蜡笔小新小爱的小说:MPLS 多协议标签交换 (自译整理稿)

http://en.wikipedia.org/wiki/Multiprotocol_Label_Switching
Multiprotocol Label Switching
This page was last modified on 2 October 2010 at 17:25
多协议标签交换 (自译整理稿)
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Multiprotocol Label Switching (MPLS) is a mechanism in high-performancetelecommunications networks which directs and carries data from one network node to the next. MPLS makes it easy to create "virtual links" between distant nodes. It can encapsulate packets of variousnetwork protocols.
多协议标签交换（MPLS）是在高性能电信网络中的一种机制，它引导和携带数据从一个走向下一个网络节点。MPLS使在距离远隔的节点之间创建“虚拟链路”变得容易。它可以封装各种网络协议的分组数据包。
MPLS is a highly scalable, protocol agnostic, data-carrying mechanism. In an MPLS network, data packets are assigned labels. Packet-forwarding decisions are made solely on the contents of this label, without the need to examine the packet itself. This allows one to create end-to-end circuits across any type of transport medium, using any protocol. The primary benefit is to eliminate dependence on a particularData Link Layer technology, such asATM,frame relay,SONET orEthernet, and eliminate the need for multiple Layer 2 networks to satisfy different types of traffic. MPLS belongs to the family ofpacket-switched networks.
MPLS是一个高度可伸缩的，协议无关的，数据承载机制。在MPLS网络中，数据包被配以标签。包转发决策完全取决于该标签的内容，而不需要考察包本身。这就允许其创建的端对端电路能跨越其使用任何协议的任何类型的传输介质。其主要的好处是消除了依赖于一个特定的数据链路层技术，如ATM ，帧中继 ，SONET或以太网 ，并消除了为满足不同类型的流通而需要多种第二层的网络。MPLS属于分组交换网络族。
MPLS operates at anOSI Model layer that is generally considered to lie between traditional definitions of Layer 2 (Data Link Layer) and Layer 3 (Network Layer), and thus is often referred to as a "Layer 2.5" protocol. It was designed to provide a unified data-carrying service for bothcircuit-based clients andpacket-switching clients which provide adatagram service model. It can be used to carry many different kinds of traffic, including IPpackets, as well as nativeATM,SONET, andEthernet frames.
MPLS工作在OSI模型中处于通常被认为是介于传统定义的第2层（数据链路层 ）和第3层（网络层 ）之间的，因而通常称之为“2.5层”协议的OSI模型层中。已提供了一个数据报服务模型，它是被设计用来作为一种统一的数据承载业务，既用于基于电路交换的客户，也用于分组交换的客户。它可以用来承载许多不同种类的流量，包括IP数据包 ，以及原生的ATM ，SONET ，和以太网等帧。
A number of different technologies were previously deployed with essentially identical goals, such asframe relay andATM. MPLS technologies have evolved with the strengths and weaknesses ofATM in mind. Many network engineers agree thatATM should be replaced with a protocol that requires less overhead, while providing connection-oriented services for variable-length frames. MPLS is currently replacing some of these technologies in the marketplace. It is highly possible that MPLS will completely replace these technologies in the future, thus aligning these technologies with current and future technology needs.[1]
以前曾有若干种不同的技术部署用于基本相同的目标，如帧中继和ATM。MPLS技术发展了ATM 的强势，改进了其弱点。许多网络工程师都认为，ATM应代之以一个开销很少，又能为可变长度帧提供面向连接服务的协议。当前，在市场上，MPLS正取代着其中的一些技术。MPLS极有可能将完全取代那些技术，MPLS正以当前和将来所需要的技术瞄准着那些将被取代的技术。[1]
In particular, MPLS dispenses with the cell-switching and signaling-protocol baggage of ATM. MPLS recognizes that small ATM cells are not needed in the core of modern networks, since modern optical networks (as of 2008) are so fast (at 40 Gbit/s and beyond) that even full-length 1500 byte packets do not incur significant real-time queuing delays (the need to reduce such delays — e.g., to support voice traffic — was the motivation for the cell nature of ATM).
特别是，MPLS调整了ATM信元交换和ATM信令协议包。MPLS确认，在现代核心网络中不需要小尺寸的ATM单元，因为现代光网络（自2008年起 ）是如此之快（以超过40 Gbit / s的速度），即使全长1500字节的数据包也不会蒙受显著的实时排队延迟（而减少这类延误的需要-- 例如 ，支持语音流通通信--曾是ATM信元本性的诱惑所在）。
At the same time, MPLS attempts to preserve thetraffic engineering andout-of-band control that made frame relay and ATM attractive for deploying large-scale networks.
