Cisco ENetwork Chapter 4
计算机网络 自顶向下 方法4
application transport network data link physical
Network Layer
4-3
Two Key Network-Layer Functions
forwarding: move
packets from router‟s input to appropriate router output
Network Layer 4-7
Network layer service models:
Network Architecture Internet ATM Service Model
Congestion Bandwidth Loss Order Timing feedback no
yes yes no no no yes no yes no (inferred via loss) no congestion no congestion yes no
datagram network provides network-layer
connectionless service VC network provides network-layer connection service analogous to the transport-layer services, but:
performance-wise network actions along source-to-dest path
call setup, teardown for each call
before data can flow
each packet carries VC identifier (not destination host
Chapter_4_V6-03
Network Layer 4-10
Connection, connection-less service
datagram network provides network-layer connectionless service virtual-circuit network provides network-layer connection service analogous to TCP/UDP connecton-oriented / connectionless transport-layer services, but: service: host-to-host no choice: network provides one or the other implementation: in network core
4.1 introduction 4.2 virtual circuit and datagram networks 4.3 what’s inside a router 4.4 IP: Internet Protocol
datagram format IPv4 addressing ICMP IPv6
call setup, teardown for each call before data can flow each packet carries VC identifier (not destination host address) every router on source-dest path maintains “state” for each passing connection link, router resources (bandwidth, buffers) may be allocated to VC (dedicated resources = predictable service)
CCNA 3 - Chapter 4
CCNA 3 - Chapter 4Posted by beotron at 9:14 PM1. Refer to the exhibit. Switch1 is not participating in the VTP management process with the other switches shown in the exhibit. What are two possible reasons for this? (Choose two.)• Switch2 is in transparent mode.• Switch1 is in client mode.• Switch1 is using VTP version 1 and Switch2 is using VTP version 2.• Switch2 is in server mode.• Switch1 is in a differe nt management domain.• Switch1 has no VLANs.2. Refer to the exhibit. Switches SW1 and SW2 are interconnected via a trunk link but failed to exchange VLAN information. The network administrator issued the show vtp status command to troubleshoot the problem. On the basis of the output provided, what could be done to fix the problem?• The switches must be interconnected via access link.• Switch SW2 must be configured as a VTP client.• Both switches must be configured as VTP clients.• Both switches must b e configured with the same VTP revision number.• The switches must be configured with the same VTP domain name.3. Refer to the exhibit. Which two facts can be confirmed by this output? (Choose two.)• If this switch is added to an established network, th e other VTP-enabled switches in the same VTP domain will consider their own• VLAN information to be more recent than the VLAN information advertised by this switch.• This switch shows no configuration revision errors.• This switch has established two-way communication with the neighboring devices.• This switch is configured to advertise its VLAN configuration to other VTP-enabled switches in the same VTP domain.• This switch is configured to allows the network manager to maximize bandwidth by restricti ng traffic to specific network devices.4. Which two statements describe VTP transparent mode operation? (Choose two.)• Transparent mode switches can create VLAN management information.• Transparent mode switches can add VLANs of local significance only.• Transparent mode switches pass any VLAN management information that they receive to other switches.• Transparent mode switches can adopt VLAN management changes that are received from other switches.• Transparent mode switches originate updates about the status of their VLANS and inform other switches about that status.5. Refer to the exhibit. Switch2 was previously used in a lab environment and has been added to the production network in server mode. The lab and production networks use the same VTP domain name,so the network administrator made no configuration changes to Switch2 before adding it to the production network. The lab domain has a higher revision number. After Switch2 was added to the production network, many computers lost network connectivity. What is the quickest way to solve the problem?