An endtoend usage of the IPv6 flow label

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An end-to-end usage of the IPv6 flow label

• ltdraft-metzler-ipv6-flowlabel-00.txtgt
• jochen.metzler_at_icn.siemens.de

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Today's definition of the flow label 1

• The usage of the flow label is not completely
  specified within RFC2460
• "The 20-bit Flow Label field in the IPv6 header
  may be used by a source to label sequences of
  packets for which it requests special handling by
  the IPv6 routers, such as non-default quality of
  service or "real-time" service."
• "Hosts or routers that do not support the
  functions of the Flow Label field are required to
  set the field to zero when originating a packet,
  pass the field on unchanged when forwarding a
  packet, and ignore the field when receiving a
  packet."

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Today's definition of the flow label 2

• Understanding of the term flow
• "A flow is a sequence of packets sent from a
  particular source to a particular (unicast or
  multicast) destination for which the source
  desires special handling by the intervening
  routers."
• The flow is uniquely identified within the
  network by the flow label and its source address.
• All packets belonging to one flow should be
  treated within the network in the same way.

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End-to-end usage of the flow label 1

• Reasons from an application point of view
• common understanding of flows from an application
  point of view as well as from a network point of
  view.
• make use of QoS enhancements for flows (e.g.
  traffic engineering)
• request a special handling by the network for
  every single stream (e.g. wanting all packets
  belonging to one single stream to take the same
  way through the network)

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End-to-end usage of the flow label 2

• Usage from the Application
• End-to-end semantics of the flow label required
• flow label does not change, or
• network ensures that receivers receive packets
  with the same flow label as it has been sent by
  the data source
• Application must be able to select the label that
  should be used
• this does not mean, that the application can
  choose the label free
• Global Management of label Space
• unique (pseudo-randomly) assignment per IP source
  address

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Treatment of the flow label within the network

• Network elements that do not support the function
  of the flow label field MUST set the field to
  zero when originating a packet, pass the field on
  unchanged when forwarding a packet and ignore the
  field when receiving a packet.
• Network elements that do support the function of
  the flow label field but do not know the specific
  flow MUST set the field to zero when originating
  a packet, ignore the field when receiving a
  packet, pass the field on unchanged when
  forwarding a packet. The whole packet should be
  passed on in a standard way.
• Network elements that do support the function of
  the flow label and know the specific flow label
  MUST process that packet in the agreed way.
• Network elements MUST NOT change the flow label
  or MUST ensure that the original flow label would
  be re-set before the packet reaches its
  destination.

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Conclusion

• The flow label should have end-to-end
  characteristic.
• Minimize the restrictions to the network layer
• A fully standardized flow label would help both
  application and network design.

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Would You like to completely standardize the flow
label soon ?

• End-to-end usage of the label ?
• Access from the application ?