Network Working Group G. Huston
Request for Comments: 3221 Internet Architecture Board
Category: Informational December 2001
Network Working Group G. Huston
Request for Comments: 3221 Internet Architecture Board
Category: Informational December 2001
Commentary on Inter-Domain Routing in the Internet
Internet域间路由述评
Status of this Memo
本备忘录的状况
This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
本备忘录为互联网社区提供信息。它没有规定任何类型的互联网标准。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (2001). All Rights Reserved.
版权所有（C）互联网协会（2001年）。版权所有。
Abstract
摘要
This document examines the various longer term trends visible within the characteristics of the Internet's BGP table and identifies a number of operational practices and protocol factors that contribute to these trends. The potential impacts of these practices and protocol properties on the scaling properties of the inter-domain routing space are examined.
本文件审查了互联网BGP表特征中可见的各种长期趋势，并确定了促成这些趋势的一些操作实践和协议因素。研究了这些实践和协议特性对域间路由空间的伸缩特性的潜在影响。
This document is the outcome of a collaborative exercise on the part of the Internet Architecture Board.
本文件是互联网体系结构委员会合作实践的成果。
Table of Contents
目录
1. Introduction................................................. 2
2. Network Scaling and Inter-Domain Routing ................... 2
3. Measurements of the total size of the BGP Table ............ 4
4. Related Measurements derived from BGP Table ................ 7
5. Current State of inter-AS routing in the Internet .......... 11
6. Future Requirements for the Exterior Routing System ........ 14
7. Architectural Approaches to a scalable Exterior
Routing Protocol........................................... 15
8. Directions for Further Activity ............................ 21
9. Security Considerations .................................... 22
10. References ................................................. 23
11. Acknowledgements ........................................... 24
12. Author's Address ........................................... 24
13. Full Copyright Statement ................................... 25
1. Introduction................................................. 2
2. Network Scaling and Inter-Domain Routing ................... 2
3. Measurements of the total size of the BGP Table ............ 4
4. Related Measurements derived from BGP Table ................ 7
5. Current State of inter-AS routing in the Internet .......... 11
6. Future Requirements for the Exterior Routing System ........ 14
7. Architectural Approaches to a scalable Exterior
Routing Protocol........................................... 15
8. Directions for Further Activity ............................ 21
9. Security Considerations .................................... 22
10. References ................................................. 23
11. Acknowledgements ........................................... 24
12. Author's Address ........................................... 24
13. Full Copyright Statement ................................... 25
This document examines the various longer term trends visible within the characteristics of the Internet's BGP table and identifies a number of operational practices and protocol factors that contribute to these trends. The potential impacts of these practices and protocol properties on the scaling properties of the inter-domain routing space are examined.
本文件审查了互联网BGP表特征中可见的各种长期趋势，并确定了促成这些趋势的一些操作实践和协议因素。研究了这些实践和协议特性对域间路由空间的伸缩特性的潜在影响。
These impacts include the potential for exhaustion of the existing Autonomous System number space, increasing convergence times for selection of stable alternate paths following withdrawal of route announcements, the stability of table entries, and the average prefix length of entries in the BGP table. The larger long term issue is that of an increasingly denser inter-connectivity mesh between ASes, causing a finer degree of granularity of inter-domain policy and finer levels of control to undertake inter-domain traffic engineering.
这些影响包括现有自治系统编号空间耗尽的可能性、路由公告撤销后选择稳定备用路径的收敛时间增加、表条目的稳定性以及BGP表中条目的平均前缀长度。更大的长期问题是，ASE之间的互连网格越来越密集，导致域间策略的粒度更细，域间流量工程的控制级别更高。
Various approaches to a refinement of the inter-domain routing protocol and associated operating practices that may provide superior scaling properties are identified as an area for further investigation.
对域间路由协议和相关操作实践进行改进的各种方法，可提供优越的扩展特性，被确定为进一步研究的领域。
This document is the outcome of a collaborative exercise on the part of the Internet Architecture Board.
本文件是互联网体系结构委员会合作实践的成果。
Are there inherent scaling limitations in the technology of the Internet or its architecture of deployment that may impact on the ability of the Internet to meet escalating levels of demand? There are a number of potential areas to search for such limitations. These include the capacity of transmission systems, packet switching capacity, the continued availability of protocol addresses, and the capability of the routing system to produce a stable view of the overall topology of the network. In this study we will look at this latter capability with the objective of identifying some aspects of the scaling properties of the Internet's routing system.
互联网技术或其部署架构是否存在固有的扩展限制，可能会影响互联网满足不断升级的需求的能力？有许多潜在的领域可以寻找这些限制。其中包括传输系统的容量、分组交换容量、协议地址的持续可用性，以及路由系统生成网络整体拓扑的稳定视图的能力。在这项研究中，我们将着眼于后一种能力，目的是确定互联网路由系统的扩展特性的某些方面。
The basic structure of the Internet is a collection of networks, or Autonomous Systems (ASes) that are interconnected to form a connected domain. Each AS uses an interior routing system to maintain a coherent view of the topology within the AS, and uses an exterior routing system to maintain adjacency information with neighboring ASes to create a view of the connectivity of the entire system.
互联网的基本结构是一组网络或自治系统（ASE），它们相互连接形成一个连接域。每个AS使用内部布线系统维护AS内拓扑的一致视图，并使用外部布线系统维护与相邻AS的邻接信息，以创建整个系统的连接视图。
This network-wide connectivity is described in the routing table used by the BGP4 protocol (referred to as the Routing Information Base, or RIB). Each entry in the table refers to a distinct route. The attributes of the route, together with local policy constraints, are used to determine the best path from the local AS to the AS that is originating the route. Determining the 'best path' in this case is determining which routing advertisement and associated next hop address is the most preferred by the local AS. Within each local BGP-speaking router this preferred route is then loaded into the local RIB (Loc-RIB). This information is coupled with information obtained from the local instance of the interior routing protocol to form a Forwarding Information Base (or FIB), for use by the local router's forwarding engine.
BGP4协议（称为路由信息库或RIB）使用的路由表中描述了这种网络范围的连接。表中的每个条目都指向一个不同的路由。路由的属性以及本地策略约束用于确定从本地AS到发起路由的AS的最佳路径。在这种情况下，确定“最佳路径”是确定哪个路由播发和关联的下一跳地址是本地AS最首选的。在每个本地BGP语音路由器内，该首选路由随后加载到本地RIB（Loc RIB）中。该信息与从内部路由协议的本地实例获得的信息耦合以形成转发信息库（或FIB），供本地路由器的转发引擎使用。
The BGP routing system is not aware of finer level of topology of the network on a link-by-link basis within the local AS or within any remote AS. From this perspective BGP can be seen as an inter-AS connectivity maintenance protocol, as distinct from a link-level topology management protocol, and the BGP routing table can be viewed as a description of the current connectivity of the Internet using an AS as the basic element of connectivity computation.
BGP路由系统不知道本地AS内或任何远程AS内的逐链路网络拓扑的更精细级别。从这个角度来看，BGP可被视为as间连接维护协议，与链路级拓扑管理协议不同，BGP路由表可被视为使用as作为连接计算基本元素的互联网当前连接的描述。
There is an associated dimension of policy determination within the routing table. If an AS advertises a route to a neighboring AS, the local AS is offering to accept traffic from the neighboring AS which is ultimately destined to addresses described by the advertised routing entry. If the local AS does not originate the route, then the inference is that the local AS is willing to undertake the role of transit provider for this traffic on behalf of some third party. Similarly, an AS may or may not choose to accept a route from a neighbor. Accepting a route implies that under some circumstances, as determined by the local route selection parameters, the local AS will use the neighboring AS to reach addresses spanned by the route. The BGP routing domain is intended to maintain a coherent view of the connectivity of the inter-AS domain, where connectivity is expressed as a preference for 'shortest paths' to reach any destination address as modulated by the connectivity policies expressed by each AS, and coherence is expressed as a global constraint that none of the paths contains loops or dead ends. The elements of the BGP routing domain are routing entries, expressed as a span of addresses. All addresses advertised within each routing entry share a common origin AS and a common connectivity policy. The total size of the BGP table is therefore a metric of the number of distinct routes within the Internet, where each route describes a contiguous set of addresses that share a common origin AS and a common reachability policy.
