router question on DHCP and static DNS entries?

Question

I'm somewhat tech savvy, but I'm a little confused about DHCP servers and the relationship to DNS servers. I have a linksys WRT54G with dd-wrt firmware on it and it works great. Occasionally (once a year?) I have issues with DNS servers changing from my Internet provider (comcast cable) and have to update the entries in the setup and otherwise fiddle with things till they work. I'd like to avoid this, since after a year passes I always forget what I did the previous time.

If I understand correctly, my router uses DHCP to get an IP address, DNS, etc, from the cable modem. This information is always up-to-date provide it power-cycles occasionally which it does.

Now I also have the option of running a DHCP server from the router as well, which is a little confusing. How can I enable this, but not specify manually the 3 "Static DNS 1,2,3" entries in the table?

It allows me to assign them all to 0.0.0.0, but does this mean something special like "get them from the modem automatically" or something bad like "we won't have a DNS at all"?

I would like for the computers connecting to my router (via WiFi and ethernet) to always get the latest DNS that my provider gives me, but I can't do that if I statically assign them manually in the setup.

To confuse things, I do use a static IP assignment for one particular computer assigned by the router via MAC address, but does using this option require static DNS entries to be set on the router DHCP server?

Thanks for un-confusing me..!

Answer 1

The short answer is, you should always use dynamic DHCP unless you absolutely have to. This will assign the device (router or computer) an IP address, Subnet mask (don't worry about this) and a DNS server.



Ideally your router should get this from your ISP every so often. When the IP lease expires it will ask for a new one. Occasionally, the ISP experiences a hiccup with its DNS service and you are stuck. My ISP is notorious for this. Nothing you can do about it except assign a static DNS server. I don't recommend this unless you absolutely HAVE to have the connection right now. Check out OpenDNS on the internet. It will have the IP addresses you can use to point at some publically available DNS servers. Otherwise, be patient and the service will usually resolve itself in 5-25 minutes.



You should set the WAN side of your router to get it's DHCP info (incl DNS) dynamically. The LAN side, which points to your computer, should be running a DHCP server so it assigns any computers it recieves request from thier own IP addresses and forwards the DNS info from the ISP.



As for the computer with the static IP, no worries. Just because it has a statically assigned IP address does not mean it can not use a dynamically assigned DNS service. Just make sure the IP address you statically assign also falls in the range of the ones the router is giving out.



Hope this helps.

Answer 2

Static Dns

Answer 3

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Firstly i'm no expert on best practice -but i've setup a few windows servers so hopefully this helps. On your server you should have the ip set to local host assuming it is running a dns server also. Iirc windows automatically configures your server to be able to lookup/forward internet dns records. Also you should set it up so that your client pc's obtain their ip from the server as if you have the dhcp server enabled on the server it assists with dynamically updating dns records for local clients (i had major problems with one machine when i had dhcp configured on the router instead with stale dns records not being removed) so either disable dhcp on the router and enable on the server or configure relay (but be very careful not to make it an open relay otw someone may be able to gain access to you network. If you're not too worried about local names being resolved it would be fine to set these to your isp's dns servers. If your dns is configured as i said (dhcp/dns via the same server with the appropriate forwards setup within the dns server) then it should work flawlessly You never set the DNS to the routers ip - this just causes problems with a lot of routers that don't forward the request - best bet is setting to the servers ip imo. Advanced you shouldnt need to play with - the primary dns suffix should be set already and unless you want to add more than 2 dns servers or multiple local ip's for the server then you shouldn't need to do anything in advanced. Edit: btw when i said setting it to the servers ip i mean the servers local ip address. Also appologies if it's not overly detailed as much as i'd like to access my old clients systems to give you more information i'm no longer a tech so it would be unethical (assuming they haven't changed the passwords :P)