与此同时，MPLS试图保留流量工程和带外控制这样一些在部署大型网络时凸显帧中继和ATM吸引力的功能。
While the traffic management benefits of migrating to MPLS are quite valuable (better reliability, increased performance), there is a significant loss of visibility and access into the MPLS cloud for IT departments.[2]
（将路由技术）迁移到MPLS，对于流通管理的好处是相当有价值的（更良好的可靠性，和提高的性能），但对IT部门而言，明显损失了对MPLS云的可见性和深入访问。[2]

MPLS Layer MPLS层
Contents内容
[hide]
§         1 History                  1 历史
§         2 How MPLS works           2 MPLS如何工作
§         3 Installing and removing MPLS paths3 安装和删除MPLS路径
§         4 MPLS and IP             4 MPLS和IP
4.1 MPLS local protection (Fast Reroute)
4.1 MPLS的本地保护（快速重路由）
§         5 MPLS and Multicast      5 MPLS和组播
§         6 Comparison of MPLS versus Frame Relay
6 MPLS与帧中继的比较
§         7 Comparison of MPLS versus ATM
7 MPLS与ATM的比较
§         8 MPLS deployment         8 MPLS部署
§         9 Competitors to MPLS     9 MPLS的竞争对手
§         10 Access to MPLS networks10 访问MPLS网络
§         11 See also                11 参见
§         12 References             12 参考资料
§         13 Books                   13 参考书
§         14 External links         14 外部链接
[编辑] 术语解释
转发等效类（Forwarding Equivalence Class,FEC）
是一系列具有某些共性的数据流集合(目的地相同、使用的转发路径相同、具有相同的服务等级等)，这些数据在转发的过程中被LSR以相同的方式进行处理;
标记（Tag或Label）
简短的、长度固定的、具有本地意义的标识符，用以表征转发等价类（FEC）。
边缘标记交换路由器（LER： Label Edge Router）
根据LSP标签分发协议（LDP：Label Distribution Protocol ）等因素给分组加标签的路由器。
标记交换路由器（LSR：Label Switched Router）
具有标记交换能力的路由器，它是标记交换的基本构成单元。
数据流（stream）
沿着同一路径、属于同一FEC的一组包被视为一个数据流。
业务流（flow）
一个应用到应用的数据流称为业务流。
上游（upstream）和下游（downstream）
“上游”和“下游”是根据数据流的流向而定的。
转发信息库（FIB）
FIB用于存放下一跳的相关信息。
流分类
在业务流进入LSR时首先需要进行分类，也就是将业务流划分为不同的FEC。
标记交换的封装
标记交换是一种支持多协议的技术，它可以在多种链路协议上运行。
流量工程（Traffic Engineering）
根据用户数据业务量及当前网络状态 选择数据传输路径的过程，主要用来平衡网络中的负荷；
标签分发协议（LDP：Label Distribution Protocol ）
控制LSR之间交换标签与FEC绑定消息，协调LSR之间工作的一系列规程。主要功能：让LSR实现FEC与标签的绑定，并将这种绑定通知给相邻的LSR，使各LSR对收到的标签绑定达成共识。
标签堆栈
MPLS中分组可以携带多个标签，这些标签在分组包中以“堆栈”的形式存在，对标签堆栈的操作按照“后进先出”的原则。从而可以始终按栈顶标签决定如何转发分组包。
[edit ] History
[编辑 ] 历史
MPLS was originally proposed by a group of engineers fromIpsilon Networks, but their "IP Switching" technology, which was defined only to work over ATM, did not achieve market dominance.Cisco Systems, Inc., introduced a related proposal, not restricted to ATM transmission, called "Tag Switching".[3] It was a Cisco proprietary proposal, and was renamed "Label Switching". It was handed over to theIETF for open standardization. The IETF work involved proposals from other vendors, and development of a consensus protocol that combined features from several vendors' work.
MPLS最初是由来自Ipsilon网络公司的一群工程师所建议 ，但他们只定义了在ATM上工作的“IP交换”技术，并没有占据市场的统治地位。思科系统公司，出台了一个并不限于ATM传输的有关建议，叫做“标志交换”；[3]这是一个有思科专利的建议，并更名为“标签交换”。它被作为开放标准移交给IETF。IETF的工作成果包含了其他厂商的建议，组合了来自几个厂商成果的特点，开发出一个一致同意的协议。
One original motivation was to allow the creation of simple high-speed switches, since for a significant length of time it was impossible to forward IP packets entirely in hardware. However, advances inVLSI have made such devices possible. Therefore the advantages of MPLS primarily revolve around the ability to support multiple service models and perform traffic management. MPLS also offers a robust recovery framework[4] that goes beyond the simple protection rings ofsynchronous optical networking (SONET/SDH).
最初的动机是要简化高速交换机制作，因为在当时，在相当长的时间内，不可能完全采用硬件来转发IP数据包。然而，随着VLSI的进步，作出这样的设备已成为可能。于是MPLS的优势主要用来解决围绕着能够支持多种服务模式和执行流通管理的能力上。MPLS还提供了一个稳固的恢复框架[4]，它被认为其超越了简单的同步光网络 （SONET / SDH）的保护环的性能。
[edit ] How MPLS works
[编辑 ] MPLS如何工作
MPLS works by prefixing packets with an MPLS header, containing one or more "labels". This is called a labelstack. Each label stack entry contains four fields:
l       A 20-bit label value.
l       a 3-bit Traffic Class field for QoS (quality of service) priority (experimental) and ECN (Explicit Congestion Notification).
l       a 1-bit bottom of stack flag. If this is set, it signifies that the current label is the last in the stack.
an 8-bit TTL (time to live) field.
MPLS通过在数据包上加上MPLS首部作为前缀来工作，该首部包含着一个或多个标签。这就是所谓的标签栈。每个标记栈项包含四个字段(32位)：
§          一个20位的标签值。
§          3位流通类字段，用于QoS（服务质量 ）优先级别（实验）和ECN（显式拥塞通知）。
§          1位栈底标记。如果该位置位，则表示当前标签处于堆栈中的最后。
§          一个8位TTL（生存时间 ）字段。
These MPLS-labeled packets are switched after a label lookup/switch instead of a lookup into the IP table. As mentioned above, when MPLS was conceived, label lookup andlabel switching were faster than arouting table or RIB (Routing Information Base) lookup because they could take place directly within theswitched fabric and not theCPU.