路由表中存在策略确定的关联维度。如果AS播发到相邻AS的路由，则本地AS提供接受来自相邻AS的流量，该流量最终将发送到播发的路由条目所描述的地址。如果本地AS不发起路线，则推断本地AS愿意代表某第三方承担该交通的运输提供商角色。类似地，AS可能会也可能不会选择接受来自邻居的路由。接受路由意味着在某些情况下，如本地路由选择参数所确定，本地as将使用相邻as来到达路由跨越的地址。BGP路由域旨在维护AS域间连接性的一致视图，其中连接性表示为到达任何目的地地址的“最短路径”偏好，由每个AS表示的连接性策略进行调制，一致性表示为一个全局约束，即所有路径都不包含循环或死角。BGP路由域的元素是路由条目，表示为地址范围。每个路由条目中公布的所有地址共享一个公共源AS和一个公共连接策略。因此，BGP表的总大小是Internet内不同路由数量的度量，其中每个路由描述了一组连续的地址，这些地址共享一个共同的源和一个共同的可达性策略。
When the scaling properties of the Internet were studied in the early 1990s two critical factors identified in the study were, not surprisingly, routing and addressing [2]. As more devices connect to the Internet they consume addresses, and the associated function of maintaining reachability information for these addresses, with an assumption of an associated growth in the number of distinct provider networks and the number of distinct connectivity policies, implies ever larger routing tables. The work in studying the limitations of the 32 bit IPv4 address space produced a number of outcomes, including the specification of IPv6 [3], as well as the refinement of techniques of network address translation [4] intended to allow some degree of transparent interaction between two networks using different address realms. Growth in the routing system is not directly addressed by these approaches, as the routing space is the cross product of the complexity of the inter-AS topology of the network, multiplied by the number of distinct connectivity policies multiplied by the degree of fragmentation of the address space. For example, use of NAT may reduce the pressure on the number of public addresses required by a single connected network, but it does not necessarily imply that the network's connectivity policies can be subsumed within the aggregated policy of a single upstream provider.
20世纪90年代初，当研究互联网的扩展特性时，研究中确定的两个关键因素是路由和寻址[2]。随着越来越多的设备连接到互联网，它们会使用地址，而保持这些地址的可达性信息的相关功能（假设不同提供商网络数量和不同连接策略数量的相关增长）意味着越来越大的路由表。研究32位IPv4地址空间限制的工作产生了许多成果，包括IPv6规范[3]，以及网络地址转换技术的改进[4]，旨在允许使用不同地址域的两个网络之间进行某种程度的透明交互。这些方法不能直接解决路由系统的增长问题，因为路由空间是网络内部as拓扑结构复杂性乘以不同连接策略的数量乘以地址空间碎片化程度的叉积。例如，使用NAT可以减少单个连接网络所需的公共地址数量的压力，但这并不一定意味着网络的连接策略可以包含在单个上游提供商的聚合策略中。
When an AS advertises a block of addresses into the exterior routing space this entry is generally carried across the entire exterior routing domain of the Internet. To measure the common characteristics of the global routing table, it is necessary to establish a point in the default-free part of the exterior routing domain and examine the BGP routing table that is visible at that point.
当AS向外部路由空间播发一个地址块时，该条目通常会在Internet的整个外部路由域中携带。要测量全局路由表的公共特征，必须在外部路由域的默认空闲部分中建立一个点，并检查在该点可见的BGP路由表。
Measurements of the size of the routing table were somewhat sporadic to start, and a number of measurements were taken at approximate monthly intervals from 1988 until 1992 by Merit [5]. This effort was resumed in 1994 by Erik-Jan Bos at Surfnet in the Netherlands, who commenced measuring the size of the BGP table at hourly intervals in 1994. This measurement technique was adopted by the author in 1997, using a measurement point located at the edge of AS 1221 at Telstra in Australia, again using an hourly interval for the measurement. The initial measurements were of the number of routing entries contained within the set of selected best paths. These measurements were expanded to include the number of AS numbers, number of AS paths, and a set of measurements relating to the prefix size of routing table entries.
路由表大小的测量在开始时有些零散，从1988年到1992年，Merit公司以大约每月一次的间隔进行了大量测量[5]。荷兰Surfnet的Erik Jan Bos于1994年恢复了这项工作，他于1994年开始每小时测量BGP表的大小。该测量技术由作者于1997年采用，使用位于澳大利亚Telstra AS 1221边缘的测量点，再次使用每小时一次的测量间隔。最初测量的是所选最佳路径集中包含的路由条目的数量。这些度量被扩展为包括AS编号的数量、AS路径的数量以及与路由表条目的前缀大小相关的一组度量。
This data contains a view of the dynamics of the Internet's routing table growth that spans some 13 years in total and includes a very detailed view spanning the most recent seven years [6]. Looking at just the total size of the BGP routing table over this period, it is possible to identify four distinct phases of inter-AS routing practice in the Internet.
这些数据包含了互联网路由表增长的动态视图，该视图总共跨越了约13年，并包含了一个跨越最近七年的非常详细的视图[6]。仅从这段时间内BGP路由表的总大小来看，就有可能确定Internet中inter AS路由实践的四个不同阶段。
The initial characteristics of the routing table size from 1988 until April 1994 show definite characteristics of exponential growth. If continued unchecked, this growth would have lead to saturation of the available BGP routing table space in the non-default routers of the time within a small number of years.
从1988年到1994年4月，路由表大小的初始特征显示出指数增长的明确特征。如果继续不加检查，这种增长将导致在不到几年的时间内，非默认路由器中可用的BGP路由表空间饱和。
Estimates of the time at which this would've happened varied somewhat from study to study, but the overall general theme of these observations was that the growth rates of the BGP routing table were exceeding the growth in hardware and software capability of the deployed network, and that at some point in the mid-1990's, the BGP table size would have grown to the point where it was larger than the capabilities of available equipment to support.
对发生这种情况的时间的估计因研究而异，但这些观察的总体主题是BGP路由表的增长率超过了已部署网络的硬件和软件能力的增长，并且在20世纪90年代中期的某个时候，BGP表的大小将增长到超过可用设备支持能力的程度。
The response from the engineering community was the introduction of a hierarchy into the inter-domain routing system. The intent of the hierarchical routing structure was to allow a provider to merge the routing entries for its customers into a single routing entry that spanned its entire customer base. The practical aspects of this change was the introduction of routing protocols that dispensed with the requirement for the Class A, B and C address delineation, replacing this scheme with a routing system that carried an address prefix and an associated prefix length. This approached was termed Classless Inter-Domain Routing (CIDR) [5].
工程界的反应是在域间路由系统中引入层次结构。分层路由结构的目的是允许提供商将其客户的路由条目合并为跨越其整个客户群的单个路由条目。这一变化的实际方面是引入了路由协议，免除了A类、B类和C类地址划分的要求，用带有地址前缀和相关前缀长度的路由系统取代了该方案。这种方法被称为无类域间路由（CIDR）[5]。
A concerted effort was undertaken in 1994 and 1995 to deploy CIDR routing in the Internet, based on encouraging deployment of the CIDR-capable version of the BGP protocol, BGP4 [7].
1994年和1995年，在鼓励部署具有CIDR功能的BGP协议版本BGP4[7]的基础上，进行了协调一致的努力，在互联网上部署CIDR路由。
The intention of CIDR was one of hierarchical provider address aggregation, where a network provider was allocated an address block from an address registry, and the provider announced this entire block into the exterior routing domain as a single entry with a single routing policy. Customers of the provider were encouraged to use a sub-allocation from the provider's address block, and these smaller routing elements were aggregated by the provider and not directly passed into the exterior routing domain. During 1994 the
CIDR的意图是一种层次化的提供者地址聚合，其中网络提供者从地址注册表中分配一个地址块，提供者将整个地址块作为一个具有单一路由策略的单一条目发布到外部路由域中。鼓励提供商的客户使用来自提供商地址块的子分配，这些较小的路由元素由提供商聚合，而不是直接传递到外部路由域。1994年期间
size of the routing table remained relatively constant at some 20,000 entries as the growth in the number of providers announcing address blocks was matched by a corresponding reduction in the number of address announcements as a result of CIDR aggregation.
路由表的大小在大约20000个条目上保持相对稳定，因为由于CIDR聚合，公布地址块的提供商数量的增长与地址公告数量的相应减少相匹配。
For the next four years until the start of 1998, CIDR proved effective in damping unconstrained growth in the BGP routing table. During this period, the BGP table grew at an approximate linear rate, adding some 10,000 entries per year.
在接下来的四年中，直到1998年初，CIDR在抑制BGP路由表的无约束增长方面被证明是有效的。在此期间，BGP表以近似线性的速度增长，每年增加约10000个条目。
A close examination of the table reveals a greater level of stability in the routing system at this time. The short term (hourly) variation in the number of announced routes reduced, both as a percentage of the number of announced routes, and also in absolute terms. One of the other benefits of using large aggregate address blocks is that instability at the edge of the network is not immediately propagated into the routing core. The instability at the last hop is absorbed at the point where an aggregate route is used in place of a collection of more specific routes. This, coupled with widespread adoption of BGP route flap damping, was very effective in reducing the short term instability in the routing space during this period.
