Hi folks,
I'm confused about another thing too.
I have an external backup drive, connected via a network cable.  When 
things boot up, it gets IP addresses for its drives from my dhcp server.
This used to work fine.  Recently however, I find that the drive's 
complaining of a "DHCP network addressing problem" (according to the 
blinking light code!).  If, before the drive boots I disable my UFW 
firewall with sudo ufw disable, then boot the drive, then enable the 
firewall, everything's OK.  If I don't disable the firewall while the 
drive's getting an IP address, I get the error.
I'm running dnsmasq as a dhcp server.
My ufw rules are like this
$ sudo ufw status
Status: active
To                         Action      From
--                         ------      ----
67                         ALLOW       169.254.0.0/16
68                         ALLOW       169.254.0.0/16
67                         ALLOW       0.0.0.0
68                         ALLOW       0.0.0.0
192.168.55.66              ALLOW       192.168.55.0/24
I've omitted 4 rules which open up specific ports, with a format like 
this as they're not relevant (at least I think they're not relevant)
192.168.55.66 123          ALLOW       Anywhere
192.168.55.66 456/tcp      ALLOW       Anywhere
As I understand it, the ports I need to allow access to are 67 and 68. 
When something asks for an IP address and it hasn't already got one, it 
broadcasts from the broadcast address 0.0.0.0.
Sometimes, a machine will assign itself an IP address in the 
169.254.0.0/16 range - e.g. a Windows machine that can't find a DHCP 
server on the network.  If I allow this range then such machines can 
contact the DHCP server.
The final line should allow anything with an address in the range 
192.168.55.0 - 192.168.55.255 to contact any port on my server 
192.168.55.66, which is where the DHCP server is.
It seems to me I must have something wrong with the UFW rules, otherwise 
why would disabling it allow the drive to get a DCHP lease?
What have I got wrong?
Any ideas appreciated.
Cheers
Steve