Subj : Re: 0.0.0.0
To   : Michiel van der Vlist
From : Wilfred van Velzen
Date : Thu Jan 14 2016 01:12 pm

Hi Michiel,

On 2016-01-14 12:48:22, 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?

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


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

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

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

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

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


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

Only 4 seems applicable when it's returned in a DNS query...

Bye, Wilfred.

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