[Day 6] 7. Static and Default Routing

Static Routing

Static routing involves manually specifying routes in the routing table.

• Command:

  Copy
  A(config)# ip route <Destination Network> <Subnet Mask> <Next Hop Address>  
  

• Example:

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  A(config)# ip route 172.16.30.0 255.255.255.0 172.16.20.2  
  B(config)# ip route 172.16.10.0 255.255.255.0 172.16.20.1  
  

• Explanation:

  • 172.16.30.0: Destination network.
  • 255.255.255.0: Subnet mask for the destination network.
  • 172.16.20.2: Next-hop IP address (IP address of the next router).

Important Commands

Use these after you specify the static routes:

• Save Configuration:

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  A# copy run start  
  

  This saves the running configuration to the startup configuration.

• Display Routing Table:

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  A# show ip route  
  

  This command displays the router's IP routing table, listing all known networks and the paths to reach them.

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Default Route

A default route is used when no other route is available for a destination network. It is often used for routing traffic to the internet or other external networks.

• Command:

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  A(config)# ip route 0.0.0.0 0.0.0.0 <Next Hop Address>  
  

• Example:

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  A(config)# ip route 0.0.0.0 0.0.0.0 172.16.20.2  
  

  This tells the router to send all traffic destined for any network not explicitly listed in the routing table to the next-hop IP address.

Combining Routes

• Specific Routes are considered first.
• Default Routes are used if no specific route matches.

Example:

Copy
A(config)# ip route 172.16.10.0 255.255.255.0 172.16.20.1  (Specific Route)  
A(config)# ip route 0.0.0.0 0.0.0.0 172.16.40.2         (Default Route)  

Steps for Basic Router Configuration

1. Copy

   Router(config)#hostname A

   (Provide hostname for the router)
2. Copy

   A(config)#enable secret (password)

3. Copy

   A(config)#line con 0 / aux 0 / vty 0 4

4. Copy

   A(config)#password (password)

5. Copy

   A(config)#login

6. Copy

   A(config)#exit

7. Copy

   A(config)#interface (id like g0/0)

8. Copy

   A(config)#no shut

9. Copy

   A(config)#ip address (ip) (subnet mask)

10. Copy

    A(config)#ip route (destination network) (subnet mask) (next-hop-address)

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Exit Interface

The exit interface refers to the network interface on a router used to forward packets towards their destination. It specifies the physical or virtual interface used for outbound traffic.

• Routing Table Example:

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  10.1.1.0/24 [90/30720] via 192.168.1.1, 00:00:10, FastEthernet0/1  
  

  • 10.1.1.0/24: Destination network.
  • via 192.168.1.1: Next-hop IP address.
  • FastEthernet0/1: Exit interface.

  In this example, packets destined for 10.1.1.0/24 are forwarded out of the FastEthernet0/1 interface to reach the next-hop IP address 192.168.1.1.

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Drawbacks

• Multi-Access Network Scenario:
  If the next network has multiple exit points, the exit interface may not always work effectively.
• Solution:
  The best solution is to use the next-hop address rather than relying on the exit interface in such scenarios.

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