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The original OSPF, created to exchange routing information for IPv4, began life as Version
1 and was later enhanced as Version 2. The original OSPFv2 RFC (1247) made draft standard
status in 1991. Although some changes and additions have occurred in OSPFv2 over
the years, the OSPF many companies have used for a long time is OSPFv2.
To support IPv6, an IETF working group took the OSPFv2 standard and made changes to
the protocol to support IPv6, resulting in the new protocol named OSPF Version 3
(OSPFv3). OSPFv3 does advertises IPv6 prefixes, but it does not advertise IPv4 prefixes,
so in most OSPF shops that begin migration to IPv6, the routers run OSPFv2 for IPv4
support and OSPFv3 for IPv6 support, just like a network running EIGRP for IPv4 would
then add configuration for EIGRP for IPv6.
As with the earlier sections about RIPng and EIGRP for IPv6, this section first examines
the similarities and differences between the IPv6 version of OSPF and the earlier IPv4 version.
It then looks at the OSPFv3 configuration and finally OSPFv3 verification.
Comparing OSPFv2 and OSPFv3
Because OSPFv2 should already be somewhat familiar to you after reading Part 3 of this
book, this section summarizes the similarities and differences, and then explains some of
the differences briefly. To that end, Table 17-7 summarizes a wide variety of OSPF features,
comparing OSPFv2 and OSPFv3.
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Some of the comparisons in the table require further explanation:
■ The multicast addresses used by OSPFv3 of course differ, but they keep similar numbers
compared to OSPFv2.
■ OSPF uses IPv6’s inherent IPsec capabilities, rather than defining a separate authentication
process.
■ As with RIPng and EIGRP for IPv6, OSPFv3 does not require neighboring routers to
be in the same subnet as a requirement for becoming neighbors. However, OSPFv3
does follow all other neighbor verification checks as compared with OSPFv2, as summarized
in Table 5-5 in Chapter 5, “OSPF Overview and Neighbor Relationships.”
■ Support for multiple instances of OSPF on a single link, whereas OSPFv2 supports
only a single instance per link.
■ OSPF uses the neighbor’s link local IPv6 address as the next-hop IP address.
■ The RID is still based on IPv4 addresses, not IPv6 addresses. Like EIGRP for IPv6, a
router must have a RID before OSPFv3 will work.
Other differences exist as well, particularly when examining the details listed in the
OSPFv3 LSDB. However, keeping to a scope that includes general concepts, configuration,
and verification, this chapter does not get into those details.
Key
Topic
Table 17-7 Comparing OSPFv2 and OSPFv3
Feature OSPFv2 OSPFv3
Uses interface cost metric, derived from interface bandwidth
Yes Yes
Metric meaning infinity 216 – 1 216 – 1
Supports route tags Yes Yes
Elects DR based on highest priority, then highest RID Yes Yes
Periodic reflooding every... 30 minutes
30 minutes
Multicast–all SPF routers 224.0.0.5 FF02::5
Multicast–All Designated routers 224.0.0.6 FF02::6
Authentication OSPFspecific
Uses IPv6 AH/ESP
Neighbor checks compared to OSPFv2 (table 5-5) Same Same, except no “same
subnet” check
Multiple instances per interface No Yes
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Configuring OSPFv3
OSPFv3 configuration requires no new steps and few changes syntactically when compared
to the newer style of OSPFv2 configuration discussed in Chapter 5’s section “Enabling
OSPF Neighbor Discovery on LANs.” That section explained how to configure
OSPF using the interface ip ospf area interface subcommand to enable OSPF on an interface,
rather than relying on the indirect reference made by OSPFv2’s network router subcommand.
With OSPFv3, only one configuration style is supported, using the similar ipv6
ospf area command to enable OSPFv3 on an interface. IOS does not support a network
command for OSPFv3.
The basic OSPFv3 configuration matches the newer style of OSPFv2 configuration, except
for substituting ipv6 instead of ip in the configuration commands. The following list
shows the basic configuration steps, including the assignment of an IPv6 address to the
interface.
Step 1. Enable IPv6 routing with the ipv6 unicast-routing global command.
Step 2. Create an OSPFv3 routing process using the ipv6 router ospf process-id
global configuration command.
Step 3. Enable IPv6 on the interface, typically by configuring static IPv6 addresses as
follows:
Configure an IPv6 unicast address on each interface, using the ipv6 address
address/prefix-length [eui-64] interface command.