仔细检查该表可以发现，此时路由系统的稳定性更高。公布路线数量的短期（每小时）变化减少，无论是以公布路线数量的百分比还是以绝对值计算。使用大型聚合地址块的另一个好处是，网络边缘的不稳定性不会立即传播到路由核心。最后一跳的不稳定性在使用聚合路由代替更具体路由集合的点处被吸收。这一点，再加上广泛采用BGP路由襟翼阻尼，非常有效地减少了在此期间路由空间的短期不稳定性。
In late 1998 the trend of growth in the BGP table size changed radically, and the growth for the period 1998 - 2000 is again showing all the signs of a re-establishment of a growth trend with strong correlation to an exponential growth model. This change in the growth trend appears to indicate that pressure to use hierarchical address allocations and CIDR has been unable to keep pace with the levels of growth of the Internet, and some additional factors that impact the growth in the BGP table size have become more prominent in the Internet. This has lead to a growth pattern in the total size of the BGP table that has more in common with a compound growth model than a linear model. A good fit of the data for the period from January 1999 until December 2000 is a compound growth model of 42% growth per year.
1998年末，BGP表规模的增长趋势发生了根本性变化，1998-2000年期间的增长再次显示出与指数增长模型密切相关的增长趋势重新建立的所有迹象。这种增长趋势的变化似乎表明，使用分层地址分配和CIDR的压力已无法跟上互联网的增长水平，影响BGP表大小增长的其他一些因素在互联网上变得更加突出。这导致BGP表总大小的增长模式与复合增长模型比线性模型更为相似。1999年1月至2000年12月期间的数据很好地符合每年42%的复合增长模型。
An initial observation is that this growth pattern points to some weakening of the hierarchical model of connectivity and routing within the Internet. To identify the characteristics of this recent trend it is necessary to look at a number of related characteristics of the routing table.
一个初步的观察结果是，这种增长模式表明互联网内部连接和路由的层次模型有所削弱。为了确定这一最新趋势的特征，有必要查看路由表的一些相关特征。
BGP table size data for the first half of 2001 shows different trends at various measurement points in the Internet. Some measurement points where the local AS has a relative larger number of more specific routes show a steady state for the first half of 2001 with no appreciable growth, while other measurement points where the local AS has had a lower number of more specific routes initially show a continuation of table size growth. There are a number of commonly observed discontinuities in the data for 2001, corresponding to events where a significant number of more specific entries have been replaced by an encompassing aggregate prefix.
2001年上半年的BGP表格大小数据显示了互联网上不同测量点的不同趋势。局部AS具有相对较多数量的更具体路线的一些测量点显示2001年上半年处于稳定状态，没有明显增长，而局部AS具有较少数量的更具体路线的其他测量点最初显示表大小的持续增长。2001年的数据中存在许多常见的不连续性，对应于大量更具体的条目被包含的聚合前缀替换的事件。
The level of analysis of the BGP routing table has been extended in an effort to identify the factors contributing to this growth, and to determine whether this leads to some limiting factors in the potential size of the routing space. Analysis includes measuring the number of ASes in the routing system, and the number of distinct AS paths, the range of addresses spanned by the table and average span of each routing entry.
扩展了BGP路由表的分析级别，以确定导致这种增长的因素，并确定这是否会导致路由空间潜在大小的某些限制因素。分析包括测量路由系统中ASE的数量、不同AS路径的数量、表跨越的地址范围以及每个路由条目的平均跨度。
Each network that is multi-homed within the topology of the Internet and wishes to express a distinct external routing policy must use a unique AS number to associate its advertised addresses with such a policy. In general, each network is associated with a single AS, and the number of ASes in the default-free routing table tracks the number of entities that have unique routing policies. There are some exceptions to this, including large global transit providers with varying regional policies, where multiple ASes are associated with a single network, but such exceptions are relatively uncommon.
在Internet拓扑结构中具有多个主机且希望表示不同外部路由策略的每个网络都必须使用唯一的AS号将其公布的地址与此类策略相关联。通常，每个网络都与单个AS关联，默认自由路由表中的ASE数跟踪具有唯一路由策略的实体数。这方面也有一些例外情况，包括具有不同区域政策的大型全球运输提供商，其中多个ASE与单个网络相关联，但此类例外情况相对少见。
The number of unique ASes present in the BGP table has been tracked since late 1996, and the trend of AS number deployment over the past four years is also one that matches a compound growth model with a growth rate of 51% per year. As of the start of May 2001 there were some 10,700 ASes visible in the BGP table. At a continued rate of growth of 51% p.a., the 16 bit AS number space will be fully deployed by August 2005. Work is underway within the IETF to modify the BGP protocol to carry AS numbers in a 32-bit field. [8] While the protocol modifications are relatively straightforward, the major responsibility rests with the operations community to devise a transition plan that will allow gradual transition into this larger AS number space.
自1996年底以来，BGP表中存在的独特ASE的数量已被跟踪，过去四年中AS数量部署的趋势也符合复合增长模型，每年的增长率为51%。截至2001年5月初，BGP表中约有10700例ASE可见。以每年51%的持续增长率，16位AS数字空间将于2005年8月完全部署。IETF正在修改BGP协议，使其在32位字段中以数字形式携带。[8] 虽然协议修改相对简单，但主要责任在于运营部门设计一个过渡计划，允许逐步过渡到这个更大的数字空间。
It is also possible to track the total amount of address space advertised within the BGP routing table. At the start of 2001 the routing table encompassed 1,081,131,733 addresses, or some 25.17% of the total IPv4 address space, or 25.4% of the usable unicast public address space. By September 2001 this has growth to 1,123,124,472 addresses, or some 26% of the IPv4 address space. This has grown from 1,019,484,655 addresses in November 1999. However, there are a number of /8 prefixes that are periodically announced and withdrawn from the BGP table, and if the effects of these prefixes is removed, a compound growth model against the previous 12 months of data of this metric yields a best fit model of growth of 7% per year in the total number of addresses spanned by the routing table.
还可以跟踪BGP路由表中公布的地址空间总量。2001年初，路由表包含1081131733个地址，约占IPv4总地址空间的25.17%，或可用单播公共地址空间的25.4%。到2001年9月，这一数字已增长到1123124472个地址，约占IPv4地址空间的26%。从1999年11月的1019484655个地址增长到现在。然而，有许多/8前缀会定期公布并从BGP表中撤销，如果这些前缀的影响被消除，那么针对该度量的前12个月数据的复合增长模型将产生一个最佳拟合模型，即路由表跨越的地址总数每年增长7%。
Compared to the 42% growth in the number of routing advertisements, the growth in the amount of address space advertised is far lower. One possible explanation is that much of the growth of the Internet in terms of growth in the number of connected devices is occurring behind various forms of NAT gateways. In terms of solving the perceived finite nature of the address space identified just under a decade ago, this explanation would tend to indicate that the Internet appears so far to have embraced the approach of using NATs, irrespective of their various perceived functional shortcomings. [9] This explanation also supports the observation of smaller address fragments supporting distinct policies in the BGP table, as such small address blocks may encompass arbitrarily large networks located behind one or more NAT gateways. There are alternative explanations of this difference between the growth of the table and the growth of address space, including a trend towards discrete exterior routing policies being applied to finer address blocks.
