OSPFv3 Extensions for Mobile Ad Hoc Networks

To optimize the use of OSPFv3 with MANETs, Cisco software implements extensions to OSPFv3 as defined in draft-chandra-ospf-manet-ext-02 . The result is a well-understood routing protocol (OSPF) used in a network topology that is constantly changing and where bandwidth is limited.

OSPF is optimized in these ways:

• Tightly couples OSPFv3 with Radio Aware Routing (RAR)-compliant radios to provide faster convergence and reconvergence through neighbor presence indications and help determine accurate, real-time link metric costs.
• Minimizes OSPFv3 packet size by implementing incremental hellos.
• Minimizes the number of OSPFv3 packet transmissions by caching multicast link-state advertisements (LSAs).
• Implements optimized flooding (overlapping relay) functionality to minimize the number of flooded LSAs.
• Implements selective peering to reduce the OSPF network overhead by minimizing the number of redundant full adjacencies that an OSPF node maintains.

The RAR-compliant radio reports link-quality metrics to the router that are used by OSPFv3 as link metrics. You can fine-tune to adjust how these radio metrics are used by OSPFv3:

1. Configure how the radio-reported bandwidth, latency, resource, and relative link-quality metrics are converted to an OSPFv3 link cost.
2. Configure a hysteresis threshold on this resultant link cost to minimize the propagation of LSAs that report link-metric changes.

OSPFv3 receives raw radio-link data and computes a composite. In computing these metrics, you should consider these factors (see the figure "OSPF Cost Calculation for VMI Interfaces"):

• Maximum data rate--the theoretical maximum data rate of the radio link, in bytes per second
• Current data rate--the current data rate achieved on the link, in bytes per second
• Resources--a percentage (0 to100) that can represent the remaining amount of a resource (such as battery power)
• Latency--the transmission delay packets encounter, in milliseconds
• Relative link quality (RLQ)--a numeric value (0 to 100) representing relative quality, with 100 being the highest quality

You can weight metrics during the configuration process to emphasize or de-emphasize particular characteristics. For example, if throughput is a particular concern, you can weight the current data rate metric so that it is factored more heavily into the composite metric. Similarly, you can omit a metric that is of no concern from the composite calculation.

Link metrics can change rapidly, often by very small degrees, which can result in a flood of meaningless routing updates. In a worst-case scenario, the network churns almost continuously as it struggles to react to minor variations in link quality. To alleviate this concern, you can use a tunable dampening mechanism to configure threshold values. Any metric change that falls below the threshold is ignored.

With the tunable hysteresis mechanism, you can adjust the threshold to the routing changes that occur when the router receives a signal that a new peer has been discovered, or that an existing peer is unreachable. The tunable metric is weighted and is adjusted dynamically to account for these characteristics:

• Current and maximum bandwidth
• Resources
• Latency
• Hysteresis

You can deconfigure individual weights and clear all weights so that the cost is returned to the default value for the interface type. Based on the routing changes that occur, the cost can be determined by the application of these metrics.

• Dynamic Cost Metric for Virtual Multipoint Interfaces

interface vmi1
ospfv3 6 cost dynamic weight throughput 0
ospfv3 6 cost dynamic hysteresis percent 10
ospfv3 6 cost dynamic weight resources 29
ospfv3 6 cost dynamic weight latency 29
ospfv3 6 cost dynamic hysteresis percent 10
ospfv3 6 cost dynamic weight L2-factor 29

Selective peering reduces the OSPF network overhead by minimizing the number of redundant full adjacencies that an OSPF node maintains. Adjacencies to nodes that do not provide additional reachability can be kept in a two-way state. Selective peering reduces control-plane bandwidth utilization by reducing the number of database exchanges and routing updates.

Note	Dataplane connectivity is not reduced when selective peering is enabled. User traffic flows over two-way links if they provide the best path through the network.

In the simplest example, selective peering determines if an adjacency should be formed when a new neighbor is discovered (a hello is received from a new neighbor). If the neighbor is not in the OSPF link state database, or if it is not reachable in the Shortest Path Tree (SPT), then the adjacency is formed. If the neighbor is in the OSPF link state database and is reachable, the neighbor is kept in the two-way state if the configured number of redundant paths to this neighbor is already formed.

Topology changes might cause the number of redundant paths to a given neighbor to fall below the configured level. When this occurs, selective peering can bring up adjacencies that were previously kept in the two-way state.

Selective peering takes link cost into consideration when determining which adjacencies to form. The objective is to have the reduced numbers of adjacencies formed over the lowest cost links. You can manually configure per-neighbor OSPF link costs, but with RAR-compliant radio interfaces, link costs are dynamically obtained from the radio through the VMI.

