[Day 7] 2. Dynamic Routes

Dynamic Routing

Dynamic routing refers to the process by which routers automatically learn and update routes in the routing table based on the network topology. Unlike static routing, where routes are manually configured, dynamic routing allows routers to adjust their routes based on the network's state and conditions, such as changes in topology, link failures, or network congestion.

Dynamic routing protocols use algorithms to determine the best path for routing data and automatically adjust the routes when network conditions change. Common dynamic routing protocols include RIP, OSPF, and EIGRP.

RIP (Routing Information Protocol)

The Routing Information Protocol (RIP) is a distance-vector routing protocol used in both local area networks (LANs) and wide area networks (WANs). RIP enables routers to exchange routing information with one another, allowing for the automatic learning of routes and adjustments based on network changes.

• Broadcast Address: RIP uses

  Copy

  255.255.255.255

  as its broadcast address, also called "All ones broadcast."

• Routing Entries: Routes learned via RIP are denoted with a capital R in the routing table.

• Hop Count: RIP calculates the distance to a destination based on hop count. The maximum allowed hop count is 15, and a destination that requires 16 or more hops is considered unreachable.

• Routing Behavior:

  • Routes with a lower hop count are prioritized.
  • If multiple routes exist, the path with the lower hop count is chosen. If the smaller path fails, higher hop count paths can be used.

• Load Balancing:

  • RIP can balance traffic among up to 4 routes by default (Equal Cost Load Balancing).
  • If configured, RIP can balance traffic among up to 6 routes.

Example of RIP in Action

Consider the following network model with Router A and Router B:

• Router A:
  • Copy

    172.16.10.1/24

  • Copy

    172.16.20.1/24

• Router B:
  • Copy

    172.16.20.2/24

  • Copy

    172.16.30.1/24

RIP Configuration Steps:

1. Enable RIP on both routers:

   • On Router A:

     Copy
     A(config)# router rip  
     A(config-router)# network 172.16.10.0  
     A(config-router)# network 172.16.20.0  
     

   • On Router B:

     Copy
     B(config)# router rip  
     B(config-router)# network 172.16.20.0  
     B(config-router)# network 172.16.30.0  
     

2. Verification:
   After configuring RIP, you can verify the routing table by using the command:

   Copy
   A# show ip route  
   B# show ip route  
   

   This will show the RIP-learned routes in the routing table, denoted by R.

3. Routing Decision:

   • If Router A needs to reach 172.16.30.0/24 (connected to Router B), it will use Router B’s interface
     Copy

     172.16.20.2/24

     to route the traffic.
   • If Router A cannot reach 172.16.30.0/24 via the primary path, RIP will provide an alternate route using the next available route with a higher hop count if needed.