• Reset the revision number on Switch2 with either the delete VTP command or by changing the domain name and then changing it back.• Change Switch1 to transparent VTP mode to reclaim all VLANs in vlan.dat, and then change back to server mode.• Change Switch2 to client mode so the VLANs will automatically repopulate.• Re-enter all appropriate VLANs, except VLAN 1, manually on Switch1 so that they repropagate throughout the network.6. What causes a VTP configured switch to issue a summary advertisement?• A new host has been attached to a switch in the management domain.• A port on a switch in the management domain has changed to blocking mode.• A five-minute update timer has elapsed.• The advertise ment revision number has reached n+1.7. Which two statements describe VTP client mode operation. (Choose two.)• can add VLANs of local significance only• can only adopt VLAN management changes• can create and adopt updated VLAN management information• can only pass VLAN management information without adopting changes• can add VLANs to domain• cannot add VLANs8 Which statement is true when VTP is configured on a switched network that incorporates VLANs? • VTP is only compatible with the 802.1Q standa rd.• VTP adds to the complexity of managing a switched network.• A switch configured for VTP can belong to more than one VTP domain.• VTP dynamically communicates VLAN additions, deletions and modifications to all switches in the same VTP domain.• VTP advertisements are passed over access links to other switches.9. Refer to the exhibit. All switches in the VTP domain are new. Switch SW1 is configured as a VTP server, switches SW2 and SW4 are configured as VTP clients, and switch SW3 is configured in VTP transparent mode. Which switch or switches receive VTP updates and synchronize their VLAN configuration based on those updates?• All switches receive updates and synchronize VLAN information.• Only switch SW2 receives updates and synchronizes VLAN info rmation.• SW3 and SW4 receive updates, but only switch SW4 synchronizes VLAN information.• Only switches SW3 and SW4 receive updates and synchronize VLAN information.10. Refer to the exhibit. What information can be learned from the output provided?• I t verifies the configured VTP password.• It verifies the VTP domain is configured to use VTP version 2.• It verifies VTP advertisements are being exchanged.• It verifies the VTP domain name is V1.11. Which statement is true about the VTP pruning process?• VTP pruning automatically updates all switches within the VTP domain with VLAN information.• VTP pruning updates all switches within the VTP domain with information about pruning-eligible VLANs. • VTP pruning updates all switches within the VTP domai n with information about pruning-ineligible VLANs.• VTP pruning prevents flooded traffic from crossing trunk links to switches that do not need to process the flood traffic.12. Refer to the exhibit. The switches in the exhibit are connected with trunks within the same VTP management domain. Each switch is labeled with its VTP mode. A new VLAN is added to Switch3. This VLAN does not show up on the other switches. What is the reason for this?• VLANs cannot be created on transparent mode switches.• Server mode switches neither listen to nor forward VTP messages from transparent mode switches. • VLANs created on transparent mode switches are not included in VTP advertisements.• There are no ports assigned to the new VLAN on the other switches.• Transparent mode switches do not forward VTP advertisements.13. What does a client mode switch in a VTP management domain do when it receives a summary advertisement with a revision number higher than its current revision number?• It suspends forwarding until a sub set advertisement update arrives.• It issues an advertisement request for new VLAN information.• It increments the revision number and forwards it to other switches.• It deletes the VLANs not included in the summary advertisement.• It issues summary ad vertisements to advise other switches of status changes.14. Which three VTP parameters must be identical on all switches to participate in the same VTP domain? (Choose three.)