rfc1992.txt

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4.2 An Example

   Figure 2 shows a physical network.  Hosts are drawn as squares,
   routers as diamonds, and communication links as lines.  The network
   shown has the following components: five ethernets ---EA through EE;
   five routers---RA through RE; and four hosts---HA through HD. Routers
   RA, RB, and RC interconnect the backbone ethernets---EB, EC and ED.
   Router RD connects backbone EC to a network consisting of ethernet EA
   and hosts HA and HB.  Router RE interconnects backbone ED to a
   network consisting of ethernet EE and hosts HC and HD. The assigned
   locators appear in lower case beside the corresponding physical
   entity.

   Figure 3 shows a Nimrod map for that network.  The nodes of the map
   are represented as squares.  Lines connecting nodes represent two
   adjacencies in opposite directions.  Different regions of the network
   are represented at different detail.  Backbone b1 is represented as a
   single node.  The region of the network with locators prefixed by "a"
   is represented as a single node.  The region of the network with
   locators prefixed by "c" is represented in full detail.







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RFC 1992              Nimrod Routing Architecture            August 1996


4.3 Multiple Locator Assignment

   Physical elements can form part of, or implement, more than one node.
   In this sense it can be said that they can be assigned more than one
   locator.  Consider figure 4, which shows a physical network.  This
   network is composed of routers (RA, RB, RC, and RD), hosts (HA, HB,
   and HC), and communication links.  Routers RA, RB, and RC are
   connected with point-to-point links.  The two horizontal lines in the
   bottom of the figure represent ethernets.  The figure also shows the
   locators assigned to hosts and routers.

   In figure 4, RA and RB have each been assigned one locator (a:t:r1
   and b:t:r1, respectively).  RC has been assigned locators a:y:r1 and
   b:d:r1; one of these two locators shares a prefix with RA's locator,
   the other shares a prefix with RB's locator.  Hosts HA and HB have
   each been assigned three locators.  Host HC has been assigned one
   locator.  Depending on what communication paths have been set up
   between points, different Nimrod maps result.  A possible Nimrod map
   for this network is given in figure 5.
































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RFC 1992              Nimrod Routing Architecture            August 1996


                                             a:h1 +--+      a:h2 +--+
                                                  |HA|           |HB|
                                                  |  |           |  |
                                                  +--+           +--+
                                           a:e1    |              |
                                               --------------------- EA
                                                       |
                                 /\                    /\
                                /RB\ b1:r1            /RD\ b2:r1
                               /\  /\                 \  /
                              /  \/  \                 \/
    EB         b1:t:e1       /        \                 |   EC
    ------------------------          -------------------------- b2:e1
               /                             \
              /                               \
             /\                                \
            /RA\ b1:r2                          \/\
            \  /                                /RC\  b2:t:r2
             \/                                 \  /
               \                                 \/
                \                               /   ED
                  ----------------------------------- b3:t:e1
                                    |
                                    |
                                    |
                                   /\
                                  /RE\ b3:t:r1
                                  \  /
                      EE           \/
                      -----------------------------   c:e1
                         |                   |
                        +--+                +--+
                        |HC|   c:h1         |HD|    c:h2
                        |  |                |  |
                        +--+                +--+


                    Figure 2:  Example Physical Network













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                             +-----+               +-----+
   +----------+              |     |               |     |
   |          |--------------| b2  | --------------| a   |
   |          |              |     |               |     |
   |    b1    |              +-----+               +-----+
   |          |                 |
   |          |                 |
   |          |                 |
   +----------+                 |
               \                |
                \               |
                 \              |
                  \             |
                   \         +--------+
                    \        |        |
                     ------- | b3:t:e1|
                             |        |
                             +--------+
                                |
                                |
                                |
                                |
                             +-------+
                             |       |
                             |b3:t:r1|
                             |       |
                             +-------+
                                  |
                 +-----+       +-----+     +-----+
                 |     |       |     |     |     |
                 | c:h1|-------| c:e1|-----| c:h2|
                 |     |       |     |     |     |
                 +-----+       +-----+     +-----+



                           Figure 3:  Nimrod Map














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RFC 1992              Nimrod Routing Architecture            August 1996


                      a:t:r1              b:t:r1
                         +--+            +--+
                         |RA|------------|RB|
                         +--+            +--+
                           \             /
                            \           /
                             \         /
                              \       /
                               \     /
                                \   /
                                 \ /
                                  \
                                 +--+
                                 |RC|  a:y:r1
                                 +--+  b:d:r1
                                  |
                     ---------------------------
                      |        |             |
             a:y:h1  +--+     +--+          +--+    a:y:h2
             b:d:h2  |HA|     |RD| c:r1     |HB|    b:d:h1
             c:h1    +--+     +--+          +--+    c:h2
                                |
                                |
                         --------------------
                                  |
                                 +--+
                                 |HC| c:h3
                                 +--+




                        Figure 4:  Multiple Locators


















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           a                       b                   c
     +-------------+       +-------------+         +---------------+
     |             |       |             |         |               |
     |        a:t  |       |      b:t    |         |               |
     |   +--+      |       |  +--+       |         |               |
     |   |  |--------------|--|  |       |         |               |
     |   +--+      |       |  +--+       |         |               |
     |     |       |       |    |        |         |               |
     |   +--+      |       |  +--+       |         |               |
     |   +  +      |       |  +  +       |         |               |
     |   +--+ a:y  |       |  +--+ b:d   |         |               |
     |             |       |             |         |               |
     +-------------+       +-------------+         +---------------+




                           Figure 5:  Nimrod Map

   Nodes and adjacencies represent the *configured* clustering and
   connectivity of the network.  Notice that even though a:y and b:d are
   defined on the same hardware, the map shows no connection between
   them: this connection has not been configured.  A packet given to
   node `a' addressed to a locator prefixed with "b:d" would have to
   travel from node a to node b via the arc joining them before being
   directed towards its destination.  Similarly, the map shows no
   connection between the c node and the other two top level nodes.  If
   desired, these connections could be established, which would
   necessitate setting up the exchange of routing information.  Figure 6
   shows the map when these connections have been established.

   In the strict sense, Nimrod nodes do not overlap: they are distinct
   entities.  But, as we have seen in the previous example, a physical
   element can be given more than one locator, and, in that sense,
   participate in implementing more than one node.  That is, two
   different nodes might be defined on the same hardware.  In this
   sense, Nimrod nodes can be said to overlap.  But to notice this
   overlap one would have to know the physical-to-map correspondence.
   It is not possible to know when two nodes share physical assets by
   looking only at a Nimrod map.











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5. Forwarding

   Nimrod supports four forwarding modes:

 1. Connectivity Specification Chain (CSC) mode: In this mode, packets
    carry a list of connectivity specifications.  The packet is
    required to go through the nodes that own the connectivity
    specifications using the services specified.  The nodes associated
    with the listed connectivity specifications should define a
    continuous path in the map.  A more detailed description of the
    requirements of this mode is given in section 5.3.








































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RFC 1992              Nimrod Routing Architecture            August 1996


   +--------+                                               +--------+
   |        |                                               |        |
   | a:t:r1 |-----------------------------------------------| b:t:r1 |
   |        |                                               |        |
   +--------+                                               +--------+
     |                                                             |
     |                                                             |
     |         /-----------------------------------------\         |
     |         |                                         |         |
     |         |                                         |         |
     |  +--------+       +--------+                    +--------+  |