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MPLS

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. 1. 2. Defining Flows. Multilayer Switched Environment. p2. p3. p1. Host A. Host B. Conventional Environment. First Packet. Host A. Host B. Subsequent Packets.

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MPLS

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  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

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