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classful and classless routing

hi,

could someone explain to me the functioning of classful and classless routing with this scenario:

router A's routing table contains subnets of 10.0.0.0 and a default route. a packet with destination IP address 192.1.1.1 arrives at its interface.

according to whether classful or classless routing is used, what happens to this packet?

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Hall of Fame Super Gold

Re: classful and classless routing

wassim

Given the scenario that you describe where the routing table has subnets of 10.0.0.0 and has a default route then the routing decision for a packet with destination 192.1.1.1 is exactly the same no matter whether it is classful routing or classless routing. In either case the router will forward using the default route.

The difference between classful and classless routing comes into play when you are making a routing decision for a subnet of a network where you have some subnets of the network in the routing table but do not have the particular subnet. So to follow your scenario assume that the routing table has routes for 10.1.1.0/24, 10.2.1.0/24, and 10.56.1.0/24 and you get a packet with destination address 10.99.2.6. In this case it makes a difference whether the router is operating classful or classless. If the router is operating classful then it drops the packet as destination unreachable. If the router is operating classless then it will forward the packet using the default route.

HTH

Rick

3 REPLIES
Hall of Fame Super Gold

Re: classful and classless routing

wassim

Given the scenario that you describe where the routing table has subnets of 10.0.0.0 and has a default route then the routing decision for a packet with destination 192.1.1.1 is exactly the same no matter whether it is classful routing or classless routing. In either case the router will forward using the default route.

The difference between classful and classless routing comes into play when you are making a routing decision for a subnet of a network where you have some subnets of the network in the routing table but do not have the particular subnet. So to follow your scenario assume that the routing table has routes for 10.1.1.0/24, 10.2.1.0/24, and 10.56.1.0/24 and you get a packet with destination address 10.99.2.6. In this case it makes a difference whether the router is operating classful or classless. If the router is operating classful then it drops the packet as destination unreachable. If the router is operating classless then it will forward the packet using the default route.

HTH

Rick

New Member

Re: classful and classless routing

thanks very much

New Member

Re: classful and classless routing

write the subnet mask. But...

One network 10.0.0.0 witch default subnet 255.0.0.0 no happen with the addressing classful all networks 10.a.b.c can be acessible.

If you use RIP:

network 10.0.0.0 will send gateway for 10.0.0.0.

On network 10.10.10.0 subnet mask 255.255.255.0 with classless:

if you use RIP for example:

send gateway for network 10.10.10.0

On this network and netmask with classful:

with RIP will send 10.0.0.0 for this same network and netmask.

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