# A bit of background is needed here.
#
#   - nahanni is the name of my machine on my local Ethernet.  My local
#     network is a subnet of a class C network.  This subnet has 29 bits for
#     for the network address and 3 bits for the host address.  Consequently,
#     "nahanni/29" matches anything on my local network.
#
#   - avalon is a (pseudonym) for a machine out on the interned that I trust
#     completely.
#
#   - zona is the name of my end of the PPP link to my old place of work.
#     This name corresponds to an IP address on their class C network.
#     Consequently, "zona/24" matches any IP address on their network.
#
#   - xnahanni is my end of my PPP link to the university (i.e. the Internet).
#
#   - dab-nahanni is my end of the PPP link to my new place of work.  They
#     have a class B network so "dab-nahanni/16" matches any IP address on
#     their network.

# Start from scratch.

ipfw flush

# Basic accept filters to provide local sanity.
# These are the IP addresses of the interfaces on my local machine.
# The first is an Ethernet interface.  The rest are PPP interfaces.

ipfw addf accept all from nahanni to 0/0
ipfw addf accept all from xnahanni to 0/0
# handled below:  ipfw addf accept all from zona to 0/0
# handled below:  ipfw addf accept all from dab-nahanni to 0/0

# Trust my local network.

ipfw addf accept all from nahanni/29 to 0/0

# Allow anything from avalon.

ipfw addf accept all from avalon to 0/0

# Allow anything from our old work (they have a class C network so /24 is appropriate).
# This also allows anything from zona (our end of the work PPP link).

ipfw addf accept all from zona/24 to 0/0

# Allow anything from the new work (and from our end of the PPP link to the
# new place of work).

ipfw addf accept all from dab-nahanni/16 to 0/0

# Allow me to contact any external UDP service and others to contact a few
# of my special udp services.

ipfw addf accept udp from 0/0 to 0/0 900:5000 domain bootp talk ntalk route

# Allow me to contact other services available on untrusted hosts.
# This one is a bit tricky.  We allow packets from any foreign port number
# to any local port in the range 900 to 5000.  When we are outbound, privileged
# applications use port numbers slightly less than 1024 and normal applications
# allow the local port number to be set by the system (which always picks
# port numbers in the range 1024 to 5000.
# The only services that we offer are for port numbers either below 900
# or over 5000.
#
# This approach theoretically allows outsiders to connect to any services
# that we may offer in the 900:5000 range.  The /etc/services file lists
# couple of services in this range (in my humble opinion, this is a bug
# in the /etc/services file).  Since we don't run any of these services,
# allowing outsiders to connect to services in this range doesn't constitute
# a security hole.

ipfw addf accept tcp from 0/0 to 0/0 900:5000

# Allow others to contact X-servers on my local network.
# Depend on xhosts to protect things.

ipfw addf accept tcp from 0/0 to nahanni/29 6000

# Allow others to connect to a few basic services.
# We don't actually run the auth service.  Allowing it means that others
# get a "connection refused" which is better than the total silence that
# they get if we block it.  Also, I've noticed a few sites try to connect
# to it when I send them e-mail.  Might as well be polite ...
#
# Note that I don't accept packets destined for sendmail.  I send my e-mail
# via the Internet but I receive my e-mail via uucp. If you get your e-mail
# via the Internet then you'll have to add smtp to the list of ports to allow.

ipfw addf accept tcp from 0/0 to 0/0 daytime time nameserver auth

# Allow icmp stuff from anywhere (this isn't described in the README - sorry).

ipfw addf accept icmp from 0/0 to 0/0