Open Shortest Path First Version 3 (OSPFv3)

Date: Dec 24, 2023 By , , , . Sample Chapter is provided courtesy of Cisco Press.

In this sample chapter from CCNP and CCIE Enterprise Core ENCOR 350-401 Official Cert Guide, 2nd Edition, you will learn OSPFv3 routing protocol, configuration, and IPv4 support. OSPF Version 3 (OSPFv3), which is the latest version of the OSPF protocol, includes support for both the IPv4 and IPv6 address families. This book covers topics from the Cisco Enterprise Core v1.1 (ENCOR 350-401) exam.

This chapter covers the following subjects:

  • OSPFv3 Fundamentals: This section provides an overview of the OSPFv3 routing protocol and the similarities to OSPFv2.

  • OSPFv3 Configuration: This section demonstrates the configuration and verification of an OSPFv3 environment.

  • IPv4 Support in OSPFv3: This section explains and demonstrates how OSPFv3 can be used for exchanging IPv4 routes.

OSPF Version 3 (OSPFv3), which is the latest version of the OSPF protocol, includes support for both the IPv4 and IPv6 address families. The OSPFv3 protocol is not backward compatible with OSPFv2, but the protocol mechanisms described in Chapters 8, “OSPF,” and 9, “Advanced OSPF,” are essentially the same for OSPFv3. This chapter expands on Chapter 9 and discusses OSPFv3 and its support of IPv6.

“Do I Know This Already?” Quiz

The “Do I Know This Already?” quiz enables you to assess whether you should read the entire chapter. If you miss no more than one of these self-assessment questions, you might want to move ahead to the “Exam Preparation Tasks” section. Table 10-1 lists the major headings in this chapter and the “Do I Know This Already?” quiz questions covering the material in those headings so you can assess your knowledge of these specific areas. The answers to the “Do I Know This Already?” quiz appear in Appendix A, “Answers to the ‘Do I Know This Already?’ Questions.”

Table 10-1 “Do I Know This Already?” Foundation Topics Section-to-Question Mapping

Foundation Topics Section

Questions

OSPFv3 Fundamentals

1–2

OSPFv3 Configuration

3–4

IPv4 Support in OSPFv3

5

  1. OSPFv3 uses ___________ packet types for inter-router communication.

    1. three

    2. four

    3. five

    4. six

    5. seven

  2. The OSPFv3 hello packet uses the ___________ for the destination address.

    1. MAC address 00:C1:00:5C:00:FF

    2. MAC address E0:00:00:06:00:AA

    3. IP address 224.0.0.8

    4. IP address 224.0.0.10

    5. IPv6 address FF02::A

    6. IPv6 address FF02::5

  3. How do you enable OSPFv3 on an interface?

    1. Use the command network prefix/prefix-length under the OSPF process.

    2. Use the command network interface-id under the OSPF process.

    3. Use the command ospfv3 process-id ipv6 area area-id under the interface.

    4. Nothing. OSPFv3 is enabled on all IPv6 interfaces upon initialization of the OSPF process.

  4. True or false: On a brand-new router installation, OSPFv3 requires only that an IPv6 link-local address be configured and that OSPFv3 be enabled on that interface to form an OSPFv3 neighborship with another router.

    1. True

    2. False

  5. True or false: OSPFv3 support for IPv4 networks only requires that an IPv4 address be assigned to the interface and that the OSPFv3 process be initialized for IPv4.

    1. True

    2. False

OSPFv3 Fundamentals

OSPFv3 is different from OSPFv2 in the following ways:

  • Support for multiple address families: OSPFv3 supports IPv4 and IPv6 address families.

  • New LSA types: New LSA types have been created to carry IPv6 prefixes.

  • Removal of addressing semantics: The IP prefix information is no longer present in the OSPF packet headers. Instead, it is carried as LSA payload information, making the protocol essentially address family independent, much like IS-IS. OSPFv3 uses the term link instead of network because the SPT calculations are per link instead of per subnet.

  • LSA flooding: OSPFv3 includes a new link-state type field that is used to determine the flooding scope of LSA, as well as the handling of unknown LSA types.

  • Packet format: OSPFv3 runs directly over IPv6, and the number of fields in the packet header has been reduced.

