Who is WHOIS?

I am using the WHOIS client a lot these days since I am migrating some RIPE objects such as ASes, inetnum/inet6num, etc. Meanwhile, I recognized that I have never captured this TCP port 43 protocol, nor looked at it with Wireshark. That’s what this post is all about, incl. a downloadable pcap for your own analysis.

For this trace, I basically queried a couple of different names which resulted in a couple of different WHOIS queries to *some* destinations. To be honest, I don’t know exactly which destinations are chosen, but this seems to be correct. ;) Citing the manpage of whois: “the whois client tries to guess the right server to ask for the specified object”. If you are interested in more details of the tool itself, please have a look at:

Basically, WHOIS is a telnet-like TCP protocol running at port 43. Single query – single response. It is not encrypted at all but in plain text. Since all queried information is public anyway, that’s not a big deal. (However, a passive attacker can record which queries you’re sending.)

Download the pcap, 7zipped, 21 KB. I left all those surrounding DNS and ICMP packets in there intentionally:

Wireshark screenshots:

Demo Requests

These are the queries you’ll find in the trace. Besides querying the keywords that the server supports, I asked for some domains of different TLDs (which failed for *.blog), IPv4 and IPv6 networks, an ASN, a RIPE handle (which worked with the -a option) and a full name (which is quite common in German and hence lists many different persons):

Here is the full listing with all answeres: (Grr, for whatever reason after each line starting with a %, the listing plugin adds a newline. Sorry.)

Real World Use Case: traceroute -A

One major, but probably unknown, use case of WHOIS is the traceroute tool when performed with the -A option to perform AS path lookups in routing registries. It then does not only issue IP packets with increased hop limits (and printing the ICMP hop limit exceeded error messages) but also sends WHOIS queries along with DNS PTR requests.

Two demo runs in the trace:

That’s it. God bless!

Featured image “Who” by Adrian Scottow is licensed under CC BY-SA 2.0.

2 thoughts on “Who is WHOIS?

Leave a Reply

Your email address will not be published. Required fields are marked *