I have a dev server with a Comcast static ip that has worked wonderfully for 10 years...went to upgrade to Ubuntu 18.04 and whats this NetPlan biznezz and why will it not accept my subnet?

Followed all documentation from Comcast (like I have every other time I have formatted this machine) and it is asking for xx.xx.xx.xx/xx bit set. I generally know what this means but I am lost...

Let me be a tad bit clearer...I am doing a fresh install and choosing my network device from the start...so essentially setting up the netplan config from "go"....

  • Have you set up your netplan file? May we see a redacted copy, like xx.154.23.18, etc. What is the response to: sudo netplan apply?
    – chili555
    May 10, 2018 at 12:29
  • I dont have a netplan file as of yet. There is no response because I cannot get that far. This is an external static ip from Comcast. the ip is 75.151.xxx.226. The gateway is 75.151.xxx.230. Comcast tells me the subnet is I do not know what the bit set would be. Comcast says to use /30. Or /29 for a range. Neither worked.
    – mr_wahoo
    May 10, 2018 at 12:37
  • No netplan file?? What is the result of: cat /etc/netplan/*.yaml? This may get you started. If needed, I will write a complete answer in a few hours. askubuntu.com/questions/1019610/…
    – chili555
    May 10, 2018 at 13:19
  • Okay...currently, I am on the installations screen for network devices. On my first attempt at installation. I did not reading and shot straight for /etc/network/interfaces. After reading, I went to /etc/netplan/50--.yaml and tried to configure it there. Didnt work. I can just install the whole thing and come back to the netplan file, but that does me no good if I do not know what works in it.
    – mr_wahoo
    May 10, 2018 at 13:33
  • According to subnet-calculator.com/subnet.php?net_class=A when I put in say as your IP, which is just a guess and when I need the gateway, that is a /29 or netmask. Given that Comcast is putting in the gateway in your same subnet. I just have CenturyLink and their is completely different where they mask at or /32 with a gateway that is not in the subnet. They do it by routing.
    – Terrance
    May 10, 2018 at 13:41

2 Answers 2


That is called CIDR notation where the first part is your IP address like and the second part is your netmask like /24.

Together they would look like:

The /24 CIDR is actually for the netmask like the following:

/24  |   
/25  |  
/26  |  
/27  |  
/28  |  
/29  |  
/30  |  
/31  |  
/32  |  

/24 is the most common in home networks. Linksys and other such routers will assign on IPv4 DHCP records that will look like where the gateway or router IP address is And with a subnet mask of /24 or that means that the IP address octets have to match from 192.168.1.xxx where the last 3 digits can be anything from 1-254 to be in the same subnet.

One tool that I use on a daily basis especially with my job is the Online IP Subnet Calculator. Just to give you something along what your IP might be. I am not sure what your IP is. I am assuming it is a Public Static IP. So, I am going to use a made up IP as with your mask of

enter image description here

Just on the quick image there we can see that the Mask Bits is 30, so the notation would be Which would mean that our gateway should be which has to be in the same subnet as our IP address. Clicking on the CIDR just above switches to a slightly different calculator, but I input the same information and received about the same in return.

enter image description here

There we can see that our route would be as our network and our network CIDR Notation would be but that is not our IP address. Our broadcast on that network is as that is the highest IP. This is the equivalent of an IP of mask network where our network CIDR Notation would be and our broadcast would be and our gateway IP would be more than likely at

Hope this helps!

  • This isnt a home network. This is a development web/* server utilizing Comcast static ips. My problem is when I try to apply the subnet. I do not know what the /* would be. I keep getting a "has bits set" error. I would really like to use this version but I may either not use netplan or go back to 16. I really appreciate any help. Thanks!
    – mr_wahoo
    May 10, 2018 at 12:32
  • @mr_wahoo I added in some more edits and a tool that I use on a daily basis that might help you determine what your /* would be. I am assuming that yours would have to be a /30 on a masked network.
    – Terrance
    May 10, 2018 at 13:33
  • Hey! I got it. The guy above sent me the same link. Never knew about that site. Thanks so much for your responses. I hope to be able to answer as fast for ppl as you guys do one day! Thanks again!
    – mr_wahoo
    May 10, 2018 at 14:13
  • @mr_wahoo Keep learnin! There is so much potential out there and believe it or not, but I have fun with this! I find it challenging and when I help people I in turn learn a lot myself. :) Keep up the good work!
    – Terrance
    May 10, 2018 at 14:27
  • @mr_wahoo By the way, I am that same guy! =)
    – Terrance
    May 10, 2018 at 14:29

The way you do it at the beginning of Ubuntu 18.x plus installation, if you go static is:

Netmask: (don´t put, it won´t work)
DNS: etc

That should work!

  • I apologize. I forgot to mark the answer. I appreciate your input. Thanks!
    – mr_wahoo
    Mar 22, 2019 at 17:35

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.