I sometimes had the issue that I received an error when starting an existing vagrant box with vagrant up:

A host only network interface you're attempting to configure via DHCP
already has a conflicting host only adapter with DHCP enabled. The
DHCP on this adapter is incompatible with the DHCP settings. Two
host only network interfaces are not allowed to overlap, and each
host only network interface can have only one DHCP server. Please
reconfigure your host only network or remove the virtual machine
using the other host only network.

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This is a bug in vagrant < 2.2.9. To work around this issue, put the following snippet to the top of your Vagrantfile:

class VagrantPlugins::ProviderVirtualBox::Action::Network
  def dhcp_server_matches_config?(dhcp_server, config)
    true
  end
end