could anyone of you explain me the difference? Is it simply that for first Ethernet authentication like CHAP, PAP and so on, don't apply? Or what?
My point of view is limited only to 831's model where for 12.4 IOS version Cisco explicitly tells the 2nd Ethernet port is not usable for WAN operations.
But know I must decide which module to buy for a 3640 that needs a 2nd Ethernet port that must be connected to a 350 bridge connected to a 4Mbits/s wireless connection. Do I need a WAN module for3640 or not?