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As mentioned in the previous section, not all routing protocols (or all versions of some
routing protocols) are compatible with IPv6. For example, although OSPFv2 is incompatible
with IPv6, OSPFv3 can be used on IPv6 networks. This section discusses OSPFv3’s
characteristics and configuration. Additionally, you will learn some common OSPFv3
troubleshooting issues and commands.
Characteristics of OSPFv3
OSPFv3 builds on OSPFv2. Therefore, when you are working with OSPFv3, you will notice
many similarities with OSPFv2. Following are some of these similarities:
■ Uses a hierarchical structure divided into areas.
■ Requires direct connectivity from the backbone area to all other areas.
■ Uses many of the same packet types (for example, Hello packets).
■ Adjacencies formed with neighbors.
Beyond the characteristics OPSFv3 has in common with OSPFv2, several enhancements
have been made to provide support for IPv6 networks. Following is a sampling of some of
OSPFv3’s enhancements:
■ Routes over links rather than over networks.
■ Uses IPv6 link-local addresses to identify neighbors.
■ Can support multiple IPv6 subnets on a single link.
■ Allows communication between two nodes connected to a common link, even
though the two nodes might not share a common subnet.
■ Supports multiple instances of OSPFv3 running over a common link.
■ Does not require the use of ARP.
Configuring OSPFv3
The primary difference in configuring OSPFv3, as opposed to OSPFv2, is that you go into
interface configuration mode to tell an interface to participate in an OSPF routing process.
In OSPFv2, you would go into router configuration mode for an OSPF process and specify
network addresses and wildcard masks. These addresses and masks determined which
of a router’s interface would participate in the OSPF routing process.
Table 12-4 provides basic OSPFv3 configuration commands.
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Chapter 12: IPv6 Troubleshooting 383
Example 12-4 shows a sample OSPFv3 configuration on a router (that is, router R1), which
is illustrated in Figure 12-5. Notice that an interface can simultaneously be configured
with both IPv4 and IPv6 addresses. Also, notice the ipv6 ospf 100 area 1 command issued
in interface configuration mode for the Fast Ethernet 0/0 and 0/1 interfaces. This
command causes both interfaces to participate in OSPFv3 routing process 100 as members
of Area 1. The OSPFv3 process was started with the ipv6 router ospf 100 command,
and then in router configuration mode, an IPv4 address of 10.1.1.1 was specified as the address
to use for the OSPF router ID.
Example 12-4 Sample OSPFv3 Configuration
R1# show run
...OUTPUT OMITTED...
interface FastEthernet0/0
ip address 192.168.1.11 255.255.255.0
ipv6 address A:A:A:A::11/64
ipv6 ospf 100 area 1
!
interface FastEthernet0/1
ip address 192.168.0.11 255.255.255.0
Table 12-4 OSPFv3 Configuration Commands
Command Description
ipv6 ospf process-id area areaid
Interface configuration mode command that allows the
IPv6 address configured on an interface to participate in
an OSPFv3 routing process.
ipv6 router ospf process-id Global configuration mode command that enables an
OSPFv3 routing process on a router.
router-id ipv4-address Router configuration mode command that specifies an
IPv4 address to be used by OSPFv3 as a router’s router
ID.
B:B:B:B::X/64
192.168.0.0/24
192.168.1.0/24
.11
Fa0/1
Area 1 Area 0
Fa0/0 Fa0/0
.11 .22 Fa0/0
.33
S1/0
.1
S1/0
.2
R1 R2 R3
A:A:A:A::X/64 C:C:C:C::X/64
172.16.1.0/30
D:D:D:D::X/64
172.16.1.0/24
Figure 12-5 OSPFv3 Sample Configuration Topology
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Many of the same root causes for an OSPFv2 issue could also result in an OSPFv3 issue.
As just a few examples, consider the following list of potential reasons an OSPFv3 adjacency
might not be formed:
■ Mismatched HELLO parameters
■ Mismatched IP MTU setting
■ Interface configured as passive
■ Mismatched area type
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Table 12-5 OSPFv3 Troubleshooting Commands
Command Description
show ipv6 ospf Displays OSPFv3 routing process, router ID, various timers, and information
about each area on a router.
show ipv6 ospf
interface
Shows IPv6 link local address, area ID, process ID, router ID, and cost.
show ipv6 ospf
neighbor
Lists the state of a router’s adjacency with all configured OSPFv3 neighbors.
debug ipv6 ospf
adj
Displays information about OSPFv3 adjacencies.
debug ip ipv6
ospf hello
Shows OSPFv3 HELLO packet information.
ipv6 address B:B:B:B::11/64
ipv6 ospf 100 area 1
!
ipv6 router ospf 100
router-id 10.1.1.1
...OUTPUT OMITTED...
Troubleshooting OSPFv3
When troubleshooting an OSPFv3 issue, you can draw on your knowledge of troubleshooting
OSPFv2, because many of the same troubleshooting issues arise in both environments.
In fact, you do not need to relearn a completely different set of syntax for
troubleshooting OSPFv3. In many cases, you can simply replace the ip keyword in a show
command with a keyword of ipv6. For example, when troubleshooting OSPFv2, you
might issue the show ip ospf interface command to view an interface’s OSPF parameters.
In an OSPFv3 environment, you could simply replace ip with ipv6, and give the show
ipv6 ospf interface command. Table 12-5 provides a command reference of commonly
used commands for troubleshooting OSPFv3 issues.

Although OSPFv2 and OSPFv3 do have many common characteristics, understanding the
subtle differences between these OSPF versions can be valuable in your troubleshooting
efforts. A listing of major differences was provided earlier in this section. To reinforce
these OSPFv3 troubleshooting concepts, the next section in this chapter presents an
OSPFv3 trouble ticket.