Re: mast(4)

Mostly-new section in document:
http://www.monmouth.com/~jsd/vpn/ipsec+routing/mast.htm#sec-multi-access
including new figure:
http://www.monmouth.com/~jsd/vpn/ipsec+routing/mast.htm#fig-arp-needed

Executive summary:

Layer-2 addressing versus layer-3 addressing....

destination subnets may be disjoint, in which case life is simple
... but we must consider the case where they are not disjoint,
i.e. overlapping or even identical. There are good reasons for
non-disjoint destination subnets, including fault tolerance in
analogy to figure 3, mobility, and load-sharing to improve
throughput.

It is easy to see how to handle this situation. We treat the mast
device as a multi-access device just like ether (but without
ether's broadcast and multicast features). This is calld NBMA
- Non-Broadcast Multi-Access. When an IP packet arrives at
the mast device, we must consult the routing table(s) before
we can figure out what to do with it. Tunnel ID numbers play
the role corresponding to MAC addresses.