Issues with Setting Static IP and DNS

I set up a Debian server on an old laptop while on my home network that uses a Netgear Genie WNDR4500v2 as the router. When I set up the Debian server with a static IP it worked fine at home. It was able to do updates and resolve urls like

Here is the contents of the /etc/network/interfaces file on the Debian server

source /etc/network/interfaces.d/*

# the loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto enp1s0
iface enp1s0 inet static

When I moved this “Debian server” to my work a small office that use a Comcast Business Class Router, DNS no longer worked. I tried ping and it failed. I tried ping and that got an immediate response, so my guess is that I had access to the internet but I didn’t have DNS working at the office. When I changed the /etc/network/interfaces file from “static” to “dhcp” and commented out the “address” and “gateway” lines and rebooted, I got a different IP address assigned, but now I had DNS. I could ping and get a response.

The router at home and the router at the office are both found at

  1. Any thoughts why I had DNS at home but not at the office when using a static IP?
  2. Is there an additional setting that I could add to the /etc/network/interfaces file that I neglected?

I know that one solution that I could probably do is to reserve an IP address for the “Debian Server” when it is at the office through the interface of the Comcast Router. Perhaps that is the best solution, but I’m checking to see if I missed something else in my mobile home lab set up.

Your DNS configuration is set in /etc/resolv.conf; when you have DHCP configured, it updates your DNS configuration based on what the DHCP server specifies. I’m thnking that the DNS server you had set originally wasn’t allowed on your office network. (ping just does an ICMP ECHO, so you could still ping even if DNS queries weren’t allowed, for example).

Thanks @Buffy , I’m not sure that was the issue, and I think I discovered something else during my trouble shooting this afternoon. I should not have used the Quad 9 IP address as my ping example because I probably gave the impression that I had set Quad 9 as my DNS in /etc/resolve.conf.

However, when I checked /etc/resolve.conf I actually had this:


which are the DNS servers for Comcast my internet provider at home and at the office so those DNS servers should be allowed on either my home or my office network.

However, here is something curious. With the /etc/network/interfaces mentioned above in place, I rebooted the Debian server. When I do ip address it reports what you would expect as the ip address:

However, when I log into the Comcast Business Router it lists the debianserver as connected, but when I look at the details it sees it as:

And once again DNS fails. So I guess my best option is not to set a static ip through the configuration files on Debian 11 because for some reason the Comcast Router does not honor those settings or requests. I will have to Reserve an IP through the Comcast Router interface which will work fine, I don’t plan to move this server laptop often anyway.

Hm, is that .220 static address within the range your CBR (Comcast Business Router) is allocating for DHCP? It might be that it’s modifying some of the firewall rules based on what DHCP leases (the .230) it has given out?