Open Shortest Path First - OSPF V3 Packet Formats

OSPF V3 Packet Formats

The "Main OSPF Packet Header" is the same for all 5 types of packets (with exception of the Type field) whereas the following sub-headers will vary from type to type and are shown below the Main OSPF Packet Header.

The Main OSPF Packet Header
Octet Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
0 0 Version Type Packet Length
4 32 Router ID
8 64 Area ID
12 96 Checksum Instance ID 0

As per Appendix A.3 of RFC 5340 (OSPFv3 for IPv6) there are 5 OSPF Packet formats as follows:

Type Description
1 Hello
2 Database Description
3 Link State Request
4 Link State Update
5 Link State Acknowledgement

The five different formats for each "Type" of OSPF v3 packet are listed below:

Type 1: The Hello Packet
Octet Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
0 0 3 {Ver} 1 {Type} Packet Length
4 32 Router ID
8 64 Area ID
12 96 Checksum Instance ID 0
16 128 Interface ID
20 160 Rtr Priority Options (Explained below)
24 192 HelloInterval RouterDeadInterval
28 224 Designated Router ID
32 256 Backup Designated Router ID
36 288 Neighbor ID
~ ~ ...
Type 2: The Database Description Packet
Octet Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
0 0 3 {Ver} 2 {Type} Packet Length
4 32 Router ID
8 64 Area ID
12 96 Checksum Instance ID 0
16 128 0 Options (Explained below)
20 160 Interface MTU 0 0 0 0 0 0 I M M
S
24 192 DD sequence number
28 224 An LSA Header
32 256
36 288
40 320
44 352
~ ~ ...
Type 3: The OSPF Link State Request Packet
Octet Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
0 0 3 {Ver} 3 {Type} Packet Length
4 32 Router ID
8 64 Area ID
12 96 Checksum Instance ID 0
16 128 0 LS Type
20 160 Link State ID
24 192 Advertising Router
~ ~ ...
Type 4: The OSPF Link State Update Packet
Octet Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
0 0 3 {Ver} 4 {Type} Packet Length
4 32 Router ID
8 64 Area ID
12 96 Checksum Instance ID 0
16 128 # LSAs
20 160 LSAs
24 192
28 224
32 256
36 288
~ ~ ...
Type 5: The OSPF Link State Acknowledgement Packet
Octet Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
0 0 3 {Ver} 5 {Type} Packet Length
4 32 Router ID
8 64 Area ID
12 96 Checksum Instance ID 0
16 128 An LSA Header (Shown below)
20 160
24 192
28 224
32 256
~ ~ ...

The OSPFv3 (24 Bit) Options Field

This "Options Field" is used in OSPF Hello packets, Database Description packets, and certain LSAs (router-LSAs, network-LSAs, inter-area-router-LSAs, and link-LSAs).
(Note: Previous OSPF versions {v1 & v2} DO NOT support all of the options/fields listed here.)
Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
* * DC R N x E V6
Explanation of the bits in the Options field:
There are currently only 7-bits assigned.
V6-bit: "V6" stands for IP routing calculations are to be used.
E-bit: "E" stands for xternal as in AS-External-LSA flooding as specified in OSPFv2.
x-bit: This is currently deprecated. It was previously used by MOSPF.
N-bit: "N" stands for SSA (Not So Stubby Area) and used for routers which are attached to NSSA networks.
R-bit: "R" stands for outer and specifies whether the router is Active or not.
DC-bit: "DC" stands for emand ircuts and is specified in RFC 1793.
*-bits: These two bits are reserved for migration of OSPFv2 protocol extensions.
The remaining 16-bits have yet to be assigned.

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