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DHCP to DNS

From Michael Majetich

Answered By Heather Stern

Hello again!

I posted the question below a week ago.

I remind you (or inform you, if you've never read the top of our web pages) that The Answer Gang does not quarantee that we will or can answer you.

IF any amongst the Gang do, though, we also can't guarantee that it will be in a timely manner. The longest anyone who HAS gotten an answer waited was months ... I think it might have been over a year ... because back in issue 36 Jim went through his entire backlog. We weren't the "Gang" yet, and a full backlog check isn't likely to ever happen again.

Somehow lucky for you, you got me in a good mood even though you make this annoying assumption that we'd give you instant feedback. Often that wouldn't be enough - in fact it would encourage me to shuffle your mail away, since as an editor here I see ALL the TAG mail, and have to go through it in much detail later - but I see an opportunity to get some useful data to everyone else out there too. So you win the "Answer Gang" lotto and I'll give it a shot. You get a slight roasting for free.

Sadly for you, I still use Bind8, and so any tech I know to sync dhcp with bind (very little; DHCP's not my specialty anyway and my own network presently does use static IPs) might not be as useful. Not that this sort of lack of knowledge has ever stopped me before

Can anybody at least point me someplace to get the answer

[HOWTO use search engines effectively]

However in going to the Google! Linux area (http://www.google.com/linux and make sure NOT to put the slash at the end) ... giving it the keywords: bind9 dhcp

...the second item might be useful, as he's discussing doing something like that and gives some parts as a study example: http://www.asp.ogi.edu/people/paja/linux/dns

[FAQ item # infinity]

Q. I need a fast answer for my problem <foo>, and I didn't find it here. Time's running out for me! What am I gonna DO?

A. If you need a timely reply from someone who specifically knows a topic, I recommend hiring a paid consultant on that topic.

Generically, you may be able to find them by visiting the Consultants HOWTO in the LinuxDoc project: http://www.linuxdoc.org/LDP/lcg/html

That howto is maintained by the folks at LinuxPorts; they also have searches into it at: http://www.linuxports.com

That's pretty decent for finding individuals as well as companies of varying size, just in case you have any prejudice against mega-consultant houses.

Specifically, any companies who commercially maintain code related to the programs you are using, may offer "professional services". It is worth checking their sites for further documentation first though.

[Now for the good stuff, answers from the real world, that might be able to lead you in the right direction. Though the direction you eventually choose may not be where you were heading when you began.]

I have a "Mixed" network of linux and microcrap so this would be a big help. I would rather not use fixed IPs.

I can certainly sympathize with that; another possibility is to use network address translation (sometimes called NAT) and the private, reserved address ranges. Under RFC 1918 (I used http://asg.web.cmu.edu/rfc/rfc1918.html but there are mirrors everywhere) these ranges are:


192.168.0.0 - 192.168.255.255 (192.168/16 prefix)

readable by the rest of us less netmask-aligned sorts as:


192.168.*.*

although a lot of people wimp out and only use 192.168.0.* or 192.168.1.*, you can do some pretty cool stuff by using more of them, or avoid possible collisions with other nets coming in by using s third octet value other than 1 or 0.


172.16.0.0 - 172.31.255.255 (172.16/12 prefix)

aka


172.[16-31].*.*

For some reason a lot of people forget about this one entirely.

and the possibly infamous "10 net":


10.0.0.0 - 10.255.255.255 (10/8 prefix)

aka


10.*.*.*

where again, a wide tendency to use 0 or 1 sometimes leads people to unnecessary collisions.

That is, you could use static IPs for machines which are not going to move around a lot, without having to request more from your provider. This does not negate some good uses for DHCP though:

1. it's much easier to renumber a zillion MSwin boxes if they all just use dhcp. Note renumbering is far less needed with private addresses. Note if they all come on at the same time there will be a broadcast storm while the busy server hands out everybody's addresses.
2. You may want laptops to only use a limited range of IP addresses. Your laptop users may not be up to setting their static IP settings to match your office, and then away to something else for other sites they'll be visiting.

However, you do not really need to tie bind to dhcp unless the machines need to be able to be addressed in the DNS by name. In other words, if they are providing services of some sort. Most companies of any notable size think it's a bad idea to let their individual desktops be addressed by the outside world anyway. But the inside world... well, you could be using split DNS I suppose. That is, the DNS your inside folk see for your domain is a more complete version, which is not shown to the outside world. Outsiders only see the usual obvious things like your web server a few mail servers, and of course, an outside-world nameserver or three.

This is my first post. I assume that this question has been asked 1000 times already, but I can't find a resonable answer on the web.

How do you get the dhcpd to update BIND9. I am running SuSE7.3 with the servers on the same machine. In dhcpd.conf I've made the ddns-hostname(tried both name and IP) , domain, update-style(ad-hoc) entries. In Bind I've allowed update from localnet, and localhost. Nothing happens. both start with no errors that I can see. What am I missing?

-- Mike Majetich

Bind (aka named) and DHCP are maintained by the Internet Software Consortium.

http://www.isc.org

They have consulting. They point at a book, "DHCP" by Ted Lemon and Ralph E. Droms.

Although I will mention that the OpenBSD folk also heartily recommend "DNS and Bind" by Paul Albitz and Cricket Liu, as being an excellent intro to the topic.

In my personal involvements in the community, I also know that Nominum did a bunch of coding in the Bind9 project. They're a big commercial creature, and it so happens they are one of the entities offered at ISC as your possible consultant: http://www.nominum.com

The other one -- if you're in Europe somewhere it's probably closer to you -- is Mind: http://mind.be

If you go "the enterprise route" then purchasing your support contract through ISC supports their efforts, bandwidth use, etc. towards these really rather cool projects.

For just general DNS questions I find that the very best web based resource is "Ask Mr.DNS" - although Acme Byte and Wire was bought up, the new owners have graciously allowed his to continue doing that, and the archives stay online: http://www.acmebw.com/askmrdns

Cool, he's got a category just for dynamic updates such as you're asking after...

Best of luck, happy holidays. If things work for you, please feel free to let us know, or even to write up an article for us. If you did that, then the next time someone asks this sort of thing, we can point them at your successful efforts

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Published in issue 74 of Linux Gazette January 2002

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