Comment 8 for bug 173470

The broadcast address is correct (see the 'lan' interface below). The reason I'm not using @LOCAL or @IF(lan) is a different bug (http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=343535). My network setup has changed a bit since then but the bug apparently still exists: if i use @LOCAL or @IF(lan), I get no broadcast packets over 631.

$ ip a s
1: lo: <LOOPBACK,UP,10000> mtu 16436 qdisc noqueue
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
2: dsl: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:40:f4:8b:2d:15 brd ff:ff:ff:ff:ff:ff
3: lan: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:40:f4:8b:2d:14 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.1/24 brd 192.168.1.255 scope global lan
4: unused: <BROADCAST,MULTICAST> mtu 1500 qdisc noop qlen 1000
    link/ether 00:40:f4:8b:2d:13 brd ff:ff:ff:ff:ff:ff
5: modem: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:40:f4:8b:2d:12 brd ff:ff:ff:ff:ff:ff
    inet 192.168.8.2/30 brd 192.168.8.3 scope global modem
14: ppp0: <POINTOPOINT,MULTICAST,NOARP,UP,10000> mtu 1456 qdisc htb qlen 3
    link/ppp
    inet 217.86.173.33 peer 217.5.98.2/32 scope global ppp0
% ip r s
217.5.98.2 dev ppp0 proto kernel scope link src 217.86.173.33
192.168.8.0/30 dev modem proto kernel scope link src 192.168.8.2
192.168.1.0/24 dev lan proto kernel scope link src 192.168.1.1
default dev ppp0 scope link

The machine also runs shorewall but there are no rules that limit traffic on the lan interface.
CUPS' error_log doesn't show any error message when trying @LOCAL or IF(lan). Just a few debug lines:
I [03/Dec/2007:21:22:15 +0100] Listening to 127.0.0.1:631 (IPv4)
I [03/Dec/2007:21:22:15 +0100] Listening to 192.168.1.1:631 (IPv4)
I [03/Dec/2007:21:22:15 +0100] Listening to /var/run/cups/cups.sock (Domain)
...
I [03/Dec/2007:21:22:15 +0100] Listening to 127.0.0.1:631 on fd 8...
I [03/Dec/2007:21:22:15 +0100] Listening to 192.168.1.1:631 on fd 9...
I [03/Dec/2007:21:22:15 +0100] Listening to /var/run/cups/cups.sock on fd 10...
I [03/Dec/2007:21:22:15 +0100] Resuming new connection processing...
D [03/Dec/2007:21:22:16 +0100] cupsdNetIFUpdate: "lo" = localhost...
D [03/Dec/2007:21:22:16 +0100] cupsdNetIFUpdate: "lan" = server.jknet...
D [03/Dec/2007:21:22:16 +0100] cupsdNetIFUpdate: "modem" = 192.168.8.2...
D [03/Dec/2007:21:22:16 +0100] cupsdNetIFUpdate: "ppp0" = 217.86.173.33...

Notably absent from this log is a line like:

I [03/Dec/2007:21:23:52 +0100] Sending browsing info to 192.168.1.255:631 (IPv4)

I only get that when specifying the broadcast address directly.