• revision number• domain name• pruning• mode• domain password• version nu mber15. Refer to the exhibit. All switches in the network participate in the same VTP domain. What happens when the new switch SW2 with a default configuration and revision number of 0 is inserted in the existing VTP domain Lab Network?• The switch opera tes as a VTP client.• switch operates in VTP transparent mode.• The switch operates as a VTP server and deletes the existing VLAN configuration in the domain.• The switch operates as a VTP server, but does not impact the existing VLAN configuration in t he domain.16. Refer to the exhibit. Switch S1 is in VTP server mode. Switches S2 and S3 are in client mode. An administrator accidentally disconnects the cable from F0/1 on S2. What will the effect be?• S2 loses all VLANs until the cable is reconnected.• S2 automatically transitions to VTP transparent mode.• S2 does not send a VTP request advertisement unless it is reloaded.• S2 automatically sends a VTP request advertisement to 172.17.99.11 when the cable is reconnected.17. Which two statements are true about the implementation of VTP? (Choose two.)• Switches must be connected via trunks.• The VTP domain name is case sensitive.• Transparent mode switches cannot be configured with new VLANs.• The VTP password is mandatory and case sensitive.• Swit ches that use VTP must have the same switch name.。
CCNA课程-第4章-IP地址-子网划分-VLSM-CIDR
VLSM的实现(5)
VLSM的实现(6)
无类域间路由 (CIDR)
CIDR的概念：忽略A、B、C类网络的规则， 定义前缀相同的一组网络为一个块，即一条 路由条目。（如：199.0.0.0/8）
CIDR的优点
• 减少了网络数目，缩小了路由选择表 • 从网络流量、CPU和内存方面说，开销更低 • 对网络进行编址时，灵活性更大
“借用”主机位来“制造”新的“网络”
划分子网方法
划分子网方法: 1.你所选择的子网掩码将会产生多少个子网?:2 的x 次方(x 代表掩码位数) 2.每个子网能有多少主机?: 2 的y 次方-2(y 代表主机位数) 3.有效子网是?:有效子网号=256-10 进制的子网掩码(结果 叫做block size 或base number) 4.每个子网的广播地址是?:广播地址=下个子网号-1 5.每个子网的有效主机分别是?:忽略子网内全为0 和全为1 的地址剩下的就是有效主机地址. 最后有效1 个主机地址=下个子网号-2(即广播地址-1)
缺省情况下的子网掩码
172.16.2.160 255.255.0.0
网络
主机
网络号
172
16
0
0
缺省情况下子网未划分
172.16.2.200 172.16.2.2
172.16.2.160
子网地址
172.16.3.1
E1
E0 172.16.2.1
172.16.3.5 172.16.3.100 172.16.3.150
B类地址子网划分例子2
B 类地址例子2:网络地址:172.16.0.0;子网掩码 255.255.255.224(/27) 1.子网数=2 的11 次方=2048(因为B 类地址默认掩码是 255.255.0.0,所以网络位为8+3=11) 2.主机数=2 的5 次方-2=30 3. 有效子网?:block size=256-224=32; 所以第一个子网为 172.16.0.0, 第二个为172.16.0.32,最后一 个为172.16.255.224 4.广播地址:下个子网-1.所以第一个子网的广播地址是 172.16.0.31,第二个为172.16.0.63,最后一个为172.16.255.255 5.有效主机范围是:第一个子网的主机地址是172.16.0.1到 172.16.0.30;第二个是172.16.0.33到172.16.0.62最后1 个是 172.16.255.225 到172.16.255.254
计算机网络Chapter4_cut
packet belonging to VC carries VC number
(rather than dest address) VC number can be changed on each link.
New VC number comes from forwarding table
application transport 5. Data flow begins network 4. Call connected data link 1. Initiate call application 3. Accept call 2. incoming call
Network Layer 4-8
Virtual circuits
“source-to-dest path behaves much like telephone circuit”
performance-wise network actions along source-to-dest path
Network Layer
4-1
Chapter 4: Network Layer
Chapter goals:
services:
understand principles behind network layer
instantiation, implementation in the Internet
call setup, teardown for each call
before data can flow
each packet carries VC identifier (not destination host
CCNA_ERouting_Chapter_4
1Which event will cause a triggered update?an update routing timer expiresa corrupt update message is receiveda route is installed in the routing tablethe network is converged2T hree routers running a distance-vector routing protocol lost all power, including the battery backups. When the routers relo happen?They will share all routes saved in NVRAM prior to the power loss with their directly connected neighbors.They will multicast hello packets to all other routers in the network to establish neighbor adjacencies.They will send updates that include only directly connected routes to their directly connected neighbors.They will broadcast their full routing table to all routers in the network.3What is a routing loop?a packet bouncing back and forth between two loopback interfaces on a routera condition where a return path from a destination is different from the outbound path forming a "loop"a condition where a packet is constantly transmitted within a series of routers without ever reaching its intended destinthe