what is SIOCADDRT?
 

i perform these commands:
# /sbin/ifconfig lo 127.0.0.1
then
#/sbin/route add -net 127.0.0.0
it shows
SIOCADDRT: Invalid argument <==what is this?

I found this link on google.com/linux.

Are you using ipsec or something like that?

Remember, www.google.com/linux is your friend! :D

the message appears because that route is already set up for you.
Try:
# route -v

and you'll see your routes.
Normally you don't have to setup the routing for the loopback interface (lo); at least on modern Unix.
(wow... an SCO lawyer in my door... for I said Unix without paying the bill !)

Re: what is SIOCADDRT?
 

What kernel are you using? The reason why i'm asking is that linux kernels 2.2.XX do not need the route -net add command. Check with ifconfig if the route already exists.

i use 2.4.20-6 kernel.
another question, is it important to update to newest kernel?

Sometimes, it really depends on what you are doing with your machine. If it's a server it might somethimes be a good idea to keep it up-to-date. Also note that there's allways newly added support for hardware and minor bug fixes...

Then you don't need to add the the 127.0.0.0