下面是小編為大家整理的mtu,廣播域,ospf學(xué)習(xí)筆記（廣播域,ospf學(xué)習(xí)筆記,mtu）（2022年）,供大家參考。

　mtu 廣播域 ospf 學(xué)習(xí)筆記（廣播域 ospf 學(xué)習(xí)筆記 mtu）

　什么是 MTU？

　是 MTU 最大傳輸單元的縮寫(xiě)。意思是網(wǎng)絡(luò)上傳送的最大數(shù)據(jù)包。MTU的單位是字節(jié)。大部分網(wǎng)絡(luò)設(shè)備的 MTU MTU MTU 都是 1500。如果本機(jī)的比網(wǎng)關(guān)的大，大的數(shù)據(jù)包就會(huì)被拆開(kāi)來(lái)傳送，這樣會(huì)產(chǎn)生很多數(shù)據(jù)包碎片，增加丟包率，降低網(wǎng)絡(luò)速度。把本機(jī)的 MTU MTU 小或相同設(shè)成比網(wǎng)關(guān)的，就可以減少丟包。3、如何檢測(cè)網(wǎng)關(guān)的 MTU？在本機(jī)打開(kāi) DOS 窗口，執(zhí)行：平 F L 1472 192.168.0.1 其中 192.168.0.1是網(wǎng)關(guān) IP 地址，1472 是數(shù)據(jù)包的長(zhǎng)度。請(qǐng)注意，上面的參數(shù)是“L”（小寫(xiě)的 L），而不是“- 1”。如果能平通，表示數(shù)據(jù)包不需要拆包，可以通過(guò)網(wǎng)關(guān)發(fā)送出去如果出現(xiàn)：包需要。支離破碎但 DF 集。表示數(shù)據(jù)包需要拆開(kāi)來(lái)發(fā)送。此時(shí)，減少數(shù)據(jù)包長(zhǎng)度，再執(zhí)行上面的平命令。從 1400 到 1472 之間多試幾次，就能找到合適的數(shù)據(jù)包長(zhǎng)度了。把數(shù)據(jù)包長(zhǎng)度加上數(shù)據(jù)包頭 28 字節(jié)，就得到 MTU MTU 的值。如果檢測(cè)到網(wǎng)關(guān)的值是 1500，不需要修改。如果網(wǎng)關(guān)有防火墻平不通，可以試試直接把 MTU 設(shè)為 1400. 4、如何修改本機(jī)的 MTU？修改方法如下：（1）、運(yùn)行注冊(cè)表（2）、瀏覽到：hkey_local_machine \系統(tǒng)\ CurrentControlSet \服務(wù)\ TCPIP \參數(shù)接口如圖 2（3）、接口下有多個(gè)子項(xiàng)，每個(gè)子項(xiàng)對(duì)應(yīng)一個(gè)網(wǎng)卡。請(qǐng)按如下方法選擇網(wǎng)卡：（一）確定本機(jī)用來(lái)連接的網(wǎng)卡或撥號(hào)連接的 IP 網(wǎng)絡(luò)，如 192.168.0.19；（b）用鼠標(biāo)點(diǎn)擊接口上的子項(xiàng)，查看鍵值列表中的 IPAddress 項(xiàng)；（c）如果 IPAddress 的鍵值與（一）中的 IP 相同，即 192.168.0.19，則該子項(xiàng)就是要找的網(wǎng)卡。（4）、進(jìn)入該子項(xiàng)，在右邊的窗口里按鼠標(biāo)右鍵，選擇”新建”->“雙字節(jié)值”，輸入名稱(chēng)“奔馳”，按回車(chē)。再用鼠標(biāo)雙擊“奔馳”，彈出修改窗口：如圖 3：填入 MTU 的值。填寫(xiě)前請(qǐng)先把基數(shù)設(shè)為十進(jìn)制設(shè)置好后，需要重啟機(jī)器才能生效。

　廣播域

　廣播域（廣播域）是一個(gè)邏輯上的計(jì)算機(jī)組，該組內(nèi)的所有計(jì)算機(jī)都

　會(huì)收到同樣的廣播信息沖突域：在同一個(gè)沖突域中的每一個(gè)節(jié)點(diǎn)都能收到所有被發(fā)送的幀。

　廣播域：網(wǎng)絡(luò)中能接收任一設(shè)備發(fā)出的廣播幀的所有設(shè)備的集合

　沖突域是基于第一層（物理層）

　廣播域是機(jī)于第二層（數(shù)據(jù)鏈路層）

　廣播域就是說(shuō)如果站點(diǎn)發(fā)出一個(gè)廣播信號(hào)后能接收到這個(gè)信號(hào)的范圍。通常來(lái)說(shuō)一個(gè)局域網(wǎng)就是一個(gè)廣播域。

　沖突域：一個(gè)站點(diǎn)向另一個(gè)站點(diǎn)發(fā)出信號(hào)。除目的站點(diǎn)外，有多少站點(diǎn)能收到這個(gè)信號(hào)。這些站點(diǎn)就構(gòu)成一個(gè)沖突域。

　樞紐所有端口都在同一個(gè)廣播域，沖突域內(nèi)。

　OSPF 基本概念及單區(qū)域配置

　-內(nèi)部網(wǎng)關(guān)路由協(xié)議

　OSPF 內(nèi)部網(wǎng)關(guān)路由協(xié)議：用于在單一自治系統(tǒng)（自治系統(tǒng)）內(nèi)決策路由

　自治系統(tǒng)（AS）：執(zhí)行統(tǒng)一路由策略的一組網(wǎng)絡(luò)設(shè)備的組合

　-區(qū)域

　為了適應(yīng)大型的網(wǎng)絡(luò)，OSPF 在作為內(nèi)劃分多個(gè)區(qū)域

　每個(gè) OSPF 路由器只維護(hù)所有區(qū)域的完整的鏈路狀態(tài)信息

　 -鏈路狀態(tài)路由協(xié)議

　OSPF 是鏈路狀態(tài)路由協(xié)議，鏈路狀態(tài)路由協(xié)議中的路由器了解 OSPF網(wǎng)絡(luò)內(nèi)的鏈路狀態(tài)信息

　鏈路狀態(tài)路由協(xié)議中，直連的路由器之間建立鄰接關(guān)系，互相”交流”鏈路信息，來(lái)”畫(huà)”出完整的網(wǎng)絡(luò)結(jié)構(gòu)

　我為了標(biāo)識(shí)鏈路信息是由誰(shuí)發(fā)出的，用路由器 ID 標(biāo)識(shí)路由器

　我相鄰路由器之間建立鄰接關(guān)系，保存在鄰居列表中

　我路由器學(xué)習(xí)到的鏈路信息，表存在鏈路狀態(tài)數(shù)據(jù)庫(kù)中

　路由器 ID

　是在 OSPF 路由器 ID：區(qū)域內(nèi)唯一標(biāo)識(shí)一臺(tái)路由器的 IP 地址

　路由器 ID 選取規(guī)則：

　我首先，路由器選取它所有回送接口上數(shù)值最高的 IP 地址

　我如果沒(méi)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

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