[Bloat] mDNS

[Juliusz Chroboczek]

> But my point is that the OpenWrt router has no way to predict what
> address/subnet will be assigned to its WAN port.

In principle, the ISP should assign either a global address, or an address in
the range 100.64.0.0/10 (RFC 6598).  This range was deliberately chosen to
not collide with RFC 1918 space, so that the NAT box can choose any RFC 1918
prefix on its downstream interfaces.

In practice, however, ISPs don't necessarily obey the RFCs, and people do
chain NAT boxes, so none of the above is guaranteed.

> Consequently, at boot-time, OpenWrt should simply choose some different
> subnet for its LAN subnet(s), and then advertise an mDNS name.

I'm not sure how that could happen at boot time, it would need to happen
whenever a DHCPv4 lease changes.  This implies that the router might need
to renumber if the ISP changes its allocation, and there are no
renumbering procedures for IPv4 (I'm not sure if anyone implements RFC 3203).

It would also make addressing non-deterministic, which would make
debugging slightly more difficult.  But then, we already have
non-deterministic addressing in IPv6, so I guess that's something we can
live with.

-- Juliusz