* Tom Callaway > On 03/02/2012 04:39 PM, Tore Anderson wrote: >> This one *most likely* works (it assumes /sbin/dhclient in Fedora will >> *always* use a link-local source address when building a DHCPv6 request. >> I believe that is the case, but I have not reviewed its source code to >> verify): >> >> ip6tables -A INPUT -p udp --dport 546 -d fe80::/64 -j ACCEPT > > Can you please confirm that in the source code? I agree that this seems > like the better option.
Hi again, I've been poking around in the ISC-dhcp code for a while now, but I think I don't have sufficient C skills to follow what is going on 100%. I *think* it doesn't specify the source address anywhere, leaving it up to either glibc or the kernel to pick one when the packet is put on the wire. The ff02::1:2 multicast address (All_DHCP_Relay_Agents_and_Servers) has the link-local scope, so if the entity doing source address selection (be it the kernel or glibc) implements RFC 3484 correctly, the link-local source should be chosen, due to the the "prefer matching scope" rule. (If that didn't come into play, the "prefer longest common prefix" rule would also have ensured the link-local address was used for the source.) On my own system, where the interface is configured both with a link-local address and a global address (from SLAAC) at the time DHCPv6 is invoked, the link-local address is being used (so the "-d fe80::/64" restriction works for me). So, based on observed behaviour, my reading of the IETF standards, and the fact that I cannot find anything that would suggest otherwise in the ISC dhcp sources; my estimate is that it's >95% certain that including "-d fe80::/64" will work in all cases. Or, to put it another way, it's ∞ better than what we have today, and since I assume people would be more comfortable with including that particular restriction in an enabled-by-default ip6tables exception, I say go for it. If it turns out there's someone out there it won't work for, then we can consider changing the rule (or the DHCPv6 client). Best regards, -- Tore Anderson -- devel mailing list devel@lists.fedoraproject.org https://admin.fedoraproject.org/mailman/listinfo/devel