Configure the ipv6 enable command, which enables IPv6 and causes the
router to derive its link local address.
Step 4. Enable OSPFv3 on the interface with the ipv6 ospf process-id area areanumber
interface subcommand.
Step 5. If no OSPF router ID has been automatically chosen, due to not having at least
one working interface with a IPv4 address, configure an OSPF router ID with
the router-id rid command in OSPFv3 configuration mode.
Note: for a complete discussion of options for enabling IPv6 on an interface, as mentioned
at Step 3, refer to Chapter 16’s Table 16-11.
Note: Unlike a new EIGRP for IPv6 routing process, a newly created OSPFv3 routing
process defaults to an administratively enabled state. As a result, the previous configuration
checklist does not include the no shutdown OSPFv3 subcommand. However, the
router mode subcommands shutdown and no shutdown can be used to disable and reenable
the OSPFv3 routing process.
To be complete, Example 17-5 lists the OSPFv3 configuration on Router R1 from Figure
17-. Figure 17-2 shows the area design used for the configuration.
Key
Topic
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Chapter 17: IPv6 Routing Protocols and Redistribution 591
R3
R4
SW1
R2
R1
Area 34
SW2
Area 0
SW3
Figure 17-2 Area Design Used for Example 17-5
Example 17-5 Configuring IPv6 Routing and Routing Protocols on R1
R1# show running-config
! output is edited to remove lines not pertinent to this example
! Step 1: Enable IPv6 routing
ipv6 unicast-routing
!
! On five interfaces, do steps 3 and 4: configure static IPv6 addresses,
! and enable OSPFv3 process 5, in the appropriate areas
interface FastEthernet0/0.1
ipv6 address 2012::1/64
ipv6 ospf 5 area 0
!
interface FastEthernet0/0.2
ipv6 address 2017::1/64
ipv6 ospf 5 area 0
!
interface FastEthernet0/1.18
ipv6 address 2018::1/64
ipv6 ospf 5 area 0
!
interface Serial0/0/0.3
ipv6 address 2013::1/64
ipv6 ospf 5 area 34
!
interface Serial0/0/0.4
ipv6 address 2014::1/64
ipv6 ospf 5 area 34
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! Steps 2 and 5 – creating the OSPFv3 process, and defining the RID
ipv6 router ospf 5
router-id 1.1.1.1
The configuration example shows two interface subcommands on each interface: an ipv6
address command that defines a global unicast IPv6 address, plus the ipv6 ospf area command
to enable OSPFv3 on the interface. The interface subcommands place each interface
into the correct area. But these interface subcommands have no effect unless the configuration
also includes a matching ipv6 router ospf 5 global command, with the 5 in this
case matching the ipv6 ospf 5 area commands on the interfaces.
Beyond this basic OSPFv3 configuration, many of the optional OSPF features match
when comparing the OSPFv2 and OSPFv3 configuration as well, for example:
■ The concept and commands related to OSPF stub areas are literally identical, using
commands such as area 34 stub. (See Table 7-3 for a reminder of the commands for
OSPFv2.)
■ Like OSPFv2, OSPFv3 can only summarize routes on ABRs and ASBRs, using the
similar command area x range ipv6-prefix/length router subcommand, with the
only difference being that the command lists an IPv6 prefix rather than an IPv4 subnet
and mask.
■ Like OSPFv2, OSPFv3 uses the concept of OSPF interface types as configured with
the ipv6 ospf network type interface subcommand. These types dictate whether
OSPFv3 attempts to elect a DR, and whether routers need to configure neighbors with
the ipv6 ospf neighbor interface subcommand, with the same issues seen with
OSPFv2.
Verifying OSPFv3
Most of the show commands for OSPFv3 have similar output compared to the OSPFv2
versions of the commands. The biggest differences exist in the output related to the OSPF
database, both due to the changes in LSA terminology, the addition of new LSA types,
and that some LSDB information is located with a different LSA type when comparing
OSPFv2 and OSPFv3. Table 17-8 lists a cross-reference comparing the key commands related
to both OSPFv2 and OSPFv3, with the second column listing the parameters after
show ip, and the third column listing parameters after show ipv6.
Table 17-8 Comparing OSPF Verification Commands: show ip and show ipv6...
Function show ipv4... show ipv6...