用一个标签查找/标签交换代替进入到IP表中去查找，完成之后，这些被标志了的MPLS数据包就被交换。如上所述，可以想象，MPLS进行标签查找和标签交换将快于路由表或RIB(路由信息库)查找，因为它们可以不经CPU，立即发生在交换构架内。
The entry and exit points of an MPLS network are calledlabel edge routers (LER), which, respectively, push an MPLS label onto an incoming packet and pop it off the outgoing packet. Routers that perform routing based only on the label are calledlabel switch routers (LSR). In some applications, the packet presented to the LER already may have a label, so that the new LER pushes a second label onto the packet. For more information seepenultimate hop popping.
MPLS网络的入口和出口被称为标签边缘路由器 （LER），其中，分别将一个MPLS标签压入输入数据包，和从输出数据包中弹出它。这种只基于标签以执行路由的路由器称为标签交换路由器( LSR）。.在某些应用中，提交给边缘路由器的数据包可能已经有了一个标签，导致新的边缘路由器压入第二个标签到数据包中。欲了解更多信息，请参阅倒数第二个跳步弹出 。
（From  http://en.wikipedia.org/wiki/Penultimate_hop_popping ）
Penultimate Hop Popping (PHP) is a function performed by certain routers in anMPLS enabled network. It refers to the process whereby the outermost label of anMPLS tagged packet is removed by aLabel Switch Router (LSR) before the packet is passed to an adjacentLabel Edge Router .
倒数第二跳弹出（PHP）是在一个MPLS网络中的某个路由器执行的一个功能。 It refers to the process whereby the outermost label of anMPLS tagged packet is removed by aLabel Switch Router (LSR) before the packet is passed to an adjacentLabel Edge Router (LER).它指的是一个过程，通过标签交换路由器 （LSR），将MPLS标签的数据包的最外层标签去除，然后将数据包传递给相邻的标签边缘路由器(LER)。
The process is important in aLayer 3 MPLS VPN (RFC2547) environment as it reduces the load on the LER. If this process didn't happen, the LER would have to perform at least 2 label lookups:
The outer label, identifying that the packet was destined to have its label stripped on this router.
The inner label, to identify whichVirtual Routing/Forwarding (VRF) instance to use for the subsequent IP routing lookup.
The process is important in aLayer 3 MPLS VPN (RFC2547) environment as it reduces the load on the LER.这一过程在第三层MPLS VPN的 （RFC2547）的环境中是重要的，因为它减少了边缘路由器的负担。 If this process didn't happen, the LER would have to perform at least 2 label lookups:如果这个过程没有发生，边缘路由器必须执行至少两次标签查找：
The outer label, identifying that the packet was destined to have its label stripped on this router.标识外面的标签是这个包确定要剥离这台路由器上的标签；
标识The inner label, to identify whichVirtual Routing/Forwarding (VRF) instance to use for the subsequent IP routing lookup.内层标签，以确定哪个虚拟路由/转发（VRF）实例为以下的IP路由查找所使用。
In a large network this can result in the CPU load on the LER reaching unacceptable levels. By having PHP for an LER done on the LSRs connected to it, the load is effectively distributed among its neighbour routers.
在一个大型网络中这可能会导致CPU对于边缘路由器的负载达到不可接受的水平上。 By having PHP for an LER done on the LSRs connected to it, the load is effectively distributed among its neighbour routers.通过连接到LER的LSR 上完成PHP，负担便有效地分布在它的邻近的路由器之中。
PHP functionality is achieved by the LER advertising a label with a value of 3 to its neighbours. This label is defined asimplicit-null and informs the neighbouring LSR(s) to perform PHP.
PHP functionality is achieved by the LER advertising a label with a value of 3 to its neighbours. PHP功能是通过边缘路由器以值3作为标签通告其邻居。 This label is defined asimplicit-null and informs the neighbouring LSR(s) to perform PHP .这个标签被定义为隐含空 ，并通知邻近的LSR（们）执行PHP 。
Retrieved from "http://en.wikipedia.org/wiki/Penultimate_Hop_Popping "取自“http://en.wikipedia.org/wiki/Penultimate_Hop_Popping “
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Labels are distributed between LERs and LSRs using the “Label Distribution Protocol” (LDP).[5] Label Switch Routers in an MPLS network regularly exchange label and reachability information with each other using standardized procedures in order to build a complete picture of the network they can then use to forward packets. Label Switch Paths (LSPs) are established by the network operator for a variety of purposes, such as to create network-based IP virtual private networks or to route traffic along specified paths through the network. In many respects, LSPs are not different fromPVCs in ATM or Frame Relay networks, except that they are not dependent on a particular Layer 2 technology.
在边缘路由器LERs和标签交换路由器LSRs ( LSR）之间的标签分配是使用“标签分配协议 ”(LDP)来进行的。[5]在一个MPLS网络中，各标签交换路由器，彼此采用标准化的方法，定期交换标签和可达性信息，以便建立一个完整的网络图，使它们此后能够转发数据包。网络运营商为用于各种用途建立了各种标签交换路径（LSPs），如建立基于网络的IP虚拟专有网络，或沿指定的路径来路由流量以通过网络。在许多方面，LSP不同于ATM的虚电路或帧中继网络，除了它们都不依赖于某一特定的第二层技术。
In the specific context of an MPLS-basedvirtual private network (VPN), LSRs that function asingress and/oregress routers to the VPN are often called PE (Provider Edge) routers. Devices that function only as transit routers are similarly called P (Provider) routers. SeeRFC 2547.[6] The job of a P router is significantly easier than that of aPE router, so they can be less complex and may be more dependable because of this.
