Externip should be set to external ip
Localnet set to local network(check using ifconfig).
Sure
nat=comedia,rportforce_rport
(nat=yes not work in modern versions).
; nat = no ; Do no special NAT handling other than RFC3581
; nat = force_rport ; Pretend there was an rport parameter even if there wasn't
; nat = comedia ; Send media to the port Asterisk received it from regardless
; ; of where the SDP says to send it.
; nat = auto_force_rport ; Set the force_rport option if Asterisk detects NAT (default)
; nat = auto_comedia ; Set the comedia option if Asterisk detects NAT