Two A records in different zones

[Mathias Körber]

> Can I have two A records pointing to the same IP in different=20
> zones? Should
> I even have records pointing to each other in different zones? We have =
a
> domain which is being converted from a subdomain in our edu zone=20
> to a .com.
> Example:
> prometheus.gwu.edu
> prometheus.com
>=20
> I have a host, hephaestos.prometheus.gwu.edu which is also=20
> prometheus.com. I
> guess I have to make prometheus.com the A and hephaestos the CNAME. Or
> should I make A records in each zone? But which one gets the pointer
> record?!

Sure you do this (in several different ways).
Whether you use two seperate A records or one A and a CNAME depends on a =
few
factors, but is basically your choice:

a) If the new domain is prometheus.com, and this is also the hostname, =
you cannot
use a CNAME for it, as you will have to also put SOA, NS records for =
prometheus.com,
and having any other record with the same owner (here: prometheus.com) =
is illegal.

b) If either of the two hostnames (hephaestos.prometheus.gwu.edu and =
prometheus.com) is
also uses as target for NS or MX records (ie either acts as nameserver =
or receiving mailserver
without having a separate name for that function), you cannot use a =
CNAME as MX and NS records
may not point to names which own CNAMES instead of Address records.

c) Whether you are the administrator of both zones may influence the =
decision. A CNAME might
make changes easier, as you need only change the IP address of the host =
in one zone and
the other will just reference it. However, if the name in the referenced =
zone changes, you will
have to update the CNAME record. This could be an issue if the two zones =
are not administered
by the same people. I personally prefer A records for most things, so I =
don't have to
remember whether a name is referenced by a foreign CNAME if I change =
names etc.
So you see, CNAMES can buy you less admin work when IP addresses change, =
but could as easily
add admin work when changing names etc.

d) Which of the names the PTR record should point to is again a choice =
issue. Usually the name
pointed to is the 'canonical' name, ie the name the machine knows itself =
under (hostname).
Usually this is the name it identifies itself with when accepting or =
making connections (such
as an SMTP 220 message etc). This does tend to get more difficult these =
days when sendmail (and
other programs) can use different names on different interfaces or =
depending on who
is conncting etc, but you get the idea.

HTH HAND