Cisco Back to Back Line AUX Ports

This is example back to back through line AUX ports on Cisco router.

# config

ROUTER-A#

interface Async1
 description Connected to ROUTER-B
 ip address 172.16.4.1 255.255.255.0
 encapsulation ppp
 async dynamic routing
 async mode dedicated
!
line aux 0
 modem InOut
 transport input all
 flowcontrol hardware

ROUTER-B#

interface Async65
 description Connected to ROUTER-A
 ip address 172.16.4.3 255.255.255.0
 encapsulation ppp
 async dynamic routing
 async mode dedicated
!
line aux 0
 modem InOut
 transport input all
 flowcontrol hardware

# verify

ROUTER-A#

show async status 
Async protocol statistics:

       Int           Local          Remote Qd     InPack     OutPac Inerr  Drops  MTU
*        1      172.16.4.1      172.16.4.3  0       6189       6389     0      0 1500


  Rcvd: 6189 packets, 316489 bytes
        0 format errors, 0 checksum errors, 0 overrun
  Sent: 6389 packets, 325431 bytes, 0 dropped

How to determine interface async value 1, 65 or other, look at this

ROUTER-A

show line 
   Tty Typ     Tx/Rx    A Modem  Roty AccO AccI   Uses   Noise  Overruns   Int
*    0 CTY              -    -      -    -    -      0       0     4/121606218   -
A    1 AUX   9600/9600  - inout     -    -    -      1    2501     0/0       -
     2 VTY              -    -      -    -    -      0       0     0/0       -
     3 VTY              -    -      -    -    -      0       0     0/0       -
     4 VTY              -    -      -    -    -      0       0     0/0       -
     5 VTY              -    -      -    -    -      0       0     0/0       -
     6 VTY              -    -      -    -    -      0       0     0/0       -

ROUTER-B

show line 
   Tty Typ     Tx/Rx    A Modem  Roty AccO AccI   Uses   Noise  Overruns   Int
*    0 CTY              -    -      -    -    -      0      33     2/40237371   -
A   65 AUX   9600/9600  - inout     -    -    -     22       0     0/35770   -
    66 VTY              -    -      -    -    -      0       0     0/0       -
    67 VTY              -    -      -    -    -      0       0     0/0       -
    68 VTY              -    -      -    -    -      0       0     0/0       -
    69 VTY              -    -      -    -    -      0       0     0/0       -
    70 VTY              -    -      -    -    -      0       0     0/0       -