Can Mail Servers Work With Dynamic IPs?

rpandya asks: "I'm considered switching from DSL to Sprint ION but they don't yet provide static IPs. Now I think I should register my domain with granitecanyon.com and dyndns.org, and host my own mail & Web service, instead. I'm switching my main home server from NT to Linux, and it's already behind a SonicWall firewall with NAT, so it's pretty reliable and secure. However, I'm concerned that the dynamic IP issues might cause some hiccups in mail service. I'd be interested in hearing if anyone else has tried something like this, or has any thoughts on how well it would work."

Comments

What happens to your old IP, though?

[Anonymous Coward]

I've been looking at this setup for a couple of weeks, but there *is* a snag. Setting myhost.mine.nu as primary MX (with secondary MX spooling when I'm offline) is fine, until you go offline, and the next guy on your old IP recieves your mail. I've tried setting dns to a private IP before I go offline, but usually this fails (rapid DNS updates are interpreted as abuse by many freeDNS services). Stumped as a stumpy thing. Time to bone up on fetchmail multidrop....

Re:What happens to your old IP, though?

[rcgreenw]

You bring up some good points. My machine is hardly ever off-line, it reconnects whenever is gets disconnected. Quite often, I keep the same IP for weeks at a time. I have my TTL set to an hour, so caching is less of a problem. I can update my primary DNS as often as I want, and dyndns.org only locks you out if you update with the same IP (they don't want the extra load). All in all, I'm very happy with my setup. My biggest problem is all the e-mail that my system has to bounce because everyone uses bogus addresses at my domain when they fill in forms that require e-mail addresses ;)
--Rich

Spam filtering

[Cris]

It is very relevant for you to consider SPAM. A lot of mail servers refuse to accept mail from dynamic ips because of the fact that they are often the source of bulk emailers. This isn't true of all, or most, mail servers, but it is true of a pretty notable chunk of them and therefore I would not want to be in such a situation. Instead, I'd personally buy an account with some web hosting company where you have a couple POP accounts for mail, maybe even web. For low traffic, it's cheap and it's temporary anyway, probably more sanity-preserving than dealing with a dynamic situation.

Re:Spam filtering

[garver]

The other way to handle this is set your mail server up to always relay through your ISP/DSL provider. To the ISP, your mail server will be like any other customer and the message will be sent on to its destination by the ISP's server which has a static IP and is trusted.

Still, what's the point? There are hosting companies that will do it for free, if you want to put up with some advertising... Then again, I do a lot of things that are pointless, just because I can...

Re:I do just that

[earlytime]

Speaking of RR, I've been having lots of problems with my roadrunner lately. I'm on cox cable and running off redhat 6.1
the problem that I'm having is that the box dosen't get a new address when the old one expires. They used to let me keep the same address for weeks, but now it will only stay up for a few days at a time. Did you have to do anything special to get yours working properly? I think there's problems with the dhcp server I get my address from, because after the lease expires, it takes at least a day for me to be able to get a new address. I've tried all kinds of reboots, commandline options, about everything i can think of. I was using pump before, but I've switched to dhcpcd instead since its been more usable for me.
as a side question, is there a linux rr page that might have some info for me?
-earl

I do just that

[SecretAsianMan]

I run my own mail server, soon to be a web, news, quake, etc. server off of a Roadrunner cable modem connection with a dynamic IP.

I use dynamic DNS service from tzo.com, and their service has been pretty much configure-and-forget -- in other words, great for non-super-sysadmins like me. They don't use an update program like some other services, but instead, a URL. To update your dynamic DNS redirection, you point a browser to the URL and blammo, it's done. I took their simple scripts and wrote my own that send in an update whenever my DHCP lease is refreshed. My scripts pass the proper URL to lynx in batch mode and dump the output to a log file. Not hard at all.

You can get groovyname.sillydomain.tld kind of service or myowndomain.tld service. I have the second. They claim to have five (?) servers, all in different time zones using different colocation. I haven't experienced a problem with it.

Re:Your name

[SecretAsianMan]

Thanks. I was singing "Secret Agent Man" one day and noticed how much it sounded like I was saying "asian". I'm not even Asian, but the name stuck.

Re:Good idea

[rcgreenw]

Running services from a dynamic IP works fine. I have Pacific Bell DSL and I got it just after they stopped doing single static IPs, so I got stuck with a dynamic.

I use qmail for mail and apache with mod_ssl for web service. (Yes, that's really my domain name.) I have several NameVirtualHosts defined for apache (my home page is the same machine), so I have to restart apache whenever I get a new IP. No big deal. I have my domain name pointing to a friends nameserver. The nameserver is updated whenever I get a new IP using Bind 8's dynamic updating features and public key authentication. I havn't had any problems so far.

If you don't have a friend that runs a nameserver, I also have it update my dyndns.org entry and that doesn't seem to have any problems either. All in all, I'm happy with it, and with Bind 8's dynamic updating, having a static IP isn't so crucial any more.

--Rich

Re:Good idea

[b0sst0ne]

However, you need to be careful what the Time to Live is set in the Start of Authority of your zone on your friend's name server. Caching DNS servers are going to hold that record for the length of time that it designates. You'll most likely need a low TTL, and even then, you have a chance that sometimes your DNS will hiccup for a few minutes, until the caching servers update their host records with your new record. Dynamic IP's suck, but I guess you gotta work with what you have. All I can say is... if the authoritative server can handle it, keep the TTL low, like 15 minutes or so... or 900 :)

Re:Your name

[Lord Kano]

It took all of my self control not to burst into laughter here at work when I read your name. It reminded me of a time back in college when after a party I saw something on TV that contained the sonc "Secret Agent Man".

For about the next hour I sat in my room Singing "Secret Asian Man".

I'm just waiting for the Dr. Demento or Weird Al version of that song.

LK

Good idea

[dlc]

This is probably the way to go, for a few reasons:

• Many (most) services are, or can be, name-based rather than address based, so this shouldn't be an issue for most processes other than routing.
• With many of these services, you get to choose your own hostname, so you can choose something groovy. I believe some will also provide free TLD DNS service on one of these dynamic addresses, so you don't have to settle for groovyhost.sillydomain.com or something similar.
• If (when) ION goes to static IPs, you are already set up to handle the services, so there will be no rearranging of addresses and client configurations.

You can get/write scripts that will tell your daemons what their hostname/IP is (the ones that need to know -- sendmail probably, maybe Apache) as you change the address.

Plus, running your own servers is inherantly more satisfying. Knowing that you have control over (almost) all aspects of your services can be a pretty, albeit scary, proposition.

Cthulhu for President!