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I've been banging my head against this problem for days and can't find a solution.

I have a network with a server with two interfaces, one for normal traffic and one with an address 10.72.0.23/12 (for nfs), and a similar client with also two interfaces, one with an address at 10.76.0.17/12.

I've tried about a billion iterations of the netplan options, but at the core I'm constantly stalled by the fact that these two interfaces refuse to connect to each other in this configuration.

If I configure interfaces like so, they connect:

server: 10.72.0.23/12
client: 10.72.0.17/12

or

server: 10.76.0.23/12
client: 10.76.0.17/12

But if I set them up like this, they refuse to communicate (Destination host unreachable):

server: 10.72.0.23/12
client: 10.76.0.17/12

Sadly, for my purposes, I'm unable to configure them the first way permanently - the client and server addresses need to have more than 255 available IPs. These addresses are supposed to connect as they have the same subnet (10.64.0.0/12), yet they do not do so.

There's no firewall. There's no ip conflict. They're on the same subnet. They have the same routes configured. Since they can connect when they have the same first two octets, I know the hardware is working. Everything stops dead the moment I give them the IPs above (or nearby ones).

Is this a bug, or is there some undocumented feature of linux routing at play here?

  • Which Ubuntu release, and which versions of the netplan.io and systemd packages are installed? What are the netmasks on the interfaces as shown by 'ip addr show'? – slangasek Jan 13 at 1:17
  • (the reason for this question is I believe there was a bug that caused /24 netmasks to be used unconditionally, but that this bug has been fixed in latest versions of the packages) – slangasek Jan 13 at 6:36

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