Re: [EXIM] To relay or not to relay, that is the question...

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Author: Jeffrey Goldberg
Date:  
To: Steve Lamb
CC: Exim-users
Subject: Re: [EXIM] To relay or not to relay, that is the question...
On Fri, 31 Jul 1998, Steve Lamb wrote:


> >sender_net_accept_relay = 192.168.0.0/16


Instead of 192.168.0.0/0

>
> <DUNCE>
>     OK, what is the difference?
> </DUNCE>


The number after the slash tells you the number of significant bits of the
ip address. The parts between dots correspond to 8 bits each (numbers
between 0-255).

So 192.168.0.0/16

is sort of like

192.168.*.*

while

192.168.0.0/0

is like

*.*.*.*

since 0 bits are significant.

A reason for the / notation is that it allows easier masking of groups of
addresses that don't always fall into blocks of 8 bits. So one could have

192.168.1.128/25

(I think I've got that right).

-j
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Jeffrey Goldberg                +44 (0)1234 750 111 x 2826
 Cranfield Computer Centre      FAX         751 814
 J.Goldberg@???     http://WWW.Cranfield.ac.uk/public/cc/cc047/
Relativism is the triumph of authority over truth, convention over justice.



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