Using the ip default-network Command
RIP and EIGRP can inject absence routes by application the ip default-network command. To do so, the
following charge be accurate on the bounded router:
■ The bounded router charge configure the ip default-network net-number command, with netnumber
being a classful arrangement number.
■ The classful arrangement charge be in the bounded router’s IP acquisition table, via any means.
■ For EIGRP only, the classful arrangement charge be advertised by the bounded router into EIGRP, again
through any means.
■ This adjustment is not accurate by OSPF.
When application the ip default-network command, RIP and EIGRP alter in how they acquaint the
default. RIP advertises a avenue to 0.0.0.0/0, but EIGRP flags its avenue to the classful arrangement as a
candidate absence route. Because EIGRP flags these routes as candidates, EIGRP charge again also
be announcement those classful networks. However, because RIP does not banderole the classful network
as a applicant absence route, RIP does not absolutely accept to acquaint the classful network
referenced in the ip default-network command.
Example 10-10 shows the key aberration amid RIP and EIGRP with attention to the ip defaultnetwork
command. In this case, R1 will acquaint about classful arrangement 10.0.0.0 application EIGRP
due to the auto-summary command.
Static Absence Avenue with Avenue Redistribution
! EIGRP will acquaint classful arrangement 10.0.0.0/8 due to its arrangement command,
! analogous R1’s fa0/0 interface, and the auto-summary command. Also, R1 charge have
! a avenue to classful arrangement 10.0.0.0/8, in this case due to a changeless route.
! RIP will not acquaint classful arrangement 10.0.0.0/8, but it will still be able
! to inject a absence avenue based on the ip default-network command.
router eigrp 1
network 10.0.0.0
network 14.0.0.0
auto-summary
!
router rip
version 2
network 13.0.0.0
!
ip classless
ip default-network 10.0.0.0
ip avenue 10.0.0.0 255.0.0.0 10.1.1.102
! On R3, RIP learns a avenue to 0.0.0.0/0 as its default.
R3# appearance ip avenue rip
R* 0.0.0.0/0 [120/1] via 13.1.1.1, 00:00:19, Serial0/0/0.1
! On R4, agenda that EIGRP abstruse a avenue to 10.0.0.0/8, apparent with a * that
! flags the avenue as a applicant absence route.
R4# appearance ip route
! curve bare for brevity
ia - IS-IS inter area, * - applicant default, U - per-user changeless route
o - ODR, P - alternate downloaded changeless route
Gateway of aftermost resort is 14.1.1.1 to arrangement 10.0.0.0
D* 10.0.0.0/8 [90/2172416] via 14.1.1.1, 00:05:35, Serial0/0/0.1
14.0.0.0/24 is subnetted, 2 subnets
C 14.1.2.0 is anon connected, FastEthernet0/0
C 14.1.1.0 is anon connected, Serial0/0/0.1