Last Update: 03 October 2020 | 3 min read | Author: Xander Billa

Routing

The term Routing refers to taking a packet from one device and sending it through the inter network to another device on a different network.

Here is an important list of the minimum factors routers must know to be able to effectively route packets:

  • Destination Address
  • Neighbor routers from which it can learn about remote networks
  • Possible route to all remote networks 
  • The best route to each remote network
  • How to maintain and verify the routing information

Routing Table: A map of the inter network, describing how to find remote networks. If a network isn't directly connected to the router, the router must use one of the two ways to learn how to get to the remote network location into the routing table.

But when Dynamically Routing is used, a protocol on one router communicates with the same protocol running on neighboring routers.

This is a simple network, with a router having 4 interfaces facing in different directions to different devices it might be some intermediate device or it might be some end devices like PC (in this case), laptop or smartphone... etc.


By using the command sh ip route on a router, we can see the routing table.

Lab_A#sh ip route
Codes: L - local, C - connected, S - static,
[output cut]
10.0.0.0/8 is variably subnetted, 6 subnets, 4 masks
C 10.0.0.0/8 is directly connected, FastEthernet0/3
L 10.0.0.1/32 is directly connected, FastEthernet0/3
C 10.10.0.0/16 is directly connected, FastEthernet0/2
L 10.10.0.1/32 is directly connected, FastEthernet0/2
C 10.10.10.0/24 is directly connected, FastEthernet0/1
L 10.10.10.1/32 is directly connected, FastEthernet0/1
S* 0.0.0.0/0 is directly connected, FastEthernet0/0

In this routing table we can clearly see that there are four interfaces and out of four, three are directly connected - interface FastEthernet0/1, FastEthernet0/2 and FastEthernet0/3. Meanwhile FastEthernet0/0 is directly connected with another router statically. In the above routing table:

C - connected: The network from the interface is connected.
L - local: The IP Address of the device the interface connected locally.
S - static: Indicates that the interface have active Static Route
* - Default Route: Indicate the Default-Route.