At 08:41 PM 09/24/2000 -0500, Yee, Jason wrote:
>With this command if a route is not found in the routing table it will take
>the gateway of last resort if it is set .
>
>Without this command it will just drop the packet if a classful route is not
>found in the routing table.
>
>Jason
>
Without the IP classless command a router sees routes as classful
So lets say you on your router you have a serial interface with the address
10.0.0.1 /30
and an ethernet with the address 220.110.60.1
and a default route pointing out the serial interface
Without the ip classless command
if someone on the 220.110.60 network is trying to reach 10.10.10.10 (which
does not fall within the 10.0.0.0 /30 network)
then the router would see that it had a piece of the 10 net on it and
assume it should be able to access the whole 10 net, but actually only
knowing a route to 10.0.0.0 /30 it would drop the packet
If you were trying to reach 11.0.0.1 if would forward the packet out the
serial as per the default route because it doesn't already know a route to
a piece of that class A.
With ip classless in place traffic is routed based on its stated network
address, AKA CIDR.
ip classless is the way to go! Without it you're generally asking for
trouble, especially if your ISP uses any class A or B address space.
also if you plan on using the zero net of any classfull address then you'll
also need the command
ip subnet-zero
my $.02
Tom Pruneau
Trainer Network Operations
GENUITY
3 Van de Graff Drive Burlington Ma. 01803
24 Hr. Network Operations Center 800-436-8489
If you need to get a hold of me my hours are 7AM-3PM ET Mon-Fri
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