
| 192.168.0.100
| 255.255.255.255
| 127.0.0.1
| 127.0.0.1
| 10
|-
| 192.168.0.1
| 255.255.255.255
| 192.168.0.100
| 192.168.0.100
| 10
|}

* The columns '''Network destination''' and '''Netmask''' together describe the '''Network identifier''' as mentioned earlier. For example, destination '''192.168.0.0''' and netmask '''255.255.255.0''' can be written as '''192.168.0.0/24'''. 
* The '''Gateway''' column contains the same information as the '''Next hop''', i.e. it points to the gateway through which the network can be reached. 
* The '''Interface''' indicates what locally available interface is responsible for reaching the gateway. In this example, gateway '''192.168.0.1''' (the internet router) can be reached through the local network card with address '''192.168.0.100'''. 
* Finally, the '''Metric''' indicates the associated cost of using the indicated route. This is useful for determining the efficiency of a certain route from two points in a network. In this example, it is more efficient to communicate with the computer itself through the use of address '''127.0.0.1''' (called ''localhost'') than it would be through '''192.168.0.100''' (the IP address of the local network card).