GRE port

It's mainly used with Cisco VPN's. Generic Routing Encapsulation "Computer security." — Oxymoron

Supposed to be easier to configure, less firewall issues, and less overhead than a higher security tunnel. Also for some legacy issues. I read it wrong and answer it wrong too. So get off my case you peanut.

thnank you for ur information, but as far as i concern is that GRE is used by default with PPTP (port # 1723), so if we open this port 1723 we also have to open gre port? if yes than what is the GRE port? Thank you

GRE is a type of tunnel or VPN. It makes the internet act as if it wasn't there. The two computers between the end points of a GRE act as if only a lan cable is between them. (simple terms) See also here. http://articles.techrepublic.com.co... and here if you do have Cisco routers at each end. http://www.cisco.com/warp/public/70... I read it wrong and answer it wrong too. So get off my case you peanut.

GRE has a protocol number on IP not a port. It's protocol # is 47. THANKS.

rais is correct. GRE is a protocol. Your router needs to enable PPTP/GRE pass through.