Some DSL routers prevent NAT loopback. Security is sometimes cited as the reason. Is NAT loopback really a security issue? And if so, how is this exploited?
NAT loopback... where a machine on the LAN is able to access another machine on the LAN via the external IP address of the LAN/router (with port forwarding set up on the router to direct requests to the appropriate machine on the LAN). Without NAT loopback you must use the internal IP address of the device when on the LAN.
EDIT: The mentions of security are admittedly from unofficial sources, which is why I would like to clarify this...
From the BT Community Forums:
This is not a fault. Most routers will not send out and receive data on the same interface (Loopback), as this is a security risk.
And further down the same page, from the same user:
As a network engineer I work with Cisco and Brocade routers daily and these will not allow loopback due to the inherent security issues. BT have adopted an approach that security is very important and as with enterprise class routers, loopback is not permitted.
Many DSL routers/modems prevent loopback connections as a security feature.
To be honest, up until now I have always assumed that failure to support NAT loopback was simply a failure in the hardware/firmware, not a 'security feature'?! It's omission is a far greater problem IMHO. (If you hadn't guessed, my router does not support NAT loopback.)