distribution of routes from one routing protocol into another4Refer to the exhibit. If all routers are using RIP, how many rounds of updates will occur before all routers know all networks1234565What actions will occur after RouterA loses connectivity to network 114.125.16.0? (Choose two.)RouterB will include network 123.92.76.0 and 136.125.85.0 in its update to RouterA.During the next update interval, RouterB will send a RIP update out both ports that includes the inaccessible network.During the next update interval, RouterC will send an update to RouterB stating that network 114.125.16.0 is accessibRouter C will learn of the loss of connectivity to network 114.125.16.0 from RouterB.RouterB will include network 123.92.76.0 and 136.125.85.0 in its update to RouterC.6What does the RIP holddown timer do?ensures an invalid route has a metric of 15prevents a router from sending any updates after it has introduced a routing loop into the networkensures every new route is valid before sending an updateinstructs routers to ignore updates, for a specified time or event, about possible inaccessible routes 7W hich of the following can exist in a distance vector network that has not converged? (Choose three.)routing loopsinconsistent traffic forwardingno traffic forwarding until system convergesinconsistent routing table entriesrouting table updates sent to wrong destinations8What is the purpose of the TTL field in the IP header?used to mark routes as unreachable in updates sent to other routersprevents regular update messages from reinstating a route that may have gone badprevents a router from advertising a network through the interface from which the update camelimits the time or hops that a packet can traverse through the network before it should be discardeddefines a maximum metric value for each distance vector routing protocol by setting a maximum hop count9W hich three routing protocols are distance vector routing protocols? (Choose three).RIPv1EIGRPOSPFIS-ISRIPv210The graphic shows a network that is configured to use RIP routing protocol. Router2 detects that the link to Router1 has go then advertises the network for this link with a hop count metric of 16. Which routing loop prevention mechanism is in effectsplit horizonerror conditionhold-down timerroute poisoningcount to infinity11Which statement is true regarding cisco’s RIP_JITTER variable?It prevents the synchronization of routing updates by buffering the updates as they leave the router interfaces.It prevents the synchronization of routing updates by subtracting a random length of time ranging from 0% to 15% of interval time from the next routing update interval.It prevents the synchronization of routing updates by causing the router to skip every other scheduled update time.It prevents the synchronization of routing updates by forcing the router to listen when its time for other updates on th sending its update.12W hich of the following methods does split horizon use to reduce incorrect routing information?Routing updates are split in half to reduce the update time.Information learned from one source is not distributed back to that source.New route information must be learned from multiple sources to be accepted.The time between updates is split in half to speed convergence.New route information is suppressed until the system has converged.13Which two statements are true regarding the function of the RIPv1 routing updates? (Choose two).updates are broadcast only when there are changes to the topologyupdates are broadcast at regular intervalsbroadcast are sent to 0.0.0.0broadcasts are sent to 255.255.255.255updates contain the entire network topologyonly changes are included in the updates14A network administrator is evaluating RIP versus EIGRP for a new network. The network will be sensitive to congestion a respond quickly to topology changes. What are two good reasons to choose EIGRP instead of RIP in this case? (ChooseEIGRP uses periodic updates.EIGRP only updates affected neighbors.EIGRP uses broadcast updates.EIGRP updates are partial.EIGRP uses the efficient Bellman-Ford algorithm.11Which statement is true regarding cisco’s RIP_JITTER variable?It prevents the synchronization of routing updates by buffering the updates as they leave the