  • Router ID: The router ID is used to identify neighbors, regardless of the network type in OSPFv3. When you’re configuring OSPFv3 on IOS routers, the ID must always be manually assigned in the routing process.

  • Authentication: Neighbor authentication has been removed from the OSPF protocol and is now performed through IPsec extension headers in the IPv6 packet.

  • Neighbor adjacencies: OSPFv3 inter-router communication is handled by IPv6 link-local addressing. Neighbors are not automatically detected over non-broadcast multiple access (NBMA) interfaces. A neighbor must be manually specified using the link-local address. IPv6 allows for multiple subnets to be assigned to a single interface, and OSPFv3 allows for neighbor adjacency to form even if the two routers do not share a common subnet.

  • Multiple instances: OSPFv3 packets include an instance ID field that may be used to manipulate which routers on a network segment are allowed to form adjacencies.

OSPFv3 Link-State Advertisement

The OSPF link-state database information is organized and advertised differently in Version 3 than in Version 2. OSPFv3 modifies the structure of the router LSA (type 1), renames the network summary LSA to inter-area prefix LSA, and renames the ASBR summary LSA to inter-area router LSA. The principal difference is that the router LSA is only responsible for announcing interface parameters such as the interface type (point-to-point, broadcast, NBMA, point-to-multipoint, and virtual links) and metric (cost).

IP address information is advertised independently by two new LSA types:

  • Intra-area prefix LSA

  • Link LSA

The OSPF Dijkstra calculation used to determine the shortest path tree (SPT) only examines the router and network LSAs. Advertising the IP prefix information using new LSA types eliminates the need for OSPF to perform full shortest path first (SPF) tree calculations every time a new IP address (prefix) is added or changed on an interface. The OSPFv3 link-state database (LSDB) creates a shortest path topology tree based on links instead of networks.

OSPFv3 Communication

OSPFv3 packets use protocol number 89 in the IPv6 header, and routers communicate with each other using the local interface’s IPv6 link-local address as the source. It also uses the same five packet types and logic as OSPFv2. Depending on the packet type, the destination address is either a unicast link-local address or a multicast link-local scoped address:

Answers to the “Do I Know This Already?” quiz:

1 C 2 F 3 C 4 B 5 B

  • FF02::05: OSPFv3 AllSPFRouters

  • FF02::06: OSPFv3 AllDRouters

Every router uses the AllSPFRouters multicast address FF02::5 to send OSPF hello messages to routers on the same link. The hello messages are used for neighbor discovery and detecting whether a neighbor relationship is down. The DR and BDR routers also use this address to send link-state update and flooding acknowledgment messages to all routers.

Non-DR/BDR routers send an update or link-state acknowledgment message to the DR and BDR by using the AllDRouters address FF02::6.

OSPFv3 Configuration

The process of configuring OSPFv3 involves the following steps:

  • Step 1. Initialize the routing process. As a prerequisite, ipv6 unicast-routing must be enabled on the router. Afterward, the OSPFv3 process is configured with the command router ospfv3 [process-id].

  • Step 2. Define the router ID. The command router-id router-id assigns a router ID to the OSPF process. The router ID is a 32-bit value that does not need to match an IPv4 address. It may be any number in IPv4 address format (for example, 0.1.2.3), as long as the value is unique within the OSPF domain.

    OSPFv3 uses the same algorithm as OSPFv2 for dynamically locating the RID. If there are not any IPv4 interfaces available, the RID is set to 0.0.0.0 and does not allow adjacencies to form.

  • Step 3. (Optional) Initialize the address family. The address family is initialized within the routing process with the command address-family {ipv6 | ipv4} unicast. The appropriate address family is enabled automatically when OSPFv3 is enabled on an interface.

  • Step 4. Enable OSPFv3 on an interface. The interface command ospfv3 process-id ipv6 area area-id enables the protocol and assigns the interface to an area.

Figure 10-1 displays a simple four-router topology to demonstrate OSPFv3 configuration. Area 0 consists of R1, R2, and R3, and Area 34 contains R3 and R4. R3 is the ABR.

