I am upgrading my 2600 router with new 2800 router with the latest IOS image and trying to copy the configuration from the old router to new router. On the new router the command "IP CLASSLESS" is not seen instead there is the command "ip forward-protocol nd"
Is it the default behaviour in new IOS?
Jon is correct that ip classless is the default in current IOS. The behavior changed quite a long time ago. In old versions of IOS the default was no ip classless. Then Cisco changed the default and it became ip classless. For many versions of IOS the statement ip classless still appeared in the running config, even though it was the default behavior. Cisco did this to prevent confusion about what the behavior was. In current versions of IOS the statement no longer appears. I believe that Cisco now is confident that people will correctly understand that ip classless is the default behavior. The fact that the statement no longer appears does not reflect any change in the behavior.
Jon is also correct that ip forward-protocol nd is for an old Sun protocol. You do not need it. You did not put it in but it was put there by the particular version of IOS that you are now running. It is not anything that you should be concerned about.
The 2 commands are not related.
IP classless is used by the router to determine whether or not to forward packets for a unknown subnet of a major network.
The reason you are not seeing it in the configuration is because it is now the default so it won't appear. To verfiy you can type at config mode
2800(config)# no ip classless
then in your config you should see the line "no ip classless". Just make sure you put ip classless back on ie.
2800(config)# ip classless
IP forward-protocol is used by the router to determine which ports and protocols to forward when it receives broadcasts. ND in this case refers to old SUN workstations so i'm fairly sure you don't need this.