router interfaces.It prevents the synchronization of routing updates by subtracting a random length of time ranging from 0% to 15% of interval time from the next routing update interval.It prevents the synchronization of routing updates by causing the router to skip every other scheduled update time.It prevents the synchronization of routing updates by forcing the router to listen when its time for other updates on th sending its update.12W hich of the following methods does split horizon use to reduce incorrect routing information?Routing updates are split in half to reduce the update time.Information learned from one source is not distributed back to that source.New route information must be learned from multiple sources to be accepted.The time between updates is split in half to speed convergence.New route information is suppressed until the system has converged.13Which two statements are true regarding the function of the RIPv1 routing updates? (Choose two).updates are broadcast only when there are changes to the topologyupdates are broadcast at regular intervalsbroadcast are sent to 0.0.0.0broadcasts are sent to 255.255.255.255updates contain the entire network topologyonly changes are included in the updates14A network administrator is evaluating RIP versus EIGRP for a new network. The network will be sensitive to congestion a respond quickly to topology changes. What are two good reasons to choose EIGRP instead of RIP in this case? (ChooseEIGRP uses periodic updates.EIGRP only updates affected neighbors.EIGRP uses broadcast updates.EIGRP updates are partial.EIGRP uses the efficient Bellman-Ford algorithm.15Refer to the exhibit. What path will packets from the 192.168.1.0/24 network travel to reach the 10.0.0.0/8 network if RIP is routing protocol?The path will be router A -> router B -> router C -> router E.The path will be router A -> router D -> router E.Router A will load balance between the router A -> router D -> router E and router A -> router B -> router C -> router E Packets will alternate paths depending on the order they arrive at router A.\\Which of the following statements are correct about RIP?uses a broadcast to update all other routers in the network every 60 secondsuses a multicast address to update other routers every 90 secondswill send out an update if there is a failure of a linkupdates only contain information about routes that have changed since last updateRefer to the exhibit. The routers in this network are running RIP. Router A has not received an upda minutes. How will Router A respond?The Holddown timer will wait to remove the route from the table for 60 seconds.The Invalid timer will mark the route as unusable if an update has not been received in 180 seThe Update timer will request an update for routes that were learned from Router B.The Hello timer will expire after 10 seconds and the route will be flushed out of the routing tab What metric does the RIP routing protocol consider to be infinity?1516224255。
Chapter4章课件
To discuss how routers forward packets in a connectionless packet-switch network using the destination address of the packet and a routing table.
Circuit switching
Circuit switching： a physical circuit is established between the source and the destination before the delivery of the message. After the transmission is complete, the network opens all switches and provides the links and the connecting devices for another connection. It is mostly used at the physical layer.
Message
A
Internet
Message
Application Transport Network Data link Physical
B
Figure 4.1 Internet as a block box
Introduction
Figure 4.2 Internet as a combination of LANs and WANs connected together
CCNA第四章IOS和SDM精品PPT课件
正大教育计算机培训中心
使用增强的编辑命令
Router>$ value for customers, employees, and partners.
<Ctrl-A> <Ctrl-E> <Esc-B>
(一行中长字串会自动滚卷). 光标移动到命令行的开始位置. 光标移动到命令行的结束位置. 回移一个单词
Check hardware 1L.o启ad动B前oo确ts认tr正ap确连接线缆和控制线 2. 按下电源开关 Find and load Cisco IOS 3s.o观ftw察a启re动im顺ag序e FinCdisacnod IaOpSp输ly出ro到ut控er制台上的内容 configuration information
正大教育计算机培训中心
基本IOS命令结构
每个 IOS 命令都具有特定的格式或语法，并在相应的提示符下执行。 常规命令语法为命令后接相应的关键字和参数。 某些命令包含一个关键字和参数子集，此子集可提供额外功能。
正大教育计算机培训中心
使用 CLI 帮助
IOS 提供多种形式的帮助：
➢ 对上下文敏感的帮助 ➢ 命令语法检查 ➢ 热键和快捷方式
正大教育计算机培训中心
使用增强的编辑命令
Router>$ value for customers, employees, and partners.