Figure 10-1 OSPFv3 Topology

Example 10-1 provides the OSPFv3 and IPv6 address configurations for R1, R2, R3, and R4. IPv6 link-local addressing has been configured so that all router interfaces reflect their local numbers (for example, R1’s interfaces are set to FE80::1) in addition to traditional IPv6 addressing. The link-local addressing is statically configured to assist with any diagnostic output in this chapter. The OSPFv3 configuration has been highlighted in this example.

Example 10-1 IPv6 Addressing and OSPFv3 Configuration

OSPFv3 Verification

The commands for viewing OSPFv3 settings and statuses are similar to those used in OSPFv2; they essentially replace ip ospf with ospfv3 ipv6. Supporting OSPFv3 requires verifying the OSPFv3 interfaces, neighborship, and the routing table.

For example, to view the neighbor adjacency for OSPFv2, the command show ip ospf neighbor is executed, and for OSPFv3, the command show ospfv3 ipv6 neighbor is used. Example 10-2 shows this command executed on R3.

Example 10-2 Identifying R3’s OSPFv3 Neighbors

Example 10-3 shows R1’s GigabitEthernet0/2 OSPFv3-enabled interface status with the command show ospfv3 interface [interface-id]. Notice that address semantics have been removed compared to OSPFv2. The interface maps to the interface ID value 3 rather than an IP address value, as in OSPFv2. In addition, some helpful topology information describes the link. The local router is the DR (192.168.1.1), and the adjacent neighbor router is the BDR (192.168.2.2).

Example 10-3 Viewing the OSPFv3 Interface Configuration

A brief version of the OSPFv3 interface settings can be viewed with the command show ospfv3 interface brief. The associated process ID, area, address family (IPv4 or IPv6), interface state, and neighbor count are provided in the output.

Example 10-4 demonstrates this command being executed on the ABR, R3. Notice that some interfaces reside in Area 0, and others reside in Area 34.

Example 10-4 Viewing a Brief Version of OSPFv3 Interfaces

The OSPFv3 IPv6 routing table is viewed with the command show ipv6 route ospf. Intra-area routes are indicated with O, and inter-area routes are indicated with OI.

Example 10-5 shows this command being executed on R1. The forwarding address for the routes is the link-local address of the neighboring router.

Example 10-5 Viewing the OSPFv3 Routes in the IPv6 Routing Table

Passive Interface

OSPFv3 supports the ability to mark an interface as passive. The command is placed under the OSPFv3 process or under the specific address family. Placing the command under the global process cascades the setting to both address families. An interface is marked as being passive with the command passive-interface interface-id or globally with passive-interface default, and then the interface is marked as active with the command no passive-interface interface-id.

Example 10-6 shows how to make the LAN interface on R1 explicitly passive and how to make all interfaces passive on R4 while marking the Gi0/3 interface as active.

Example 10-6 Configuring OSPFv3 Passive Interfaces

The active/passive state of an interface is verified by examining the OSPFv3 interface status using the command show ospfv3 interface [interface-id] and searching for the Passive keyword. In Example 10-7, R1 confirms that the Gi0/3 interface is passive.

Example 10-7 Viewing an OSPFv3 Interface State

Summarization

The ability to summarize IPv6 networks is as important as summarizing routes in IPv4 (and it may even be more important, due to hardware scale limitations). Example 10-8 shows the IPv6 routing table on R4 before summarization is applied on R3.

Example 10-8 R4’s IPv6 Routing Table Before Summarization

Summarizing the Area 0 router’s loopback interfaces (2001:db8:0::1/128, 2001:db8:0::2/128, and 2001:db8:0::3/128) removes three routes from the routing table.

Summarization of internal OSPFv3 routes follows the same rules as in OSPFv2 and must occur on ABRs. In our topology, R3 summarizes the three loopback addresses into the 2001:db8:0:0::/65 network. Summarization involves the command area area-id range prefix/prefix-length, which resides under the address family in the OSPFv3 process.

Example 10-9 shows R3’s configuration for summarizing these prefixes.

Example 10-9 IPv6 Summarization

Example 10-10 shows R4’s IPv6 routing table after configuring R3 to summarize the Area 0 loopback interfaces. The summary route is highlighted in this example.

Example 10-10 R4’s IPv6 Routing Table After Summarization

Network Type

OSPFv3 supports the same OSPF network types as OSPFv2. Example 10-11 shows that R2’s Gi0/3 interface is set as a broadcast OSPF network type and is confirmed as being in a DR state.

