[Detnet] IPv6 encapsulation in dataplane doc

["Pascal Thubert (pthubert)" <[e-mail]>]

Dear all

This is about the IPv6 encapsulation and more precisely


                        Therefore, if a DetNet-aware end system only

   inserted the DetNet Destination Option into the IPv6 but e.g., a

   DetNet Edge node is configured to enforce an explicit route for the

   IPv6 packet using a source routing header, then it has no other

   possibility than add an outer tunneling IPv6 header with required

   extension headers in it.  The processing of IPv6 packets in a DetNet

   Edge node is discussed further in Section 6.4.1<https://tools.ietf.org/html/draft-ietf-detnet-dp-sol-01#section-6.4.1>.


With the current spec, a source sends a DetNet packet as

                    +---------------------------------+
                    |                                 |
                    |           DetNet Flow           |
                    |             Payload             |
                    |                                 |
                    /---------------------------------\
                    H   Optional DetNet DstOpt Hdr    H
                    \---------------------------------/
                    |          IPv6 header            |
                    |     (with set Flow label)       |
                    +---------------------------------+

And then the ingress node needs to re-encapsulate as



                    +---------------------------------+

                    |                                 |

                    |           DetNet Flow           |

                    |             Payload             |

                    |                                 |

                    /---------------------------------\

                    H        DetNet DstOpt Hdr        H
                    \---------------------------------/
                    |          IPv6 header            |
                    |     (with set Flow label)       |
                    +=================================+

                    |          Routing header         |

                    /---------------------------------\

                    H        DetNet DstOpt Hdr        H

                    \---------------------------------/

                    |          IPv6 header            |

                    |     (with set Flow label)       |

                    +---------------------------------+

This creates a duplication of the DetNet Destination Option.

There are alternatives


a)  whereby the packet is tunneled from the source to the detnet ingress, and based on its state the DetNet ingress accepts the packet, processes it and then resends it. The tunneled version of this could be:

                    +---------------------------------+
                    |                                 |
                    |           DetNet Flow           |
                    |             Payload             |
                    |                                 |
                    +---------------------------------+
                    |          IPv6 header            |
                    |   (dest = final destination)    |
                    /=================================\
                    H   Optional DetNet DstOpt Hdr    H
                    \---------------------------------/
                    |          IPv6 header            |
                    |   (dest = DetNet ingress edge)  |
                    |     (with set Flow label)       |
                    +---------------------------------+

Which allows the ingress to tunnel to the egress as follows:
                    +---------------------------------+
                    |                                 |
                    |           DetNet Flow           |
                    |             Payload             |
                    |                                 |
                    +---------------------------------+
                    |          IPv6 header            |
                    |      (to final destination)     |
                    +=================================+

                    |          Routing header         |

                    /---------------------------------\
                    H   Optional DetNet DstOpt Hdr    H
                    \---------------------------------/
                    |          IPv6 header            |
                    |   (dest = DetNet egress edge)   |
                    |     (with set Flow label)       |
                    +---------------------------------+



b)  whereby the PREF is done by the end nodes and the tunnel is transport only, meaning that there are 2 tunnels A and B and that the source sends twice a packet like this:

                    +---------------------------------+
                    |                                 |
                    |           DetNet Flow           |
                    |             Payload             |
                    |                                 |
                    /---------------------------------\
                    H   Optional DetNet DstOpt Hdr    H
                    \---------------------------------/
                    |          IPv6 header            |
                    |   (dest = DetNet ingress edge X)|
                    |     (with set Flow label)       |
                    +---------------------------------+

And then the ingress node needs to re-encapsulate as



                    +---------------------------------+

                    |                                 |

                    |           DetNet Flow           |

                    |             Payload             |

                    |                                 |

                    /---------------------------------\

                    H        DetNet DstOpt Hdr        H
                    \---------------------------------/
                    |          IPv6 header            |
                    |   (dest = final destination)    |
                    |     (with set Flow label)       |
                    +=================================+

                    |          Routing header         |

                    +---------------------------------+

                    |          IPv6 header            |

                    |   (dest = DetNet egress edge X) |

                    |     (with set Flow label)       |

                    +---------------------------------+

Cheers,

Pascal