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(Pi router & DNS and ...) Re: Berkeley Pi: Getting ready for next week.

From: "tom r lopes" <tomrlopes@gmail.com>
Subject: Berkeley Pi: Getting ready for next week.
Date: Sat, 22 Feb 2020 18:51:13 -0800



So I have been thinking about how to make the Pi get togethers better.

Problem is, It'd be nice to run the Pi headless so you don't need to lug
around
monitors and stuff.  But at a Cafe you don't have access to the router, so
how do
you find the Raspberry Pi ip address?
So I thought to just bring in my own router.
How about a Pi 4 as router!   So I followed the tutorial on raspberrypi.org
.
Now we have a Pi 4 with USB wifi dongle.  The USB connects to Cafe Blue
Door
WIFI which is then shared to the builtin WIFI.
So the Pi 4 broadcasts a network as "Pihub" with a passphrase "BerkeleyPi"
You can connect to Pihub and the Pi 4 does dhcp and bridges the connection
to
Cafe Blue Door WIFI.  I'll attach a screen with output of the dhcp so you
can see the
ip there.
I still have to figure out how you'd distinguish between various Pi clients
(maybe hostname?)


So ... pi.berkeleylug.com - dynamic DNS updates - at least proof-of-concept
has been done.  Can make that live for pi.berkeleylug.com in not too
horribly distant future (when I have some time, and Thomas is ready).
Could potentially even adjust to have clients be able to update their
own DNS entries - as subdomains of pi.berkeleylug.com (and
disallowing www.pi.berkeleylug.com - or anything else we'd want to not
let "any client" update for its own IP).  But with RFC-1918 IPs,
might have to have that Rasperry Pi router do a wee bit more on that ...
or maybe have the clients just update on the Rasperry Pi router itself,
and it could also serve (augmented) DNS to the clients, and have
the clients update their DNS - for many/most dhcp clients that's also
the default behavior anyway - at least they attempt to update DNS
for themselves ... even the relatively standard Linux dhclient
does/attempts this.

Ah, and too, RFC-1918 ... not Internet addressable, ... but, IPv6, no
shortage of IPv6 IPs ... if the venue doesn't provide those, the
Pi router could initiate an IPv6 tunnel, and would then have plenty of
Internet addressable IPv6 IPs for the Pis at the event, ... and they
could update their DNS via dynamic DNS updates.

Also, I have the LUG DNS domains set up so anyone/anything can do
AXFR and dump the whole domain ... so that'd be fairly easy way to see
who/what is on the (sub)domain.

Oh, and if one does full routing on Pi to share upstream Wi-Fi &
(single) IPv4 IP, that may restrict bandwidth, as venue's Wi-Fi may do
(relatively) fair sharing among the IPs it has actively allocated.
Might be feasible way(s) to do that a bit differently, so the
Pi router doesn't reduce downstream Pis bandwidth through limiting to
a single IPv4 of the venue Wi-Fi, but rather uses and passes down (even if
NATed), one per (client) Pi.

Anyway, I may have to think about that some more ... and/or (likely)
someone has already figured out some good/slick solutions to this - and
relevant software/configuration and such, already.

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