DNS settings from DHCP...?

[Koldov]

Ok, so I'm going to ask some really basic questions in this post (possibly more so than usual), but please bear with me as I haven't even had to look at this in over 10 years....

 

I inherited a strange hybrid DNS/DHCP set-up and now I'm looking to move servers onto Hyper-V, I need to look at the DNS.

 

I'm researching how to move DNS so I can get it done over the summer, but I'm a bit stuck on the DHCP part.

 

DNS is done through the servers (which I can try to deal with), but DHCP is done through the CISCO switches (which I have limited access to)...

 

I'm just thinking that the DHCP will carry on as usual through the switches no problem, but how are DNS servers advertised/updated? I was somehow under the impression that this was done through DHCP (as it is in the same section as - I.P. address/subnet mask/default gateway)... and if that is correct, how do I get the 'new' DNS servers out to all the clients?

 

As this is a first time thing for me, I am looking to make it as simple as possible. I haven't had to look at 'how' these things work as I either enter all the details manually for a static, or set to 'obtain automatically' and it all gets magically filled in...

[jthompson]

DHCP option 006 is what you're after, I suspect.

[djm968]

You are right, DNS addresses are usually issued to clients from the DHCP server (Option 006) My recommendation would be to move DHCP to a sever too, but this may not be easy if you only have limited access to the Cisco switches and you may have to factory reset them unless you can obtain an unrestricted password. Edited July 11, 2022 by djm968

[Koldov]

DHCP option 006 is what you're after, I suspect.

 

Hmmm...from what I can see that seems to be a setting on the DHCP scope on a Windows server running that role?

 

We don't have DHCP run by the Windows server, it is run on the CISCO switches.

 

My recommendation would be to move DHCP to a sever too, but this may not be easy if you only have limited access to the Cisco switches and you may have to factory reset them unless you can obtain an unrestricted password.

 

Access is limited but I have picked up a thing or two over the years so it might be possible to at least change a variable in a line of code, plus I can ask the company who support it if I really need to (if anyone can tell me this is definitely what's happening) although they are on a break/fix support contract an any config changes are chargeable.

 

Not sure I want to dump managing DHCP into my lap just yet as well as everything else, it has actually worked fine this way for over 10 years and factory resetting the core switch I think would come with a whole heap of trouble as my knowledge certainly isn't up to recreating the whole network from scratch (VLANs, ACLs, I.P. reservations etc.).

[mavhc]

Could always not change the IP

[Davit2005]

Jus a matter of setting the DNS server IP on the DHCP settings where ever you move the DHCP to.

 

The DNS and a lot more settings can be distributed depending on the options on the DHCP server.

[djm968]

Access is limited but I have picked up a thing or two over the years so it might be possible to at least change a variable in a line of code, plus I can ask the company who support it if I really need to (if anyone can tell me this is definitely what's happening) although they are on a break/fix support contract an any config changes are chargeable.

 

IF you can change the config on the cisco switch, the code is relatively straight forward.

 

Router(config)# ip dhcp pool (name of pool)

Router(config-dhcp)# no dns-server (existing DNS server IPs e.g 192.168.0.1 10 0.0.1

Router(config-dhcp)# dns-server 192.168.0.2 "another DNS server IP"

Router(config-dhcp)# exit

Edited July 11, 2022 by djm968