a question on EIGRP protocol

Yes EIGRP supports classless routing along with OSPF, ISIS and RIPv2.

Essential to supporting classless routing is that the subnet mask be carried in routing update messages.

actually somewhat better - in RIP even in v2 'network' command still uses classfull notation, which results in enabling updates on all interfaces that fall into major Class A, B or C network, while with EIGRP you can specify wildcard bits to limit routing updates only to those interfaces that really need it. While there is workaround for RIP with distribute-list and/or RADIUS 'Framed-Routing' attribute, it's still a bit clumsy. EIGRP is more clean, but unfortunately not widely supported beyond Cisco (not a problem if you just run only Cisco equipment, but there are many organizations/companies who don't).

Kind regards, iLya

Thanks for the replies.

That's the answer I wanted to hear :)