• Tom Herbert's avatar
    ipv6: Flow label state ranges · 82a584b7
    Tom Herbert authored
    This patch divides the IPv6 flow label space into two ranges:
    0-7ffff is reserved for flow label manager, 80000-fffff will be
    used for creating auto flow labels (per RFC6438). This only affects how
    labels are set on transmit, it does not affect receive. This range split
    can be disbaled by systcl.
    
    Background:
    
    IPv6 flow labels have been an unmitigated disappointment thus far
    in the lifetime of IPv6. Support in HW devices to use them for ECMP
    is lacking, and OSes don't turn them on by default. If we had these
    we could get much better hashing in IPv6 networks without resorting
    to DPI, possibly eliminating some of the motivations to to define new
    encaps in UDP just for getting ECMP.
    
    Unfortunately, the initial specfications of IPv6 did not clarify
    how they are to be used. There has always been a vague concept that
    these can be used for ECMP, flow hashing, etc. and we do now have a
    good standard how to this in RFC6438. The problem is that flow labels
    can be either stateful or stateless (as in RFC6438), and we are
    presented with the possibility that a stateless label may collide
    with a stateful one.  Attempts to split the flow label space were
    rejected in IETF. When we added support in Linux for RFC6438, we
    could not turn on flow labels by default due to this conflict.
    
    This patch splits the flow label space and should give us
    a path to enabling auto flow labels by default for all IPv6 packets.
    This is an API change so we need to consider compatibility with
    existing deployment. The stateful range is chosen to be the lower
    values in hopes that most uses would have chosen small numbers.
    
    Once we resolve the stateless/stateful issue, we can proceed to
    look at enabling RFC6438 flow labels by default (starting with
    scaled testing).
    Signed-off-by: default avatarTom Herbert <tom@herbertland.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    82a584b7
ipv6.h 26.8 KB