在一个基于MPLS的虚拟专用网络 （VPN）的特定衔接关系中，LSRs，对VPN而言，其功能象入口和/或出口路由器，通常被称为PE（供应商边缘）路由器。功能仅作为过路路由器的设备，类似地称为P （Provider）路由器。见RFC 2547 。[6]P路由器作业明显地比PE路由器容易 ，这样它们就可以不那么复杂，因此就可能更可靠。
When an unlabeled packet enters the ingress router and needs to be passed on to an MPLS tunnel, the router first determines theforwarding equivalence class (FEC) the packet should be in, and then inserts one or more labels in the packet's newly-created MPLS header. The packet is then passed on to the next hop router for this tunnel.
当一个未标记数据包进入入口路由器，且需要传递到一个MPLS隧道上时，路由器首先确定数据包要放入的转发等价类 （FEC），然后将一个或多个标签插入到数据包的新创建的MPLS首部。该数据包然后传递到这条隧道的下一跳路由器上。
When a labeled packet is received by an MPLS router, the topmost label is examined. Based on the contents of the label a swap, push (impose) or pop (dispose) operation can be performed on the packet's label stack. Routers can have prebuilt lookup tables that tell them which kind of operation to do based on the topmost label of the incoming packet so they can process the packet very quickly.
当一个标记包被一个MPLS路由器接收，最顶上的标签就被检查。基于标签上的内容，一个交换，推（ 加入 ）或弹出（ 舍弃 ）的操作就可在包的标签堆栈上执行。路由器可能预置了查找表，它告诉人们基于送入的数据包中最上面的标签做哪一种操作，使他们能够非常迅速地处理数据包。
In a swap operation the label is swapped with a new label, and the packet is forwarded along the path associated with the new label.在交换操作中，标签与一个新的标签互换，同时数据包带着新标签沿新路径被转发。
In a push operation a new label is pushed on top of the existing label, effectively "encapsulating" the packet in another layer of MPLS. This allows hierarchical routing of MPLS packets. Notably, this is used byMPLS VPNs.
在压入操作中，新标签被压入现有标签的顶部，有效地将数据包“封装”到MPLS的另一个层。这样就能允许有层次地路由MPLS数据包。很明显，这是用于MPLS VPN 的。
In a pop operation the label is removed from the packet, which may reveal an inner label below. This process is called "decapsulation". If the popped label was the last on the label stack, the packet "leaves" the MPLS tunnel. This is usually done by the egress router, but see Penultimate Hop Popping (PHP) below.
在弹出操作中标签从包中删除，这可以暴露下一个内部标签。这一过程被称为“解封”。如果弹出标签是标签堆栈上最后一个，数据包就“离开”MPLS隧道。这通常是由出口路由器完成的，请看下面的‘倒数第二跳步的弹出（PHP）’
During these operations, the contents of the packet below the MPLS Labelstack are not examined. Indeed transit routers typically need only to examine the topmost label on the stack. The forwarding of the packet is done based on the contents of the labels, which allows "protocol-independent packet forwarding" that does not need to look at a protocol-dependentrouting table and avoids the expensive IPlongest prefix match at each hop.
在这些操作中，低于MPLS标签堆栈的数据包内容不被检查。事实上过路路由器通常只需要检查堆栈上的最顶端的标签。报文转发是基于标签的内容完成的。允许“协议无关的数据包转发”，这并不需要关注协议相关的路由表 ，避免了在每一跳中耗费IP最长前缀匹配。
At the egress router, when the last label has been popped, only the payload remains. This can be an IP packet, or any of a number of other kinds of payload packet. The egress router must therefore have routing information for the packet's payload, since it must forward it without the help of label lookup tables. An MPLS transit router has no such requirement.
在出口路由器，当最后一个标签被弹出后，只有有效载荷仍然存在。这可能是一个IP数据包，或任何其他种类有效载荷包。因此，出口路由器必须具有路由信息用于数据包的有效载荷，因为它必须在没有查找表的帮助下转发它。一个MPLS过境路由器则没有这样的需求。
In some special cases, the last label can also be popped off at the penultimate hop (the hop before the egress router). This is calledPenultimate Hop Popping (PHP). This may be interesting in cases where the egress router has lots of packets leaving MPLS tunnels, and thus spends inordinate amounts of CPU time on this. By using PHP, transit routers connected directly to this egress router effectively offload it, by popping the last label themselves.
在某些特殊情况下，最后一个标签，也可以在倒数第二跳步（在出口路由器前的跳步）弹出。这就是所谓的倒数第二跳步弹出（PHP）。这可能是很有趣的，因为当出口路由器有很多的数据包要离开MPLS隧道时，通常会在其上耗费过度的CPU时间。通过使用PHP，用弹出最后一个标签本身来实现有效地卸载它，从而可以实现由过境路由器直接连接到这个出口路由器。
MPLS can make use of existing ATM network infrastructure, as its labeled flows can be mapped to ATM virtual circuit identifiers, and vice versa.
