what is IP classless? can u get away without using it?

[gman10]

hey guys,

how imperative is the use of IP classless? I noticed this statement on my router... furthermore, is "permanent" needed at the end of the 2 piece statement?

ip nat translation timeout 60
ip nat pool INTERNET 206.226.217.3 prefix-length 24
ip nat inside source list 10 pool INTERNET overload
ip classless
ip route 0.0.0.0 0.0.0.0 10.200.210.1
ip route 10.0.0.0 255.0.0.0 206.226.217.2 permanent
access-list 10 permit 10.0.0.0 0.255.255.255


thanks guys,

gman

 

[jimmyzz]

gman,
The ip classess command allows your router to support classless routing protocols.

Classfull protocols summarise their network to the traditional IP network class, ie: class A, B and C. For example, the network for 10.10.10.1 is 10.0.0.0 (class A)

Classless protocols allows you to define the network boundary through the use of Variable Length Subnet Masks (VLSM). For example, the 10.10.10.1/24 (mask 255.255.255.0) is 10.10.10.0

Classfull routing protocols include: RIP, IGRP
Classless routing protocols include: OSPF, EIGRP, RIPv2

IP classless is set by default, so its not a problem to leave it in your config as you may want to use VLSM. You can get a more in depth definition of classless Vs classfull on the cisco website or any technical reference.

JimmyZ

 

[gman10]

thanks JimmyZ,

So this is a default route parameter for the sake of talking? am I correct?

gman

 

[wybnormal]

for the sake of talking? Yeah.. if you want the routers to work properly. Unless you have a very small or unique network, in todays world virtually everyone runs classless IPs. What this means is that in the *old* days, you would send a route update of something like "I know about 66.0.0.0" and the mask was assumed to be 255.0.0.0. But, nowdays, it is "I know about 66.140.200.0 and my mask is 255.255.255.0 (/24)". This is classless.. you are using a class C mask with a class A address. Old protocols like RIP version 1 do not carry the mask information so you would lose that in the routing update. The router needs to know if its talking classful or classless.

The word "permanent" tells the router to remember the route even if the route goes down. Of course, if the route goes away, then there will be a problem since the router has no choice but to send the packets to a dead interface/route etc.

MikeS


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Sun Tzu

 

[gman10]

thanks, that detailed info u can chew on!!

GT