Telnet returns Name or service not known

Question

I'm trying to telnet from Centos 7 to Centos 6.8 on port 1521:

#telnet 192.168.1.100 1521

And I get the following error

telnet: 192.168.1.100:1521: Name or service not known 192.168.1.100:1521: Unknown host

Firewall is disable on both machines. Selinux is disabled on both machines. Ping is working fine on both machines.

Solution

On a RHEL7 system, typing telnet 192.168.1.100:1521 results in exactly your error message:

telnet: 192.168.1.100:1521: Name or service not known
192.168.1.100:1521: Unknown host

... so it seems likely to me that there was an accidental copy/paste of the command with a colon instead of a space:

telnet 192.168.1.100 1521

Tested with:

rpm -qf $(type -p telnet)
telnet-0.17-64.el7.x86_64

Comments

[Bodo]

Are you sure you typed telnet 192.168.1.100 1521 (correct)? Or did you type telnet 192.168.1.100:1521 (wrong)?

[Ali Golestan]

as you see in the question i typed telnet 192.168.1.100 1521

[Bodo]

I asked because I get a similar error message when I use a colon : between IP address and port number instead of whitespace. Your error message means that telnet was not able to resolve a host name 192.168.1.100:1521 which apparently is the combination of an IP address and a port number. If you really separated IP address and port number with space: Do you have an alias or function named telnet?

[Philip Couling]

On Debian telnet separates host and port in an error message with a / eg: telnet: could not resolve example.com/1521: Name or service not known. So if you really did call telnet 192.168.1.100 1521 then what version of telnet are you using and on what operating system.

[Арсений Черенков]

1) I see no reason to DV, 2) I don't have centos available, but in redhat that looks like correct syntax. 3) what is the result of whereis telnet and alias telnet ?