Example 10-11 Viewing the Dynamic Configured OSPFv3 Network Type

The OSPFv3 network type is changed with the interface parameter command ospfv3 network {point-to-point | broadcast}. Example 10-12 shows the interfaces associated with the 2001:DB8:0:23::/64 network being changed to point-to-point.

Example 10-12 Changing the OSPFv3 Network Type

After the changes are typed in, the new settings are verified in Example 10-13. The network is now a point-to-point link, and the interface state shows as P2P for confirmation.

Example 10-13 Viewing the Statically Configured OSPFv3 Network Type

IPv4 Support in OSPFv3

RFC 5838 specifies that OSPFv3 should support multiple address families by setting the instance ID value from the IPv6 reserved range to the IPv4 reserved range (64 to 95) in the link LSAs.

Enabling IPv4 support for OSPFv3 is straightforward:

  • Step 1. Ensure that the IPv4 interface has an IPv6 address (global or link local) configured. Remember that configuring a global address also places a link-local address; alternatively, a link-local address can statically be configured.

  • Step 2. Enable the OSPFv3 process for IPv4 on the interface with the command ospfv3 process-id ipv4 area area-id.

Using the topology shown in Figure 10-1, IPv4 addressing has been placed onto R1, R2, R3, and R4 using the conventions outlined earlier. Example 10-14 demonstrates the deployment of IPv4 using the existing OSPFv3 deployment.

Example 10-14 Configuration Changes for IPv4 Support

Example 10-15 verifies that the routes were exchanged and installed into the IPv4 RIB.

Example 10-15 Verifying IPv4 Route Exchange with OSPFv3

The command show ospfv3 interface [brief] displays the address families enabled on an interface. When IPv4 and IPv6 are both configured on an interface, an entry appears for each address family. Example 10-16 lists the interfaces and associated address families.

Example 10-16 Listing of OSPFv3 Interfaces and Their Address Families

Example 10-17 shows how to view the OSPFv3 neighbors to display the neighbors enabled for IPv4 and IPv6 as separate entities.

Example 10-17 Verifying OSPFv3 IPv4 Neighbors

Exam Preparation Tasks

You have a couple of choices for exam preparation: the exercises here, Chapter 30, “Final Preparation,” and the exam simulation questions in the Pearson Test Prep Software Online.

Review All Key Topics

Review the most important topics in the chapter, noted with the Key Topic icon in the outer margin of the page. Table 10-2 lists these key topics and the page number on which each is found.

Table 10-2 Key Topics for Chapter 10

Key Topic Element

Description

Page

Section

OSPFv3 Fundamentals

231

Section

OSPFv3 Verification

235

Paragraph

OSPFv3 summarization

238

List

IPv4 support on OSPFv3

240

Use the Command Reference to Check Your Memory

Table 10-3 lists the important commands from this chapter. To test your memory, cover the right side of the table with a piece of paper, read the description on the left side, and see how much of the command you can remember.

Table 10-3 Command Reference

Task

Command Syntax

Configure OSPFv3 on a router and enable it on an interface

router ospfv3 [process-id]

interface interface-id

ospfv3 process-id {ipv4 | ipv6} area area-id

Configure a specific OSPFv3 interface as passive

passive-interface interface-id

Configure all OSPFv3 interfaces as passive

passive-interface default

Summarize an IPv6 network range on an ABR

area area-id range prefix/prefix-length

Configure an OSPFv3 interface as a point-to-point or broadcast network type

ospfv3 network {point-to-point | broadcast}

Display OSPFv3 interface settings

show ospfv3 interface [interface-id]

Display OSPFv3 IPv6 neighbors

show ospfv3 ipv6 neighbor

References in This Chapter

RFC 5340, OSPF for IPv6, R. Coltun, D. Ferguson, J. Moy, A. Lindem, and IETF. http://www.ietf.org/rfc/rfc5340.txt, July 2008.

RFC 5838, Support of Address Families in OSPFv3, A. Lindem, S. Mirtorabi, A. Roy, M. Barnes, R. Aggarwal, and IETF. http://www.ietf.org/rfc/rfc5838.txt, April 2010.

