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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,Defining Flows,Host B,p1,Host A,p3,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,Host B,Conventional E
2、nvironment,First Packet,Subsequent Packets,Host A,Multilayer Switched Environment,p2,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。,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
3、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,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
4、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。,CISCO 标签交换（Tag Switching）,目前主要的 MPLS技术,IBM ARIS (集中式基于路由的IP交换技术),*采用控制流量而不是 采用数据流量来设置前向表,MLS Components,MLS-SEMultilayer Switching Switch Engine,MLSPMultilayer Switching Protocol,Multicast Hello Messages sent to MLS-SE by MLS-RP to In
5、form: MAC addresses used on different VLANs Routing/accesslists changes occurring on MLS-RP,Cisco 85xx 75XX 72XX 4XXX,OR,RSM,MLS-RPMultilayer Switching Route Processor,多层交换路由处理器,多层交换交换机引擎,多层交换协议,MLS-RP Advertisement,MLS-RP sends out multicast hello messages Messages contain MAC, VLAN, and route info
6、rmation Messages use the CGMP multicast well-known address CGMP(Cisco组管理协议),确保SWITCH的互操作性,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,Receiving MLSP Hello Messages,Hello Mes
7、sage,I am not a Layer 3 Switch but I will still pass on the message.,Assigning XTAGs,MLS-RP A,MLS-RP B,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
8、exits the network,MLS-RP C,MLS-RP A = XTAG34 MLS-RP B = XTAG11 MLS-RP C = XTAG28,Establishing an MLS Cache Entry,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,
9、B,0010.0679.5800 172.16.68.13,0090.b133.7000 172.16.22.57,Cache Entry?,B,0010.0679.5800 172.16.68.13,0090.b133.7000 172.16.22.57,Establishing an MLS Cache Entry (cont.),The MLS-RP receives the frame and consults the routing table The MLS-RP rewrites the header with the new destination MAC address Th
10、e MLS-RP enters its own MAC address for the source address The MLS-RP forwards the frame to the MLS-SE,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,Establishing an MLS Cache Entry (cont.),A,B,0010.f663.d000 172.16.10.123,0010.0679.5800 172.16.68.13
11、,0090.b133.7000 172.16.22.57,MLS Cache,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,Switching Subsequent Frames in a Flow,The MLS-SE r
12、eceives 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,Incoming Frame,Source MAC = 0010.f663.d000 Destination MAC = 0010.0679.5800,L3 Information,L2 Information,Source
13、 IP = 172.16.10.123 Destination IP = 172.16.22.57,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,0010.f663.d000 172.16.10.123,0090.b133.7000 172.16.22.57,A,B,MLS Topology Example 1,R2,MLS-RP,B,R
14、2,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
15、 switched,MLS Topology Example 2,MLS-RP,MLS-SE3,MLS-SE2,MLS-SE1,B,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
16、 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,Summarize,Host B,First Packet,Subsequent Packets,Host A,Multilayer Switched Environment,MPLS,Route Once Switch Many,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。,MPLS发展前景和意义,Everything over IP,骨干走向边缘 替代ATM 结合底层光设备,简化IPv6实施 为新厂商带来商机 提高网络使用率,