RIPng fundamentals

Routing Information Protocol next generation (RIPng) allows routers to exchange information for computing routes through an IPv6–based network. You should implement RIPng only on routers. IPv6 provides neighbor router information required by RIPng protocol to function as intended. A RIPng router is assumed to have interfaces in several networks and the protocol relies primarily on the metric of each network to compute routes using the distance vector algorithm.

RIP identifies network reachability based on cost, and cost is defined as hop count. One hop is the distance from one router to the next. This cost, or hop count, is the metric.

RIPng-enabled routers use UDP port 521 (the RIPng port) to exchange routing information. RIPng responds to a request by sending a message to the port from which the request originates. Specific queries can be sent from ports other than the RIPng port, but they must be directed to the RIPng port on the target machine.

Each router advertises routing information by sending an update every 30 seconds (one interval). If RIPng does not receive information about a network for 180 seconds, the metric associated with the network rises to infinity (U); that is, the metric resets to 16, which means the network becomes unreachable. If RIP does not receive information about a network for 120 seconds, it removes the network from the routing table.
Note

Note

These time interval values are default values which are configurable by the user.

Each router that implements RIPng contains a routing table. This table contains one entry for every destination that is reachable throughout the system operating RIPng. At a minimum, each routing table entry contains the following information:

RIPng protocol implementation is specified in IETF document RFC 2080.

RIPng messages and packet format

RIPng-enabled routers use UDP port 521 (the RIPng port) to send and receive datagrams.

The following figure shows the RIPng packet format:
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RIPng packet format
A RIPng packet header consists of the following components:
  • command: Specifies the purpose of the message.

  • version: The version of RIPng.

Originate Default route

Generally you use a default route when it is not convenient to list every possible network in RIPng updates, and one or more routers in the system are able to handle traffic to networks that RIPng does not explicitly list.

RIPng is enabled with the default route only option. When you enable default route only on an interface, it suppresses all other routes in the update sent for the interface, and advertises only the default route.

Timers

RIPng states four different timer intervals for protocol operation:
  • Update timer: The RIPng process sends a complete routing table to each neighboring router every 30 seconds. To prevent collisions on broadcast networks, the process adds an offset value to the timer.

  • Timeout time interval: This is a 180 second time interval associated with every route. If the time interval expires, the metric for this route updates to the value of infinity (16) and the route is no longer valid. However, the routing table retains the value for another 120 seconds.

  • Garbage collection time interval: After the timeout time interval expires and the route becomes invalid, it remains in the routing table until the garbage collection time interval expires. The garbage collection time interval is 120 seconds. Until the garbage collection time interval expires all updates sent by this router include the invalid route. When the garbage collection timer expires, the process removes the route from the routing table.

  • Triggered update time interval: The triggered update time interval is set to a random value between 1 and 5 seconds after a triggered update is sent. A single update is sent even if multiple triggered updates occur before the timer expires.

Configuration of timers or time intervals is supported only at the CLI/SNMP/EDM level. Configuration of timers or time intervals is not supported at the interface/port level.