netplan 0.40.1~18.04.4 (ubuntu 18.04) fails when dhcp server provides multiple search domains

[Tessa]

just ran into some rather serious issues for our environment because of netplan. looks like when the DHCP server provides multiple search domains, netplan strips all the spaces out and munges the multiple domains together into one long broken domain. for example:

DHCP server provides search domain string "zone1.ourdns zone2.ourdns zone3.ourdns", but netplan mangles that in /etc/resolv.conf to "search zone1.ourdnszone2.ourdnszone3.ourdns".

this is a pretty basic bit of functionality, so I'm pretty surprised it hasn't been tested. is there a clear way to disable netplan entirely? it really doesn't feel production ready.

[Tessa (unit3)]

found the docs for disabling and going back to /etc/network/interfaces in that file. is there a way to vote for not having this enabled by default while it's still so buggy? looking at the bug reports here, it looks like it doesn't really handle a fraction of what the old ifupdown stuff does yet.

[Mathieu Trudel-Lapierre (cyphermox)]

I'm sorry you've had issues with netplan so far.

As far as search domains are concerned, this absolutely does work; at least for the general cases. Having multiple search domains isn't something new or obscure. However, we may be running into a compatibility issue here with the exact *way* in which this data is provided by the DHCP server. Nothing of this is caused by netplan, but it may be a bug in systemd-networkd to not be handling the values correctly when received in this particular way.

Do you have access to the DHCP server, and if so, could you please inform us on how the search domains are being passed over DHCP? Is it using DHCP Option 119, DHCP Option 135 or some other feature?

[Tessa (unit3)]

These domains are provided by a DHCP server I don't have access to for our corporate VPN, unforunately. I'll try and get a packet capture of the DHCP protocol traffic when I connect and pick out what's happening, when I get a chance.

[Ryan Harper (raharper)]

There may be info about the DHCP response in /run/systemd/netif/leases/<ifindex>

Note, it will have IP and other specific details you may want to redact.