MPLS可以利用现有的ATM网络基础设施，因为MPLS的标记流可以映射到ATM的虚电路标识符。反之亦然。
[edit ] Installing and removing MPLS paths
[编辑 ] 安装和删除MPLS路径
There are two standardized protocols for managing MPLS paths:LDP (Label Distribution Protocol) andRSVP-TE, an extension of theResource Reservation Protocol (RSVP) for traffic engineering.[7][8] Furthermore, there exist extensions of theBGP protocol that can be used to manage an MPLS path.[9][10][11]
有两个标准化协议用于管理的MPLS路径：标签分发协议(LDP )，以及RSVP - TE ---一个资源预留协议 (RSVP）的扩展，用于流量工程。[7][8]此外，还有BGP协议的扩展，可用于管理的MPLS路径。。 [9][10][11]
An MPLS header does not identify the type of data carried inside the MPLS path. If one wants to carry two different types of traffic between the same two routers, with different treatment by the core routers for each type, one has to establish a separate MPLS path for each type of traffic.
一个MPLS首部并不鉴别MPLS路径内所运载的数据类型。如果MPLS在相同的两个路由器之间要运载两个不同类型的流量，而核心路由器对每一种类型采用不同的处理，该MPLS就必须为每种流通类型建立分开的MPLS路径。
[edit ] MPLS and IP
[编辑 ] MPLS和IP
MPLS cannot be compared to IP as a separate entity because it works in conjunction with IP and IP'sIGP routing protocols. MPLSLSPs provide dynamic, transparent virtual networks with support for traffic engineering, the ability to transport Layer-3 (IP) VPNs with overlapping address spaces, and support for Layer-2pseudowires using Pseudowire Emulation Edge-to-Edge (PWE3)[12] that are capable of transporting a variety of transport payloads (IPv4, IPv6, ATM, Frame Relay, etc). MPLS-capable devices are referred to asLSRs. LSR devices provide traffic engineering functions can be defined using
l       explicit hop-by-hop configuration,
l       dynamically routed by theConstrained Shortest Path First (CSPF) algorithm, or
§          configured as a loose route that avoids a particular IP or that is partly explicit and partly dynamic.
MPLS不可以作为单独的实体来与IP作比较，因为它是与IP的IGP路由协议结合在一起工作的。MPLS的LSPs提供了动态的、透明的虚拟网络，以支持流量工程；支持传输带有重叠地址空间的第三层（IP）虚拟专用网VPNs的能力；以及支持传输各种流通的有效载荷（IPv4，IPv6，ATM，帧中继，等等）的能力，这种能力是使用边缘到边缘伪连线仿真（PWE3）[12 ] 支持用于第二层的伪连线，这是一个能够。LSR的设备提供的流量工程功能，可以通过下面的配置来使用：
§          显式的逐跳配置，
§          按约束最短路径优先（CSPF）算法动态路由或
§          配置为一个松散的路线，以避免具体的IP，或者是部分显式和部分动态。
In a pure IP network, the shortest path to a destination is chosen even when it becomes more congested. Meanwhile, in an IP network with MPLS Traffic Engineering CSPF routing, constraints such as the RSVP bandwidth of the traversed links can also be considered, such that the shortest path with available bandwidth will be chosen. MPLS Traffic Engineering relies upon the use of TE extensions to OSPF or IS-IS and RSVP. Besides the constraint of RSVP bandwidth, users can also define their own constraints by specifying link attributes and special requirements for tunnels to route (or not to route) over links with certain attributes.[13]
IP网络中，总是选择到目的地的最短路径，即使它会变得更加拥挤。而在有MPLS流量工程CSPF路由的IP网络中，常被考虑予以限制，如穿越链路的RSVP带宽；这样，可用带宽的最短路径将被选择。MPLS流量工程依赖于对OSPF或IS – IS以及RSVP带宽使用TE扩展。除了约束RSVP带宽以外，用户还可以定义自己的约束通过指定隧道的链路属性和特殊的需求，根据链路上的某些属性确定路由（或不路由）。[13]
[edit ] MPLS local protection (Fast Reroute)
[编辑 ] MPLS的本地保护（快速重路由）
Main article:MPLS local protection
主条目：MPLS的本地保护
In the event of a network element failure when recovery mechanisms are employed at the IP layer, restoration may take several seconds which is unacceptable for real-time applications such asVoIP.[14][15][16] In contrast,MPLS local protection meets the requirements of real-time applications with recovery times comparable to those ofSONET rings of less than 50 ms.[14][16][17]
当时在IP层上使用恢复机制时，在一个网络元素失效的情况下，修复可能需要几秒钟，而这对于象VoIP这样的实时应用是不可接受的。[ 14 ][ 15 ][ 16 ]对比而言，MPLS 本地保护的恢复时间可以与少于50ms的SONET环路恢复时间相当，满足了实时应用的需要。[ 14 ][ 16 ][ 17 ]
[edit ] MPLS and Multicast
[编辑 ] MPLS和组播
Multicast was for the most part an after-thought in MPLS design. It was introduced by point-to-multipoint RSVP-TE.[18] It was driven by Service Provider requirements to transport broadband video over MPLS. Since the inception ofRFC 4875 there has been tremendous surge in interest and deployment of MPLS multicast and this has led to several new developments both in the IETF and in shipping products.