All OSPF-learned routes ... route ospf ... route ospf
Router ID, Timers, ABR, SPF statistics ... ospf ... ospf
List of routing information sources ... protocols
... ospf neighbor
... ospf neighbor
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The first verification example focuses on some of the differences between OSPFv2 and
OSPFv3 for the display of neighbor status. Example 17-6 shows output from Router R3, as
shown in Figures 17-1 and 17-2. The output highlights the only noticeable difference between
the output of the show ip ospf neighbor and show ipv6 ospf neighbor commands:
OSPFv2 displays the interface IP address of neighbors, but OSPFv3 displays an interface ID.
OSPFv3 routers create a locally significant interface ID, using that in LSAs that describe the
intra-area topology, rather than using neighbor IPv4 addresses to describe the topology.
OSPFv3 separates the topology information from the Layer 3 addressing information, so
OSPFv3 uses the interface ID concept to identify how a router reaches a particular neighbor.
Example 17-6 IPv6 OSPFv3 Interface IDs on Router R3
! On R3, IPv4 OSPFv2 neighbors are listed, with interface IPv4 addresses.
R3# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
2.2.2.2 0 FULL/ - 00:00:31 10.10.23.2 Serial0/0/0.2
1.1.1.1 0 FULL/ - 00:00:31 10.10.13.1 Serial0/0/0.1
4.4.4.4 1 FULL/DR 00:00:39 10.10.34.4
FastEthernet0/0
! On R3, IPv6 OSPFv3 neighbors are listed, with interface IDs.
R3# show ipv6 ospf neighbor
Neighbor ID Pri State Dead Time Interface ID Interface
2.2.2.2 1 FULL/ - 00:00:36 19 Serial0/0/0.2
1.1.1.1 1 FULL/ - 00:00:35 19 Serial0/0/0.1
4.4.4.4 1 FULL/DR 00:00:34 3
FastEthernet0/0
! Next, the LSA for R3 (RID 3.3.3.3) lists its own interface ID and
! the neighbor interface ID, for each link.
R3# show ipv6 ospf database router adv-router 3.3.3.3
OSPFv3 Router with ID (3.3.3.3) (Process ID 5)
Interfaces assigned to each area ... protocols
... ospf interface
brief
... protocols
... ospf interface
brief
OSPF interfaces–costs, state, area, number
of neighbors
... interface brief ... interface brief
Detailed information about OSPF interfaces ... ospf interface ... ospf interface
Displays summary of OSPF database ... ospf database ... ospf database
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Router Link States (Area 34)
LS age: 996
Options: (V6-Bit, E-Bit, R-bit, DC-Bit)
LS Type: Router Links
Link State ID: 0
Advertising Router: 3.3.3.3
LS Seq Number: 80000007
Checksum: 0xDC04
Length: 72
Number of Links: 3
Link connected to: another Router (point-to-point)
Link Metric: 64
Local Interface ID: 17
Neighbor Interface ID: 19
Neighbor Router ID: 2.2.2.2
Link connected to: another Router (point-to-point)
Link Metric: 64
Local Interface ID: 16
Neighbor Interface ID: 19
Neighbor Router ID: 1.1.1.1
Link connected to: a Transit Network
Link Metric: 1
Local Interface ID: 3
Neighbor (DR) Interface ID: 3
Neighbor (DR) Router ID: 4.4.4.4
Example 17-7 displays the output of a few other IPv6 show command, just for perspective.
The show ipv6 ospf interface brief command lists the same kind of information
shown in the similar show ip ospf interface brief command, but again listing the interface
ID as new information. The show ipv6 protocols command lists much sparser information
as compared to the similar show ip protocols command. Note that both commands identify
which OSPFv3 interfaces have been assigned to each area.
Example 17-7 Finding Interfaces and Areas for OSPFv3, on Router R3
R1# show ipv6 protocols
IPv6 Routing Protocol is “connected”
IPv6 Routing Protocol is “ospf 1”
Interfaces (Area 34):
Serial0/0/0.1
Serial0/0/0.2
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FastEthernet0/0
Redistribution:
None
R1# show ipv6 ospf interface brief
Interface PID Area Intf ID Cost State Nbrs F/C
Se0/0/0.1 1 34 19 64 P2P 1/1
Se0/0/0.2 1 34 19 64 P2P 1/1
Fa0/0 1 34 3 1 BDR 1/1
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