Installation manual network config fails with "x.x.x.x is not in contained in x.x.x.x/yy"

Asked by Leon Castellanos on 2021-01-04

1) lsb_release -rd

Description: Ubuntu 20.04.1 LTS
Release: 20.04

2) Package version
Unknown. Whatever version is part of ubuntu-20.04.1-live-server-amd64.iso 2020-07-31 17:35

3) What I expected

For valid manual network settings to work.

4) What happened instead

Manual network configuration fails saying:

"'' is not contained in ''"

With network settings:


Subnet certainly contains -

We attempted to define /23 on Address instead, but that is not allowed.

I work for NASA GSFC and we're having to proceed without network and then manually edit /etc/netplan/*.yaml after install.

If this is an error on our part, can you please clarify what we were supposed to enter for subnet? Since Subnet line requires an entry in CIDR form with error "should be in CIDR form (xx.xx.xx.xx/yy)"

Manual network config works fine with:

# This is the network config written by 'subiquity'
  version: 2
  renderer: networkd
      dhcp4: no
          addresses: [,]

**IPs redacted for security purposes

Question information

English Edit question
Ubuntu subiquity Edit question
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Solved by:
Leon Castellanos
Last query:
Last reply:

Figured out it's not looking for the subnet MASK but just the net cidr ( in my case)

IMHO this is the stupidest way to do this.

I don't understand why you have chosen to do this in a completely unintuitive way to how every other operating system is configured using the netmask.

Bernard Stafford (bernard010) said : #2

It might let you range the IPs like in this exmple.
option subnet-mask;
option broadcast-address;
option routers;
option domain-name-servers,;
option domain-name "mydomain.example";

subnet netmask {

Bernard Stafford (bernard010) said : #3

could it be defined as subnet-mask

Hi, I already stated in my comment that the solution is entering the subnet CIDR "xx.xx.16.0/23" and not the subnet mask.

Manfred Hampl (m-hampl) said : #5

Don't confuse "subnet mask" and "subnet address"!

You're making it sound like I missed something obvious.

The prompt doesn't say "Subnet ADDRESS". It just says "Subnet: ".

Every other OS (UNIX/Linux) I've installed in my 30 years of sysadmin experience has requested a "Subnet MASK".

This is the first time I've seen an installer request a COMPLETELY UNINTUITIVE subnet address...

It's just dumb and it unnecessarily confuses people.

My colleagues here at NASA Goddard Space Flight Center said "WTF" once we figured out what it was asking for.

The prompt should say "Subnet Address" at the very least.