下面是小编为大家整理的mtu,广播域,ospf学习笔记（广播域,ospf学习笔记,mtu）（2022年）,供大家参考。
mtu 广播域 ospf 学习笔记（广播域 ospf 学习笔记 mtu）
什么是 MTU？
是 MTU 最大传输单元的缩写。意思是网络上传送的最大数据包。MTU的单位是字节。大部分网络设备的 MTU MTU MTU 都是 1500。如果本机的比网关的大，大的数据包就会被拆开来传送，这样会产生很多数据包碎片，增加丢包率，降低网络速度。把本机的 MTU MTU 小或相同设成比网关的，就可以减少丢包。3、如何检测网关的 MTU？在本机打开 DOS 窗口，执行：平 F L 1472 192.168.0.1 其中 192.168.0.1是网关 IP 地址，1472 是数据包的长度。请注意，上面的参数是“L”（小写的 L），而不是“- 1”。如果能平通，表示数据包不需要拆包，可以通过网关发送出去如果出现：包需要。支离破碎但 DF 集。表示数据包需要拆开来发送。此时，减少数据包长度，再执行上面的平命令。从 1400 到 1472 之间多试几次，就能找到合适的数据包长度了。把数据包长度加上数据包头 28 字节，就得到 MTU MTU 的值。如果检测到网关的值是 1500，不需要修改。如果网关有防火墙平不通，可以试试直接把 MTU 设为 1400. 4、如何修改本机的 MTU？修改方法如下：（1）、运行注册表（2）、浏览到：hkey_local_machine \系统\ CurrentControlSet \服务\ TCPIP \参数接口如图 2（3）、接口下有多个子项，每个子项对应一个网卡。请按如下方法选择网卡：（一）确定本机用来连接的网卡或拨号连接的 IP 网络，如 192.168.0.19；（b）用鼠标点击接口上的子项，查看键值列表中的 IPAddress 项；（c）如果 IPAddress 的键值与（一）中的 IP 相同，即 192.168.0.19，则该子项就是要找的网卡。（4）、进入该子项，在右边的窗口里按鼠标右键，选择”新建”->“双字节值”，输入名称“奔驰”，按回车。再用鼠标双击“奔驰”，弹出修改窗口：如图 3：填入 MTU 的值。填写前请先把基数设为十进制设置好后，需要重启机器才能生效。
广播域
广播域（广播域）是一个逻辑上的计算机组，该组内的所有计算机都
会收到同样的广播信息冲突域：在同一个冲突域中的每一个节点都能收到所有被发送的帧。
广播域：网络中能接收任一设备发出的广播帧的所有设备的集合
冲突域是基于第一层（物理层）
广播域是机于第二层（数据链路层）
广播域就是说如果站点发出一个广播信号后能接收到这个信号的范围。通常来说一个局域网就是一个广播域。
冲突域：一个站点向另一个站点发出信号。除目的站点外，有多少站点能收到这个信号。这些站点就构成一个冲突域。
枢纽所有端口都在同一个广播域，冲突域内。
OSPF 基本概念及单区域配置
-内部网关路由协议
OSPF 内部网关路由协议：用于在单一自治系统（自治系统）内决策路由
自治系统（AS）：执行统一路由策略的一组网络设备的组合
-区域
为了适应大型的网络，OSPF 在作为内划分多个区域
每个 OSPF 路由器只维护所有区域的完整的链路状态信息
-链路状态路由协议
OSPF 是链路状态路由协议，链路状态路由协议中的路由器了解 OSPF网络内的链路状态信息
链路状态路由协议中，直连的路由器之间建立邻接关系，互相”交流”链路信息，来”画”出完整的网络结构
我为了标识链路信息是由谁发出的，用路由器 ID 标识路由器
我相邻路由器之间建立邻接关系，保存在邻居列表中
我路由器学习到的链路信息，表存在链路状态数据库中
路由器 ID
是在 OSPF 路由器 ID：区域内唯一标识一台路由器的 IP 地址
路由器 ID 选取规则：
我首先，路由器选取它所有回送接口上数值最高的 IP 地址
我如果没有回送接口，
Select the highest value of the IP address on all physical ports
- the type of database in the link state routing protocol
Neighbor list: lists neighbor routers that have established adjacency relationships for each router
Link state database (LSDB): lists the information of other routers in the network, thus showing the network topology of the whole network
Routing table: lists the best path to reach each connected network calculated by the SPF algorithm
Link state generation process
Build adjacency relationships - (learning link state information) - link state database - (Djkstra algorithm) - shortest path tree - routing table
- the process of establishing neighborhood relationships
Init: receives the HELLO message of the other party and converts it to the initial state
2-way: see your Router ID in the HELLO message sent by the other party and change to a two-way state
ExStart: determines the sequence number of the database description message and converts it to the initial state of information exchange - DBD (Seq)
ExChange: send the database description message to the state of information exchange - DBD
ExChange: send the link status message request packet to obtain the unknown link status information - LSR
Loading: send link status update message, synchronous link status database - LSU
Full: know that the link state database of the two routers is exactly the same, forming adjacency relations
Conditions required to satisfy the adjacency relation of -OSPF
Neighbor: if two routers do not meet the following conditions, they cannot become neighbors:
L Area-id: two routers must be on a common network segment. Their ports must belong to the same area on the network segment and belong to the same subnet
L authentication (Authentication OSPF): the same area router must exchange the same authentication password to become a neighbor
The L, Hello, Interval, and Dead Interval:OSPF protocols require two neighbor routers to have the same time intervals, otherwise they cannot be neighbors routers
L Stub zone mark: two routers can become neighbors in Hello messages by negotiating the tags of the Stub region
-OSPF network type
The router interface type is different, and the OSPF router performs a slightly different operation when setting up
neighborhood relationships
Example of network type
Broadcast Ethernet
Non broadcast multiple access, NBMA, frame relay, X.25
Point to point PPP, HDLC
A collection of point to multipoint and multiple point-to-point links
-OSPF"s DR and BDR
Designated router (DR): other routers on a network segment are related to the designated router (DR) instead of forming adjacency relationships with each other
Select DR and BDR via the Hello message to represent the OSPF segment
