-An LSA type 1, called a router LSA, identifies an OSPF router based on its OSPF router ID (RID).
-Each router creates a Type 1 LSA for itself and floods the LSA throughout the same area.
-To flood the LSA, the originating router sends the Type 1 LSA to its neighbors inside the same area,
who in turn send it to their other neighbors inside the same area, until all routers in the area have a copy of the LSA.
-Internal routers each create a single Type 1 LSA for themselves, but ABRs create multiple Type 1 LSAs for themselves: one per area.
-As with all OSPF LSAs, OSPF identifies a Type 1 LSA using a 32-bit link state identifier (LSID).
-When creating its own Type 1 LSA, each router uses its own OSPF RID value as the LSID.
Below is a summary of Type 1 LSAs R1 has:
R1#show ip ospf database
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 1439 0x80000005 0x00AC60 8
2.2.2.2 2.2.2.2 1456 0x80000003 0x00E955 1
3.3.3.3 3.3.3.3 1435 0x80000003 0x00435F 2
4.4.4.4 4.4.4.4 1447 0x80000003 0x005E36 2
5.5.5.5 5.5.5.5 1462 0x80000003 0x00A2E1 2
9.9.9.9 9.9.9.9 1468 0x80000002 0x000D4D 2
R1 is an internal OSPF router, so it creates its own single Type 1 LSA, for Area 0:
R1#show ip ospf database router 1.1.1.1
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 0)
LS age: 331
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 1.1.1.1
Advertising Router: 1.1.1.1
LS Seq Number: 80000006
Checksum: 0xAA61
Length: 120
Number of Links: 8
Link connected to: a Stub Network
(Link ID) Network/subnet number: 192.168.100.100
(Link Data) Network Mask: 255.255.255.255
Number of TOS metrics: 0
TOS 0 Metrics: 1
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 9.9.9.9
(Link Data) Router Interface address: 192.168.0.21
Number of TOS metrics: 0
TOS 0 Metrics: 64
Link connected to: a Stub Network
(Link ID) Network/subnet number: 192.168.0.20
(Link Data) Network Mask: 255.255.255.252
Number of TOS metrics: 0
TOS 0 Metrics: 64
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 5.5.5.5
(Link Data) Router Interface address: 192.168.0.17
Number of TOS metrics: 0
TOS 0 Metrics: 64
Link connected to: a Stub Network
(Link ID) Network/subnet number: 192.168.0.16
(Link Data) Network Mask: 255.255.255.252
Number of TOS metrics: 0
TOS 0 Metrics: 64
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 4.4.4.4
(Link Data) Router Interface address: 192.168.0.13
Number of TOS metrics: 0
TOS 0 Metrics: 64
Link connected to: a Stub Network
(Link ID) Network/subnet number: 192.168.0.12
(Link Data) Network Mask: 255.255.255.252
Number of TOS metrics: 0
TOS 0 Metrics: 64
Link connected to: a Transit Network
(Link ID) Designated Router address: 192.168.0.3
(Link Data) Router Interface address: 192.168.0.1
Number of TOS metrics: 0
TOS 0 Metrics: 10
We can also check another router's Type 1 LSA (related to the same area) on R1:
R1#show ip ospf database router 5.5.5.5
OSPF Router with ID (1.1.1.1) (Process ID 1)
Router Link States (Area 0)
LS age: 1735
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 5.5.5.5
Advertising Router: 5.5.5.5
LS Seq Number: 80000003
Checksum: 0xA2E1
Length: 48
Number of Links: 2
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 1.1.1.1
(Link Data) Router Interface address: 192.168.0.18
Number of TOS metrics: 0
TOS 0 Metrics: 64
Link connected to: a Stub Network
(Link ID) Network/subnet number: 192.168.0.16
(Link Data) Network Mask: 255.255.255.252
Number of TOS metrics: 0
TOS 0 Metrics: 64
Note: Stub Network refers to a network/subnet to which only one OSPF router is connected (on which no DR has been elected - example: point-to-point).
Transit Network refers to a network/subnet over which two or more OSPF routers have become neighbors.
Router R9, which is an ABR, creates a Type 1 LSA for each area it is connected to:
R9#show ip ospf database
OSPF Router with ID (9.9.9.9) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 1370 0x80000005 0x00AC60 8
2.2.2.2 2.2.2.2 1387 0x80000003 0x00E955 1
3.3.3.3 3.3.3.3 1366 0x80000003 0x00435F 2
4.4.4.4 4.4.4.4 1378 0x80000003 0x005E36 2
5.5.5.5 5.5.5.5 1393 0x80000003 0x00A2E1 2
9.9.9.9 9.9.9.9 1397 0x80000002 0x000D4D 2
...
Router Link States (Area 2)
Link ID ADV Router Age Seq# Checksum Link count
9.9.9.9 9.9.9.9 1442 0x80000006 0x00C00D 3
10.10.10.10 10.10.10.10 1422 0x80000006 0x00051D 3
11.11.11.11 11.11.11.11 1393 0x80000005 0x000A0D 3
...
Router Link States (Area 3)
Link ID ADV Router Age Seq# Checksum Link count
9.9.9.9 9.9.9.9 463 0x80000004 0x00A752 1
12.12.12.12 12.12.12.12 518 0x80000005 0x000E18 2
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