Question

Telnet: connecting to IP Could not open connection to the host, on port 23: Connect failed

Asked by: DBBurnsIN

I have a remote SCO 5.05 server that has several netterminals accessing with telnet just fine. I also have a new router with firewall enabled. Port 23 is routing to the SCO server and a pcanywhere port routing to a workstation.

I can connect to the workstation fine with PCAnywhere but I cannot telnet to the server successfully from outside the local network.

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Asked On
2004-02-23 at 10:04:23ID20894931
Tags

open

,

connection

,

could

,

port

,

23

Topic

Unix Networking

Participating Experts
2
Points
125
Comments
20

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Answers

 

by: ahoffmannPosted on 2004-02-23 at 10:40:22ID: 10434387

> .. cannot .. from outside the local network
hmm most likely a firewall or routing problem
It's hard without additional information to identify the problem.
I'd first start with routing: can you please check this out
If routing works: is there a firewall inbetween?

 

by: DBBurnsINPosted on 2004-02-23 at 12:27:41ID: 10435284

I have a firwall in the router that has port 23 open and directed to the IP address of the SCO server
I also can ping the router IP address from outside.
I also have the PCAnywhere port open on the router directing to a workstation on the LAN that works fine from outside the network.
There are no other firewal components between the router and the server.

 

by: ahoffmannPosted on 2004-02-23 at 12:47:35ID: 10435462

what does /etc/hosts.* contain on SCO?
Best you start with tcpdump on SCO to see if the packets arrive.

 

by: DBBurnsINPosted on 2004-02-23 at 13:18:16ID: 10435748

127.0.0.1            localhost
192.168.144.1     router
192.168.144.200 delmar
192.168.144.201 deb-om
192.168.144.202 netterm1
192.168.144.203 winstation1
192.168.144.230 mactol

I cannot find tcpdump on the sco box?

 

by: DBBurnsINPosted on 2004-02-23 at 13:26:28ID: 10435830

I did enable the logging on the router and it shows that telnet is being routed from my ip address.

 

by: ahoffmannPosted on 2004-02-23 at 14:50:22ID: 10436544

are the names listed in yur /etc/hosts those machines which connect fine with telnet?
If so, can you reverse lookup on SCO the hosts trying to connect?
Are there any messages logged (/var/log/messages not shure for SCO)

 

by: DBBurnsINPosted on 2004-02-24 at 05:07:29ID: 10440354

yes the names in the hosts file do work with the exception of router which I added as an attempt to get telnet to work.

the only thing listed in the /var/adm/messages is the boot information.

 

by: gheistPosted on 2004-02-24 at 22:40:52ID: 10448142

TCP connections are bidirectional, so you need to route in both directions.
SSH is more secure over public internet

 

by: DBBurnsINPosted on 2004-02-25 at 03:16:52ID: 10449317

Port 23 is on the router is set for both TCP an UDP so I believe that takes care of that issue.

 

by: gheistPosted on 2004-02-25 at 07:02:47ID: 10450924

Are NAT or Packet Filters or IP Chains or Firewalls involved???

 

by: DBBurnsINPosted on 2004-02-25 at 14:50:03ID: 10455031

Only the firewall in the router

 

by: ahoffmannPosted on 2004-02-26 at 00:34:26ID: 10458207

please answer all question asked so far.
1. can you reverse lookup on SCO the hosts trying to connect?
2. TCP connections are bidirectional, so you need to route in both directions.
   is your firewall open in *both* directions (TCP)?
3.  Are NAT or Packet Filters or IP Chains [snipped] involved???

Also: are all names listed in /etc/hosts which try to connect?
  (is a variation of 1. see above)

 

by: DBBurnsINPosted on 2004-02-26 at 04:06:00ID: 10459371

1: It appears that no logging to the syslog, utmp, utmpx, wtmp, wtmpx is occuring when an attempt to telnet from the outside happens.

2: I do not have the option to specify the direction in the router port settings. So I can only assume that opening the port opens it in both directions.

3: The router uses NAT to redirect the packets.

All names are listed in the /etc/hosts I added the IP addresses found in the router logs for the telnet entries but it did not help.

The incomming logs in the router show the PCAnywhere and the Telnet attempts. The PCAnywhere are successful but the Telnet are not.
Since there are no log updates happening on the sco box during these attempts the telnet attemps must not be getting through the router.

 

by: ahoffmannPosted on 2004-02-26 at 04:45:04ID: 10459617

> Since there are no log updates happening on the sco box during these attempts the telnet attemps must not be getting through the router.
hmm, does this statement not proof that it is a router, and not SCO, problem?

But again:
 you did not answer my first question: does nslookup work or not?

 

by: DBBurnsINPosted on 2004-02-26 at 07:19:22ID: 10460838

Running nslookup only returns the local host information. I have never used nslookup before so I may be doing it wrong. What should I be looking for as a return. and what arguments should I be using?

 

by: ahoffmannPosted on 2004-02-27 at 02:16:34ID: 10467924

assuming the name of the remote host trying to connect to SCO is: host.remote.tld
then try following:

  nslookup host.remote.tld

if it does not return a IP, then your DNS failed to resolv the name/IP mapping. This may have various reasons.
If nslookup fails, try to add that name with the proper IP in /etc/hosts and try telnet again.

 

by: ahoffmannPosted on 2005-02-01 at 01:03:42ID: 13190805

what's the reason for the refund?

20120131-EE-VQP-002

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