与路由广告数量42%的增长相比，地址空间广告数量的增长要低得多。一种可能的解释是，就连接设备数量的增长而言，互联网的大部分增长都发生在各种形式的NAT网关后面。就解决不到十年前确定的地址空间的感知有限性而言，这一解释倾向于表明，迄今为止，互联网似乎已经接受了使用NAT的方法，而不管它们的各种感知功能缺陷如何。[9] 这一解释还支持在BGP表中观察支持不同策略的较小地址片段，因为这样的小地址块可能包含位于一个或多个NAT网关后面的任意大网络。对于表的增长和地址空间的增长之间的这种差异，有其他解释，包括离散外部路由策略应用于更精细地址块的趋势。
The intent of CIDR aggregation was to support the use of large aggregate address announcements in the BGP routing table. To confirm whether this is still the case the average span of each BGP announcement has been tracked for the past 12 months. The data indicates a decline in the average span of a BGP advertisement from 16,000 individual addresses in November 1999 to 12,100 in December 2000. As of September 2001 this span has been further reduced to an average 10,700 individual addresses per routing entry. This corresponds to an increase in the average prefix length from /18.03 to /18.44 by December 2000 and a /18.6 by September 2001. Separate observations of the average prefix length used to route traffic in operation networks in late 2000 indicate an average length of 18.1 [11]. This trend towards finer-grained entries in the routing table is potentially cause for concern, as it implies the increasing spread
CIDR聚合的目的是支持在BGP路由表中使用大型聚合地址公告。为了确认是否仍然如此，在过去12个月内，已跟踪了BGP每次公告的平均跨度。数据显示，BGP广告的平均跨度从1999年11月的16000个个人地址下降到2000年12月的12100个。截至2001年9月，这一跨度已进一步缩小到每个路由条目平均10700个单独地址。这相当于到2000年12月，平均前缀长度从/18.03增加到/18.44，到2001年9月，平均前缀长度从/18.6增加到/18.44。对2000年末运营网络中用于路由流量的平均前缀长度的单独观察表明，平均长度为18.1[11]。路由表中更细粒度条目的趋势可能会引起关注，因为这意味着分布越来越广
of traffic over greater numbers of increasingly smaller forwarding table entries. This, in turn, has implications for the design of high speed core routers, particularly when extensive use is made of a small number of very high speed cached forwarding entries within the switching subsystem of a router's design.
在越来越多越来越小的转发表条目上的通信量。这反过来又对高速核心路由器的设计产生影响，特别是在路由器设计的交换子系统中大量使用少量高速缓存转发条目时。
A similar observation can be made regarding the number of addresses advertised per AS. In December 1999 each AS advertised an average of 161,900 addresses (equivalent to a prefix length /14.69, and in January 2001 this average has fallen to 115,800 addresses, an equivalent prefix length of /15.18.
关于根据AS公布的地址数量，可以进行类似的观察。1999年12月，每个AS广告的平均地址数为161900个（相当于前缀长度/14.69），2001年1月，这一平均值下降到115800个地址，相当于前缀长度/15.18。
This points to increasingly finer levels of routing detail being announced into the global routing domain. This, in turn, supports the observation that the efficiencies of hierarchical routing structures are no longer being fully realized within the deployed Internet. Instead, increasingly finer levels of routing detail are being announced globally in the BGP tables. The most likely cause of this trend of finer levels of routing granularity is an increasingly dense interconnection mesh, where more networks are moving from a single-homed connection with hierarchical addressing and routing into multi-homed connections without any hierarchical structure. The spur for this increasingly dense connectivity mesh in the Internet may well be the declining unit costs of communications bearer services coupled with a common perception that richer sets of adjacencies yields greater levels of service resilience.
这意味着在全局路由域中公布的路由细节级别越来越精细。这反过来又支持了这样一种观察，即分层路由结构的效率在已部署的Internet中不再得到充分实现。取而代之的是，越来越精细的路由细节级别在BGP表中全局公布。这种路由粒度级别更细的趋势最可能的原因是互连网格越来越密集，越来越多的网络正在从具有分层寻址和路由的单宿连接转移到没有任何分层结构的多宿连接。互联网中这种日益密集的连接网的推动力很可能是通信承载服务的单位成本不断下降，再加上人们普遍认为更丰富的邻接集会产生更高水平的服务弹性。
In addition to looking at the average prefix length, the analysis of the BGP table also includes an examination of the number of advertisements of each prefix length.
除了查看平均前缀长度外，BGP表的分析还包括检查每个前缀长度的广告数量。
An extensive program commenced in the mid-nineties to move away from intense use of the Class C space and to encourage providers to advertise larger address blocks, as part of the CIDR effort. This has been reinforced by the address registries who have used provider allocation blocks that correspond to a prefix length of /19 and, more recently, /20.
九十年代中期开始了一项广泛的计划，以摆脱对C类空间的过度使用，并鼓励提供商宣传更大的地址块，作为CIDR工作的一部分。地址注册中心使用了与前缀长度/19和最近的前缀长度/20相对应的提供程序分配块，这一点得到了加强。
These measures were introduced in the mid-90's when there were some 20,000 - 30,000 entries in the BGP table. Some six years later in April 2001 it is interesting to note that of the 108,000 entries in the routing table, some 59,000 entries have a /24 prefix. In absolute terms the /24 prefix set is the fastest growing set in the BGP routing table. The routing entries of these smaller address blocks also show a much higher level of change on an hourly basis. While a large number of BGP routing points perform route flap
这些措施是在90年代中期引入的，当时BGP表中有大约20000-30000个条目。大约六年后的2001年4月，有趣的是，在路由表中的108000个条目中，大约59000个条目具有/24前缀。就绝对值而言，/24前缀集是BGP路由表中增长最快的集。这些较小地址块的路由条目每小时也显示出更高级别的变化。而大量的BGP路由点执行路由翻转
damping, nevertheless there is still a very high level of announcements and withdrawals of these entries in this particular area of the routing table when viewed using a perspective of route updates per prefix length. Given that the numbers of these small prefixes are growing rapidly, there is cause for some concern that the total level of BGP flux, in terms of the number of announcements and withdrawals per second may be increasing, despite the pressures from flap damping. This concern is coupled with the observation that, in terms of BGP stability under scaling pressure, it is not the absolute size of the BGP table that is of prime importance, but the rate of dynamic path re-computations that occur in the wake of announcements and withdrawals. Withdrawals are of particular concern due to the number of transient intermediate states that the BGP distance vector algorithm explores in processing a withdrawal. Current experimental observations indicate a typical convergence time of some 2 minutes to propagate a route withdrawal across the BGP domain. [10]
然而，当使用每个前缀长度的路由更新透视图查看时，在路由表的这个特定区域中，这些条目的通知和撤销仍然非常高。鉴于这些小前缀的数量正在迅速增长，有理由担心，尽管襟翼阻尼带来了压力，但就每秒的公告和撤回数量而言，BGP流量的总水平可能正在增加。这一担忧与以下观察结果相结合：就BGP在标度压力下的稳定性而言，最重要的不是BGP表的绝对大小，而是公告和撤销后发生的动态路径重新计算的速率。由于BGP距离向量算法在处理取款时探索的瞬态中间状态的数量，取款尤其令人关注。目前的实验观察表明，在BGP域中传播路由撤回的典型收敛时间约为2分钟。[10]
An increase in the density of the BGP mesh, coupled with an increase in the rate of such dynamic changes, does have serious implications in maintaining the overall stability of the BGP system as it continues to grow. The registry allocation policies also have had some impact on the routing table prefix distribution. The original registry practice was to use a minimum allocation unit of a /19, and the 10,000 prefix entries in the /17 to /19 range are a consequence of this policy decision. More recently, the allocation policy now allows for a minimum allocation unit of a /20 prefix, and the /20 prefix is used by some 4,300 entries as of January 2001, and in relative terms is one of the fastest growing prefix sets. The number of entries corresponding to very small address blocks (smaller than a /24), while small in number as a proportion of the total BGP routing table, is the fastest growing in relative terms. The number of /25 through /32 prefixes in the routing table is growing faster, in terms of percentage change, than any other area of the routing table. If prefix length filtering were in widespread use, the practice of announcing a very small address block with a distinct routing policy would have no particular beneficial outcome, as the address block would not be passed throughout the global BGP routing domain and the propagation of the associated policy would be limited in scope. The growth of the number of these small address blocks, and the diversity of AS paths associated with these routing entries, points to a relatively limited use of prefix length filtering in today's Internet. In the absence of any corrective pressure in the form of widespread adoption of prefix length filtering, the very rapid growth of global announcements of very small address blocks is likely to continue. In percentage terms, the set of prefixes spanning /25 to /32 show the largest growth rates.
BGP网格密度的增加，加上此类动态变化率的增加，在BGP系统持续增长的过程中，确实对维持其整体稳定性具有严重影响。注册表分配策略也对路由表前缀分布产生了一些影响。登记处最初的做法是使用a/19的最低分配单位，而/17至/19范围内的10000个前缀项是这一政策决定的结果。最近，分配政策现在允许最小分配单位为/20前缀，截至2001年1月，大约4300个条目使用/20前缀，相对而言，它是增长最快的前缀集之一。相对而言，与非常小的地址块（小于a/24）相对应的条目数量（占BGP路由表总数的比例）增长最快。就百分比变化而言，路由表中/25到/32前缀的数量增长速度快于路由表的任何其他区域。如果前缀长度过滤被广泛使用，宣布具有不同路由策略的非常小的地址块的实践将不会有特别有利的结果，因为地址块不会在全局BGP路由域中传递，并且相关策略的传播将在范围上受到限制。这些小地址块数量的增长，以及与这些路由条目相关的AS路径的多样性，表明在今天的互联网中前缀长度过滤的使用相对有限。在没有任何纠正压力的情况下，前缀长度过滤的广泛采用，非常小的地址块的全球公告很可能会继续快速增长。就百分比而言，跨越/25到/32的前缀集显示了最大的增长率。
With the CIDR routing structure it is possible to advertise a more specific prefix of an existing aggregate. The purpose of this more specific announcement is to punch a 'hole' in the policy of the larger aggregate announcement, creating a different policy for the specifically referenced address prefix.
