Thank you for filing a bug.
The firewall policy is a combination of the default policy for each of
'incoming', 'outgoing' and 'routed' (forward) along with the policies
shipped in before{,6}.rules, after{,6}.rules and whatever gets added to
user{,6}.rules. Specifically, what is in before{,6}.rules is designed
with default deny for incoming (and forward), default allow for outgoing
and default accept for established connections. Considering that dhcp
uses port 68/udp for the client and port 67/udp for the server, the
shipped default policy allows:
* outgoing from this host port 68/udp to any port 67/udp (via default allow
outgoing; eg, for dhcp request)
* incoming for established connection (via before.rules RELATED,ESTABLISHED;
eg, dhcp reply from the server we connected to on port 67/udp)
* incoming from port 67/udp (via the before.rules you mentioned; eg, for a
server responding to the broadcast)
I suspect that you've updated your default policy to deny to perform
egress filtering so you need to add a corresponding 'ufw allow out to
any port 67 proto udp comment "dhcp discover"' rule or similar.
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https://bugs.launchpad.net/bugs/1882484
Title:
Firewall rule in before.rules for dhcp is wrong
Status in ufw package in Ubuntu:
Invalid
Bug description:
The file delivered - /usr/share/ufw/iptables/before.rules
which is then copied to - /etc/ufw/before.rules
Delivered by Package:
# allow dhcp client to work
-A ufw-before-input -p udp --sport 67 --dport 68 -j ACCEPT
The ports for
--sport and --dport are swapped
Should be:
-A ufw-before-input -p udp --sport 68 --dport 67 -j ACCEPT
Package version found in:
0.36-0ubuntu0.1
Note: ISC DHCP uses RAW sockets, which bypasses iptables anyway and doesn't
drop the packets with the incorrect configuration. This has had me stumped for
the last hour.
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https://bugs.launchpad.net/ubuntu/+source/ufw/+bug/1882484/+subscriptions
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