Question on RIP v1 subnet mask
workfrom925
Member Posts: 196
in CCNA & CCENT
RIP v1 can only do classful routing. IP network 172.30.0.0 has its default subnet mask /16. Then how does a router figure out all subnets have a /24 mask?
R2#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
<snapped>
Gateway of last resort is not set
172.30.0.0/24 is subnetted, 3 subnets
R 172.30.1.0 [120/1] via 172.30.2.1, 00:00:14, Serial0/0/0
C 172.30.2.0 is directly connected, Serial0/0/0
C 172.30.3.0 is directly connected, FastEthernet0/0
192.168.4.0/30 is subnetted, 1 subnets
C 192.168.4.8 is directly connected, Serial0/0/1
R 192.168.5.0/24 [120/1] via 192.168.4.10, 00:00:13, Serial0/0/1
R2#
R2#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
<snapped>
Gateway of last resort is not set
172.30.0.0/24 is subnetted, 3 subnets
R 172.30.1.0 [120/1] via 172.30.2.1, 00:00:14, Serial0/0/0
C 172.30.2.0 is directly connected, Serial0/0/0
C 172.30.3.0 is directly connected, FastEthernet0/0
192.168.4.0/30 is subnetted, 1 subnets
C 192.168.4.8 is directly connected, Serial0/0/1
R 192.168.5.0/24 [120/1] via 192.168.4.10, 00:00:13, Serial0/0/1
R2#
Comments
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NetworkVeteran
Member Posts: 2,338 ■■■■■■■■□□
That's because classful routing and subnetting are entirely compatible. It knows 172.30.x.x has a /24 subnet mask because you configured one of the directly connected interfaces with the address 172.30.2.0/24.