Routing is the process that routesrs use to determine the path that IP packets should take over a network to reach their destination. Routers store routes to all of their known destinations in a routing table. When routers receibe packets, they look in the routing table to find the best route to forward that packet.
There are two main routing methods:
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Dynamic Routing: routers use dynamic routing protocols (i.e. OSPF) to share routing information with each other automatically and build their routing tables.
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Static Routing: a network engineer/admin manually configures routes on the router
A route tells the router to:
- send a packet to destination X, you should send the package to next-hop Y
next-hop= the next router in the path to the destination
- send the packet directly to the destination (if it is directly connected to the router)
- receive the packet for yourself (if the destination is the router's own IP address)
For simplicity we'll only show R1's config.
show ip routeto view routing table 🔥
- Route to the network the interface is connected to
- R1 G0/2 IP =
192.168.1.1/24 - Network address =
192.168.1.0/24 - It provides a route to all hosts in that network (i.e. 192.168.1.10, 192.168.1.232, etc)
- R1 knows: "if I need to send a packet to any host in 192.168.1.0/24, I should send it out to
G0/2"
- Route to the exact IP address configured in the interface
/32netmask is used to specify the exact IP address of the interface- Even tough R1's G0/2 is configured as
192.168.1.1/24, the local route is192.168.1.1/32 - R1 knows: "if I receive a package destined for this IP address, the message is for me"
A packet destined for 192.168.1.1 is matched by 2 routes in the example above:
192.168.1.0/24192.168.1.1/32
It will choose the most specific matching route.
- most specific matching route = the matching route with the longest prefix length 🔥