• Yasuyuki Kozakai's avatar
    [NETFILTER]: Add nf_conntrack subsystem. · 9fb9cbb1
    Yasuyuki Kozakai authored
    
    
    The existing connection tracking subsystem in netfilter can only
    handle ipv4.  There were basically two choices present to add
    connection tracking support for ipv6.  We could either duplicate all
    of the ipv4 connection tracking code into an ipv6 counterpart, or (the
    choice taken by these patches) we could design a generic layer that
    could handle both ipv4 and ipv6 and thus requiring only one sub-protocol
    (TCP, UDP, etc.) connection tracking helper module to be written.
    
    In fact nf_conntrack is capable of working with any layer 3
    protocol.
    
    The existing ipv4 specific conntrack code could also not deal
    with the pecularities of doing connection tracking on ipv6,
    which is also cured here.  For example, these issues include:
    
    1) ICMPv6 handling, which is used for neighbour discovery in
       ipv6 thus some messages such as these should not participate
       in connection tracking since effectively they are like ARP
       messages
    
    2) fragmentation must be handled differently in ipv6, because
       the simplistic "defrag, connection track and NAT, refrag"
       (which the existing ipv4 connection tracking does) approach simply
       isn't feasible in ipv6
    
    3) ipv6 extension header parsing must occur at the correct spots
       before and after connection tracking decisions, and there were
       no provisions for this in the existing connection tracking
       design
    
    4) ipv6 has no need for stateful NAT
    
    The ipv4 specific conntrack layer is kept around, until all of
    the ipv4 specific conntrack helpers are ported over to nf_conntrack
    and it is feature complete.  Once that occurs, the old conntrack
    stuff will get placed into the feature-removal-schedule and we will
    fully kill it off 6 months later.
    Signed-off-by: default avatarYasuyuki Kozakai <yasuyuki.kozakai@toshiba.co.jp>
    Signed-off-by: default avatarHarald Welte <laforge@netfilter.org>
    Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@mandriva.com>
    9fb9cbb1