Q: Can STUN be configured in one Cisco router with two serial lines?
A: Yes it is supported, but it is rarely done since most people use a modem eliminator for the task. Note the "direct" keyword at the end of the "stun route" commands. Also, note that "proxy polling" (or Local Acknowledgement in 9.1) won't run in these setups.
! stun peer 131.108.1.1 ! stun protocol-group 1 sdlc ! interface serial 0 888 This is the 3725 interface encapsulation stun stun group 1 stun route all interface serial 1 direct interface serial 1 888 This is the 3174 interface encapsulation stun stun group 1 stun route all interface serial 0 direct !