<Ctrl-A> <Ctrl-E> <Esc-B> <Ctrl-F> <Ctrl-B> <Esc-F>
(一行中长字串会自动滚卷). 光标移动到命令行的开始位置. 光标移动到命令行的结束位置. 回移一个单词 下移一个字符. 回移一个字符. 下移一个单词
2024年Cisco交换机培训教程(目录版)
Cisco交换机培训教程(目录版)Cisco交换机培训教程引言：随着网络技术的不断发展，交换机作为网络设备的核心组件之一，扮演着至关重要的角色。
Cisco作为全球领先的网络安全解决方案提供商，其交换机产品在市场上具有广泛的应用。
本教程旨在为读者提供关于Cisco交换机的基本知识和操作技巧，帮助读者更好地理解和应用Cisco交换机。
第一章：Cisco交换机简介1.1交换机的基本概念交换机是一种网络设备，用于在局域网（LAN）中连接多个网络设备，如计算机、打印机等。
其主要功能是根据MAC地质，将数据包从一个端口转发到另一个端口，实现设备之间的通信。
1.2Cisco交换机系列Cisco提供了多种交换机系列，包括CiscoCatalyst系列、CiscoNexus系列等。
每个系列都有其独特的特点和适用场景。
本教程将主要介绍CiscoCatalyst系列交换机。
第二章：Cisco交换机的安装和配置2.1交换机的安装在安装Cisco交换机之前，需要准备好相应的设备，包括交换机、网线、电源线等。
安装过程包括将交换机放置在机架上，连接电源线和网线，然后进行开机启动。
2.2交换机的配置交换机的配置可以通过命令行接口（CLI）进行。
需要通过串口或网络连接到交换机，然后输入用户名和密码进行登录。
在CLI 中，可以执行各种命令进行交换机的配置，包括配置端口、VLAN、路由等。
第三章：Cisco交换机的管理3.1SNMP管理简单网络管理协议（SNMP）是一种用于网络设备管理的标准协议。
通过SNMP，可以远程监控和管理交换机，包括获取设备信息、配置参数、性能指标等。
3.2CLI管理CLI是交换机配置和管理的主要方式。
通过CLI，可以执行各种命令进行交换机的配置和管理。
熟练掌握CLI命令是进行交换机管理的基础。
3.3Web管理除了CLI，Cisco交换机还支持通过Web界面进行管理。
通过Web界面，可以直观地查看和配置交换机的各种参数，方便用户进行操作。
CCNA网络基础知识2-4章
考试浏览器- ENetwork Chapter 2 - CCNA Exploration(版本4.0)第二章下面是考试的考试试题以及与题目关联的评分规则。
在考试浏览器中使用考试信息时，必须遵守您与Cisco 签订的“Academy Connection 网站使用协议”中的条款。
考试浏览器意在提供支持说明但又不损害其他CiscoNetworking Academy 或学生的考试安全。
不得在无监考和不受控制的环境中发布此材料。
如果发现有滥用行为，将采取措施限制访问考试内容。
使用考试浏览器之后，切记要注销并关闭浏览器窗口。
1下列哪些陈述正确指出了中间设备在网络中的作用？（选择三项）确定数据传输路径发起数据通信重新定时和重新传输数据信号发送数据流管理数据流数据流最后的终止点评分规则： correctnessof response2选择关于网络协议的正确陈述。
（选择三项）定义特定层PDU 的结构规定实现协议层功能的方式概述层与层之间通信所需的功能限制了硬件兼容性需要取决于协议层的封装过程杜绝厂商之间的标准化评分规则： correctness ofresponse3封装的关键功能是什么？（选择三项）供传输前修改原始数据标识数据片段属于同一通信为通信提供统一的网络路径确保数据片段可以转发到正确的接收端设备实现完整消息的重组跟踪终端设备之间的延迟评分规则： correctness ofresponse4数据链路层封装添加的报尾信息有何主要功能？支持差错校验确保数据按照顺序到达确保送达正确目的标识本地网络中的设备帮助中间设备进行处理和路径选择评分规则： correctness ofresponse5OSI 模型哪两层的功能与TCP/IP 模型的网络接入层（选择两项）网络层传输层物理层数据链路层会话层评分规则： correctnessof response6什么是PDU？传输期间的帧损坏在目的设备上重组的数据因通信丢失而重新传输的数据包特定层的封装评分规则： correctnessof response7以下哪种特征正确代表了网络中的终端设备？管理数据流发送数据流重新定时和重新传输数据信号确定数据传输路径评分规则： correctnessof response8请参见图示。
