IP default-network and static route configuration Statement Analysis

It should be said that the statement for configuring static routes is still very complicated. At the same time, we should pay special attention to some details during the configuration process. The difference between configuring static routes and using the Cisco command IP default-network is confusing for some people preparing to take the CCNA and CCNP exams. They are all the same in their first day. The result is to configure a destination so that the router knows where the package will be sent if no route is specified in the routing table.

The main difference between them is that configuring a static default route only defines a route for you to configure a static route, and ip default-network will be transmitted through the routing protocol used. Next, we will test the ip default-network command in the hub-and-spoke network of a star network. R1 is the center, R2 and R3 leaves. They are connected through the network 172.12.123.0/24, and each router is configured with a 32-bit LOOPBACK address 1.1.1.1/32 according to its router number, and so on ). The routing protocol uses the RIP Protocol, and the LOOPBACK address is broadcast in the network.

The static route configuration in R1 has a serial port with the address 10.1.1.1/24. This network is configured as a default network by using the command ip default-network 10.0.0.0. It has not been broadcast by RIP. Next, the routing protocol broadcasts this route. When RIP is used, the default network is broadcasted as 0.0.0.0. If IGRP is used, it displays the network number but is identified as an external route of IGRP ). This route is specified as a default route of R1, as we can see below.

 
 

  
  
R1 # show ip route
  
  
Gateway of last resort is not set
  
  
1.0.0.0/32 is subnetted, 1 subnets
  
  
C 1.1.1.1 is directly connected, Loopback0
  
  
R 2.0.0.0/8 [120/1] via 172.12.123.2, 00:00:11, Serial0
  
  
R 3.0.0.0/8 [120/1] via 172.12.123.3, 00:00:11, Serial0
  
  
172.12.0.0/16 is variably subnetted, 2 subnets, 2 masks
  
  
C 172.12.21.0/30 is directly connected, BRI0
  
  
C 172.12.123.0/24 is directly connected, Serial0
  
  
* 10.0.0.0/24 is subnetted, 1 subnets
  
  
C 10.1.1.0 is directly connected, Serial1
  
  
On R2 and R3, the default RIP route also appears:
  
  
R2 # show ip route
  
  
Gateway of last resort is 172.12.123.1 to network 0.0.0.0
  
  
R 1.0.0.0/8 [120/1] via 172.12.123.1, 00:00:00, Serial0.213
  
  
2.0.0.0/32 is subnetted, 1 subnets
  
  
C 2.2.2.2 is directly connected, Loopback0
  
  
R 3.0.0.0/8 [120/2] via 172.12.123.1, 00:00:00, Serial0.213
  
  
172.12.0.0/16 is variably subnetted, 2 subnets, 2 masks
  
  
C 172.12.21.0/30 is directly connected, BRI0
  
  
C 172.12.123.0/24 is directly connected, Serial0.213
  
  
R * 0.0.0.0/0 [120/1] via 172.12.123.1, 00:00:00, Serial0.213
  
  
R3 # show ip route
  
  
Gateway of last resort is 172.12.123.1 to network 0.0.0.0
  
  
R 1.0.0.0/8 [120/1] via 172.12.123.1, 00:00:27, Serial0.31
  
  
R 2.0.0.0/8 [120/2] via 172.12.123.1, 00:00:28, Serial0.31
  
  
3.0.0.0/32 is subnetted, 1 subnets
  
  
C 3.3.3.3 is directly connected, Loopback0
  
  
172.12.0.0/24 is subnetted, 1 subnets
  
  
C 172.12.123.0 is directly connected, Serial0.31
  
  
R * 0.0.0.0/0 [120/1] via 172.12.123.1, 00:00:28, Serial0.31