在MPLS设计中后来想到的很大一部分是组播。它是由点对多点的RSVP - TE引进的。[18] 这是受服务供应商在MPLS上传输宽带视频的需求而驱动的。自RFC 4875 创建以来对MPLS的兴趣和MPLS的部署，出现了巨大的热情，导致在IETF产品和移动产品方面了出现了若干新的事态发展。
[edit ] Comparison of MPLS versus Frame Relay
[编辑 ] MPLS与帧中继的比较
Frame relay aimed to make more efficient use of existing physical resources, which allow for the underprovisioning of data services bytelecommunications companies (telcos) to their customers, as clients were unlikely to be utilizing a data service 100 percent of the time. In more recent years, frame relay has acquired a bad reputation in some markets because of excessive bandwidthoverbooking by these telcos.
帧中继的目的是为了更有效地利用现有的物理资源；它允许电信公司(telcos)为他们的客户提供不能充分保障的数据服务，因为客户不太可能在100%的时间比内使用数据服务。在最近几年中，帧中继在某些市场中由于这些电信公司超售了过度的带宽而获得了一个不好的声誉。
Telcos often sell frame relay to businesses looking for a cheaper alternative todedicated lines; its use in different geographic areas depended greatly on governmental and telecommunication companies' policies.
电信运营商往往卖帧中继给寻找专用线廉价替代品的企业；它在不同的地理区域的使用，极大地依赖于当地政府和电信公司的政策。
AT&T is currently (as of June 2007) the largest frame relay service provider in the United States, with local networks in 22 states, plus national and international networks. This number is expected to change between 2007 and 2009 when most of these frame relay contracts expire. Many customers are likely to migrate from frame relay to MPLS over IP or Ethernet within the next two years, which in many cases will reduce costs and improve manageability and performance of their wide area networks.[19]
AT＆T公司的帧中继服务，包括22个州的本地网络，加上国家和国际网络，是目前（截至2007年6月）美国最大的提供商。这个数字预期到2007年和2009年之间当这些帧中继合约大部分到期时会有变化，。在未来两年内，许多客户可能会从帧中继迁移到MPLS over IP或以太网上，因为在很多情况下会降低成本，改善可管理性以及他们的广域网的性能。[19]
[edit ] Comparison of MPLS versus ATM
[编辑 ] MPLS与ATM的比较
While the underlying protocols and technologies are different, both MPLS andATM provide aconnection-oriented service for transporting data across computer networks. In both technologies, connections are signaled between endpoints, connection state is maintained at each node in the path, and encapsulation techniques are used to carry data across the connection. Excluding differences in the signaling protocols (RSVP/LDP for MPLS andPNNI:Private Network-to-Network Interface for ATM) there still remain significant differences in the behavior of the technologies.
虽然底层的协议和技术是不同的，无论是MPLS还是ATM都提供了面向连接的服务，用于跨越计算机网络来传输数据。在这两种技术中，都是通过信令实现端点间的连接，连接的状态都维持在路径中的每个节点中；封装技术用于承载着跨越连接的数据。除了在信令协议中不同外（RSVP/LDP用于MPLS，以及PNNI ：专用网--网接口用于ATM）在技术行为方面仍然存在显著差别。
The most significant difference is in the transport and encapsulation methods. MPLS is able to work with variable length packets while ATM transports fixed-length (53 byte) cells. Packets must be segmented, transported and re-assembled over an ATM network using an adaptation layer, which adds significant complexity and overhead to the data stream. MPLS, on the other hand, simply adds a label to the head of each packet and transmits it on the network.
最重大的差别是在传输方法和封装方法上。MPLS有能力工作中在可变长的数据包上，而ATM则传输固定长度（53字节）的信元。在ATM网络上，数据包在ATM适配层中必须被分割，传输和重新组装，显著增加了数据流的复杂性和开销。另一方面，MPLS却只需简单的添加一个标签给每个数据包的报头，并将它发送到网络上。
Differences exist, as well, in the nature of the connections. An MPLS connection (LSP) is unidirectional—allowing data to flow in only one direction between two endpoints. Establishing two-way communications between endpoints requires a pair of LSPs to be established. Because 2 LSPs are required for connectivity, data flowing in the forward direction may use a different path from data flowing in the reverse direction. ATM point-to-point connections (virtual circuits), on the other hand, arebidirectional, allowing data to flow in both directions over the same path (only SVC ATM connections are bidirectional; PVC ATM connections are unidirectional).
同时差别还存在在连接的本性上。MPLS连接（LSP ）是单向的，两个端点之间只允许数据在一个方向流动。端点之间建立双向通信，需要建立一对LSP。因为2个 LSP都需要进行连接，数据在前进方向流动的通路可能使用不同的从相反的方向流动的数据通路。另一方面，ATM点至点连接（虚电路）是双向的 ，允许数据在同一路径的两个方向上流动（只有SVC的ATM连接是双向的;PVC ATM连接则是单向的）。
Both ATM and MPLS support tunneling of connections inside connections. MPLS uses label stacking to accomplish this while ATM uses virtual paths. MPLS can stack multiple labels to form tunnels within tunnels. The ATM virtual path indicator (VPI) and virtual circuit indicator (VCI) are both carried together in the cell header, limiting ATM to a single level of tunnelling.
ATM和MPLS都支持在连接内隧通连接。MPLS使用标签栈操作来完成此工作，而ATM则使用虚拟路径。 MPLS可以栈堆多个标签，以在隧道内形成隧道。ATM虚拟路径指示器（VPI）和虚拟电路指示器（VCI）都一起承载在信元头部，从而限制ATM只能到单级隧通。
The biggest single advantage that MPLS has over ATM is that it was designed from the start to be complementary to IP. Modern routers are able to support both MPLS and IP natively across a common interface allowing network operators great flexibility in network design and operation. ATM's incompatibilities with IP require complex adaptation, making it comparatively less suitable for today's predominantly IP networks.
