Subj : 0.0.0.0
To   : Wilfred van Velzen
From : Michiel van der Vlist
Date : Thu Jan 14 2016 12:48 pm

Hello Wilfred,

On Thursday January 14 2016 11:40, you wrote to me:

 MvdV>> https://en.wikipedia.org/wiki/0.0.0.0

 MvdV>> So hard coding 0.0.0.0 als "target unavailable" may block more
 MvdV>> than intended.

 WV> Like what?

I don't know. The Wiki article mentions five possible uses:


1 The address a host claims as its own when it has not yet been assigned an 
address. Such as when sending the initial DHCPDISCOVER packet when using DHCP.

2 The address a host assigns to itself when address request via DHCP has 
failed, provided the host's IP stack supports this. This usage has been 
replaced with the APIPA mechanism in modern operating systems.

3 A way to specify "any IPv4-host at all". It is used in this way when 
specifying a default route.

4 A way to explicitly specify that the target is unavailable.[1]

5 A way to specify "any IPv4 address at all". It is used in this way when 
configuring servers (i.e. when binding listening sockets). This is known to TCP 
programmers as INADDR_ANY. (bind(2) binds to addresses, not interfaces


Only # 4 is what I would suggest for unconditional blocking. All the others... 
I am not in favour of hard coded unconditional unmaskable blocking without 
knowing exactly what I block.



Cheers, Michiel

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