[Swan-dev] overlapping address pools

D. Hugh Redelmeier hugh at mimosa.com
Sun Apr 20 08:23:40 EEST 2014

Antony and I are having a debate.

Address pools are a range of IP addresses that can be doled out by a 
host to clients.  IPv4-only.  Antony added this feature to Pluto.

Each conn can have an address pool.  If two conns' address pools are 
identical, they are shared (a single common pool).

If two address-pools overlap, but not exactly, each pool is separate in 
the addresspool logic: each pool could allocate the same address without 
being aware of it.

I think that this is crazy and should be considered an error: the conn 
specifying an overlapping pool should be rejected.

Antony thinks that the user might know what they are doing so that the 
conn loading should succeed, but with a warning.

My feeling is that this is like Russian Roulette: Bad Things will happen 
if both conns allocate the same address.  Which can be the only reason to 
have overlapping addresspools.  Great idea in security software.

What the heck is the use-case?

Alternative "I want this to work, dammit" approach: when the second
conn is loaded, chop off the overlap from one range or the other
(assuming none of the addresses is in use) and proceed.  But scenario
seems too obscure and insufficiently useful to be worth investing much
effort into.  (The current simpler addresspool logic has taken a lot
of work already.)

So: you've heard my side.  Antony may present his view.

What do you think?

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