1. MPLS • 主要内容： • Defining MPLS • MPLS发展简史 • 目前主要的MPLS技术 • MLS components • MPLS应用领域 • MPLS发展前景和意义

2. 1 2 Defining Flows Multilayer Switched Environment p2 p3 p1 Host A Host B Conventional Environment First Packet Host A Host B Subsequent Packets • Each packet of a traditional flow must be processed by the router • The first packet of an MLS flow is processed by the router; all subsequent packets are switched

3. A B Defining MPLS • 多协议标记交换 • （Multiprotocol Label Switching，MPLS） • 是一种介于第二层和 • 第三层之间的标记交换技术， • 是专门为IP设计的， • 可以将第二层的高速交换能力 • 和第三层的灵活特性结合起来， • 使IP网具备高速交换、流量控制、 • QoS等性能。

4. MPLS发展简史 • 多年以前，人们期盼ATM能做任何事情，随着Internet的发展，人们试图通过ATM传语音、传图像，但由于ATM自身的一些限制，使得它无法适应Internet高速发展的今天。同时，由于点到点的连接，人们难以承受其高昂价格以及对带宽资源的严重浪费。然而，由于IP网的开放性，人们又很难实现端到端的连接，同时，语音数据包的传输也带来了很多问题。因而，将ATM网和IP网合二为一是人们早期的一个初衷

5. 当时最早采用的方式是IP over ATM，但遇到了非常多的问题和困难，如IP地址与ATM地址之间的映射问题。ATM的优点在于其固定长度的包，主要特点用硬件实现转发，因为固定长度的包，只看到包头的这些转发信息就可直接转发。因此，硬把两个协议捆绑在一起不能成功，也不能真正推广。后来，另外一些人试图尝试把两种协议的优势结合起来,即将传统的ATM网的转发机制和IP网的寻址和路由的机制结合起来，这就产生了IP交换技术进而通过IETF组织推出了MPLS协议。

6. 目前主要的MPLS技术 CISCO 标签交换（Tag Switching） *采用控制流量而不是 采用数据流量来设置前向表 IBM ARIS (集中式基于路由的IP交换技术)

7. RSM MLS Components 多层交换路由处理器 多层交换交换机引擎 MLS-RP—Multilayer Switching Route Processor MLS-SE—MultilayerSwitching Switch Engine Cisco85xx 75XX 72XX 4XXX OR 多层交换协议 MLSP—Multilayer Switching Protocol • Multicast Hello Messages sent to MLS-SE by MLS-RP to Inform: • MAC addresses used on different VLANs • Routing/access—lists changes occurring on MLS-RP

8. MLS-RP Advertisement Hello Message • MLS-RP sends out multicast hello messages • Messages contain MAC, VLAN, and route information • Messages use the CGMP multicast well-known address • CGMP(Cisco组管理协议),确保SWITCH的互操作性

9. Receiving MLSP Hello Messages I am not a Layer 3 Switch but I will still pass on the message. Hello Message Hello Message • All switches receive the hello message • Layer 3 switches process the hello message • IP multicast passes transparently through non-Cisco switches

10. Assigning XTAGs MLS-RP A MLS-RP B MLS-RP C MLS-RP A = XTAG34 MLS-RP B = XTAG11 MLS-RP C = XTAG28 • The MLS-SE assigns a unique identifier to each MSL-RP • XTAG value is a one-byte value that the MLS-SE attaches to the MAC address • Used to delete a specific Layer 3 entries when then MLS-RP fails or exitsthe network

11. Candidate Packet L3 Information Source MAC = 0010.f663.d000 Destination MAC = 0010.0679.5800 Source IP = 172.16.10.123 Destination IP = 172.16.22.57 4 1 4 2 1 2 3 3 L2 Information A 0010.f663.d000 172.16.10.123 Establishing an MLS Cache Entry 0010.0679.5800 172.16.68.13 Cache Entry? 0090.b133.7000 172.16.22.57 B • The MLS-SE receives initial frame • The MLS-SE reads and recognizes the destination MAC Address • The MLS-SE checks the MLS cache for like entries • The MLS-SE forwards the frame to the MLS-RP

