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Full Discussion: Telnet vs netcat behavior
Top Forums UNIX for Advanced & Expert Users Telnet vs netcat behavior Post 302910336 by ckmehta on Wednesday 23rd of July 2014 04:27:22 PM
Old 07-23-2014
Telnet vs netcat behavior

Currently I run a number of network tests using netcat that checks for an open port on a remote IP-address, using this syntax:
Code:
netcat -v -w 5 -z 107.249.95.5 4488

For some reason, the netcat command above is hanging (although others work fine), but a telnet is showing a valid connection like below:
Code:
%  telnet 107.249.95.5 4488
Trying 107.249.95.5...
Connected to 107.249.95.5.
Escape character is '^]'.
^]

Normally with my other netcat tests, I see an immediate result like this:
aaaa.XXX.com [102.19.5.62] 22 (ssh) open
aaaa.XXX.com [102.19.5.62] 23 (telnet): Connection timed out

The only thing different/interesting about the 107.249.95.5 address is that it is over a VPN to an MQ server.

Any idea why this network test is failing, even though its obviously connectable over telnet. If it matters, I am running this on a Solaris 10 box.

Last edited by ckmehta; 07-23-2014 at 05:32 PM..
 

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TELNET-PROBE(1) 					      General Commands Manual						   TELNET-PROBE(1)

NAME
telnet-probe - lightweight telnet-like port probe SYNOPSIS
$PCP_BINADM_DIR/telnet-probe [-c] [-v] host port DESCRIPTION
telnet-probe allows the pmdashping(1) daemons to establish connections to arbitrary local and remote service-providing daemons so that response time and service availability information can be obtained. The required host and port number arguments have the same meaning as their telnet(1) equivalents. The -c option causes telnet-probe to perform a connect(2) only. This skips the read(2) and write(2) exercise that would otherwise be done after connecting (see below). The -v option causes telnet-probe to be verbose while operating. Once the telnet connection has been established, telnet-probe reads from stdin until end-of-file, and writes all the input data to the tel- net connection. Next, telnet-probe will read from the telnet connection until end-of-file, discarding whatever data it receives. Then telnet-probe exits. To operate successfully, the input passed via telnet-probe to the remote service must be sufficient to cause the remote service to close the connection when the last line of input has been processed, e.g. ending with ``quit'' when probing SMTP on port 25. By default telnet-probe will not produce any output, unless there is an error in which case a diagnostic message can be displayed (in ver- bose mode only) and the exit status will be non-zero indicating a failure. PCP ENVIRONMENT
Environment variables with the prefix PCP_ are used to parameterize the file and directory names used by PCP. On each installation, the file /etc/pcp.conf contains the local values for these variables. The $PCP_CONF variable may be used to specify an alternative configura- tion file, as described in pcp.conf(5). DIAGNOSTICS
If telnet-probe succeeds, then 0 will be returned. If the attempt to establish a connection fails or is terminated, then a non-zero exit status is returned. SEE ALSO
PCPintro(1), pmdashping(1), pmie(1), telnet(1), connect(2), read(2) and write(2). Performance Co-Pilot PCP TELNET-PROBE(1)
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