使用CIDR路由结构，可以公布现有聚合的更具体前缀。此更具体的公告的目的是在较大的聚合公告的策略中打一个“洞”，为特定引用的地址前缀创建不同的策略。
Another use of this mechanism is to perform a rudimentary form of load balancing and mutual backup for multi-homed networks. In this model a network may advertise the same aggregate advertisement along each connection, but then advertise a set of specific advertisements for each connection, altering the specific advertisements such that the load on each connection is approximately balanced. The two forms of holes can be readily discerned in the routing table - while the approach of policy differentiation uses an AS path that is different from the aggregate advertisement, the load balancing and mutual backup configuration uses the same As path for both the aggregate and the specific advertisements. While it is difficult to understand whether the use of such more specific advertisements was intended to be an exception to a more general rule or not within the original intent of CIDR deployment, there appears to be very widespread use of this mechanism within the routing table. Some 59,000 advertisements, or 55% of the total number of routing table entries, are being used to punch policy holes in existing aggregate announcements. Of these the overall majority of some 42,000 routes use distinct AS paths, so that it does appear that this is evidence of finer levels of granularity of connection policy in a densely interconnected space. While long term data is not available for the relative level of such advertisements as a proportion of the full routing table, the growth level does strongly indicate that policy differentiation at a fine level within existing provider aggregates is a significant driver of overall table growth.
此机制的另一个用途是为多宿网络执行基本形式的负载平衡和相互备份。在该模型中，网络可沿每个连接播发相同的聚合播发，但随后为每个连接播发一组特定播发，从而改变特定播发，使得每个连接上的负载大致平衡。这两种形式的漏洞可以在路由表中很容易地识别出来——虽然策略差异化方法使用不同于聚合播发的AS路径，但负载平衡和相互备份配置使用相同的AS路径用于聚合播发和特定播发。虽然很难理解使用这种更具体的广告是否是为了作为更一般规则的例外，还是不符合CIDR部署的原始意图，但在路由表中似乎广泛使用了这种机制。大约59000个广告（占路由表条目总数的55%）用于在现有聚合公告中填补策略漏洞。其中，大约42000条路由中的绝大多数使用不同的AS路径，因此，这确实表明在紧密互联的空间中，连接策略的粒度级别更高。虽然长期数据不适用于此类广告的相对级别（作为完整路由表的一部分），但增长级别确实强烈表明，在现有提供商聚合中处于精细级别的策略差异是整个表增长的重要驱动因素。
The resumption of compound growth trends within the BGP table, and the associated aspects of finer granularity of routing entries within the table form adequate grounds for consideration of potential refinements to the Internet's exterior routing protocols and potential refinements to current operating practices of inter-AS connectivity. With the exception of the 16 bit AS number space, there is no particular finite limit to any aspect of the BGP table. The motivation for such activity is that a long term pattern of continued growth at current rates may once again pose a potential condition where the capacity of the available processors may be exceeded by some aspect of the Internet routing table.
BGP表内复合增长趋势的恢复，以及表内路由条目粒度更细的相关方面，构成了充分的理由来考虑对互联网外部路由协议的潜在改进以及对AS间连接的当前操作实践的潜在改进。除了16位作为数字空间外，BGP表的任何方面都没有特定的有限限制。此类活动的动机是，以当前速度持续增长的长期模式可能再次构成一种潜在条件，即可用处理器的容量可能会被互联网路由表的某些方面所超出。
The decreasing unit cost of communications bearers in many part of the Internet is creating a rapidly expanding market in exchange points and other forms of inter-provider peering. A model of extensive interconnection at the edges of the Internet is rapidly supplanting the deployment model of a single-homed network with a single upstream provider. The underlying deployment model of CIDR was that of a single-homed network, allowing for a strict hierarchy of supply providers. The business imperatives driving this denser mesh of interconnection in the Internet are substantial, and the casualty in this case is the CIDR-induced dampened growth of the BGP routing table.
在互联网的许多部分，通信承载者单位成本的下降正在创造一个交换点和其他形式的供应商间对等的迅速扩大的市场。互联网边缘广泛互连的模式正在迅速取代单一家庭网络和单一上游提供商的部署模式。CIDR的底层部署模型是单宿网络，允许严格的供应提供商层次结构。推动互联网中这种更密集的互联网络的业务需求是巨大的，而在这种情况下的牺牲品是CIDR导致的BGP路由表增长放缓。
It would appear that one of the major drivers of the recent growth of the BGP table is that of small networks, advertised as a /24 prefix entry in the routing table, multi-homing with a number of peers and upstream providers. In the appropriate environment where there are a number of networks in relatively close proximity, using peer relationships can reduce total connectivity costs, as compared to using a single upstream service provider. Equally significantly, multi-homing with a number of upstream providers is seen as a means of improving the overall availability of the service. In essence, multi-homing is seen as an acceptable substitute for upstream service resiliency. This has a potential side effect that when multi-homing is seen as a preferable substitute for upstream provider resiliency, the upstream provider cannot command a price premium for proving resiliency as an attribute of the provided service, and therefore has little economic incentive to spend the additional money required to engineer resiliency into the network. The actions of the network's multi-homed clients then become self-fulfilling. One way to characterize this behavior is that service resiliency in the Internet is becoming the responsibility of the customer, not the service provider.
BGP表最近增长的一个主要驱动因素似乎是小型网络，在路由表中以a/24前缀条目的形式宣传，与多个对等方和上游提供商进行多归属。在适当的环境中，与使用单个上游服务提供商相比，在相对接近的多个网络中，使用对等关系可以降低总连接成本。同样重要的是，与多个上游提供商的多归属被视为提高服务总体可用性的一种手段。本质上，多归属被视为上游服务弹性的可接受替代品。这有一个潜在的副作用，即当多归属被视为上游提供商弹性的首选替代品时，上游提供商无法要求额外的价格来证明弹性是所提供服务的一个属性，因此，几乎没有经济动机去花费额外的资金来将弹性引入网络。然后，网络的多主机客户端的操作将自我实现。描述这种行为的一种方式是，互联网上的服务弹性正在成为客户的责任，而不是服务提供商的责任。
In such an environment resiliency still exists, but rather than being a function of the bearer or switching subsystem, resiliency is provided through the function of the BGP routing system. The question is not whether this is feasible or desirable in the individual case, but whether the BGP routing system can scale adequately to continue to undertake this role.
在这样的环境中，弹性仍然存在，但不是承载或交换子系统的功能，而是通过BGP路由系统的功能提供弹性。问题不在于这在个别情况下是否可行或可取，而在于BGP路由系统是否能够充分扩展以继续承担这一角色。
Further driving this growth in the routing table is the use of selective advertisement of smaller prefixes along different paths in an effort to undertake traffic engineering within a multi-homed environment. While there is considerable effort being undertaken to develop traffic engineering tools within a single network using MPLS as the base flow management tool, inter-provider tools to achieve similar outcomes are considerably more complex when using such switching techniques.
路由表中这种增长的进一步驱动因素是使用沿不同路径的较小前缀的选择性广告，以便在多宿环境中进行流量工程。虽然在使用MPLS作为基本流管理工具的单个网络中开发流量工程工具的工作正在进行，但在使用此类交换技术时，实现类似结果的提供商间工具要复杂得多。
At this stage the only tool being used for inter-provider traffic engineering is that of the BGP routing table. Such use of BGP appears to place additional fine-grained prefixes into the routing table. This action further exacerbates the growth and stability pressures being placed on the BGP routing domain.
在这个阶段，用于提供商间流量工程的唯一工具是BGP路由表。这样使用BGP似乎会在路由表中添加额外的细粒度前缀。这一行动进一步加剧了BGP路由域的增长和稳定性压力。
There is considerable evidence of a lack of uniformity of operational practices within the inter-domain routing space. This includes the use and setting of prefix filters, the use and setting of route damping parameters and level of verification undertaken on BGP advertisements by both the advertiser and the recipient. There is some extent of 'noise' in the routing table where advertisements appear to be propagated well beyond their intended domain of applicability, and also where withdrawals and advertisements are not being adequately damped close to the origin of the route flap. This diversity of operating practices also extends to policies of accepting advertisements that are more specific advertisements of existing provider blocks.
