IPv6 Routing: OSPFv3

OSPFv3 is a routing protocol for IPv4 and IPv6. It is a link-state protocol, as opposed to a distance-vector protocol. Think of a link as being an interface on a networking device. A link-state protocol makes its routing decisions based on the states of the links that connect source and destination machines. The state of a link is a description of that interface and its relationship to its neighboring networking devices. The interface information includes the IPv6 prefix of the interface, the network mask, the type of network it is connected to, the devices connected to that network, and so on. This information is propagated in various type of link-state advertisements (LSAs).

A device's collection of LSA data is stored in a link-state database. The contents of the database, when subjected to the Dijkstra algorithm, result in the creation of the OSPF routing table. The difference between the database and the routing table is that the database contains a complete collection of raw data; the routing table contains a list of shortest paths to known destinations via specific device interface ports.

OSPFv3, which is described in RFC 5340, supports IPv6 and IPv4 unicast AFs.

Much of OSPF version 3 is the same as in OSPF version 2. OSPFv3, which is described in RFC 5340, expands on OSPF version 2 to provide support for IPv6 routing prefixes and the larger size of IPv6 addresses.

In OSPFv3, a routing process does not need to be explicitly created. Enabling OSPFv3 on an interface will cause a routing process, and its associated configuration, to be created.

In OSPFv3, each interface must be enabled using commands in interface configuration mode. This feature is different from OSPF version 2, in which interfaces are indirectly enabled using the device configuration mode.

When using a nonbroadcast multiaccess (NBMA) interface in OSPFv3, you must manually configure the device with the list of neighbors. Neighboring devices are identified by their device ID.

In IPv6, you can configure many address prefixes on an interface. In OSPFv3, all address prefixes on an interface are included by default. You cannot select some address prefixes to be imported into OSPFv3; either all address prefixes on an interface are imported, or no address prefixes on an interface are imported.

Unlike OSPF version 2, multiple instances of OSPFv3 can be run on a link.

OSPF automatically prefers a loopback interface over any other kind, and it chooses the highest IP address among all loopback interfaces. If no loopback interfaces are present, the highest IP address in the device is chosen. You cannot tell OSPF to use any particular interface.

The following list describes LSA types, each of which has a different purpose:

• Device LSAs (Type 1)--Describes the link state and costs of a device's links to the area. These LSAs are flooded within an area only. The LSA indicates if the device is an Area Border Router (ABR) or Autonomous System Boundary Router (ASBR), and if it is one end of a virtual link. Type 1 LSAs are also used to advertise stub networks. In OSPFv3, these LSAs have no address information and are network-protocol-independent. In OSPFv3, device interface information may be spread across multiple device LSAs. Receivers must concatenate all device LSAs originated by a given device when running the SPF calculation.
• Network LSAs (Type 2)--Describes the link-state and cost information for all devices attached to the network. This LSA is an aggregation of all the link-state and cost information in the network. Only a designated device tracks this information and can generate a network LSA. In OSPFv3, network LSAs have no address information and are network-protocol-independent.
• Interarea-prefix LSAs for ABRs (Type 3)--Advertises internal networks to devices in other areas (interarea routes). Type 3 LSAs may represent a single network or a set of networks summarized into one advertisement. Only ABRs generate summary LSAs. In OSPFv3, addresses for these LSAs are expressed as prefix, prefix length instead of address, mask. The default route is expressed as a prefix with length 0.
• Interarea-device LSAs for ASBRs (Type 4)--Advertises the location of an ASBR. Devices that are trying to reach an external network use these advertisements to determine the best path to the next hop. Type 4 LSAs are generated by ABRs on behalf of ASBRs.
• Autonomous system external LSAs (Type 5)--Redistributes routes from another autonomous system, usually from a different routing protocol into OSPFv3. In OSPFv3, addresses for these LSAs are expressed as prefix, prefix length instead of address, mask. The default route is expressed as a prefix with length 0.
• Link LSAs (Type 8)--Have local-link flooding scope and are never flooded beyond the link with which they are associated. Link LSAs provide the link-local address of the device to all other devices attached to the link, inform other devices attached to the link of a list of prefixes to associate with the link, and allow the device to assert a collection of Options bits to associate with the network LSA that will be originated for the link.
• Intra-Area-Prefix LSAs (Type 9)--A device can originate multiple intra-area-prefix LSAs for each device or transit network, each with a unique link-state ID. The link-state ID for each intra-area-prefix LSA describes its association to either the device LSA or the network LSA and contains prefixes for stub and transit networks.

