[nycbug-talk] Dynamic DNS MX Records

[Gordon Smith]

Disclaimer: "I've not done this sort of thing for email servers, but I have
used dynamic DNS for web servers" (I'm sure lots of BUGgers have).  

Assuming that your machine is already set up with a utility that updates DNS
when the ip address changes, one important factor to consider is the DNS TTL
setting.  The most conservative approach would be to dial down the TTL as
low as you can stand it, so that when your machine's ip address changes,
remote machines will be forced to make the chain of requests back to the
authoritative server.  As mentioned in the linked page below, "RFC 1912
cautions that 0 = no caching is not widely implemented so make no
assumptions."

Lower TTLs equals more authoritative requests, which equals higher DNS
serving costs - that's the balance that needs to be struck.

In the case of OptOnline, their dynamic ip addresses generally don't change
so long as your cable modem is always online.  I thought I heard that
Verizon may routinely change addresses every N days, but please check this
out - anyone with Verizon DSL, please comment.  Less ip address changes may
equate to a higher permissible TTL setting.  

So long as the TTL is less than most folks' SMTP servers' retransmission
expiration, you'll be ok.  You may receive email late upon an ip address
change, but the messages will still get to you.  I've seen a two day
retransmission expiration as common, but YMMV.

Some interesting background on TTL for MX records here:
http://www.zytrax.com/books/dns/apa/ttl.html

Let us know how it goes.

Cheers,
Gordon

-----Original Message-----
I am looking to use
Verizon's $14.95/month DSL, but I'm pretty sure they use dynamic
IPs and I will need to set up dynamic DNS entries.

What are people's thoughts and experiences on this?  Has anyone
lost mail due to this setup?  Are there alternatives?

-Ray-