4 ms·
Minor side bit here, > The number should preferably be in the range 1-255 so that it can be used in the WKS field in name servers. Well-known service (WKS) re
by mjn 9y ago
Minor side bit here,
> The number should preferably be in the range 1-255 so that
it can be used in the WKS field in name servers.
Well-known service (WKS) records let hosts advertise in DNS which services a given machine made available, by listing which of the assigned port numbers were open for TCP or UDP connections. This never really caught on, as few people used them, even fewer kept them up to date, and checking WKS provided very little real benefit over just attempting a connection.
They had been deprecated already in 1989 through RFC 1123 [1], but it seems that by the mid-1990s at least some people still considered them relevant.
[1] "An application SHOULD NOT rely on the ability to locate a WKS record containing an accurate listing of all services at a particular host address, since the WKS RR type is not often used by Internet sites. To confirm that a service is present, simply attempt to use it." https://www.ietf.org/rfc/rfc1123.txt https://www.ietf.org/rfc/rfc1123.txt
- nodesocket 9y agoThanks, I was curious what WKS was.
- derefr 9y agoHow similar/different is WKS to the modern SRV record?
- Crespyl 9y agoIIUC, WKS was basically just a list of ports you could expect to be open on a host, while SRV allows you to indicate a separate server to handle a given service. Wikipedia[0] has the example of a SIP telephony server, `example.com` sets a SRV record that redirects interested clients to `sipserver.example.com`. [0]https://en.wikipedia.org/wiki/SRV_record https://en.wikipedia.org/wiki/SRV_record
- mjn 9y agoYeah, there's no pointing to other hosts in WKS, just information on the host itself. I believe it come out of ideas about service discovery in the early days of the internet, when you might know of 100 other hosts, but not know which ones ran SMTP, FTP, etc. The WKS records would let you get a map of the net's services by doing a bunch of DNS lookups instead of having to portscan everyone. SRV records are more like an MX record generalized to arbitrary services, allowing a domain to point to the hosts that provides various services for that domain.