An address prefix occurs in almost all newly defined LSAs. The prefix is represented by three fields: PrefixLength, PrefixOptions, and Address Prefix. In OSPFv3, addresses for these LSAs are expressed as prefix, prefix length instead of address, mask. The default route is expressed as a prefix with length 0. Type 3 and Type 9 LSAs carry all prefix (subnet) information that, in OSPFv2, is included in device LSAs and network LSAs. The Options field in certain LSAs (device LSAs, network LSAs, interarea-device LSAs, and link LSAs) has been expanded to 24 bits to provide support for OSPFv3.

In OSPFv3, the sole function of the link-state ID in interarea-prefix LSAs, interarea-device LSAs, and autonomous-system external LSAs is to identify individual pieces of the link-state database. All addresses or device IDs that are expressed by the link-state ID in OSPF version 2 are carried in the body of the LSA in OSPFv3.

The link-state ID in network LSAs and link LSAs is always the interface ID of the originating device on the link being described. For this reason, network LSAs and link LSAs are now the only LSAs whose size cannot be limited. A network LSA must list all devices connected to the link, and a link LSA must list all of the address prefixes of a device on the link.

When a device learns multiple routes to a specific network via multiple routing processes (or routing protocols), it installs the route with the lowest administrative distance in the routing table. Sometimes the device must select a route from among many learned via the same routing process with the same administrative distance. In this case, the device chooses the path with the lowest cost (or metric) to the destination. Each routing process calculates its cost differently and the costs may need to be manipulated in order to achieve load balancing.

OSPFv3 performs load balancing automatically in the following way. If OSPFv3 finds that it can reach a destination through more than one interface and each path has the same cost, it installs each path in the routing table. The only restriction on the number of paths to the same destination is controlled by the maximum-paths command. The default maximum paths is 16, and the range is from 1 to 64.

When importing the set of addresses specified on an interface on which OSPFv3 is running into OSPFv3, you cannot select specific addresses to be imported. Either all addresses are imported, or no addresses are imported.

You can customize OSPFv3 for your network, but you likely will not need to do so. The defaults for OSPFv3 are set to meet the requirements of most customers and features. If you must change the defaults, refer to the IPv6 command reference to find the appropriate syntax.

Caution

Be careful when changing the defaults. Changing defaults will affect your OSPFv3 network, possibly adversely.

When the process keyword is used with the clear ipv6 ospf command, the OSPFv3 database is cleared and repopulated, and then the SPF algorithm is performed. When the force-spf keyword is used with the clear ipv6 ospf command, the OSPFv3 database is not cleared before the SPF algorithm is performed.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    router ospfv3 [process-id]

4.    area area-ID [default-cost | nssa | stub]

5.    auto-cost reference-bandwidth Mbps

6.    bfd all-interfaces

7.    default {area area-ID [range ipv6-prefix | virtual-link router-id]} [default-information originate [always | metric | metric-type | route-map] | distance | distribute-list prefix-list prefix-list-name {in | out} [interface] | maximum-paths paths | redistribute protocol | summary-prefix ipv6-prefix]

8.    ignore lsa mospf

9.    interface-id snmp-if-index

10.    log-adjacency-changes [detail]

11.   passive-interface [default | interface-type interface-number]