If the configured selective peering redundancy level is greater than 0, then at least two OSPFv3 control plane paths are maintained for every one hop neighbor. As new neighbors are discovered, full peering relationships are formed regardless of the link cost (as long as the cost satisfies the optionally configured minimum threshold specified in the ospfv3 manet peering link-metrics command).

As additional neighbors are brought to the full peering state to achieve the configured number of redundant paths to every neighbor, the router evaluates the path costs resulting from these new peering relationships to determine if they are incrementally better than the existing path costs. If they are not, the router keeps these links in a two-way state until other peering opportunities arise. The result is better path costs.

Consider the topology shown in the figure below. The configured redundancy level is 1 (the default), meaning that Router A attempts to maintain two paths to every one hop neighbor. Router A is in a full peering relationship with Router B and the link cost is 50. Router B is in a full peering relationship with Router D and the link cost is 30. Now Router D comes into radio range of Router A with a link cost of 70. Because the number of paths from Router A to Router D is currently 1 (through Router B), Router A brings this relationship to the full state.

You can keep Routers A and D in a two-way state until the link cost between them improves, or until another router comes into range that has better link costs to both of them. This can be achieved by configuring a redundant path cost threshold. In the figure above, if a redundant path cost threshold of 20 is configured, then Routers A and D will not transition to the full state until their link cost falls below the current path cost of 80 (50 + 30) minus 20, or 60. Because the depicted path cost is 70, the routers remain in the two-way state.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    no virtual-template subinterface

4.    ipv6 unicast-routing

5.    ipv6 cef

6.    router ospfv3 process-id

7.    router-id ip-address

8.    address-family ipv6 unicast

9.    exit

10.    exit

11.    interface virtual-template number

12.    ipv6 enable

13.    no keepalive

14.    exit

15.    interface type number

16.    ipv6 enable

17.    ospfv3 process-id area area-id ipv6 [instance instance-id ]

18.    ospfv3 process-id network manet

19.    physical-interface type number

20.    end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	no virtual-template subinterface Example: Router(config)# no virtual-template subinterface	Disables the virtual template on the subinterface.
Step 4	ipv6 unicast-routing Example: Router(config)# ipv6 unicast-routing	Enables IPv6 unicast routing.
Step 5	ipv6 cef Example: Router(config)# ipv6 cef	Enables IPv6 Cisco Express Forwarding on the router.
Step 6	router ospfv3 process-id Example: Router(config)# router ospfv3 1	Enables OSPFv3 for IPv6 router configuration mode, and enters router configuration mode.
Step 7	router-id ip-address Example: Router(config-router)# router-id 10.1.1.1	Identifies a specific router rather than allowing the dynamic assignment of the router to occur.
Step 8	address-family ipv6 unicast Example: Router(config-router)# address-family ipv6 unicast	Specifies IPv6 unicast address prefixes and enters address family configuration mode.
Step 9	exit Example: Router(config-router-af)# exit	Returns to router configuration mode.
Step 10	exit Example: Router(config-router)# exit	Returns to global configuration mode.
Step 11	interface virtual-template number Example: Router(config)# interface virtual-template 1	Enters interface configuration mode and creates a virtual template interface that can be configured and applied dynamically to virtual access interfaces.
Step 12	ipv6 enable Example: Router(config-if)# ipv6 enable	Enables IPv6 processing on the virtual template.
Step 13	no keepalive Example: Router(config-if)# no keepalive	Turns off PPP keepalive messages.
Step 14	exit Example: Router(config-if)# exit	Returns to global configuration mode.
Step 15	interface type number Example: Router(config)# interface vmi 1	Creates a VMI interface, and enters interface configuration mode.
Step 16	ipv6 enable Example: Router(config-if)# ipv6 enable	Enables IPv6 processing on the VMI interface that is not configured with an explicit IPv6 address.
Step 17	ospfv3 process-id area area-id ipv6 [instance instance-id ] Example: Router(config-if)# ospfv3 1 area 0 ipv6	Attaches the interface to a specific OSPFv3 area and enables routing of IPv6 network traffic on this interface. process-id --the value must match the ID configured with the router ospfv3 global configuration command. instance-id --automatically defaults to 0 for IPv6.
Step 18	ospfv3 process-id network manet Example: Router(config-if)# ospfv3 1 network manet	Sets the network type to MANET.
Step 19	physical-interface type number Example: Router(config-if)# physical-interface FastEthernet 0/1	Creates the physical subinterface to be associated with the VMI interfaces on the router.
Step 20	end Example: Router(config-if)# end	Returns to privileged EXEC mode.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface type number

