HP3000/HP 3000 FAQ

Last Updated: Thursday, February 01, 2007 02:38 PM

Using Back-to-Back DTC ports to permit inbound telnet without a TAC on the HP3000

4.3.3. Using Back-to-Back DTC ports to permit inbound telnet without a TAC

JD

With OpenView DTC Manager, a DTC port can be configured as one of three types - terminal, printer, or host. If configured as a host port, the port can be accessed via telnet to the DTC's IP address at a specific TCP port number, as calculated by the following formula (taken from HPSL document N2X94121300C (http://support.mayfield.hp.com/kdb-bin/wwwsdoc.pl?DOCID=N2X94121300C)):

( ( ( 32 * dtc_board_number ) + dtc_port + 1 ) * 256 ) + 23

So, for example, for a DTC at IP address 199.8.123.123 to connect to port 2 on board 0 you would use "telnet 199.8.123.123 791".

Once this port is accessible via telnet, if it is cabled to another DTC port which is configured as a normal terminal, then the incoming telnet can be passed serially to a DTC> prompt, or if switching is not enabled, pass directly to the default destination for that port. If the destination is an MPE/iX system, then we have effectively translated from telnet to rs232 to AFCP, providing a means for a user with telnet but not NS/VT capability to access the MPE/iX system from the network, without a Telnet Access Card in the DTC.

Miscellaneous supplemental notes:

The cable connecting the two DTC ports does *not* need to be crossed (i.e. null-modem).

Recommend not using speed sensing on either port, but rather just set them both to 19200bps.

The serial link between DTC ports is the slowest link in the chain here, so even if the telnet user has a T1 line, they'll only get 19200bps throughput.

Only one telnet connection per port at a time. If a second user tries to connect, they'll appear to get connected but will not receive any prompts.

Some obvious security concerns are raised by this configuration. NS/VT provides a certain level of 'security by obscurity', while telnet access is more widely understood and available.

Disconnecting from the telnet session is not automatic. Upon logging off the session will be left at a new logon prompt. Most telnet clients use ^] to escape back to a telnet> prompt, from which a 'quit' command usually closes the connection.