panel 1:

In an internal network (like in a company or school), sometimes you can connect to a machine by just typing its name, like this:

$ ping labcomputer-23

Let’s talk about how that works!

many DNS lookup functions support “local” domain names

browser, represented by a box with a smiley face: where’s lab23?
function, represented by a rectangle with squiggly lines: where’s lab23.degrassi.ca?
arrow pointing to resolver (server) represented by a box with a smiley face holding a magnifying glass

(the function appends a base domain degrassi.ca to the end)

the base domain is called a “search domain”

On Linux, search domains are configured in /etc/resolv.conf

Example: search degrassi.ca this tells getaddrinfo to turn lab23 into lab23.degrassi.ca

getaddrinfo doesn’t always use search domains

It uses an option called ndots to decide.

search degrassi.ca 
options ndots:5

this means “only use search domains if the domain name contains less than 5 dots”

search domains can make DNS queries slower

browser: where’s jvns.ca?
getaddrinfo, represented by a rectangle with squiggly lines: okay, first I’ll try jvns.ca.degrassi.ca

this is silly but it can happen!

avoid search domains by putting a “.” at the end

Use http://jvns.ca. instead of http://jvns.ca

Illustration of a smiling stick figure with curly hair.

person: “local” domain names like this mostly exist inside of big institutions like universities