[Lsr] IPv6 Flow Label QOS marking support for 5-tuple ECMP / LAG / MLAG hash

[Gyan Mishra <[e-mail]>]

Dear LSR WG experts,


Does anyone know if vendors have started or plan to start supporting IPv6
flow label 5-tuple dscp marking for ECMP hashing.

IPv6 flow label support for ECMP

https://tools.ietf.org/html/rfc6437

IPv4 has traditionally always utilized recommended BCP of flow based load
balancing due to issues related to out of order and reordering of packets.
Although per packet load balancing is supported by most vendors it is not
recommended due to forwarding plane impact.

This IPv6 flow label feature of 5-tuple hash provides significant
advantages for operators much needed ECMP load balancing entropy as compare
to traditional “flow or session” based load balancing which is the case as
well with MPLS entropy label RFC 6790 load balancing contrasted below.

IPv6 flow label has significant  benefits for operators deploying  SRv6
which utilizes the IPv6 data plane to now have “native” built in ECMP
entropy as part of the protocol as compare to its predecessor IPv4.

This gives SRv6 another significant edge over MPLS predecessor.

Excerpt from RFC 6437:

      Forwarding nodes such as routers and load distributors MUST NOT
      depend only on Flow Label values being uniformly distributed.  In
      any usage such as a hash key for load distribution, the Flow Label
      bits MUST be combined at least with bits from other sources within
      the packet, so as to produce a constant hash value for each flow
      and a suitable distribution of hash values across flows.
      Typically, the other fields used will be some or all components of
      the usual 5-tuple.  In this way, load distribution will still
      occur even if the Flow Label values are poorly distributed.

   Although uniformly distributed flow label values are recommended
   below, and will always be helpful for load distribution, it is unsafe
   to assume their presence in the general case, and the use case needs
   to work even if the flow label value is zero.

   As a general practice, packet flows should not be reordered, and the
   use of the Flow Label field does not affect this.  In particular, a
   Flow label value of zero does not imply that reordering is
   acceptable.



Below comparison of IPv6 flow label benefits over MPLS entropy label:



! MPLS Entropy label

https://tools.ietf.org/html/rfc6790



As a comparison to MPLS entropy label, the mpls entropy label reduces
the control plane label binding and LFIB forwarding plane data
structure by not having a per ECMP path label allocation per FEC by
adding an additional entropy label to the label stack.



However MPLS entropy label is still uses the traditional flow or
session based load balancing algorithm which results in

uneven load balancing.



Kind Regards


Gyan



-- 

<http://www.verizon.com/>

*Gyan Mishra*

*Network Solutions A**rchitect *



*M 301 502-134713101 Columbia Pike *Silver Spring, MD