Experimental analysis of classless and classful of router working mode

Experimental purposes:

The ability to support subnets is called classless, and this pattern can be well coordinated with subnets.

If subnets are not supported, they are called classful.

When a router is working at classful, if a partial subnet in one of the main class networks is known, packets from all other unknown subnets will be discarded, even if there is a default route and will not be forwarded in the default route, and the packets from other main class networks will be forwarded normally.

Experiment topology:

Configuration:

R1:

Interface Loopback10
IP address 10.1.1.1 255.255.255.0
!
Interface fastethernet0/0
IP address 12.1.1.1 255.255.255.0

R2:

Interface fastethernet0/0
IP address 12.1.1.2 255.255.255.0

!
Interface FASTETHERNET0/1
IP address 23.1.1.2 255.255.255.0
!
IP Route 0.0.0.0 0.0.0.0 23.1.1.3
IP Route 10.1.1.0 255.255.255.0 12.1.1.1

R3:

Interface Loopback10
IP address 10.1.2.1 255.255.255.0
!
Interface Loopback20
IP address 20.1.1.1 255.255.255.0
!
Interface FASTETHERNET0/1
IP address 23.1.1.3 255.255.255.0
!
IP Route 0.0.0.0 0.0.0.0 23.1.1.2

Description

R1,R2, R3 all turn on debug IP ICMP and R2 shutdown CEF (no IP CEF)

Analysis:

In classless mode

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