Shulou(Shulou.com)06/01 Report--

The protocol number of OSPF is 89, and when OSPF packet multicast occurs, their TTL is set to 1

1. Packet header

All OSPF packets start with a header of 24 octets

Version version

The version number of OSPF, and the version number of OSPF is 2.

Type Type

The type of packet that follows the header

Packet length Packet Length

The length of the OSPF packet, including the length of the packet header, in octet bytes

Router ID Router ID

ID of the originating router

Regional ID Area ID

The area where the router originating the packet is located

Checksum Checksum

Standard IP checksum for the entire packet, including the header

Authentication type (AuType)

Authentication mode in use

Certified Authentication

Autype = 0 does not check this field and can contain anything.

Autype = 1 contains a password with a maximum of 64 bits

Autype = 2 contains a Key ID, authentication data length, and undiminished encryption sequence number

Key ID Key ID

Represents the authentication algorithm and the security key used to create the message digest

Encrypted serial number

A number that will not be reduced to prevent recurrence.

2.Hello packet

In order to form an adjacency, a Hello packet must carry the same parameters as its neighbors

Network Mask Network Mask

The network mask of the sending packet interface. If the mask does not match the network mask of the receiving packet interface, the packet will be discarded.

Hello interval Hello Interval

The time interval between the transmission of Hello packets on an interface is a periodic period of time, in seconds

Optional Option

Used to ensure compatibility between neighbors

Router priority Router Priority

Used for DR and BDR elections, priority is 0, do not participate in the election

Router invalid interval Router Dead Interval

The length of time that the originating router will wait for Hello packets from neighboring routers before declaring the route invalid

Designated router DR

If there is no DR (not selected or the network type does not require DR), this field is set to 0.0.0.0

Back up the designated router BDR

If there is no DBR, this field is set to 0.0.0.0

Neighbor Neighbor

If the originating router has received valid Hello packets from some of its routers on the network in the past Router DeadInterval time, then the ID of all neighbors will be listed in this field

3. Database description packet

One of the main purposes of the database description packet is to describe some or all of the LSA information in the originating router database so that the receiving router can determine whether the received LSA has a matching LSA in its database, which can be done by listing the header of the LSA.

Interface MTU Interface MTU

The size, in octets, of the maximum IP packet that can be sent by the originating router interface without packet segmentation.

Optional Option

Included in the database description packet that allows the router to choose not to forward some LSA to neighboring routers that do not have the necessary support capabilities

The first five bits of the next octet of the message are not used and are set to 00000b

* I bit, initial bit Initial bit

When the first packet in a series of database description packets is sent, the bit is set to 1, and subsequent database description packets will set the bit to 0

* M bit, successor More bit

When the packet sent is not the last packet in a series of database description packets, the bit is set to 1

* MS bit, master-slave bit Master/Slave bit

During database synchronization, this bit is set to 1, which is used to indicate that the router of the database description packet is a master router, and the slave router is set to 0min MSmurbit = 0.

* Database description serial number DD sequence Number

During database synchronization, it is used to ensure that the router receives a complete sequence of database description packets

* LSA header LSA Header

4. Link-state request packet

Link-state type Link State Type

Link-state class model, used to represent the type of a LSA

Link-state ID Link State ID

Advertise router Advertising Router

Router ID of the router that originates the LSA advertisement

5. Link-state update packet

OSPF packets cannot leave the network that initiated them. A link-state packet can carry one or more LSA, but these LSA can only be delivered to the directly connected neighbors of the router that originates them. The neighbor router that receives the LSA will be responsible for re-encapsulating the relevant LSA in the new LS update packet, thus further flooding and spreading to its own neighbors.

Number of LSA Number of LSA

The number of LSA contained in this packet

Link-state advertisement LSA

6. Link-state acknowledgement packet

Used for reliable flooding and diffusion of LSA

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