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帧中继 Frame Relay

帧中继 Frame Relay. 深圳职业技术学院计算机系网络专业. 教学目标（ Objectives ）. 1. 帧中继概念（ Frame Relay Concept ） 2. 帧中继术语（ Frame Relay Terminology ） 3. 帧中继地址映射（ Frame Relay Address Mapping ） 4.LMI 操作（ LMI Operation ） 5. 帧中继反向 ARP （ Frame Relay Inverse ARP ） 6. 配置基本的帧中继（ Configuring Basic Frame Relay ）

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帧中继 Frame Relay

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  1. 帧中继Frame Relay 深圳职业技术学院计算机系网络专业

  2. 教学目标（ Objectives） • 1. 帧中继概念（Frame Relay Concept） • 2.帧中继术语（ Frame Relay Terminology） • 3.帧中继地址映射（Frame Relay Address Mapping） • 4.LMI操作（ LMI Operation） • 5.帧中继反向ARP（ Frame Relay Inverse ARP） • 6.配置基本的帧中继（ Configuring Basic Frame Relay ） • 7.配置帧中继子接口（ Configuring Frame Relay Subinterfaces）

  3. CSU/DSU 帧中继预览（Frame Relay Overview） DCE or FrameRelay Switch 帧中继用虚电路为面向连接的服务建立连接 Virtual circuits make connections for Connection-oriented service 帧中继工作在这里 Frame Relay works here.

  4. 帧中继协议族（Frame Relay Stack） OSI Reference Model Frame Relay Application Presentation Session Transport Network IP/IPX/AppleTalk, etc. Data Link Frame Relay EIA/TIA-232, EIA/TIA-449, V.35, X.21, EIA/TIA-530 Physical 帧中继工作在OSI参考模型的物理层和数据链路层 Frame Relay operate physical and datalink layer.

  5. 帧中继术语（Frame Relay Terminology） PVC DLCI: 100 DLCI: 200 LMI100=Active400=Active DLCI: 400 Local AccessLoop=64 kbps LocalAccessLoop=T1 PVC Local AccessLoop=64 kbps DLCI: 500

  6. 帧中继术语（Frame Relay Terminology） • 1.访问速率（Access rate）：连接本地环到帧中继的端口速度。 • The clock speed (port speed) of the connection (local loop) to the Frame Relay cloud. • 2.数据链路连接标识（DLCI）：在源和目的设备之间标识逻辑电路的一个数值。 • A number that identifies the end point in a Frame Relay network. • 3.本地管理接口（LMI）；是客户前端设备和帧中继交换机之间的信令标准，负责管理设备之间的连接、维护设备之间的连接状态。 • A signaling standard between the customer premises equipment (CPE) device and the Frame Relay switch that is responsible for managing the connection and maintaining status between the devices • 4.承诺信息速率（CIR）：ISP提供的有保障的速率。 • The guaranteed rate, in bits per second, which the service provider commits to providing.

  7. 帧中继术语（Frame Relay Terminology） • 5.前向显示拥塞通知（FECN）：当网络发生拥塞的时候，向目的设备发送一个FECN数据包，来通知拥塞。 • A bit set in a frame that notifies a DTE that congestion avoidance procedures should be initiated by the sending device • 6.后向显示拥塞通知（BECN）：当网络发生拥塞的时候，向源路由器发送一个BECN数据包，来通知拥塞。同时按25%的比例降低数据报发送速率。 • A bit set in a frame that notifies a DTE that congestion avoidance procedures should be initiated by the sending device. If the router receives any BECNs during the current time interval, it decreases the transmit rate by 25%. • 7.允许丢弃指示器（DE）：当路由器检测到拥塞时，帧中继交换机将会首先丢弃那些DE位设置为1的数据包。 • A set bit that indicates the frame may be discarded in preference to other frames if congestion occurs.

  8. 从ISP获得本地意义的DLCI号码 Get locally significant DLCIs from provider 把网络地址映射到DLCI Map your network addresses to DLCIs CSU/DSU 帧中继地址映射（Frame Relay Address Mapping） PVC 10.1.1.1 DLCI: 500 Inverse ARP orFrame Relay map FrameRelay IP(10.1.1.1) DLCI (500)

  9. CSU/DSU LMI类型（LMI TYPES） DLCI: 500 PVC 10.1.1.1 x LMI500=Active400=Inactive DLCI: 400 PVC Keepalive • Cisco 支持三种类型的LMI标准 • Cisco supports three LMI standards: • Cisco（默认） • ANSI • Q.933 *在路由器上配置的LMI类型必须和SP提供的匹配。 *LMI type configured on the router must match the type used by the service provider.

