Eric Blake <ebl...@redhat.com> wrote on 08/13/2010 03:56:12 PM: > [image removed]
> > On 08/13/2010 01:45 PM, Stefan Berger wrote: > >>> - // skip eth. bcast and mcast addresses, > >>> + // skip eth. bcast and mcast addresses (224.0.0.0 > > - > >>> + // 239.255.255.255), class E (255.*) > >>> // and zero address in DHCP Requests > >>> - if ((ntohl(vmaddr) & 0xc0000000) || vmaddr == 0) > > > http://en.wikipedia.org/wiki/Classful_network > > > > Class D addresses have highest bits with pattern 1110 0000 -> 0xe0 > > Class E addresses have highest bits with pattern 1111 0000 -> 0xf0 > > > > I think my masks are fine and the masking with 0xf0 00 00 00 should also > > include 254.* = 0xfe.* . > > In that case, the comments are wrong. Class E is more than 255.*, it is > 240.0.0.0-255.255.255.255. And in that case, the bit operations can be > simplified: > > if ((ntohl(vmaddr) & 0xc0000000) == 0xc0000000) || vmaddr == 0) > > In other words, the logic bug is that we were rejecting IP addresses > that had 1 or 2, but not all three, of the top three bits set. The > desired action is to reject IP packets if all three of the top bits are > simultaneously set. Right, the comment was not correct. I think the simplified if should be if ((ntohl(vmaddr) & 0xe0000000) == 0xe0000000) || vmaddr == 0) That then covers class D and E since this mask then covers 0xe0.00.00.00 - 0xff.ff.ff.ff = 225.0.0.0 - 255.255.255.255. > > Let's see a v2 that gets the comments right, and uses the simpler logic. Coming soon. Stefan
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