IOS DHCP Server question

[djcoleschmi]

Hello,

I have been scouring the Internet for an answer to what I initially thought was a simple question.

Can the basic DHCP server in the Cisco IOS update a remote DNS server (BIND) with the host names of the clients it serves?  I know this is known as a type of DDNS but many of the resources I find for configuring this setup are for an ASA or other security appliance; or it involves updating a paid DDNS service like DynDNS - that's not what I am doing.  These DNS names are for internal LAN hosts, not internet servers without a nice domain name.

Also worth noting, there is no MS DNS/DHCP available in this environment, rather a mix of iOS, OS X, Android, Windows PCs and Linux.

I know the DHCP clients can decide whether or not to share their host name with DHCP - and it may not be possible on the mobile platforms.

We are not able to touch the clients, as this is a public LAN for customers, and other uses.

We want to be able to track host names to IP mappings to ease the process of tracking down potential abuse among other reasons.

the IOS I am running is C2600-ADVSECURITYK9-M Version 12.4(19b)

Thank you!

[ghostinthenet]

You're definitely not going to find that kind of functionality in IOS 12.4's DHCP server.

My advice would be to implement the ISC DHCP server (which will happily update BIND) on the machine that hosts the BIND server. You can then use DHCP relay functionality ("ip helper-address") on the router to forward the DHCP requests to the server.

[djcoleschmi]

Hey, thanks for getting back to me.

That is not true however.  I continued to try to find an answer, and I was able to confirm the Cisco DHCP server does indeed support Dynamically Updating specified DNS server(s).  (RFC 2136)

The commands are entered either globally or unique to each DHCP pool.

With DHCP pool config context, the command syntax is:

update dns [both | never] [override] [before]

and within global config mode

ip dhcp-client update dns server [both | none]

I believe the other requirement is specifying the DNS server(s) that are to be dynamically updated in the "ip name-server" command, as this is the data the IOS will use to determine who to send the DNS updates to.

My problem is TinyDNS on pfSense does not support RFC 2136 so I will be implementing BIND later today.

[ghostinthenet · Accepted solution]

Wow! Thanks for the correction. I think I'll be taking advantage of that now.

Best of luck with the BIND implementation.

[djcoleschmi]

Thanks Jody.

Im glad you found the info useful.