12. Enable Packet L3 Information Source MAC = 0010.0679.5800 Destination MAC = 0090.b133.7000 5 8 7 6 5 6 7 8 Source IP = 172.16.10.123 Destination IP = 172.16.22.57 L2 Information A 0010.f663.d000 172.16.10.123 Establishing an MLS Cache Entry (cont.) 0010.0679.5800 172.16.68.13 0090.b133.7000 172.16.22.57 B • The MLS-RP receives the frame and consults the routing table • The MLS-RP rewrites the header with the new destination MAC address • The MLS-RP enters its own MAC address for the source address • The MLS-RP forwards the frame to the MLS-SE

13. Enable Packet XTAG = 28 Candidate Packet XTAG = 28 9 12 10 9 12 11 10 11 MLS Cache Entry Destination IP Source IP Port DstPrt SrcPrt Destination Mac Vlan Port 172.16.22.57 172.16.10.123 UDP 1238 60224 00-90-b1-33-70-00 45 2/9 Establishing an MLS Cache Entry (cont.) 0010.0679.5800 172.16.68.13 MLS Cache MLS-RP IP MLS-RP ID XTAG MLS-RP MAC-Vlans 172.16.68.13 001006795800 28 00-10-67-95-80-00 1,41,42 0010.f663.d000 172.16.10.123 0090.b133.7000 172.16.22.57 A B • The MLS-SE receives the frame • The MLS-SE compares the XTAGs of the candidate and enable packets • The MLS-SE records the enable packet information in the MLS cache • The MLS-SE forwards the frame to the destination

14. 16 14 13 14 15 16 13 15 Rewritten Frame L3 Information Source IP = 172.16.10.123 Destination IP = 172.16.22.57 Source MAC = 0010.0679.5800 Destination MAC = 0090.b133.7000 L2 Information Switching Subsequent Frames in a Flow Incoming Frame L3 Information Source IP = 172.16.10.123 Destination IP = 172.16.22.57 L2 Information Source MAC = 0010.f663.d000 Destination MAC = 0010.0679.5800 B A 0090.b133.7000 172.16.22.57 0010.f663.d000 172.16.10.123 Destination IP Source IP Port DstPrt SrcPrt Destination Mac Vlan Port 172.16.22.57 172.16.10.123 UDP 1238 60224 00-90-b1-33-70-00 45 2/9 MLS Cache Entry • The MLS-SE receives subsequent frames in the flow • The MLS-SE compares the incoming frame with the MLS cache entry • The MLS-SE rewrites the frame header • The MLS-SE forwards the frame to the destination

15. 2 1 5 3 4 5 6 2 3 4 6 1 A B MLS Topology Example 1 MLS-RP R2 R2 R1 MLS-SE • Host A sends a packet to the default gateway • R1 rewrites the frame header to reflect the destination as the next-hop router (R2) • MLS-SE forwards the frame to R2 • R2 rewrites the frame header to reflect the destination as Host B • MLS-SE forwards the frame to Host B • All subsequent frames are switched

16. 7 6 1 2 3 4 5 10 8 9 10 1 9 10 7 6 8 4 3 2 5 A B MLS Topology Example 2 MLS-RP • Host A sends a packet to the default gateway • MLS-SE1 forwards the frame to MLS-SE2 • MLS-SE2 forwards the frame to MLS-SE3 • MLS-SE3 forwards the frame to MLS-RP1 • MLS-RP1 rewrites the frame header and forwards the frame to MLS-SE3 • MLS-SE3 forwards the frame to MLS-SE2 • MLS-SE2 forwards the frame to MLS-SE1 • MLS-SE1 forwards the frame to Host B • All subsequent frames are switched through MLS-SE1 • Entries in MLS-SE2 and 3 time out MLS-SE3 MLS-SE2 MLS-SE1

17. 1 2 Summarize Multilayer Switched Environment MPLS First Packet Host A Host B Subsequent Packets Route Once Switch Many

18. MPLS应用领域 在IP网络的QoS方面；在IP网络的流量工程方面； 在IP网络的服务功能方面，如VPN。

19. MPLS发展前景和意义 简化IPv6实施为新厂商带来商机 提高网络使用率 骨干走向边缘替代ATM 结合底层光设备 Everything over IP