Re: [homenet] Which IP addresses must be avoided?

Ray Bellis <ray@bellis.me.uk> Tue, 17 May 2016 16:35 UTC

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From: Ray Bellis <ray@bellis.me.uk>
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Date: Tue, 17 May 2016 17:35:16 +0100
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Subject: Re: [homenet] Which IP addresses must be avoided?
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On 17/05/2016 16:31, Juliusz Chroboczek wrote:

> I just received a bug report for shncpd from somebody who noted that
> shncpd's DHCPv4 server will happily assign addresses a.b.c.0 and a.b.c.255
> to clients.  That's obviously broken.

As others have pointed out, that's actually perfectly legal.

However some operators have (had?) "classful" firewall rules that
prohibit packets that come from IP addresses that would have been
considered a broadcast address in a pre-CIDR world.

This very problem bit me on the backside back in about 2001 when I had
to update the RADIUS server I had written to prevent it from issuing .0
and .255 because my DSL customers getting assigned those addresses
couldn't reach Microsoft's website.

Ray