Netmask settings for Solaris 10 Zones

When the zone is created a large number of files are copied into the new zone. However, the netmask file seems to be generated as an empty file.

Consequently, when you enter ifconfig you end up seeing something like:
...
eri0:2: flags=1000843 mtu 1500 index 2
zone zone2
inet 123.123.123.11 netmask ffff0000 broadcast 123.123.123.255
...

Now obviously you can use ifconfig in the global zone to change the netmask setting interactively. That works. However, a reboot wipes that out. So you have to login to the console of the zone and amend the copied netmask file so that it contains a line like:
123.123.123.0 255.255.255.0

Alternatively, you can access the netmasks file via the global zone filesystem.