  10. 帧中继反向ARP（Frame Relay Inverse ARP） Frame Relay Cloud 1 DLCI=100 DLCI=400 172.168.5.5 172.168.5.7

  11. 帧中继反向ARP（Frame Relay Inverse ARP） Frame Relay Cloud 1 DLCI=100 DLCI=400 172.168.5.5 172.168.5.7 Status Inquiry Status Inquiry 2 2

  12. 帧中继反向ARP（Frame Relay Inverse ARP） Frame Relay Cloud 1 DLCI=100 DLCI=400 172.168.5.5 172.168.5.7 Status Inquiry Status Inquiry 2 2 Local DLCI 100=Active Local DLCI 400=Active 4 3 3

  13. 帧中继反向ARP（Frame Relay Inverse ARP） Frame Relay Cloud 1 DLCI=100 DLCI=400 172.168.5.5 172.168.5.7 Status Inquiry Status Inquiry 2 2 Local DLCI 100=Active Local DLCI 400=Active 4 3 3 Hello, I am 172.168.5.5. 4

  14. 帧中继反向ARP（Frame Relay Inverse ARP） Frame Relay Cloud DLCI=400 DLCI=100 172.168.5.7 172.168.5.5 Frame Relay Map 172.168.5.5 DLCI 400 Active 5 Hello, I am 172.168.5.7. 4 Frame Relay Map 172.168.5.7 DLCI 100 Active 5

  15. 帧中继反向ARP（Frame Relay Inverse ARP） Frame Relay Cloud DLCI=400 DLCI=100 172.168.5.7 172.168.5.5 Frame Relay Map 172.168.5.5 DLCI 400 Active 5 Hello, I am 172.168.5.7. 4 Frame Relay Map 172.168.5.7 DLCI 100 Active 5 Hello, I am 172.168.5.5. 6

  16. 帧中继反向ARP（Frame Relay Inverse ARP） Frame Relay Cloud DLCI=400 DLCI=100 172.168.5.7 172.168.5.5 Frame Relay Map 172.168.5.5 DLCI 400 Active 5 Hello, I am 172.168.5.7. 4 Frame Relay Map 172.168.5.7 DLCI 100 Active 5 Hello, I am 172.168.5.5. 6 Keepalives Keepalives 7 7

  17. 配置基本的帧中继（Configuring Basic Frame Relay） Branch HQ interface Serial10/1 ip address 10.16.0.1 255.255.255.0 encapsulation frame-relay bandwidth 64 Frame-relay lmi-type cisco interface Serial0/1 ip address 10.16.0.2 255.255.255.0 encapsulation frame-relay bandwidth 64 frame-relay lmi-type cisco • 反向ARP默认被启动 • Inverse ARP is enabled by default

  18. 配置帧中继静态映射（Configuring a Static Frame Relay Map） DLCI=110 IP address=10.16.0.1/24 p1r1 Branch HQ DLCI=100 IP address=10.16.0.2/24 interface Serial1 ip address 10.16.0.1 255.255.255.0 encapsulation frame-relay bandwidth 64 frame-relay map ip 10.16.0.2 110 broadcast

  19. 验证帧中继配置（Verifying Frame Relay Operation） Router#show interface s0/0 Serial0 is up, line protocol is up Hardware is HD64570 Internet address is 10.140.1.2/24 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255 Encapsulation FRAME-RELAY, loopback not set, keepalive set (10 sec) LMI enq sent 19, LMI stat recvd 20, LMI upd recvd 0, DTE LMI up LMI enq recvd 0, LMI stat sent 0, LMI upd sent 0 LMI DLCI 1023 LMI type is CISCO frame relay DTE FR SVC disabled, LAPF state down Broadcast queue 0/64, broadcasts sent/dropped 8/0, interface broadcasts 5 Last input 00:00:02, output 00:00:02, output hang never Last clearing of "show interface" counters never Queueing strategy: fifo Output queue 0/40, 0 drops; input queue 0/75, 0 drops <Output omitted>

