What is a "DNS lookup"?

[utkarsh]

Hi,

What is a "DNS lookup"?

I am going through some of the topics I discussed here in past and got a question on this one: viewtopic.php?p=19219#p19219

What does "DNS lookup" mean?

[zum13]

Hello.

There are IPv4 addresses which are four part dotted decimal (e.g. 10.6.33.96) and there are IPv6 addresses which are 128 bits long and in a colon-delimited hex format (e.g. 200185a3:0000:0000:8a2e7334). These are the addresses used by the machines connected to the network, but they are pretty unhelpful for us humans to use, so we have domain names which are rather more meaningful/readable (e.g. www.zmainframes.com).

In order to use a domain name needs it to be resolved to an IPv4 or IPv6 address so that the machines can communicate. A network of DNS servers contain the directory of addresses/names to enable this resolution process. A "DNS lookup" is the process of contacting your local DNS server to ask it to resolve the domain name into a network address. There are other types of lookup that can be requested from DNS, but address lookups are by far the most common.

[utkarsh]

Thanks zum13, this helps a lot. Understood.

How does this lookup for IPv4 and IPv6 applies to mainframes? Do they?

[Robert Sample]

DNS lookup applies EVERY time someone attempts to access the Internet via a name instead of an ip address. For a mainframe, TCPIP has a started task that runs from shortly after IPL until shortly before a shutdown. One of the configuration parameters specified for TCPIP is the name server(s) for the mainframe to use to resolve names into addresses. There can be multiple name servers provided for redundancy.

[utkarsh]

Thanks Robert. Never thought a DNS look-up could be required in mainframes too.