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根据图中所示的传输层报头回答，以下哪些陈述描述了建立的会话？（选择两项。）
这是 UDP 报头。
包含 Telnet 请求。
包含 TFTP 数据传输。
从这台远程主机返回的数据包将包含确认号 43693。
这是 TCP 报头。
采用 TCP/IP 数据封装时，以下哪个端口号范围标识了所有常用应用程序？
0 到 255
256 到 1022
0 到 1023
1024 到 2047
49153 到 65535
数据段的 TCP 报头中为什么包含端口号？
指示转发数据段时应使用的正确路由器接口
标识接收或转发数据段时应使用的交换机端口
确定封装数据时应使用的第 3 层协议
让接收主机转发数据到适当的应用程序
让接收主机以正确的顺序组装数据包
OSI 模型哪一层负责规范信息从源设备到目的设备准确可靠地流动？
应用层
表示层
会话层
传输层
网络层
请参见图示。主机 A 正在使用 FTP 从服务器 1 下载大型文件。在下载期间，服务器 1 没有收到主机 A 对若干字节传输数据的确认。服务器 1 将默认执
行什么操作？
创建第 1 层堵塞信号
到达超时时间后重新发送需要确认的数据
向主机发送 RESET 位
更改第 4 层报头中的窗口大小
将流量控制用于 TCP 数据传输的原因是什么？
同步设备速度以便发送数据
同步并对序列号排序，从而以完整的数字顺序发送数据
防止传入数据耗尽接收方资源
在服务器上同步窗口大小
简化向多台主机传输数据的过程
以下哪两个选项代表第 4 层编址？（选择两项）
标识目的网络
标识源主机和目的主机
标识正在通信的应用程序
标识主机之间的多个会话
标识通过本地介质通信的设备
请参见图示。此 Wireshark 捕获输出的第 7 行中执行的是哪一项 TCP 操作？
会话创建
数据段重传
数据传输
会话断开
请参见图示。从显示的输出中可以确定以下哪两项信息？（选择两项）
本地主机正在使用三个客户端会话。
本地主机正在使用到远程服务器的 Web 会话。
本地主机正在侦听使用公有地址的 TCP 连接。
本地主机使用公认端口号标识源端口。
本地主机正在执行与 192.168.1.101:1037 的三次握手。
下列哪项由源主机在转发数据时动态选择？
目的逻辑地址
源物理地址
默认网关地址
源端口
下列哪两项是用户数据报协议 (UDP) 的功能？（选择两项）
流量控制
系统开销低
无连接
面向连接
序列和确认
从源向目的传送数据段的过程中，TCP 使用什么机制提供流量控制？
序列号
会话创建
窗口大小
确认
下列哪个传输层协议提供低开销传输因而可用于不需要可靠数据传输的应用场合？
TCP
IP
UDP
HTTP
DNS
TCP 报头信息和 UDP 报头信息中都包含下列哪项信息？
定序
流量控制
确认
源端口和目的端口
下列哪三项功能使 TCP 得以准确可靠地跟踪从源设备到目的设备的数据传输？（选择三项。）
流量控制
紧急指针
尽力传输
会话创建
无连接服务
编号和定序
在 TCP 通信会话期间，如果数据包到达目的主机的顺序混乱，将对原始消息执行什么操作？
数据包将无法送达。
将从源主机重新传输数据包。
数据包将送达目的主机并重组。
数据包将送达目的主机但并不重组。
下列哪项是 UDP 的重要特征？
确认数据送达
数据传输的延迟最短
数据传输的高可靠性
同序数据传输
Web 浏览器向侦听标准端口的 Web 服务器发出请求之后，在服务器响应的 TCP 报头中，源端口号是多少？
13
53
80
1024
1728
以下哪个事件发生于传输层三次握手期间？
两个应用程序交换数据。
TCP 初始化会话的序列号。
UDP 确定要发送的最大字节数。
服务器确认从客户端接收的数据字节数。
请参见图示。Host1 正在与 Host2 建立 TCP 会话。Host1 已经发送了 SYN 信息，开始建立会话。接下来会发生什么？
Host1 会向 Host2 发送带有 ACK 标志 = 0、SYN 标志 = 0 的数据段。
Host1 会向 Host2 发送带有 ACK 标志= 1、SYN 标志 = 0 的数据段。
Host1 会向 Host2 发送带有 ACK 标志 = 1、SYN 标志 = 1 的数据段。
Host2 会向 Host1 发送带有 ACK 标志 = 0、SYN 标志 = 1 的数据段。
Host2 会向 Host1 发送带有 ACK 标志 = 1、SYN 标志 = 0 的数据段。
Host2 会向 Host1 发送带有 ACK 标志 = 1、SYN 标志 = 1 的数据段。