4.    ospfv3 process-id cost dynamic hysteresis [threshold threshold-value ]

5.    ospfv3 process-id cost dynamic weight throughput percent

6.    ospfv3 process-id cost dynamic weight resources percent

7.    ospfv3 process-id cost dynamic weight latency percent

8.    ospfv3 process-id cost dynamic weight L2-factor percent

9.    ospfv3 process-id area area-id ipv6 [instance instance-id]

10.    end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	interface type number Example: Router(config)# interface vmi 1	Creates a VMI interface, and enters interface configuration mode.
Step 4	ospfv3 process-id cost dynamic hysteresis [threshold threshold-value ] Example: Router(config-if)# ospfv3 1 cost dynamic hysteresis threshold 1000	Sets the hysteresis tolerance for the interface.
Step 5	ospfv3 process-id cost dynamic weight throughput percent Example: Router(config-if)# ospfv3 1 cost dynamic weight throughput 0	Sets the metric for the throughput threshold.
Step 6	ospfv3 process-id cost dynamic weight resources percent Example: Router(config-if)# ospfv3 1 cost dynamic weight resources 29	Sets the metric for the resource factor.
Step 7	ospfv3 process-id cost dynamic weight latency percent Example: Router(config-if)# ospfv3 1 cost dynamic weight latency 29	Sets the threshold for the latency factor.
Step 8	ospfv3 process-id cost dynamic weight L2-factor percent Example: Router(config-if)# ospfv3 1 cost dynamic weight L2-factor 29	Sets the metric for the Layer 2-to-Layer 3 delay factor.
Step 9	ospfv3 process-id area area-id ipv6 [instance instance-id] Example: Router(config-if)# ospfv3 1 area 0 ipv6 instance 1	Enables OSPF for IPv6 on an interface.
Step 10	end Example: Router(config-if)# end	(Optional) Returns to privileged EXEC mode.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    router ospfv3 process-id

4.    address-family ipv6 unicast

5.    exit

6.    manet peering selective [redundancy redundancy-count] [per-interface ]

7.    end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	router ospfv3 process-id Example: Router(config)# router ospfv3 1	Enables OSPFv3 for IPv6 router configuration mode, and enters router configuration mode.
Step 4	address-family ipv6 unicast Example: Router(config-router)# address-family ipv6 unicast	Specifies IPv6 unicast address prefixes.
Step 5	exit Example: Router(config-router-af)# exit	Returns to router configuration mode.
Step 6	manet peering selective [redundancy redundancy-count] [per-interface ] Example: Router(config-router)# manet peering selective	Enables selective peering only for instances of the OSPF process for which the corresponding interface has been configured with the ospfv3 network manet command. (Optional) redundancy redundancy-count--Changes the preferred number of redundant paths to any given peer. (Optional) per-interface--Applies selective peering on a per-interface basis.
Step 7	end Example: Router(config-router)# end	(Optional) Returns to privileged EXEC mode.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface type number

4.    ospfv3 [process-id] manet peering link-metrics [threshold]

5.    end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	interface type number Example: Router(config)# interface vmi 1	Creates a VMI interface, and enters interface configuration mode.
Step 4	ospfv3 [process-id] manet peering link-metrics [threshold] Example: Router(config-if)# ospfv3 manet peering link-metrics 200	Configures an OSPFv3 process to wait for link metrics from a neighbor before attempting selective peering with that neighbor. (Optional) threshold--Specifies that the link cost computed from the received link metrics from the radio must be below this value. Otherwise, the neighbor is held in a two-way state until metrics are received that result in a link cost below the configured level. The range is 0 to 65535.
Step 5	end Example: Router(config-if)# end	Optional) Returns to privileged EXEC mode.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface type number

4.    ospfv3 [process-id] manet peering cost {threshold threshold-value | percent percent-value}

5.    end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	interface type number Example: Router(config)# interface vmi 1	Creates a VMI interface, and enters interface configuration mode.
Step 4	ospfv3 [process-id] manet peering cost {threshold threshold-value | percent percent-value} Example: Router(config-if)# ospfv3 1 manet peering cost percent 10	Sets a minimum cost change threshold necessary before a new neighbor is considered for selective peering. Requires redundant paths to have an incrementally better path cost than the current best path cost specified either as an absolute value or as a percentage of the current best path cost.
Step 5	end Example: Router(config-if)# end	(Optional) Returns to privileged EXEC mode.