Other routers (DRothers) only form adjacency relationships with DR and BDR routers
Send Hello messages via multicast
The router with the highest OSPF priority is selected as DR
If the OSPF priority is the same, the router with the highest Router ID will be selected as DR
-OSPF package type summary
Packet type description
Hello is used to establish and maintain neighborhood relationships between neighbor routers
The database description package DBD describes the content of the link state database for each OSPF router
The link status request packet LSR requests part of the link status database
Link state update packet LSU transmits link state data notification LSA to neighbor router
The link status acknowledgment packet LSAck confirms that the neighbor"s incoming LSA has been received
-OSPF"s Hello protocol
When a OSPF process is started on the router, each router sends Hello packets at a certain interval of time
The Hello packet is sent through the multicast address 224.0.0.5
OSPF routers use Hello packages to initiate neighborhood relationships and monitor the presence and disappearance of such relationships
In a broadcast network or peer to peer network, the transmission interval of Hello is 10 seconds; on the NBMA network, the transmission interval of Hello is 30 seconds
-OSPF metrics
COST=108/BW
The OSPF protocol determines that the shortest path is based on the cost specified by each interface of the router (cost)
The cost of a route: the sum of the cost of all the interfaces that go to the routing path to the destination network
- when do I need the OSPF routing protocol?
The size of the network: routers in the network are more than 10; medium or large-scale networks
The topology of the network: the topology of the network is network, and any two routers have the demand of Hutong
Other special requirements: fast convergence when routing changes are required, and the network overhead of routing protocols is reduced as much as possible
The requirements of the router itself: when running the OSPF protocol, the router"s CPU processing capacity and memory size have certain requirements, the low performance of routers do not recommend the use of OSPF protocol
The characteristics of -OSPF routing protocol
L can be adapted to large-scale networks
The convergence of L routing is fast
L no routing ring
L supports variable length subnet mask VLSM
L support zoning
L supports sending multicast protocols with multicast addresses
Comparison of -OSPF and RIP
OSPF: link state routing protocol; no hop limit; support VLSM (VLSM); fast convergence; the use of multicast to send link state updates, use trigger updates in the link state changes, increasing the bandwidth utilization
RIP: distance vector routing protocol; RIP 15 hop limit, more than 15 hop routing is considered unreachable; V1 does not support variable length subnet mask (VLSM), V2 support; slow convergence; periodic broadcast of the routing table, application will have a big problem in low speed link and wide area network
-OSPF single zone configuration command
Configure the loopback interface address - - the Router ID used to generate the router
Router (config) #interface loopback looback-number
Router (config-if), #ip, address, IP-address, mask
Start the OSPF routing process:
Router (config) #router OSPF process number - the process number of the router used to identify multiple OSPF processes on the same router
Specify the interfaces and areas to which the OSPF protocol is running:
Router (config-router) #network network number reverse mask area zone number
* network number: can be network address, subnet address, interface address
* zone number: indicate the area referred to in the network
Modify the Cost value of the interface:
Router (config-if), #ip, OSPF, cost, number
Configuring the OSPF timer:
Router (config-if) #ip OSPF hello-interval time (s)
Router (config-if) #ip OSPF dead-interval time (s)
* in order to exchange information, the adjacent routers must have the same hello and dead intervals, usually dead times 4 times the Hello time
View neighbor list:
Router#show ip ospf neighbor
Link state database:
Router#show ip ospf database
View routing table:
Router#show IP route
View the configuration of OSPF:
Router#show ip ospf
View the OSPF interface data structure:
Router#show ip ospf interface interface