大量证据表明，域间路由空间内的操作实践缺乏统一性。这包括前缀过滤器的使用和设置、路由阻尼参数的使用和设置以及广告商和接收者对BGP广告进行的验证级别。路由表中存在一定程度的“噪声”，其中广告的传播似乎远远超出了其预期的适用范围，并且取款和广告在接近路由的原点时没有得到充分的阻尼。运营实践的多样性还扩展到接受广告的政策，这些广告是现有提供商区块的更具体的广告。
The current growth factors at play in the BGP table are not easily susceptible to another round of CIDR deployment pressure within the operator community. The denser interconnectivity mesh, the increasing use of multi-homing with smaller address prefixes, the extension of the use of BGP to perform roles related to inter-domain traffic engineering and the lack of common operating practices all point to a continuation of the trend of growth in the total size of the BGP routing table, with this growth most apparent with advertisements of smaller address blocks, and an increasing trend for these small advertisements to be punching a connectivity policy 'hole' in an existing provider aggregate advertisement.
BGP表中当前的增长因素不容易受到运营商社区内另一轮CIDR部署压力的影响。更密集的互连网络、越来越多地使用具有更小地址前缀的多归属、扩展使用BGP来执行域间流量工程相关的角色以及缺乏通用操作实践，所有这些都表明BGP路由表的总大小继续呈增长趋势，这种增长在较小地址块的广告中表现得最为明显，并且这些小广告在现有提供商聚合广告中的连接性策略“漏洞”不断增加。
It may be appropriate to consider how to operate an Internet with a BGP routing table that has millions of small entries, rather than the expectation of a hierarchical routing space with at most tens of thousands of larger entries in the global routing table.
考虑如何使用具有数百万个小条目的BGP路由表来运行因特网，而不是期望在全局路由表中具有最多数万个较大条目的分层路由空间。
It is beyond the scope of this document to define a scalable inter-domain routing environment and associated routing protocols and operating practices. A more modest goal is to look at the attributes of routing systems as understood and identify those aspects of such systems that may be applicable to the inter-domain environment as a potential set of requirements for inter-domain routing tools.
定义一个可扩展的域间路由环境以及相关的路由协议和操作实践超出了本文档的范围。一个更温和的目标是查看所理解的路由系统的属性，并确定这些系统可能适用于域间环境的方面，作为域间路由工具的一组潜在需求。
The overall intent is scalability of the routing environment. Scalability can be expressed in many dimensions, including number of discrete network layer reachability entries, number of discrete route policy entries, level of dynamic change over a unit of time of these entries, time to converge to a coherent view of the connectivity of the network following changes, and so on.
总体目标是路由环境的可伸缩性。可伸缩性可以用许多维度表示，包括离散网络层可达性条目的数量、离散路由策略条目的数量、这些条目在一个时间单位内的动态变化水平、在变化后收敛到网络连通性一致视图的时间，等等。
The basic objective behind this expressed requirement for scalability is that the most likely near to medium trend in the structure of the Internet is a continuation in the pattern of dense interconnectivity between a large number of discrete network entities, and little impetus behind hierarchical aggregating structures. It is not an objective to place any particular metrics on scalability within this examination of requirements, aside from indicating that a prudent view would encompass a scale of connectivity in the inter-domain space that is at least two orders of magnitude larger than comparable metrics of the current environment.
这一明确的可扩展性要求背后的基本目标是，互联网结构中最有可能的接近中等的趋势是大量离散网络实体之间密集互连模式的延续，而分层聚合结构背后的推动力很小。除了表明审慎的观点将包括域间空间中的连通性规模，该规模至少比当前环境的可比指标大两个数量级之外，将任何特定的可伸缩性指标放在需求检查中不是目的。
Any routing system should behave in a stable and predictable fashion. What is inferred from the predictability requirement is the behavior that under identical environmental conditions the routing system should converge to the same state. Stability implies that the routing state should be maintained for as long as the environmental conditions remain constant. Stability also implies a qualitative property that minor variations in the network's state should not cause large scale instability across the entire network while a new stable routing state is reached. Instead, routing changes should be propagated only as far as necessary to reach a new stable state, so that the global requirement for stability implies some degree of locality in the behavior of the system.
任何路由系统都应该以稳定和可预测的方式运行。根据可预测性要求推断，在相同的环境条件下，路由系统应收敛到相同的状态。稳定性意味着只要环境条件保持不变，路由状态就应保持不变。稳定性还意味着一种定性属性，即当达到新的稳定路由状态时，网络状态的微小变化不应导致整个网络的大规模不稳定。相反，路由更改应该只传播到达到新的稳定状态所需的范围内，以便全局稳定性要求意味着系统行为的某种程度的局部性。
Any routing system should have adequate convergence properties. By adequate it is implied that within a finite time following a change in the external environment, the routing system will have reached a shared common description of the network's topology that accurately describes the current state of the network and is stable. In this case finite time implies a time limit that is bounded by some upper limit, and this upper limit reflects the requirements of the routing system. In the case of the Internet this convergence time is currently of the order of hundreds of seconds as an upper bound on convergence. This long convergence time is perceived as having a negative impact on various applications, particularly those that are time critical. A more useful upper bound for convergence is of the order of seconds or lower if it is desired to support a broad range of application classes.
任何路由系统都应该具有足够的收敛性。通过适当的分析，这意味着在外部环境发生变化后的有限时间内，路由系统将达到网络拓扑的共享公共描述，该描述准确地描述了网络的当前状态，并且是稳定的。在这种情况下，有限时间意味着一个由某个上限限定的时间限制，该上限反映了路由系统的要求。就互联网而言，这种收敛时间目前大约为数百秒，是收敛的上限。这种长的收敛时间被认为对各种应用程序，特别是那些时间关键的应用程序有负面影响。如果希望支持广泛的应用程序类，则更有用的收敛上限为秒或更低。
It is not a requirement to be able to undertake full convergence of the inter-domain routing system in the sub-second timescale.
不要求能够在亚秒的时间尺度上实现域间路由系统的完全收敛。
The greater the amount of information passed within the routing system, and the greater the frequency of such information exchanges, the greater the level of expectation that the routing system can maintain an accurate view of the connectivity of the network. Equally, the greater the amount of information passed within the routing system, and the higher the frequency of information exchange, the higher the level of overhead consumed by operation of the routing system. There is an element of design compromise in a routing system to pass enough information across the system to allow each routing element to have adequate local information to reach a coherent local view of the network, yet ensure that the total routing overhead is low.
路由系统内传递的信息量越大，此类信息交换的频率越高，路由系统能够保持网络连接的准确视图的期望水平就越高。同样，在路由系统内传递的信息量越大，信息交换的频率越高，路由系统运行消耗的开销水平就越高。路由系统中存在一个设计折衷因素，即在整个系统中传递足够的信息，以允许每个路由元素具有足够的本地信息，以达到网络的一致本地视图，同时确保总路由开销较低。
This document does not attempt to define an inter-domain routing protocol that possess all the attributes as listed above, but a number of architectural considerations can be identified that would form an integral part of the protocol design process.
本文档并不试图定义具有上述所有属性的域间路由协议，但可以确定构成协议设计过程不可分割的一部分的许多体系结构考虑因素。
The two major approaches to routing protocols are distance vector and link state.
路由协议的两种主要方法是距离向量和链路状态。
In the distance vector protocol a routing node gathers information from its neighbors, applies local policy to this information and then distributes this updated information to its neighbors. In this model the nature of the local policy applied to the routing information is not necessarily visible to the node's neighbors, and the process of converting received route advertisements into advertised route advertisements uses a local policy process whose policy rules are not visible externally. This scenario can be described as 'policy opaque'. The side effect of such an environment is that a third party cannot remotely compute which routes a network may accept and which may be re-advertised to each neighbor.
在距离向量协议中，路由节点从其邻居收集信息，对该信息应用本地策略，然后将更新后的信息分发给其邻居。在该模型中，应用于路由信息的本地策略的性质不一定对节点的邻居可见，并且将接收的路由播发转换为播发的路由播发的过程使用其策略规则在外部不可见的本地策略过程。此场景可以描述为“策略不透明”。这种环境的副作用是，第三方无法远程计算网络可以接受哪些路由，哪些路由可以重新通告给每个邻居。
In link state protocols a routing node effectively broadcasts its local adjacencies, and the policies it has with respect to these adjacencies, to all nodes within the link state domain. Every node can perform an identical computation upon this set of adjacencies and associated policies in order to compute the local forwarding table. The essential attribute of this environment is that the routing node has to announce its routing policies, in order to allow a remote node to compute which routes will be accepted from which neighbor, and which routes will be advertised to each neighbor and what, if any, attributes are placed on the advertisement. Within an interior routing domain the local policies are in effect metrics of each link and these polices can be announced within the routing domain without any consequent impact.
