I'm using iptables v1.4.21, which doesn't accept 64 bit mark targets. Is there a newer version that is supposed to support 64 bit marks?
Edit:
$ uname -a
Linux sindhu 3.19.0-28-generic #30-Ubuntu SMP Mon Aug 31 15:52:51 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
$ iptables -I INPUT -s 6.6.6.6 -j MARK --set-xmark 1234567812345678/0xffffffffffffffff
MARK: Could not determine whether revision 2 is supported, assuming it is.
MARK: Could not determine whether revision 2 is supported, assuming it is.
iptables v1.4.21: MARK: bad mark value for option "--set-xmark", or out of range.
Use full 64bit mark on 64bit archs