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Reverse Telnet does block modem

Hi!

We use a Cisco 2811 with an PRI ISDN card to provide dial-out modems.

What we want to do now:

We try to use the reverse telnet feature to dial out with pppd from Linux. Dialing out and connecting our third party works fine BUT: when the PPP-session is disconnected the Cisco router still shows the modem as in use. And after 30 dial out attempts the router tells us: No more modems

How can I release this modems?

This looks like this when I issue the who command:

C2811-FABL-T#who
    Line       User       Host(s)              Idle       Location
  tty 0/322               Async interface      00:00:00  
  tty 0/323               Async interface      00:00:03  
  tty 0/324               Async interface      00:00:07  
  tty 0/325               Async interface      00:00:06  
  tty 0/326               Async interface      00:00:00  
  tty 0/327               Async interface      00:00:01  
  tty 0/328               Async interface      00:00:01  
  tty 0/329               Async interface      00:00:08  
  tty 0/330               Async interface      00:00:01  
  tty 0/331               Async interface      00:00:01  
  tty 0/332               Async interface      00:00:10  
  tty 0/333               Async interface      00:00:01  
  tty 0/334               Async interface      00:00:03  
  tty 0/335               Async interface      00:00:10  
  tty 0/336               Async interface      00:00:07  
  tty 0/337               Async interface      00:00:01  
  tty 0/338               Async interface      00:00:10  
  tty 0/339               Async interface      00:00:09  
  tty 0/340               Async interface      00:00:01  
  tty 0/341               Async interface      00:00:01  
  tty 0/342               Async interface      00:00:03  
*514 vty 0     tsea       idle                 00:00:00 10.113.1.65

  Interface    User               Mode         Idle     Peer Address

The config we use:

line 0/322 0/357
modem DTR-active
rotary 1
no exec
transport preferred telnet
transport input all

The command to connect with ppp looks like this:

/usr/sbin/pppd debug linkname 3xocL9f7HO connect "/usr/sbin/chat -T <telnr> -f connect.chat -v" disconnect "/usr/sbin/chat -f disconnect.chat -v" pty "/usr/bin/nc <router IP> 5001" user <username> password <password> 172.28.0.2:172.28.1.2

connect.chat:

ABORT BUSY
ABORT ERROR
ABORT 'NO CARRIER'
ABORT 'No Modems Available'
TIMEOUT 10
name: <Router username>
TIMEOUT 5
word: <Router password>
''    ATZ
TIMEOUT 5
OK    ATDT\T
TIMEOUT 60
CONNECT \c

disconnect.chat:

'' +++\d\dATH
TIMEOUT 5
OK   ATZ
TIMEOUT 5
OK   ^U

Sorry if I miss some important information here. I am no Cisco admin.

CU

Thomas

Everyone's tags (4)
1 REPLY
Cisco Employee

Re: Reverse Telnet does block modem

Either the Linux device needs to cleanly disconnect the TCP session or you need to set up modem control on the lines so that a disconnect on the modem forces down the TCP connection.

What you want is

line 0/322 0/357

modem inout

Provided that the modem will drop DCD between calls (the default setting for most modems) this will ensure that the TCP session is dropped.

This section will be useful to understand the different modem control configurations

http://www.cisco.com/en/US/docs/ios/12_2/dial/configuration/guide/dafstate_ps1835_TSD_Products_Configuration_Guide_Chapter.html

"debug modem" is also helfpul to monitor line states.

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