After an Ubuntu upgrade the network stopped working

LXD
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The usual steps to resolve issues like this are as follows:

  1. Confirm LXD’s dnsmasq is running and listening on your bridge’s IP (using sudo ps aux | grep dnsmasq and sudo ss -ulpn | grep dnsmasq and that nothing else is preventing LXD’s dnsmasq from listening.
  2. If you have docker running on the host check its firewall rules aren’t blocking DHCP requests to lxdbr0. See Lxd and Docker Firewall Redux - How to deal with FORWARD policy set to drop
  3. Check that you haven’t got anything else that could be adding firewall rules (using sudo iptables-save and/or sudo nft list ruleset) that could be blocking LXD’s dnsmasq from getting DHCP requests.
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