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. Let's see a v2 that gets the comments right, and uses the simpler logic. -- Eric Blake eblake@xxxxxxxxxx +1-801-349-2682 Libvirt virtualization library http://libvirt.org
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