在链路状态协议中，路由节点有效地向链路状态域内的所有节点广播其本地邻接及其与这些邻接相关的策略。为了计算本地转发表，每个节点都可以对这组邻接和相关策略执行相同的计算。该环境的基本属性是路由节点必须宣布其路由策略，以便允许远程节点计算哪些路由将从哪个邻居接受，哪些路由将播发给每个邻居，以及播发上放置了哪些属性（如果有的话）。在内部路由域中，本地策略实际上是每个链路的度量，这些策略可以在路由域中宣布，而不会产生任何后续影响。
In the exterior routing domain it is not the case that interconnection policies between networks are always fully transparent. Various permutations of supplier / customer relationships and peering relationships have associated policy qualifications that are not publicly announced for business competitive reasons. The current diversity of interconnection arrangements appears to be predicated on policy opaqueness, and to mandate a change to a model of open interconnection policies may be contrary to operational business imperatives.
在外部路由域中，网络之间的互连策略并不总是完全透明的。供应商/客户关系和对等关系的各种排列具有相关的政策资格，但由于业务竞争原因，这些资格未公开宣布。当前互联安排的多样性似乎是基于政策不透明性，强制改变开放互联政策模式可能违反运营业务要求。
An inter-domain routing tool should be able to support models of interconnection where the policy associated with the interconnection is not visible to any third party. If the architectural choice is a constrained one between distance vector and link state, then this consideration would appear to favor the continued use of a distance vector approach to inter-domain routing. This choice, in turn, has implications on the convergence properties and stability of the inter-domain routing environment. If there is a broader spectrum of choice, the considerations of policy-opaqueness would still apply.
域间路由工具应该能够支持与互连相关的策略对任何第三方都不可见的互连模型。如果架构选择是距离向量和链路状态之间的受限选择，那么这种考虑似乎有利于继续使用距离向量方法进行域间路由。这种选择反过来会影响域间路由环境的收敛性和稳定性。如果有更广泛的选择，政策不透明性的考虑仍然适用。
The current issues with the trend behaviors of the BGP space can be coarsely summarized as the growth in the number of distinct routing objects, the increased level of dynamic behaviors of these objects (in the form of announcements and withdrawals).
BGP空间趋势行为的当前问题可以粗略地概括为不同路由对象数量的增长，这些对象动态行为水平的提高（以公告和撤回的形式）。
This entails evaluating possible measures that can address the growth rate in the number of objects in the inter-domain routing table, and separately examining measures that can reduce the level of dynamic change in the routing table. The current routing architecture defines a basic unit of a route object as an originating AS number and an address prefix.
这需要评估可解决域间路由表中对象数量增长率的可能措施，并单独检查可降低路由表中动态变化水平的措施。当前路由体系结构将路由对象的基本单元定义为原始as编号和地址前缀。
In looking at the growth rate in the number of route objects, the salient observation is that the number of route objects is the byproduct of the density of the interconnection mesh and the number of discrete points where policy is imposed of route objects. One approach to reduce the growth in the number of objects is to allow each object to describe larger segments of infrastructure. Such an approach could use a single route object to describe a set of address prefixes, or a collection of ASs, or a combination of the two. The most direct form of extension would be to preserve the assumption that each routing object represents an indivisible policy entity. However, given that one of the drivers of the increasing number of route objects is a proliferation of discrete route objects, it is not immediately apparent that this form of aggregation will prove capable in addressing the growth in the number of route objects.
在查看路由对象数量的增长率时，最显著的观察结果是路由对象的数量是互连网格密度和路由对象施加策略的离散点数量的副产品。减少对象数量增长的一种方法是允许每个对象描述基础设施的更大部分。这种方法可以使用单个路由对象来描述一组地址前缀、ASs集合或两者的组合。最直接的扩展形式是保留每个路由对象表示不可分割的策略实体的假设。然而，考虑到路由对象数量不断增加的驱动因素之一是离散路由对象的激增，这种形式的聚合是否能够解决路由对象数量的增长还不是很明显。
If single route objects are to be used that encompass a set of address prefixes and a collection of ASs, then it appears necessary to define additional attributes within the route object to further qualify the policies associated with the object in terms of specific prefixes, specific ASs and specific policy semantics that may be considered as policy exceptions to the overall aggregate
如果要使用包含一组地址前缀和ASs集合的单路由对象，则似乎有必要在路由对象内定义其他属性，以进一步根据特定前缀限定与对象关联的策略，特定ASs和特定策略语义，可被视为总体聚合的策略例外
Another approach to reduce the number of route objects is to reduce the scope of advertisement of each routing object, allowing the object to be removed and proxy aggregated into some larger object once the logical scope of the object has been reached. This approach would entail the addition of route attributes that could be used to define the circumstances where a specific route object would be subsumed by an aggregate route object without impacting the policy objectives associated with the original set of advertisements.
减少路由对象数量的另一种方法是减少每个路由对象的播发范围，一旦到达对象的逻辑范围，就允许删除该对象并将其代理聚合为某个更大的对象。这种方法需要添加路由属性，这些属性可用于定义特定路由对象将被聚合路由对象包含的情况，而不会影响与原始广告集相关的策略目标。
Attempting to place greater levels of detail into route objects is intended to address the dual role of the current BGP system as both an inter-domain connectivity maintenance protocol and as an implicit traffic engineering tool.
试图在路由对象中放置更高级别的细节旨在解决当前BGP系统作为域间连接维护协议和隐式流量工程工具的双重作用。
In the current environment, advertisement of more specific prefixes with unique policy but with the same origin AS is often intended to create a traffic engineering response, where incoming traffic to an AS may be balanced across multiple paths. The outcome is that the control of the relative profile of load is placed with the originating AS. The way this is achieved is by using limited knowledge of the remote AS's route selection policy to explicitly limit the number of egress choices available to a remote AS. The most common route selection policy is the preference for more specific prefixes over larger address blocks. By advertising specific prefixes along specific neighbor AS connections with specific route attributes, traffic destined to these addresses is passed through the selected transit paths. This limitation of choice allows the originating AS to override the potential policy choices of all other ASs, imposing its traffic import policies at a higher level than the remote AS's egress policies.
在当前环境中，具有唯一策略但具有相同来源的更具体前缀的广告通常旨在创建流量工程响应，其中AS的传入流量可以跨多条路径平衡。结果是，荷载的相对剖面控制与原始AS一起放置。实现这一点的方法是使用远程AS的路由选择策略的有限知识来明确限制远程AS可用的出口选择数量。最常见的路由选择策略是优先选择更具体的前缀，而不是更大的地址块。通过将特定的前缀作为具有特定路由属性的连接沿特定的邻居发布，目的地为这些地址的流量通过选定的传输路径。这种选择限制允许始发AS覆盖所有其他ASs的潜在策略选择，将其流量导入策略施加在比远程AS的出口策略更高的级别上。
An alternative approach is the use of a class of traffic engineering attributes that are attached to an aggregate route object. The intent of such attributes is to direct each remote AS to respond to the route object in a manner that equates to the current response to more specific advertisements, but without the need to advertise specific prefix route objects. However, even this approach uses route objects to communicate traffic engineering policy, and the same risk remains that the route table is used to carry fine-detailed traffic path policies.
另一种方法是使用附加到聚合路由对象的一类流量工程属性。这些属性的目的是指示每个远程设备以等同于对更具体的播发的当前响应的方式响应路由对象，但不需要播发特定的前缀路由对象。然而，即使这种方法使用route对象来传达流量工程策略，同样的风险仍然是使用route表来承载详细的流量路径策略。
An alternative direction is to separate the functions of connectivity maintenance and traffic engineering, using the routing protocol to identify a number of viable paths from a source AS to a destination AS, and use a distinct collection of traffic engineering tools to allow a traffic source AS to make egress path selections that match the desired traffic service profile for the traffic.
