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

The cisco router Router ID chooses:

(1) if you use the router-id command to set up the router-id manually, then use the manual setting.

(2) if it is not manually set, the router selects the loopback and the highest IP address on the loop.

(3) if the loopback interface is not configured, select the IP address with the highest value on the physical interface. The interface used as router id does not necessarily need to run OSPF

Advantages of using loopback interface for router id:

* loopback interface is more stable than other physical interfaces

* Network administrators have autonomy in setting addresses

1.Hello protocol

Objective:

* ways to discover neighboring routers

* before two routers are called neighbors, you need to advertise the parameters that the two routers must agree with each other.

* Hello packets act as keepalive between neighboring routers

* ensure two-way communication between neighboring routers

* Select DR and BDR on a broadcast network or non-broadcast multiaccess network

Hello interval HelloInterval

The router that declares OSPF periodically sends Hello packets from every interface that initiates the OSPF protocol.

In the cisco router

* the default Hello time for broadcast networks is 10s.

* the default Hello time for non-broadcast networks is 30s

* use the command ip ospf hello-interval to change

Invalid route interval RouterDeadInterval

If a router does not receive an Hello packet from its neighbor during the invalid route interval, it will declare its neighbor router invalid

In the cisco router:

* the default value of the router invalid interval is 4 times the Hello interval

* use the command ip ospf dead-interval to change

The information contained in the Hello packet:

* routing ID RouterID of the originating router

* area ID AreaID of the originating router interface

* address mask of the originating router interface

* Authentication type and authentication information of the originating router interface

* Hello interval of the originating router interface

* invalid time interval for the router that originated the router interfac

* Router priority

* designated router DR and backup designated router BDR

* 5 tag bits that identify optional performance

* routing ID of all valid neighbors of the originating router

When a router receives an Hello packet from its neighbor router, it detects the following information:

Regional ID

Authentication information

Network mask

Hello interval time

Route invalid interval

Does the optional value match the pair value configured on the receiving interface?

Two-way communication two-way if a router receives a valid Hello packet and finds its own router ID in the Hello packet, the two-way communication is considered to be successful.

two。 Network Typ

The type of network defined by OSPF:

* Point-to-point network point-topoint

* broadcast Network broadcast

* non-broadcast multiaccess network NBMA

* Point to multipoint network poin-to-multipoint

* Virtual Link virtual links

* Point-to-point network point-to-point

A pair of separate links

The destination address of the packet for OSPF is 224.0.0.5, and this multicast address is called AllSPFRouter

* broadcast Network broadcast

Networks such as Ethernet

Elect DR and BDR.

Hello data originating from DR,BDR is sent to the 224.0.0.5 address in a multicast manner, and the destination MAC address of the data frame carrying these packets is 0100.5E00.0005.

All other routers will send link-state update packets and link-state acknowledgement packets in a multicast manner at 224.0.0.6 0100.5E00.0006 MAC address

* non-broadcast multiaccess network NBMA

Select DR and BDR on NBMA, and all OSPF packets are sent as unicast

* Point to multipoint network point-to-multipoint

There is no need to select DR and BDR,OSPF packets to send unicast

* Virtual Link virtual links

OSPF packets on virtual links are sent in unicast mode

3. Designated router and backup designated router

Specify the role of the router

* describe this multiaccess network and the other routers connected to it in the OSPF area

* manage the flooding diffusion process on this multi-access network

DR,BDR selection process:

.

4.OSPF interface

(1) data structure of OSPF interface

Show ip ospf interface

The router interface data interface information is described as follows:

IP address and mask IP Address and Mask

The IP address and mask configured on the router interface, which is used as the source address for OSPF packets originating on this interface

Regional ID Area ID

The area where the interface is located, and OSPF packets originating from this interface will use this area ID

Process ID ProcessID

Cisco is unique. Process ID is locally valid. Process ID is used to distinguish different OSPF processes.

