10. Routing

10. Routing

Note that as unicast site-local addresses are deprecated, and link-local addresses do not need routing, the discussion in this section only applies to multicast scoped routing.

When a routing protocol determines that it is operating on a zone boundary, it MUST protect inter-zone integrity and maintain intra-zone connectivity.

To maintain connectivity, the routing protocol must be able to create forwarding information for the global groups and for all the scoped groups for each of its attached zones. The most straightforward way of doing this is to create (conceptual) forwarding tables for each specific zone.

To protect inter-zone integrity, routers must be selective in the group information shared with neighboring routers. Routers routinely exchange routing information with neighboring routers. When a router is transmitting this routing information, it must not include any information about zones other than the zones assigned to the interface used to transmit the information.

                     *                                 *
                     *                                 *
                     *   ===========    Organization X *
                     *    |       |                    *
                     *    |       |                    *
                   +-*----|-------|------+             *
                   | *  intf1   intf2    |             *
                   | *                   |             *
                   | *             intf3 ---           *
                   | *                   |             *
                   | ***********************************
                   |                     |
                   |        Router       |
                   |                     |
         **********************       **********************
                   |       *     *       |
            Org. Y --- intf4  *   *  intf5 ---   Org. Z
                   |       *     *       |
         **********************       **********************
                   +---------------------+

         Figure 4: Multi-Organization Multicast Router

As an example, the router in Figure 4 must exchange routing information on five interfaces. The information exchanged is as follows (for simplicity, multicast scopes smaller or larger than the organization scope except global are not considered here):

• Interface 1

  • All global groups
  • All organization groups learned from Interfaces 1, 2, and 3

• Interface 2

  • All global groups
  • All organization groups learned from Interfaces 1, 2, and 3

• Interface 3

  • All global groups
  • All organization groups learned from Interfaces 1, 2, and 3

• Interface 4

  • All global groups
  • All organization groups learned from Interface 4

• Interface 5

  • All global groups
  • All organization groups learned from Interface 5

By imposing route exchange rules, zone integrity is maintained by keeping all zone-specific routing information contained within the zone.