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Gregory Feliciano
 
 
 

A single level of confusion for some CCNA and CCNP candidates is the distinction involving configuring a static default route and making use of the Cisco routing command ip default-network.

At initially glance, they appear to do the same point. Both configure a vacation destination to which packets should be routed if there is no much more precise route in the routing table.

The significant difference in between these two alternatives is that configuring a static default route only defines a default route for the router you happen to be configuring it on, while ip default-network will propagate the route by means of its routing protocol.

Let's analyze the routing tables of a hub-and-spoke network making use of the ip default-network command. R1 is the hub and R2 and R3 are the spokes. They are specifically linked through the network 172.12.123. /24, and each and every has a loopback with a 32-bit mask that are numbered according to the router amount (one.one.one.1, and so forth.) RIP is operating on all a few routers and the loopbacks are advertised.

R1 has another serial interface with the IP tackle 10.one.one.1 /24, and this network has been flagged as a default network with the command ip default-network 10... . It is not currently being advertised by RIP.

The routing protocol will then advertise this route. With RIP, the default network is marketed as ... . (With IGRP, it seems as the network amount, but is marked as an IGRP External route. ) This route has been designated a applicant default route on R1, as we see with the asterisk subsequent to the 10... /24 network (code table eliminated for brevity)

R1show ip route

Gateway of previous resort is not set

1.../32 is subnetted, 1 subnets
C 1.1.1.1 is specifically connected, Loopback0
R two.../eight 120/one via 172.twelve.123.two, 000011, Serial0
R three.../eight a hundred and twenty/one via 172.12.123.three, 000011, Serial0
172.twelve../sixteen is variably subnetted, two subnets, two masks
C 172.12.21./30 is right linked, BRI0
Do 172.12.123./24 is straight linked, Serial0
* 10.../24 is subnetted, one subnets
C ten.1.1. is immediately linked, Serial1

On R2 and R3, a default RIP route is now viewed (code tables again deleted)

R2show ip route
Gateway of last resort is 172.12.123.1 to network ...

R 1.../eight a hundred and twenty/1 through 172.twelve.123.one, 000000, Serial0.213
two.../32 is subnetted, one subnets
C 2.2.2.2 is straight connected, Loopback0
R 3.../eight one hundred twenty/2 through 172.12.123.1, 000000, Serial0.213
172.twelve../16 is variably subnetted, two subnets, two masks
Do 172.12.21./30 is straight related, BRI0
C 172.12.123./24 is right connected, Serial0.213
R* .../ one hundred twenty/one by means of 172.12.123.1, 000000, Serial0.213

R3show ip route
Gateway of previous resort is 172.12.123.one to network ...

R one.../8 a hundred and twenty/one by way of 172.12.123.1, 000027, Serial0.31
R 2.../8 one hundred twenty/2 through 172.12.123.1, 000028, Serial0.31
three.../32 is subnetted, one subnets
Do three.three.3.three is specifically connected, Loopback0
172.twelve../24 is subnetted, 1 subnets
Do 172.12.123. is specifically related, Serial0.31
R* .../ a hundred and twenty/one via 172.twelve.123.1, 000028, Serial0.31

And the default route works, considering that we can ping 10.one.one.1 from the two R2 and R3. Since they have no other match in their routing tables, they use the default route.

R2ping 10.one.1.1

Variety escape sequence to abort.
Sending five, a hundred-byte ICMP Echos to 10.1.1.1, timeout is 2 seconds
!!!!!
Achievement fee is a hundred percent (five/five), spherical-excursion min/avg/max 68/68/68 ms

R3ping 10.one.1.one

Sort escape sequence to abort.
Sending five, 100-byte ICMP Echos to ten.one.one.1, timeout is 2 seconds
!!!!!
Achievement rate is a hundred p.c (five/five), spherical-trip min/avg/max 68/68/68 ms

When determining no matter if to use a default static route or a default network, maintain in thoughts that if you want the routing protocol to propagate the default route, the ip default-network command will do that for you. But if you want only the local router to have the default route, a static IP route is the way to go.

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Gregory Feliciano

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