12.    queue-depth {hello | update} {queue-size | unlimited}

13.   router-id router-id

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Device# configure terminal	Enters global configuration mode.
Step 3	router ospfv3 [process-id] Example: Device(config)# router ospfv3 1	Enters router configuration mode for the IPv4 or IPv6 address family.
Step 4	area area-ID [default-cost | nssa | stub] Example: Device(config-router)# area 1	Configures the OSPFv3 area.
Step 5	auto-cost reference-bandwidth Mbps Example: Device(config-router)# auto-cost reference-bandwidth 1000	Controls the reference value OSPFv3 uses when calculating metrics for interfaces in an IPv4 OSPFv3 process.
Step 6	bfd all-interfaces Example: Device(config-router)# bfd all-interfaces	Enables BFD for an OSPFv3 routing process
Step 7	default {area area-ID [range ipv6-prefix | virtual-link router-id]} [default-information originate [always | metric | metric-type | route-map] | distance | distribute-list prefix-list prefix-list-name {in | out} [interface] | maximum-paths paths | redistribute protocol | summary-prefix ipv6-prefix] Example: Device(config-router)# default area 1	Returns an OSPFv3 parameter to its default value.
Step 8	ignore lsa mospf Example: Device(config-router)# ignore lsa mospf	Suppresses the sending of syslog messages when the device receives LSA Type 6 multicast OSPFv3 packets, which are unsupported.
Step 9	interface-id snmp-if-index Example: Device(config-router)# interface-id snmp-if-index	Configures OSPFv3 interfaces with Simple Network Management Protocol (SNMP) MIB-II interface Index (ifIndex) identification numbers in IPv4 and IPv6.
Step 10	log-adjacency-changes [detail] Example: Device(config-router)# log-adjacency-changes	Configures the device to send a syslog message when an OSPFv3 neighbor goes up or down.
Step 11	passive-interface [default | interface-type interface-number] Example: Device(config-router)# passive-interface default	Suppresses sending routing updates on an interface when an IPv4 OSPFv3 process is used.
Step 12	queue-depth {hello | update} {queue-size | unlimited} Example: Device(config-router)# queue-depth update 1500	Configures the number of incoming packets that the IPv4 OSPFv3 process can keep in its queue.
Step 13	router-id router-id Example: Device(config-router)# router-id 10.1.1.1	Enter this command to use a fixed router ID.

SUMMARY STEPS

1.    enable

2.    clear ospfv3 [process-id] force-spf

3.    clear ospfv3 [process-id] process

4.    clear ospfv3 [process-id] redistribution

5.    clear ipv6 ospf [process-id] {process | force-spf | redistribution}

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	clear ospfv3 [process-id] force-spf Example: Device# clear ospfv3 1 force-spf	Runs SPF calculations for an OSPFv3 process. If the clear ospfv3 force-spf command is configured, it overwrites the clear ipv6 ospf configuration. Once the clear ospfv3 force-spf command has been used, the clear ipv6 ospf command cannot be used.
Step 3	clear ospfv3 [process-id] process Example: Device# clear ospfv3 2 process	Resets an OSPFv3 process. If the clear ospfv3 force-spf command is configured, it overwrites the clear ipv6 ospf configuration. Once the clear ospfv3 force-spf command has been used, the clear ipv6 ospf command cannot be used.
Step 4	clear ospfv3 [process-id] redistribution Example: Device# clear ospfv3 redistribution	Clears OSPFv3 route redistribution. If the clear ospfv3 force-spf command is configured, it overwrites the clear ipv6 ospf configuration. Once the clear ospfv3 force-spf command has been used, the clear ipv6 ospf command cannot be used.
Step 5	clear ipv6 ospf [process-id] {process | force-spf | redistribution} Example: Device# clear ipv6 ospf force-spf	Clears the OSPFv3 state based on the OSPFv3 routing process ID, and forces the start of the SPF algorithm. If the clear ospfv3 force-spf command is configured, it overwrites the clear ipv6 ospf configuration. Once the clear ospfv3 force-spf command has been used, the clear ipv6 ospf command cannot be used.

SUMMARY STEPS

1.    enable

2.    show ospfv3 [process-id] [address-family] border-routers

3.    show ospfv3 [process-id [area-id]] [address-family] database [database-summary | internal | external [ipv6-prefix ] [link-state-id] | grace | inter-area prefix [ipv6-prefix | link-state-id] | inter-area router [destination-router-id | link-state-id] | link [interface interface-name | link-state-id] | network [link-state-id] | nssa-external [ipv6-prefix] [link-state-id] | prefix [ref-lsa {router | network} | link-state-id] | promiscuous | router [link-state-id] | unknown [{area | as | link} [link-state-id]] [adv-router router-id] [self-originate]

4.    show ospfv3 [process-id] [address-family] events [generic | interface | lsa | neighbor | reverse | rib | spf]

