Preventing Vexation and Woe: DNS Fundamentals, Part 2 - Page 2
Receiving Delegations
No, this isn't a black-tie diplomatic event, sorry. This is the official term for registering your public name server so that the Internet can find it. You need to own a domain name and a static, routable IP. First get your DNS server installed, configured, and thoroughly tested, then register it using the FQDN of your nameserver and the IP address. This puts your name server into the Verisign Global Registry. Many domain name registrars, ISPs, and DNS service providers offer name server registration. Be sure to check with your ISP's hostmaster for possible conflicts. There's no need to register a private, internal name server.
RR
Resource records are the foundation of DNS; everything about a domain or a host is recorded in resource records. A (address) records are the most commonly queried RR. An A record maps a given hostname, which is called a label, to an IP address. An A record must point to a single address only. Multiple labels 7can be assigned to the same IP; just be sure to give each one its own line. Multiple IPs can also be given to the same label; again, each gets its own line. An increasing number of Web sites no longer require the 'www' prefix:
+www.foosite.com:1.2.3.4
+foosite.com:1.2.3.4
On the other hand, some admins forget the A record specifiying 'www'. In this case, Web surfers who do use the 'www' prefix get an error message and do not reach the site. This stuff ain't magic -- computers are completely literal and must be told exactly what to do.
Perhaps there are multiple servers for load balancing or round robin DNS:
+www.foosite.com:1.2.3.4
+foosite.com:1.2.3.4
+www.foosite.com:1.2.3.5
+foosite.com:1.2.3.5
CNAME
Canonical names are simply aliases pointing to A records:
+www.foosite.com:1.2.3.4
Cfoosite.com:www.foosite.com
A CNAME must point only to a hostname with a valid A record. The advantage is when you need to change the IP, only one record needs to be changed. The disadvantage is that it forces an extra query -- two hits to get to a CNAME instead of one for an A record. I prefer making more A records. Changing IPs should be a relatively rare occurence -- why create a performance hit for daily operations?
