whois - Whois query works with telnet but not netcat

Question

I am trying to write an advanced whois client, so I have been experimenting with sending commands to whois servers using netcat (nc) in Arch Linux. For example, this works great:

$ echo domain google.com | nc whois.crsnic.net 43
# => nc outputs whois data for google.com

However, the whois server that handles suffixes like .br.com is whois.centralnic.net and that server seems to not work with netcat. When I give it any query, it seems to simply close the connection without a response:

$ echo foobar | nc whois.centralnic.net 43
# => No output from nc.

I successfully made the same query using telnet:

$ telnet whois.centralnic.net 43
Trying 193.105.170.136...
Connected to whois.centralnic.net.
Escape character is '^]'.
foobar
DOMAIN NOT FOUND
Connection closed by foreign host.

So what could possibly make a server behave differently for telnet than netcat?

I thought maybe it was a timing issue, so I unsuccessfully tried:

$ { sleep 4; echo foobar; sleep 4; } | nc whois.centralnic.net 43
# => No output from nc.

I saw that netcat has a -T option to make it behave more like telnet, so I unsuccessfully tried:

$ { sleep 4; echo foobar; sleep 4; } | nc -T whois.centralnic.net 43
# => No output from nc.

In my production system I will not be using netcat or telnet, but there seems to be some strange networking issue happening here and I would like to be aware of it. Can anyone shed some light on why netcat would work for all the whois servers but only telnet will work for whois.centralnic.net?

Answer 1

The service expects CRLF in its request, not just LF;

This works (on Ubuntu, there are multiple netcat versions, so can't speak for yours)

$ echo -e "foobar\r\n" | nc whois.centralnic.net 43
DOMAIN NOT FOUND