MPLS over ATM的最大的单一优势，在于它从一开始就是对IP设计的互补。现代路由器支持MPLS和ATM天生有能力通过一个共同的接口，允许网络运行商在网络设计和操作方面有极大的灵活性。ATM与IP的不兼容性 需要复杂的适配，使之相对地不太适合于今天的主流IP网络。
[edit ] MPLS deployment
[编辑 ] MPLS部署
MPLS is currently in use in IP-only networks and is standardized by theIETF inRFC 3031. It is deployed to connect as few as two facilities to very large deployments. For example, in the retail sector, it is not uncommon to see deployments of 2000 to 5000 locations to communicate transaction data to a headquarters data center.
MPLS当前在唯IP网络中使用，它经由IETF的RFC 3031标准化。它可以少到部署两个设施，多到非常大的部署。例如，在零售业， 部署2000个至5000个场所与与总部数据中心进行交易数据的通信也并不少见。
In practice, MPLS is mainly used to forwardIP datagrams andEthernet traffic. Major applications of MPLS aretelecommunications traffic engineering andMPLS VPN.
在实践中，MPLS是主要用于转发IP数据报以及以太网流量。MPLS的主要应用是电信流量工程和MPLS VPN 。
[edit ] Competitors to MPLS
[编辑 ] 对MPLS的竞争者

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MPLS can exist in bothIPv4 environment (IPv4 routing protocols) andIPv6 environment (IPv6 routing protocols). The major goal of MPLS development - the increase of routing speed - is no longer relevant because of the usage ofASIC,TCAM andCAM-based switching. Therefore the major usage of MPLS is to implement limited traffic engineering and Layer 3/Layer 2 “service provider type” VPNs over existing IPv4 networks.
MPLS可以同时存在于IPv4的环境（IPv4路由协议）和IPv6的环境（IPv6路由协议）。开发MPLS的主要目标-增加路由速度-由于使用ASIC，TCAM和基于CAM的交换，已不再适用。因此，MPLS的主要用途是在现有的IPv4网络上实现有限的流量工程和第三层/第二层“服务提供者类型”的VPNs。
The main competitors to MPLS areProvider Backbone Bridges (PBB), andMPLS-TP that also provide services such as service provider Layer 2 and Layer 3 VPNs.L2TPv3 has been suggested as a competitor, but has not reached any wider success.Some internet provider are offering different services to customers along with MPLS.These services mainly includes the NPLC,ILL,IPLC etc.NPLC stands for National Private Lease Circuit.In these we will take 1 example.There are City A and City B.One customer have two offices located in above both cities.Then customer want connectivity between these two offices which are located at City A and City B.Then internet provider company will have its own PoP at both cities.Then they will provide a link between both the cities.Now the offices must need a connection upto PoP.Then local loop will be provided in between PoP and Office location at both cities.In this way this NPLC will be delivered.
MPLS的主要竞争对手是运营商骨干桥 （PBB）和MPLS-TP，也提供VPN的服务，如服务供应商第2层和3层。L2TPv3已被建议作为一个竞争者，但没有达成任何广泛success.Some互联网供应商是随着MPLS.These服务提供给客户不同的服务主要包括的NPLC，馆际互借，国际专线etc.NPLC租赁Circuit.In国家的私人代表这些问题，我们将采取一example.There是城市A和客户有一个城市B在上述两种cities.Then客户想要两个办事处位于这两者之间是一个在城市与城市b.然后公司位于互联网服务提供商将有机会在自己的PoP cities.Then他们将提供两个城市之间的联系办事处之间的联系。现在，办事处必须在两个cities.In需要连接高达PoP.Then本地环路将在POP和办公地点之间提供这本的NPLC将交付方式。
IEEE 1355 is a completely unrelated technology that does something similar in hardware.
电机及电子学工程师联合会1355是一个完全不相关的技术，做一些类似的硬件研究。
IPv6 references: Grossetete, Patrick, IPv6 over MPLS, Cisco Systems 2001; Juniper Networks IPv6 and Infranets White Paper; Juniper Networks DoD's Research and Engineering Community White Paper.
IPv6的参考：Grossetete，帕特里克，IPv6的MPLS和思科系统公司2001年Juniper网络IPv6和Infranets白皮书; Juniper网络国防部的研究和工程共同体的白皮书。
[edit ] Access to MPLS networks
[编辑 ] 访问MPLS网络
MPLS supports a range of access technologies, includingT1,ATM,frame relay andDSL.
MPLS支持多种接入技术，包括T1，ATM，帧中继和DSL。
[edit] See also
l      IPv4
l      IPv6
l      VPLS, virtual private LAN service over MPLS.
[edit] References
1        ^Applied Data Communications (A Business-Oriented Approach) James E. Goldman & Phillip T. Rawles, 2004 (ISBN 0-471-34640-3)
2        ^Routers Hold key to MPLS Measurement
3        ^Y. Rekhter et al.,Tag switching architecture overview, Proc. IEEE 82 (December, 1997), 1973–1983.
4        ^Framework for Multi-Protocol Label Switching (MPLS)-based Recovery,RFC 3469, V. Sharma & F. Hellstrand, February 2003
5        ^Thomas, B; Gray, E (January)."RFC 3037: LDP Applicability".http://www.ietf.org/rfc/rfc3037.txt. Retrieved 2007-09-21
6        ^"RFC 2547 - BGP/MPLS VPNs". tools.ietf.org.http://tools.ietf.org/html/rfc2547. Retrieved 2008-06-11.
