On Thu, May 03, 2001 at 05:32:52PM -0500, Aaron Goldblatt wrote:
> If you use mail.whatever.com in your MX record, you have only to update
> your A record, which makes it less likely that in the event of a renumber,
> you'll screw it up and cut off mail service for a week. The down side is
> that this approach must, of necessity, produces another lookup for the A
> record, which produces additional load on your name servers and network to
> carry the UDP traffic.
In most cases, no. With some minor quibbles, as long as the nameserver
is authoritative for your domain (which it had better be!) and both
records (the MX and the A) are known to the nameserver, the nameserver
will provide the A record as glue when the MX is requested.
Using djbdns, here is a query for mx records for my domain, catseye.net:
$ dnsq mx catseye.net ns1.catseye.net
15 catseye.net:
152 bytes, 1+2+2+2 records, response, authoritative, noerror
query: 15 catseye.net
answer: catseye.net 86400 MX 10 mail.catseye.net
answer: catseye.net 86400 MX 20 mail.whatwerks.com
authority: catseye.net 172800 NS ns1.catseye.net
authority: catseye.net 172800 NS ns1.whatwerks.com
additional: mail.catseye.net 86400 A 64.34.131.193
additional: ns1.catseye.net 86400 A 64.34.131.193
See the "additional" records? That all came back in one query and, since
I'm authoritative, the dns resolver library can trust the glue, which
means you don't need a second query. Note that I'm *not* authoritative
for my backup, whatwerks.com, so the nameserver didn't provide glue
for mail.whatwerks.com.
Tim
--
* * * | 1) It's SLOW! --> "man tcpserver" - especially -R,-H,-l
qmail | 2) Roaming users --> http://www.lifewithqmail.org/lwq.html#relaying
FAQS | 3) Secondary MX --> list in rcpthosts, NOT in locals/virtualdomains
* * * | 4) Discard mail --> "#" line ONLY, in appropriate .qmail file