Edgeworth, Brad, Aaron Foss, and Ramiro Garza Rios, IP Routing on Cisco IOS, IOS XE, and IOS XR. Indianapolis: Cisco Press, 2014.

Cisco IOS Software Configuration Guides. http://www.cisco.com.


vceplus-200-125    | boson-200-125    | training-cissp    | actualtests-cissp    | techexams-cissp    | gratisexams-300-075    | pearsonitcertification-210-260    | examsboost-210-260    | examsforall-210-260    | dumps4free-210-260    | reddit-210-260    | cisexams-352-001    | itexamfox-352-001    | passguaranteed-352-001    | passeasily-352-001    | freeccnastudyguide-200-120    | gocertify-200-120    | passcerty-200-120    | certifyguide-70-980    | dumpscollection-70-980    | examcollection-70-534    | cbtnuggets-210-065    | examfiles-400-051    | passitdump-400-051    | pearsonitcertification-70-462    | anderseide-70-347    | thomas-70-533    | research-1V0-605    | topix-102-400    | certdepot-EX200    | pearsonit-640-916    | itproguru-70-533    | reddit-100-105    | channel9-70-346    | anderseide-70-346    | theiia-IIA-CIA-PART3    | certificationHP-hp0-s41    | pearsonitcertification-640-916    | anderMicrosoft-70-534    | cathMicrosoft-70-462    | examcollection-cca-500    | techexams-gcih    | mslearn-70-346    | measureup-70-486    | pass4sure-hp0-s41    | iiba-640-916    | itsecurity-sscp    | cbtnuggets-300-320    | blogged-70-486    | pass4sure-IIA-CIA-PART1    | cbtnuggets-100-101    | developerhandbook-70-486    | lpicisco-101    | mylearn-1V0-605    | tomsitpro-cism    | gnosis-101    | channel9Mic-70-534    | ipass-IIA-CIA-PART1    | forcerts-70-417    | tests-sy0-401    | ipasstheciaexam-IIA-CIA-PART3    | mostcisco-300-135    | buildazure-70-533    | cloudera-cca-500    | pdf4cert-2v0-621    | f5cisco-101    | gocertify-1z0-062    | quora-640-916    | micrcosoft-70-480    | brain2pass-70-417    | examcompass-sy0-401    | global-EX200    | iassc-ICGB    | vceplus-300-115    | quizlet-810-403    | cbtnuggets-70-697    | educationOracle-1Z0-434    | channel9-70-534    | officialcerts-400-051    | examsboost-IIA-CIA-PART1    | networktut-300-135    | teststarter-300-206    | pluralsight-70-486    | coding-70-486    | freeccna-100-101    | digitaltut-300-101    | iiba-CBAP    | virtuallymikebrown-640-916    | isaca-cism    | whizlabs-pmp    | techexams-70-980    | ciscopress-300-115    | techtarget-cism    | pearsonitcertification-300-070    | testking-2v0-621    | isacaNew-cism    | simplilearn-pmi-rmp    | simplilearn-pmp    | educationOracle-1z0-809    | education-1z0-809    | teachertube-1Z0-434    | villanovau-CBAP    | quora-300-206    | certifyguide-300-208    | cbtnuggets-100-105    | flydumps-70-417    | gratisexams-1V0-605    | ituonline-1z0-062    | techexams-cas-002    | simplilearn-70-534    | pluralsight-70-697    | theiia-IIA-CIA-PART1    | itexamtips-400-051    | pearsonitcertification-EX200    | pluralsight-70-480    | learn-hp0-s42    | giac-gpen    | mindhub-102-400    | coursesmsu-CBAP    | examsforall-2v0-621    | developerhandbook-70-487    | root-EX200    | coderanch-1z0-809    | getfreedumps-1z0-062    | comptia-cas-002    | quora-1z0-809    | boson-300-135    | killtest-2v0-621    | learncia-IIA-CIA-PART3    | computer-gcih    | universitycloudera-cca-500    | itexamrun-70-410    | certificationHPv2-hp0-s41    | certskills-100-105    | skipitnow-70-417    | gocertify-sy0-401    | prep4sure-70-417    | simplilearn-cisa    |
http://www.pmsas.pr.gov.br/wp-content/    | http://www.pmsas.pr.gov.br/wp-content/    |