Router ID RouterID

Network type Network Type

Cost Cost

The outbound interface cost of packets sent out this interface, using ip ospf cost

InfTransDelay

The time, in seconds, after LSA was sent from the interface of the router

Status state

Interface function status

Router priority Router Priority

The range is 0murmur255, which is used to select eight-bit unsigned integers for DR and BDR

Designated router DR

For the designated router of the network connected to the router interface, the router will record both the router id of the designated router and the interface address information of its connection to the shared network

Back up the designated router BDR

For the BDR of the network connected to the router, the router will also record the router id of the designated router and the interface address of its connection to the shared network

Hellointerval

The periodic interval between two hello packets transmitted on an interface, expressed in seconds

Cisco router defaults to 10s on broadcast networks and 30s on non-broadcast networks

RouterDeadInterval

Before declaring a neighbor router invalid, the time it takes for the local router to hear an Hello packet from a neighbor router from a network connected to an interface, counted in seconds

Cisco defaults to 4 times that of HelloInterval

Wait for timer Wait Timer

Before starting to select DR,BDR, the router waits for Hello packets of neighboring routers to advertise DR and BDR, and the time to wait for counters is the length of RouterDeadInterval.

RxmtInterval

The length of time, in seconds, that the router will have to wait to retransmit the OSPF packet without acknowledgement.

The default time of cisco is 5s

Hello timer Hello Timer

The initial value is set to HelloInterval

Neighbor router Neighboring Router

List of valid neighbor routers on the network connected to this interface

Autype

Types of authentication used on the network

OSPF authentication type: Null, simple password, encryption authentication (MD authentication)

Authentication key

If encryption authentication is enabled on the router, the authentication key is a message digest key, and encryption authentication allows multiple keys to be configured on one interface of the router

(2) OSPF interface state machine

OSPF interface status: invalidation, peer-to-peer, wait, DR, backup, DRother,loopback

* invalid Down

Initialized interface statu

* Point to point

Suitable for point-to-point, point-to-multipoint, virtual links and other network types.

* wait for waiting

Suitable for broadcast type, NBMA

* designated router DR

5.OSPF neighbor

To successfully establish an adjacency, you need to go through the following states:

* neighbor router discovery phase

* two-way communication phase

When two neighboring routers list each other's router ID in their Hello packets, the router thinks that the two-way communication is complete.

* Database synchronization phase

There will be database descriptions, link-state requests, link-state updates, and link-state acknowledgement packets between routers.

The purpose of performing this step is to make one of the neighboring routers called the master router master and the other router become the slave router slave. The master router control database describes the information exchange of the packet.

* full adjacency status

(1) neighbor data structure

Neighbor router ID Neighbor ID

Neighbor ID address Neighbor IP address

Refers to the interface IP address of a neighboring router connected to the network

Regional ID AreaID

In order to form a neighbor relationship, the area ID in the Hello packet received by the router must match the area ID configured by the router receiving interface

Interface Interface

An interface connected to the network of a neighboring router

Neighbor priority Neighbor Priority

Priority of the neighbor router, advertised in the Hello packet of the neighbor router

Status State

See the functional status of neighboring routers from the local router

Designated router DR

Back up the designated router BDR

PollInterval

Used only for related neighbor routers on NBMA networks

The default value of cisco is 120s

Neighbor router optional Neighbor option

Failure timer Inactivity Timer

(2) neighbor state machine

* failure status Down

* attempt status Attempt

Applies only to neighbors on NBMA networks, where neighbor routers are manually configured on NBMA.

* initial state Init

Indicates that the router received Hello packets from neighboring routers during the RouterDeadInterval time, but two-way communication is still not established.

* two-way communication status 2-way

Indicates that the local router has seen its own neighbor ID in the neighbor field of the Hello packet from the neighbor router

* initial status of information exchange Exstart

The local router and the neighbor router establish a master-slave relationship and confirm that the database describes the sequence number of the packet. The neighbor router with the highest router ID will become the primary router

* Information exchange status Exchange

The local router will send a database description packet to the neighbor router that describes its entire link-state database information.

The local router also sends request packets to neighboring routers requesting the latest LSA

* Information loading status Loading

The local router will send a link-state request packet to the neighboring router requesting the latest LSA advertisement

Full adjacency status Full

(3) establish an adjacency.

During the creation of an adjacency, OSPF uses the following three packet types

Database description packet type 2

Link-state request packet type 3

Link-state update packet type 4

The database describes the process of establishing adjacencies with three tag bits in the packet.

I bit, initial bit Initial bit

When you need to indicate that the first database description packet is being sent, the bit is set to 1

M bit, successor More bit

Indicates that when the last database description packet is not sent, the bit is set to 1

MS bit master-slave bit Master/Slave bit

When the database describes that the packet originated from a primary router, this bit is set to 1

Confirmation of LSA

Explicit confirmation

Acknowledge receipt of a link-state acknowledgement packet containing this LSA header

Implicit confirmation

Acknowledge receipt of an update packet containing the same instance of this LSA

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