7        ^RFC 5036— LDP Specification, IETF, October 2007,http://tools.ietf.org/html/rfc5036
8        ^RFC 3209 — RSVP-TE: Extensions to RSVP for LSP Tunnels, IETF, December 2001,http://tools.ietf.org/html/rfc3209
9        ^starting withRFC 4364BGP/MPLS IP Virtual Private Networks (VPNs)
10     ^Carrying Label Information in BGP-4,RFC 3107, Rekhter Y and Rosen E, May 2001.
11     ^Graceful Restart Mechanism for BGP with MPLS, RFC4781,Yakov Rekhter andRahul Aggarwal, January 2007.
12     ^RFC 3985— Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture, IETF, March 2005,http://tools.ietf.org/html/rfc3985
13     ^de Ghein, Luc. MPLS Fundamentals. pp. 249–326.
14      ^ab Aslam et al. (2005-02-02).NPP: A Facility Based Computation Framework for Restoration Routing Using Aggregate Link Usage Information. QoS-IP 2005 : quality of service in multiservice IP network.http://cat.inist.fr/?aModele=afficheN&cpsidt=16546516. Retrieved 2006-10-27.
15     ^Raza et al..Online routing of bandwidth guaranteed paths with local restoration using optimized aggregate usage information. IEEE-ICC 2005.http://ieeexplore.ieee.org/iel5/9996/32109/01494347.pdf. Retrieved 2006-10-27.
16      ^ab Li Li et al..Routing bandwidth guaranteed paths with local restoration in label switched networks. IEEE Journal on Selected Areas in Communications.http://ieeexplore.ieee.org/iel5/49/30289/01391048.pdf?tp=&arnumber=1391048&isnumber=30289. Retrieved 2006-10-27.
17     ^Kodialam et al..Dynamic Routing of Locally Restorable Bandwidth Guaranteed Tunnels using Aggregated Link Usage Information. IEEE Infocom. pp. 376–385. 2001.http://ieeexplore.ieee.org/iel5/7321/19793/00916720.pdf. Retrieved 2006-10-27.
18     ^RFC 4461: Extensions to Resource Reservation Protocol — Traffic Engineering (RSVP-TE) for Point-to-Multipoint TE Label Switched Paths (LSPs), R. Aggarwal, D. Papadimitriou, S. Yasukawa, Eds.
19     ^"AT&T — Frame Relay and IP-Enabled Frame Relay Service (Product Advisor)", Research and Markets, June 2007.
[edit] Books
l       "Deploying IP and MPLS QoS for Multiservice Networks: Theory and Practice" by John Evans, Clarence Filsfils (Morgan Kaufmann, 2007,ISBN 0-12-370549-5)
l       Rick Gallaher's MPLS Training Guide (ISBN 1932266003)
[edit] External links
l      MPLS Working Group, IETF.
l      MPLS IP Specifications, Broadband Forum.
Categories:MPLS networking |Internet standards |Network protocols |Tunneling protocols
This page was last modified on 2 October 2010 at 17:25
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.MPLS VPN
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http://en.wikipedia.org/wiki/MPLS_VPN
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MPLS VPN is a family of methods for harnessing the power ofMultiprotocol Label Switching (MPLS) to createvirtual private networks (VPNs). MPLS is well suited to the task as it provides traffic isolation and differentiation without substantial overhead.[citation needed]
MPLS VPN是一组方法为利用多协议标签交换 （MPLS）的能力技术来建立虚拟专用网络 （VPN）。这是这是这是 MPLS非常适合的任务，因为它提供了流通隔离和区分性而没有大量的开销。。[来源请求 ]
[edit] Layer 3 MPLS VPN
A layer 3 MPLS VPN, also known as L3VPN, combines enhancedBGP signaling, MPLS traffic isolation and router support for VRFs (Virtual Routing/Forwarding) to create an IP based VPN. Compared to other types of VPN such as IPSec VPN or ATM, MPLS L3VPN is more cost efficient and can provide more services to customers.
第3层MPLS VPN，也被称为L3VPN，结合了增强的BGP信令，MPLS流通隔离和用于VRF（虚拟路由/转发 ）的路由器支持来创建一个基于IP的VPN。 Compared to other types of VPN such as IPSec VPN or ATM, MPLS L3VPN is more cost efficient and can provide more services to customers.相对于其他类型的VPN的IPSec VPN或如ATM，MPLS L3VPN更具成本效益，能为客户提供更多的服务。
However, there is no implementation of privacy of the traffic sent over the MPLS, except to the degree that you trust the operator of the MPLS equipment along the way. If privacy is a concern, other encryption method such as end-to-endIPSec tunnels should be considered before injecting the traffic to MPLS backbone.
However, there is no implementation of privacy of the traffic sent over the MPLS, except to the degree that you trust the operator of the MPLS equipment along the way.然而，在MPLS上发送流量并没有实施隐私性，除了你信任MPLS设备运营商，可以沿此达到这种程度。然而If privacy is a concern, other encryption method such as end-to-endIPSec tunnels should be considered before injecting the traffic to MPLS backbone.如果隐私是一种担忧，其他的加密方法，例如端至端IPSec隧道，应在将流量注入到MPLS骨干网之前加以考虑。
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