doc/OSPF-SR.rst

   1 OSPF Segment Routing
   2 ====================
   3
   4 This is an EXPERIMENTAL support of draft draft-ietf-ospf-segment-routing-extensions-24.
   5 DON'T use it for production network.
   6
   7 Implementation details
   8 ----------------------
   9
  10 Segment Routing used 3 differents OPAQUE LSA in OSPF to carry the various
  11 information:
  12
  13  - Router Information: flood the Segment Routing capabilities of the node.
  14    This include the supported algorithms, the Segment Routing Global Block
  15    (SRGB) and the Maximum Stack Depth (MSD).
  16  - Extended Link: flood the Adjaceny and Lan Adjacency Segment Identifier
  17  - Extended Prefix: flood the Prefix Segment Identifier
  18
  19 The implementation follow previous TE and Router Information code. It used the
  20 OPAQUE LSA functions define in ospf_opaque.[c,h] as well as the OSPF API. This
  21 latter is mandatory for the implementation as it provides the Callback to
  22 Segment Routing functions (see below) when an Extended Link / Prefix or Router
  23 Information is received.
  24
  25 Following files where modified or added:
  26  - ospd_ri.[c,h] have been modified to add the new TLVs for Segment Routing.
  27  - ospf_ext.[c,h] implement RFC7684 as base support of Extended Link and Prefix
  28    Opaque LSA.
  29  - ospf_sr.[c,h] implement the earth of Segment Routing. It adds a new Segment
  30    Routing database to manage Segment Identifiers per Link and Prefix and
  31    Segment Routing enable node, Callback functions to process incoming LSA and
  32    install MPLS FIB entry through Zebra.
  33
  34 The figure below shows the relation between the various files:
  35
  36  - ospf_sr.c centralized all the Segment Routing processing. It receives Opaque
  37    LSA Router Information (4.0.0.0) from ospf_ri.c and Extended Prefix
  38    (7.0.0.X) Link (8.0.0.X) from ospf_ext.c. Once received, it parse TLVs and
  39    SubTLVs and store information in SRDB (which is defined in ospf_sr.h). For
  40    each received LSA, NHLFE is computed and send to Zebra to add/remove new
  41    MPLS labels entries and FEC. New CLI configurations are also centralized in
  42    ospf_sr.c. This CLI will trigger the flooding of new LSA Router Information
  43    (4.0.0.0), Extended Prefix (7.0.0.X) and Link (8.0.0.X) by ospf_ri.c,
  44    respectively ospf_ext.c.
  45  - ospf_ri.c send back to ospf_sr.c received Router Information LSA and update
  46    Self Router Information LSA with paramters provided by ospf_sr.c i.e. SRGB
  47    and MSD. It use ospf_opaque.c functions to send/received these Opaque LSAs.
  48  - ospf_ext.c send bacl to ospf_sr.c received Extended Prefix and Link Opaque
  49    LSA and send self Extended Prefix and Link Opaque LSA through ospf_opaque.c
  50    functions.
  51
  52 ::
  53
  54                     +-----------+     +-------+
  55                     |           |     |       |
  56                     | ospf_sr.c +-----+  SRDB |
  57         +-----------+           +--+  |       |
  58         |           +-^-------^-+  |  +-------+
  59         |             |   |   |    |
  60         |             |   |   |    |
  61         |             |   |   |    +--------+
  62         |             |   |   |             |
  63     +---v----------+  |   |   |       +-----v-------+
  64     |              |  |   |   |       |             |
  65     | ospf_ri.c    +--+   |   +-------+ ospf_ext.c  |
  66     | LSA 4.0.0.0  |      |           | LSA 7.0.0.X |
  67     |              |      |           | LSA 8.0.0.X |
  68     +---^----------+      |           |             |
  69         |                 |           +-----^-------+
  70         |                 |                 |
  71         |                 |                 |
  72         |        +--------v------------+    |
  73         |        |                     |    |
  74         |        | ZEBRA: Labels + FEC |    |
  75         |        |                     |    |
  76         |        +---------------------+    |
  77         |                                   |
  78         |                                   |
  79         |         +---------------+         |
  80         |         |               |         |
  81         +---------> ospf_opaque.c <---------+
  82                   |               |
  83                   +---------------+
  84
  85       Figure1: Overview of Segment Routing interaction
  86
  87
  88 Configuration
  89 -------------
  90
  91 Here it is a simple example of configuration to enable Segment Routing. Note
  92 that ``opaque capability`` must be set to activate Opaque LSA prior to Segment
  93 Routing.
  94
  95 ::
  96
  97  router ospf
  98  ospf router-id 192.168.1.11
  99  capability opaque
 100   mpls-te on
 101   mpls-te router-address 192.168.1.11
 102  router-info area 0.0.0.0
 103  segment-routing on
 104  segment-routing global-block 10000 19999
 105  segment-routing node-msd 8
 106  segment-routing prefix 192.168.1.11/32 index 1100
 107
 108 The first segment-routing statement enable it. The Second one set the SRGB,
 109 third line the MSD and finally, set the Prefix SID index for tha given prefix.
 110 Note that only prefix of Loopback interface could be configured with a Prefix
 111 SID.
 112
 113 Known limitations
 114 -----------------
 115
 116  - Only single Area is supported. ABR is not yet supported
 117  - Only SPF algorithm is supported
 118  - Extended Prefix Range is not supported
 119
 120 Credits
 121 -------
 122  * Author: Anselme Sawadogo <anselmesawadogo@gmail.com>
 123  * Author: Olivier Dugeon <olivier.dugeon@orange.com>
 124  * Copyright (C) 2016 - 2018 Orange Labs http://www.orange.com
 125
 126 This work has been performed in the framework of the H2020-ICT-2014
 127 project 5GEx (Grant Agreement no. 671636), which is partially funded
 128 by the European Commission.
 129
 130