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I am not a system engineer or a network expert (I am more a software developer) I am trying to install an Ubuntu Server using static IP address. I am using the information provided by a collegue.

These information are:

  • SERVER IP ADDRESS: 172.16.182.216
  • SUBNET: 255.255.255.0
  • GATEWAY: 172.16.182.1
  • DNS: 1.0.0.109 AND 192.168.6.101

I have some problem to set the Subnet mask: first of all I tried to insert the value as provided (255.255.255.0) but the Ubuntu installation prompt says to me that this value should be in CIDR format.

So I tried to insert value like something like 255.255.255.0/24 but then on the IP address I have this error '172.16.182.216' is not contained in '255.255.255.0/24'

enter image description here

I have tried also with other values but I have similar problem. Why? What could be a solution?

AndreaNobili
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    also note that a subnet mask (255.255.255.0) and a cidr bit length (/24) are different ways of saying the same thing so you would never express a subnet mask as `255.255.255.0/24`. you would just use one or the other. – Frank Thomas Feb 22 '22 at 16:55

1 Answers1

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It asks for the subnet specification in the 1st field, not the subnet mask.

The subnet is 172.16.182.0 and it uses a 24 bit (255.255.255.0) mask so the CIDR notation for the subnet is 172.16.182.0/24

Tonny
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    Talk about useless redundancy there, why not just accept `172.16.182.216/24` as usual, since it gives the same information anyway. – ilkkachu Feb 23 '22 at 20:50
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    @ilkkachu I agree. You either ask for ip-address in CIDR as a single field or for old-school ip+mask in 2 entry boxes. This combo is unusual and confusing. First time I encountered this variant in Ubuntu I automatically typed the mask and then did a step a back. “Wait a sec, why the mask in the 1st box? That’s odd…” Only then I realized they didn’t ask for the mask at all. Only real benefit I can see that this allows you to catch misaligned base-addresses for the subnet. Eg 192.168.101.0/23 is invalid. Some people seem to think you can just bump up the mask if 256 addresses is not enough. – Tonny Feb 23 '22 at 22:01
  • @ilkkachu ... Same in every industry, some person has the job of doing the network bit, but it would go unseen if they did it proficiently. We need "Khaby Lame" to spend a day at Ubuntu. :) – Floggedhorse Apr 30 '23 at 07:52
  • ....Ruddy ell, you've got me going... What are all those "Y"s for when you install software? Does the PC know something that I don't and it's just gloating? Does it think I'm going to change my mind? In the matter of fact has anyone ever said "No"? – Floggedhorse Apr 30 '23 at 08:13
  • @Floggedhorse I have said no a couple of times. Mainly because I noticed the bloody thing tried to foist crapware as a side-install on me. I don't want another browser plugin., search engine change, free virusscanner, etc. If i want that I will install it myself. Most of them are just annoying "get out of my way and start installing dammit" nuisances. – Tonny Apr 30 '23 at 08:36