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New Member

'Carrier Dropped' modem state hung problem


We have Cisco 3660 (IOS 12.2(7)) as a dial-up router and a pool of different modems, including Zyxel U-336E Plus (1.0.8), Zyxel Omni Neo v.92, USRobotics Courier. Lines are configured like this:

line 85 86

no motd-banner

no exec-banner

no activation-character

modem InOut

modem autoconfigure type u336ep

no exec

transport preferred none

transport input all

escape-character NONE

autoselect ppp


stopbits 1

speed 57600

flowcontrol hardware

The problem occurs on every line, despite of type of modem attached. After some time of operation (very soon, indeed, within 2 or 3 calls to the line) we get following:

# s lin 86

Tty Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns Int

I 86 TTY 57600/57600 - inout - - - 238 571 0/4 -

Idle, Carrier Dropped

Line 86, Location: "", Type: ""

Length: 24 lines, Width: 80 columns

Baud rate (TX/RX) is 57600/57600, no parity, 1 stopbits, 8 databits

Status: No Exit Banner, CTS Raised

Capabilities: EXEC Suppressed, Hardware Flowcontrol In,

Hardware Flowcontrol Out, Modem Callout, Modem RI is CD,

Line usable as async interface, Hangup on Last Close, No login banner

Modem Autoconfigure, MOTD Banner Suppressed

Modem state: Carrier Dropped

Modem hardware state: CTS noDSR DTR RTS

Special Chars: Escape Hold Stop Start Disconnect Activation

none none - - none any

Timeouts: Idle EXEC Idle Session Modem Answer Session Dispatch

00:10:00 never none not set

Idle Session Disconnect Warning


Login-sequence User Response


Autoselect Initial Wait

not set

Modem type is u336ep.

Session limit is not set.

Time since activation: 00:08:14

Editing is enabled.

History is enabled, history size is 10.

DNS resolution in show commands is enabled

Full user help is disabled

Allowed input transports are pad v120 lapb-ta telnet rlogin.

Allowed output transports are pad v120 lapb-ta telnet rlogin.

Preferred transport is none.

No output characters are padded

No special data dispatching characters

Line remains in this state until 'modem InOut' command issued for this line, or router reloaded. Modem on the line answers normally and passes handshake, but the line protocol remains down.

Can anyone advise anything to fix this?

Thanks in advance


Re: 'Carrier Dropped' modem state hung problem

Since there has been no response to your post, it appears to be either too complex or too rare an issue for other forum members to assist you. If you don't get a suitable response to your post, you may wish to review our resources at the online Technical Assistance Center ( or speak with a TAC engineer. You can open a TAC case online at

If anyone else in the forum has some advice, please reply to this thread.

Thank you for posting.

New Member

'Carrier Dropped' modem state hung problem

For those who might have this problem in the future type clear line xx  or clear line aux 0 in my case.