OSPFv3 LSA Types provide the foundation for understanding key differences between OSPFv2 and OSPFv3. In this lesson, we’ll configure both protocols in a dual-stack topology, allowing us to observe practically how OSPFv3 LSAs differ from those in OSPFv2.
Table of Contents
OSPFv2 vs. OSPFv3 LSA Types
As you may already know, LSA Types 1 to 5 and Type 7 are the primary and most widely recognized LSA types in OSPFv2. I’ll assume you’re familiar with these types, so we’ll focus primarily on changes to the LSAs in OSPFv3. But first, here’s a very brief overview of the main LSA types in OSPFv2.
In OSPFv3, there are two additional LSA types: Type 8 (Link-LSA) and Type 9 (Intra-Area-Prefix LSA), which exist only in OSPFv3. Additionally, LSA Type 1 has undergone some changes in OSPFv3, and we’ll focus on these modifications in this lesson.
To gain a practical understanding of how these LSAs have changed in OSPFv3, I have set up a dual-stack topology configured with both OSPFv2 and OSPFv3. By exploring the LSA types in the OSPFv2 and OSPFv3 databases, we can clearly see and analyze the differences.
To review and compare the OSPF configuration for IPv4 and IPv6, here are the differences in the commands used.
Enabling OSPF:
For IPv4, use the command:
router ospf [process-id].For IPv6, use:
ipv6 router ospf [process-id].
Router ID:
The
router-idparameter is a 32-bit value and is configured the same way for both IPv4 and IPv6.
Enabling Interfaces:
In IPv4, enable interfaces in OSPF using the
network [ip-address] [wildcard-mask] area [area-id]command within the OSPF context.In IPv6, use the
ipv6 ospf area [area-id]command within the interface context to enable OSPF.
Passive Interfaces:
For both versions, loopback interfaces are configured as passive interfaces using the same command:
passive-interface [interface-name].
Routing:
For IPv6, it is essential to enable routing with the command:
ipv6 unicast-routing.
Now, we are ready to examine the OSPFv2 and OSPFv3 databases and explore their practical differences. Before we proceed, here is a table illustrating the changes in Link State Advertisements (LSAs) from OSPFv2 to OSPFv3.
Router LSA (Type 1) / Intra-Area-Prefix LSA (Type 9)
The Router LSA, or LSA Type 1, is one of the most important LSAs in both IPv4 and IPv6, but there is a key difference between them.
In IPv4, the Router LSA is sent by each router to advertise both the topology and the IP addresses of the links connected to it. However, in IPv6, the Router LSA only includes the topology information for the links. IPv6 prefix (address) information no longer fits into LSA Type 1 and is instead conveyed through a separate, new LSA type called the Intra-Area-Prefix LSA (Type 9).
Let’s examine the Router LSA sent by the router IOU2 in both IPv4 and IPv6 to observe the practical differences. This can be done using the command show ip ospf database router
adv-router 2.2.2.2 for IPv4 and show
ipv6 ospf database router adv-router 2.2.2.2 for IPv6.
IOU2#show ip ospf database router adv-router 2.2.2.2
OSPF Router with ID (2.2.2.2) (Process ID 1)
Router Link States (Area 0)
LS age: 82
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 2.2.2.2
Advertising Router: 2.2.2.2
LS Seq Number: 8000001F
Checksum: 0x3133
Length: 72
Number of Links: 4
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 3.3.3.3
(Link Data) Router Interface address: 10.2.3.2
Number of MTID metrics: 0
TOS 0 Metrics: 10
Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.2.3.0
(Link Data) Network Mask: 255.255.255.0
Number of MTID metrics: 0
TOS 0 Metrics: 10
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 1.1.1.1
(Link Data) Router Interface address: 10.1.2.2
Number of MTID metrics: 0
TOS 0 Metrics: 10
Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.1.2.0
(Link Data) Network Mask: 255.255.255.0
Number of MTID metrics: 0
TOS 0 Metrics: 10
In IPv4, the Router LSA topology section shows that router IOU2 connects to two routers, IOU1 and IOU3, via point-to-point links. Address details for these links, including subnet addresses and subnet masks, are provided under the “Stub Network” tag.
In IPv6, however, the Router LSA only includes topology information, indicating that router IOU2 is connected to IOU1 and IOU3 via point-to-point links, with no address information included in this LSA.
IOU2#show ipv6 ospf database router adv-router 2.2.2.2
OSPFv3 Router with ID (2.2.2.2) (Process ID 1)
Router Link States (Area 0)
LS age: 77
Options: (V6-Bit, E-Bit, R-bit, DC-Bit)
LS Type: Router Links
Link State ID: 0
Advertising Router: 2.2.2.2
LS Seq Number: 80000021
Checksum: 0xF2A3
Length: 56
Number of Links: 2
Link connected to: another Router (point-to-point)
Link Metric: 10
Local Interface ID: 4
Neighbor Interface ID: 3
Neighbor Router ID: 3.3.3.3
Link connected to: another Router (point-to-point)
Link Metric: 10
Local Interface ID: 3
Neighbor Interface ID: 3
Neighbor Router ID: 1.1.1.1
In IPv6, address information is sent through a new LSA type called the Intra-Area Prefix LSA. This can be viewed using the command show ipv6 ospf database prefix
adv-router 2.2.2.2, where we can see the prefixes and prefix lengths associated with router IOU2 in the output.
IOU2#show ipv6 ospf database prefix adv-router 2.2.2.2
OSPFv3 Router with ID (2.2.2.2) (Process ID 1)
Intra Area Prefix Link States (Area 0)
Routing Bit Set on this LSA
LS age: 106
LS Type: Intra-Area-Prefix-LSA
Link State ID: 0
Advertising Router: 2.2.2.2
LS Seq Number: 8000001F
Checksum: 0x5146
Length: 56
Referenced LSA Type: 2001
Referenced Link State ID: 0
Referenced Advertising Router: 2.2.2.2
Number of Prefixes: 2
Prefix Address: 2001:AA:2:3::
Prefix Length: 64, Options: None, Metric: 10
Prefix Address: 2001:AA:1:2::
Prefix Length: 64, Options: None, Metric: 10
Link LSA (Type 8)
Another new LSA in IPv6 is the Link LSA (Type 8), which operates within the link-local scope. Each router on a link uses the Link LSA to advertise its link-local address and any other address prefixes associated with that link to other routers on the same link.
For example, to view the information sent through the Link LSA on router IOU2 for the Ethernet0/0 link in our topology, we can use the command show ipv6 ospf database link
interface ethernet0/0 adv-router 2.2.2.2.
As you can see, the Link LSA advertises the link-local address of router IOU2 (fe80::2) along with the additional prefix configured on this link (2001:AA:1:2::/64).
IOU2#show ipv6 ospf database link interface ethernet 0/0 adv-router 2.2.2.2
OSPFv3 Router with ID (2.2.2.2) (Process ID 1)
Link (Type-8) Link States (Area 0)
LS age: 1034
Options: (V6-Bit, E-Bit, R-bit, DC-Bit)
LS Type: Link-LSA (Interface: Ethernet0/0)
Link State ID: 3 (Interface ID)
Advertising Router: 2.2.2.2
LS Seq Number: 8000001E
Checksum: 0x460A
Length: 56
Router Priority: 1
Link Local Address: FE80::2
Number of Prefixes: 1
Prefix Address: 2001:AA:1:2::
Prefix Length: 64, Options: None