OSPF LSA Types (2), LSA Type 1: Router LSA

(Continued from previous post)

Type 1 LSA is a Router LSA. Each LSA defines one OSPF speaking router, and all its direct connections to network objects.

Network objects are (1) OSPF routers, and (2) OSPF defined networks.

Look at the diagram. The router R1 is in fact connected to 3 objects: router R2, network 10.12.12.0/24, and network 10.1.1.0/24.

No, the network 100.100.100.1/24 is not defined in this OSPF configuration, that's why it is not a connected object.

We use the command show ip ospf database router 0.0.0.1 to list the exact Type 1 Router LSAs defining R1, where 0.0.0.1 is the OSPF name (the router ID) of R1. Here is the result on R1.

R1>show ip ospf database router 0.0.0.1

OSPF Router with ID (0.0.0.1) (Process ID 1)

Router Link States (Area 0)

LS age: 1724
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 0.0.0.1
Advertising Router: 0.0.0.1
LS Seq Number: 80000003
Checksum: 0x54DC
Length: 60
AS Boundary Router
Number of Links: 3

Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 0.0.0.2
(Link Data) Router Interface address: 10.12.12.1
Number of TOS metrics: 0
TOS 0 Metrics: 64

Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.12.12.0
(Link Data) Network Mask: 255.255.255.0
Number of TOS metrics: 0
TOS 0 Metrics: 64

Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.1.1.0
(Link Data) Network Mask: 255.255.255.0
Number of TOS metrics: 0
TOS 0 Metrics: 10


R1>

Similarly, we can also list the Type 1 Router LSA of R2. Here is the result on R1, using command "show ip ospf database router 0.0.0.2"

R1>show ip ospf database router 0.0.0.2

OSPF Router with ID (0.0.0.1) (Process ID 1)

Router Link States (Area 0)

Routing Bit Set on this LSA
LS age: 1508
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 0.0.0.2
Advertising Router: 0.0.0.2
LS Seq Number: 80000004
Checksum: 0x84A8
Length: 60
Area Border Router
Number of Links: 3

Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 0.0.0.1
(Link Data) Router Interface address: 10.12.12.2
Number of TOS metrics: 0
TOS 0 Metrics: 64

Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.12.12.0
(Link Data) Network Mask: 255.255.255.0
Number of TOS metrics: 0
TOS 0 Metrics: 64

Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.2.2.0
(Link Data) Network Mask: 255.255.255.0
Number of TOS metrics: 0
TOS 0 Metrics: 10


R1>

You may have noticed, that R2 indeed is connected to more than 3 objects, how come only 3 are listed? This is because each OSPF area has its own link state database. The above 3 objects are the only objects within Area 0, the one covering both R1 and R2.


(To be continued)

OSPF LSA Types (1)

For a quick reference about OSPF LSA types, I designed this case study to demonstrate them together.

I use 4 routers, talking to each other using OSPF protocol. R1 is belonging to Area 0. R3 and R4 are belonging to Area 1. R2 is a border router, where some interfaces are in Area 0, and others in Area 1.

(To be continued)

Network Diagram
R1 Configuration
R2 Configuration
R3 Configuration
R4 Configuration