5.    show ospfv3 [process-id] [area-id] [address-family] flood-list interface-type interface-number

6.    show ospfv3 [process-id] [address-family] graceful-restart

7.    show ospfv3 [process-id] [area-id] [address-family] interface [type number] [brief]

8.    show ospfv3 [process-id] [area-id] [address-family] neighbor [interface-type interface-number] [neighbor-id] [detail]

9.    show ospfv3 [process-id] [area-id] [address-family] request-list[neighbor] [interface] [interface-neighbor]

10.    show ospfv3 [process-id] [area-id] [address-family] retransmission-list [neighbor] [interface] [interface-neighbor]

11.    show ospfv3 [process-id] [address-family] statistic [detail]

12.    show ospfv3 [process-id] [address-family] summary-prefix

13.    show ospfv3 [process-id] [address-family] timers rate-limit

14.    show ospfv3 [process-id] [address-family] traffic[interface-type interface-number]

15.    show ospfv3 [process-id] [address-family] virtual-links

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	show ospfv3 [process-id] [address-family] border-routers Example: Device# show ospfv3 border-routers	Displays the internal OSPFv3 routing table entries to an ABR and ASBR.
Step 3	show ospfv3 [process-id [area-id]] [address-family] database [database-summary | internal | external [ipv6-prefix ] [link-state-id] | grace | inter-area prefix [ipv6-prefix | link-state-id] | inter-area router [destination-router-id | link-state-id] | link [interface interface-name | link-state-id] | network [link-state-id] | nssa-external [ipv6-prefix] [link-state-id] | prefix [ref-lsa {router | network} | link-state-id] | promiscuous | router [link-state-id] | unknown [{area | as | link} [link-state-id]] [adv-router router-id] [self-originate] Example: Device# show ospfv3 database	Displays lists of information related to the OSPFv3 database for a specific device.
Step 4	show ospfv3 [process-id] [address-family] events [generic | interface | lsa | neighbor | reverse | rib | spf] Example: Device# show ospfv3 events	Displays detailed information about OSPFv3 events.
Step 5	show ospfv3 [process-id] [area-id] [address-family] flood-list interface-type interface-number Example: Device# show ospfv3 flood-list	Displays a list of OSPFv3 LSAs waiting to be flooded over an interface.
Step 6	show ospfv3 [process-id] [address-family] graceful-restart Example: Device# show ospfv3 graceful-restart	Displays OSPFv3 graceful restart information.
Step 7	show ospfv3 [process-id] [area-id] [address-family] interface [type number] [brief] Example: Device# show ospfv3 interface	Displays OSPFv3-related interface information.
Step 8	show ospfv3 [process-id] [area-id] [address-family] neighbor [interface-type interface-number] [neighbor-id] [detail] Example: Device# show ospfv3 neighbor	Displays OSPFv3 neighbor information on a per-interface basis.
Step 9	show ospfv3 [process-id] [area-id] [address-family] request-list[neighbor] [interface] [interface-neighbor] Example: Device# show ospfv3 request-list	Displays a list of all LSAs requested by a device.
Step 10	show ospfv3 [process-id] [area-id] [address-family] retransmission-list [neighbor] [interface] [interface-neighbor] Example: Device# show ospfv3 retransmission-list	Displays a list of all LSAs waiting to be re-sent.
Step 11	show ospfv3 [process-id] [address-family] statistic [detail] Example: Device# show ospfv3 statistics	Displays OSPFv3 SPF calculation statistics.
Step 12	show ospfv3 [process-id] [address-family] summary-prefix Example: Device# show ospfv3 summary-prefix	Displays a list of all summary address redistribution information configured under an OSPFv3 process.
Step 13	show ospfv3 [process-id] [address-family] timers rate-limit Example: Device# show ospfv3 timers rate-limit	Displays all of the LSAs in the rate limit queue.
Step 14	show ospfv3 [process-id] [address-family] traffic[interface-type interface-number] Example: Device# show ospfv3 traffic	Displays OSPFv3 traffic statistics.
Step 15	show ospfv3 [process-id] [address-family] virtual-links Example: Device# show ospfv3 virtual-links	Displays parameters and the current state of OSPFv3 virtual links.