File-based net lists

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Autor: Philip Hazel
Fecha:  
A: exim-users
Asunto: File-based net lists
There have been some requests for the ability to hold lists of networks
in separate files, instead of having to have large lists in the config-
uration file.

My first plan was to try to arrange for some kind of lookup item, along
the lines of the facility in host lists, but I got defeated because of
the problem of masks. I suspect that the sort of files people actually
want will have entries along the lines of

131.111.0.0/255.255.0.0
203.111.56.0/255.255.255.0
5f03:1200:836f::/48

(the last one being an IPv6 address with a 48-bit mask, and yes, I will
provide this masking syntax for v4 addresses too). In other words, the
requirement will be for each item to have its own mask. Given this, I
cannot see any way of setting up any kind of keyed database lookup,
because you don't know what mask to apply to the subject address before
looking it up.

What I have implemented today, because I think it will be useful anyway,
is the ability to give a file name instead of a network specification in
a netlist. The file is then read, and each line interpreted as if it
were an item in the list. The reading happens each time the list is
scanned, so the file can be changed without restarting the daemon.

Does anybody think I should be doing more than this, and if so, have you
any bright ideas as to how to specify it? I don't want to do anything
like inferring Class B or Class C networks from IP addresses, because
this doesn't carry over to IPv6.

-- 
Philip Hazel                   University Computing Service,
ph10@???             New Museums Site, Cambridge CB2 3QG,
P.Hazel@???          England.  Phone: +44 1223 334714