  20. 验证帧中继配置（Verifying Frame Relay Operation） • show frame-relay lmi： 命令显示LMI信息 • show frame-relay lmi ：Displays LMI information Router# show frame-relay lmi LMI Statistics for interface Serial0 (Frame Relay DTE) LMI TYPE = CISCO Invalid Unnumbered info 0 Invalid Prot Disc 0 Invalid dummy Call Ref 0 Invalid Msg Type 0 Invalid Status Message 0 Invalid Lock Shift 0 Invalid Information ID 0 Invalid Report IE Len 0 Invalid Report Request 0 Invalid Keep IE Len 0 Num Status Enq. Sent 113100 Num Status msgs Rcvd 113100 Num Update Status Rcvd 0 Num Status Timeouts 0

  21. 验证帧中继配置（Verifying Frame Relay Operation） Router# show frame-relay pvc 100 PVC Statistics for interface Serial0 (Frame Relay DTE) DLCI = 100, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0 input pkts 28 output pkts 10 in bytes 8398 out bytes 1198 dropped pkts 0 in FECN pkts 0 in BECN pkts 0 out FECN pkts 0 out BECN pkts 0 in DE pkts 0 out DE pkts 0 out bcast pkts 10 out bcast bytes 1198 pvc create time 00:03:46, last time pvc status changed 00:03:47 show frame-relay pvc 100：显示PVC状态信息 show frame-relay pvc 100：Displays PVC traffic statistics

  22. 验证帧中继配置（Verifying Frame Relay Operation） Router# show frame-relay map Serial0 (up): ip 10.140.1.1 dlci 100(0x64,0x1840), dynamic, broadcast, status defined, active • show frame-relay map ：显示帧中继映射信息,包括静态或动态 • show frame-relay map :Displays the route maps, either static or dynamic

  23. 问题：广播流量必须被发送到每一条PVC Problem: Broadcast traffic must be replicated for each pvc 1 2 3 路由更新的可达性问题（Reachability Issues with Routing Updates） B RoutingUpdate B A A C C D

  24. S0.1 S0.2 S0.3 解决可达性问题（Resolving Reachability Issues） Logical Interface PhysicalInterface Subnet A S0 Subnet B Subnet C • 方案（Solution）: • 在NBMA环境下，存在水平分割的问题 • Split horizon can cause problems in NBMA environments • 子接口可以解决水平分割的问题 • Subinterfaces can resolve split horizon issues • 一个单一的物理接口模拟多个逻辑接口 • A single physical interface simulates multiple logical interfaces

  25. 配置子接口（Configuring Subinterfaces） • 点到点（Point-to-Point） • 子接口充当专线 • Subinterfaces act as leased line • 每一个子接口有自己的子网 • Each point-to-point subinterface requires its own subnet • 应用在hub and spoke 拓扑中 • Applicable to hub and spoke topologies

  26. 配置子接口（Configuring Subinterfaces） • 多点（Multipoint） • 向NBMA网络一样，不能解决水平分割的问题 • Subinterfaces act as NBMA network so they do not resolve the split horizon issue • 使用同一子网，可以节省地址空间 • Can save address space because uses single subnet • 应用在partial-mesh 和 full-mesh 拓扑中 • Applicable to partial-mesh and full-mesh topology

  27. 配置点到点子接口实例（Configuring Point-to-Point Subinterfaces Example） 10.17.0.1s0.2 DLCI=110 10.17.0.2 A s0.3 10.18.0.1 B DLCI=120 interface Serial0 no ip address encapsulation frame-relay ! interface Serial0.2 point-to-point ip address 10.17.0.1 255.255.255.0  bandwidth 64 frame-relay interface-dlci 110 ! interface Serial0.3 point-to-point ip address 10.18.0.1 255.255.255.0  bandwidth 64 frame-relay interface-dlci 120 ! 10.18.0.2 C

  28. RTR1 RTR3 RTR4 配置多点子接口实例（Multipoint Subinterfaces Configuration Example） B DLCI=120 s2.2=10.17.0.1/24 s2.1=10.17.0.2/24 DLCI=130 DLCI=140 s2.1=10.17.0.3/24 interface Serial2 no ip address encapsulation frame-relay ! interface Serial2.2 multipoint ip address 10.17.0.1 255.255.255.0  bandwidth 64 frame-relay map ip 10.17.0.2 120 broadcast frame-relay map ip 10.17.0.3 130 broadcast frame-relay map ip 10.17.0.4 140 broadcast s2.1=10.17.0.4/24

  29. 思考题（Questions） • 1.什么是帧中继？ • 2.什么是DLCI？它是局部意义还是全局意义？ • 3.LMI有几种类型？ • 4.FECN和BECN的区别是什么？ • 5.如何查看帧中继PVC的状态？ • 6.如何建立一条帧中继的交换记录？

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