Re: [Detnet] IPv6 encapsulation in dataplane doc

["Jouni" <[e-mail]>]

Hi,

 

Yes, we discussed this to an extent in the last call. I've been thinking
this a bit more lately (cross country skiing conditions have been great thus
you got a lot of time while on the skiing tracks ;) Few concerns/points to
think I see here are:

* End systems cannot participate to DetNet service layer packet elimination
& duplication business. If they still do e.g. using DetNet DstOpt that is
separate from subnet/transport layer provided service.

* Different subnet/transport layer segments in the DetNet domain are likely
to use their own sequencing and duplication & elimination solutions. I am
not sure how independent those will be e.g., is the sequence numbering
unified across or only per segment. The former is not IMO easy and the
latter easily reduces to single points between segments to handle number
book keeping properly.  

 

Regardless the above I am keen to explore this alternative approach..

 

-          Jouni

 

 

From: detnet [mailto:[e-mail]] On Behalf Of Lou Berger
Sent: Wednesday, February 7, 2018 17:00 PM
To: Pascal Thubert (pthubert) <[e-mail]>; [e-mail]
Subject: Re: [Detnet] IPv6 encapsulation in dataplane doc

 

Pascal/all,

At the last interim a proposal was made to simplify IP processing, at least
for the initial detnet solution, by leaving PREF to the subnet/transport
layers (i.e., TSN and MPLS) and providing DetNet flow identification based
on typical IP 5-tuple perhaps + dscp. This approach has several benefits
beyond simplification, notably it will work for both ipv4 and IPv6, and
doesn't require any modification to encapsulation / formats.

It would be really valuable to get feedback from the whole working group if
this simplification is acceptable or has unacceptable limitations.

Lou

On February 7, 2018 8:28:02 AM "Pascal Thubert (pthubert)"
<[e-mail] <mailto:[e-mail]> > wrote:

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

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