Ignoring bogus route 240.0.0.0/4

[Ondrej Zajicek]

On Tue, Sep 19, 2017 at 10:32:34PM +0200, Alexander Demenshin wrote:
> Hi,
> 
> Any reason why 240.0.0.0/4+ routes are ignored by bird (1.6.3)?

Hi

I do not know why it was implemented in BIRD originally in such way
and i had to need to question that, so it stayed is it was.

If Linux and BSD kernels does accept such routes, than it is a strong
reason to support that in BIRD, even if only for purpose of defining
blackhole static route.

While i agree that hardcoding administrative assignments is a bad idea, i
would see a case for special handling of 240.0.0.0/4 in contrast to other
'special' ranges. While other ranges were later administratively
reassigned from regular uncast forwarding range, 240.0.0.0/4 was reserved
for future since deep past, and therefore it is possible that it could be
handled in some completely different way in the future (like 224.0.0.0/4
is handled by FIBs differently than unicast). If you just handle it like
regular unicast and it is later defined as something completely
different, you cannot implement that without breaking backward
compatibility. So it seems strange to me that FIBs like Linux kernel does
handle it regularly (never tried that), but perhaps they expect that now
it will never be reassigned.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
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"To err is human -- to blame it on a computer is even more so."