另一个方向是分离连接维护和流量工程的功能，使用路由协议识别从源AS到目标AS的多条可行路径，以及使用不同的流量工程工具集合来允许流量源进行出口路径选择，该出口路径选择与该流量的期望流量服务配置文件相匹配。
There is one critical difference between traffic engineering approaches as used in intra-domain environments and the current inter-domain operating practices. Whereas the intra-domain environment uses the ingress network element to make the appropriate path choice to the egress point, the inter domain traffic engineering has the opposite intent, where a downstream AS (or egress point) is attempting to influence the path choice of an upstream AS (or ingress
域内环境中使用的流量工程方法与当前域间操作实践之间存在一个关键区别。尽管域内环境使用入口网元来做出到出口点的适当路径选择，但域间流量工程具有相反的意图，其中下游AS（或出口点）正试图影响上游AS（或入口）的路径选择
point). If explicit traffic engineering were undertaken within the inter-domain space, it is highly likely that the current structure would be altered. Instead of the downstream element attempting to constrain the path choices of an upstream element, a probable approach is the downstream element placing a number of advisory constraints on the upstream elements, and the upstream elements using a combination of these advisory constraints, dynamic information relating to path service characteristics and local policies to make an egress choice.
点）。如果在域间空间内进行显式流量工程，则当前结构极有可能发生改变。与下游元件试图约束上游元件的路径选择不同，一种可能的方法是下游元件在上游元件上放置多个咨询约束，上游元件使用这些咨询约束的组合，与路径服务特征和本地策略相关的动态信息，以进行出口选择。
From the perspective of the inter-domain routing environment, such measures offer the potential to remove the advertisement of specific routes for traffic engineering purposes. However, there is a need to adding traffic engineering information into advertised route blocks, requiring the definition of the syntax and semantics of traffic engineering attributes that can be attached to route objects.
从域间路由环境的角度来看，这些措施提供了为流量工程目的删除特定路由广告的可能性。但是，需要将流量工程信息添加到公布的路由块中，需要定义可附加到路由对象的流量工程属性的语法和语义。
The CIDR routing model assumed a hierarchy of providers, where at each level in the hierarchy the routing policies and address space of networks at the lower level of hierarchy were subsumed by the next level up (or 'upstream') provider. The connectivity policy assumed by this model is also a hierarchical model, where horizontal connections within a single level of the hierarchy are not visible beyond the networks of the two parties.
CIDR路由模型假设了一个提供者的层次结构，在该层次结构的每一级，较低层次结构的路由策略和网络地址空间都被下一级（或“上游”）提供者所包含。该模型假设的连接策略也是一个层次模型，其中层次结构的单个层次内的水平连接在双方的网络之外不可见。
A number of external factors are increasing the density of interconnection including decreasing unit costs of communications services and the increasing use of exchange points to augment point-to-point connectivity models with point-to-multi-point facilities.
许多外部因素正在增加互连密度，包括降低通信服务的单位成本，以及增加使用交换点来增加点对点连接模型和点对多点设施。
The outcome of these external factors is a significant reduction in the hierarchical nature of the inter-domain space. Such a trend can be viewed with concern given the common approach of using hierarchies as a tool for scaling routing systems. BGP falls within this approach, and relies on hierarchies in the address space to contain the number of independently routing objects. The outcomes of this characteristic of the Internet in terms of the routing space is the increasing number of distinct route policies that are associated with each multi-homed network within the Internet.
这些外部因素的结果是显著降低了域间空间的层次性。考虑到使用层次结构作为扩展路由系统的工具的常用方法，可以关注这种趋势。BGP属于这种方法，它依赖于地址空间中的层次结构来包含独立路由对象的数量。就路由空间而言，互联网这一特性的结果是，与互联网内每个多宿网络相关联的不同路由策略的数量不断增加。
One way to limit the proliferation of such policies across the entire inter-domain space is to associate attributes to such advertisements that specify the conditions whereby a remote transit AS may proxy-aggregate this route object with other route objects.
限制此类策略在整个域间空间扩散的一种方法是将属性与此类广告相关联，这些广告指定远程传输代理将此路由对象与其他路由对象聚合的条件。
A final consideration is to consider whether these requirements can best be met by an approach of a set of upward-compatible extensions to BGP, or by a replacement to BGP. No recommendation is made here, and this is a topic requiring further investigation.
最后的考虑是考虑这些需求是否可以通过一组向上兼容的扩展到BGP的方法来满足，或者通过替换BGP来满足。这里没有提出建议，这是一个需要进一步调查的主题。
The general approach in extending BGP appears to lie in increasing the number of supported transitive route attributes, allowing the route originator greater control in specifying the scope of propagation of the route and the intended outcome in terms of policy and traffic engineering. It may also be necessary to allow BGP sessions to negotiate additional functionality intended to improve the convergence behavior of the protocol. Whether such changes can produce a scalable and useful outcome in terms of inter-domain routing remains, at this stage, an open question.
扩展BGP的一般方法似乎在于增加受支持的可传递路由属性的数量，允许路由发起者在指定路由的传播范围以及策略和流量工程方面的预期结果方面拥有更大的控制权。可能还需要允许BGP会话协商旨在改进协议收敛行为的附加功能。在现阶段，就域间路由而言，这些变化是否能够产生可扩展和有用的结果仍然是一个悬而未决的问题。
An alternative approach is that of a replacement protocol, and such an approach may well be based on the adoption of a link-state behavior. The issues of policy opaqueness and link-state protocols have been described above. The other major issue with such an approach is the need to limit the extent of link state flooding, where the inter-domain space would need some further levels of imposed structure similar to intra-domain areas. Such structure may well imply the need for an additional set of operator inter-relationships such as mutual transit, and this may prove challenging to adapt to existing practices.
另一种方法是替换协议，这种方法很可能基于采用链路状态行为。上面已经描述了策略不透明性和链路状态协议的问题。这种方法的另一个主要问题是需要限制链路状态泛洪的程度，其中域间空间将需要一些类似于域内区域的附加结构的进一步级别。这种结构很可能意味着需要一组额外的运营商相互关系，如相互运输，这可能证明难以适应现有实践。
The potential sets of actions include more than extend or replace the BGP protocol. A third approach is to continue to use BGP as the basic means of propagating route objects and their associated AS paths and other attributes, and use one or more overlay protocols to support inter-domain traffic engineering and other forms of inter-domain policy negotiation. This approach would appear to offer a means of transition for the large installed base currently using BGP4 as their inter-domain routing protocol, placing additional functionality in the overlay protocols while leaving the basic functionality of BGP4 intact. The resultant inter-dependencies between BGP and the overlay protocols would require very careful attention, as this would be the most critical aspect of such an approach.
可能采取的措施不只是扩展或替换BGP协议。第三种方法是继续使用BGP作为传播路由对象及其关联的as路径和其他属性的基本手段，并使用一个或多个覆盖协议来支持域间流量工程和其他形式的域间策略协商。这种方法似乎为目前使用BGP4作为域间路由协议的大型安装群提供了一种过渡方式，在覆盖协议中添加了附加功能，同时保留了BGP4的基本功能。BGP和覆盖协议之间产生的相互依赖性需要非常仔细的注意，因为这是这种方法最关键的方面。
While there may exist short term actions based on providing various incentives for network operators to remove redundant or inefficiently grouped entries from the BGP routing table, such actions are short term palliative measures, and will not provide long term answers to the need to a scalable inter-domain routing protocol.
虽然可能存在短期行动，其基础是为网络运营商提供各种激励，以从BGP路由表中删除冗余或无效分组的条目，但此类行动是短期缓解措施，不会为可扩展域间路由协议的需要提供长期答案。
One potential short term protocol refinement is to allow a set of grouped advertisements to be aggregated into a single route advertisement. This form of proxy aggregation would take a set of bit-wise aligned routing entries with matching route attributes, and under certain well identified circumstances, aggregate these routing entries into a single re-advertised aggregate routing entry. This technique removes information from the routing system, and some care must be taken to define a set of proxy aggregation conditions that do not materially alter the flow of traffic, or the ability of originating ASes to announce routing policy.
一种潜在的短期协议改进是允许将一组分组广告聚合为单个路由广告。这种形式的代理聚合将采用一组具有匹配路由属性的按位对齐的路由条目，并在某些确定的情况下，将这些路由条目聚合为单个重新公布的聚合路由条目。这种技术从路由系统中删除信息，并且必须注意定义一组代理聚合条件，这些条件不会实质性地改变流量或原始ASE宣布路由策略的能力。
A further refinement to this approach is to consider the definition of the syntax and semantics of a number of additional route attributes. Such attributes could define the extent to which specific route advertisements should be propagated in the inter-domain space, allowing the advertisement to be subsumed by a larger aggregate advertisement at the boundary of this domain. This could be used to form part of the preconditions of automated proxy aggregation of specific routes, and also limit the extent to which announcement and withdrawals are propagated across the routing domain.
这种方法的进一步改进是考虑多个附加路由属性的语法和语义的定义。此类属性可定义特定路由广告应在域间空间中传播的程度，从而允许广告被该域边界处的较大聚合广告所包含。这可用于构成特定路由的自动代理聚合的先决条件的一部分，还可限制通知和撤回在路由域中传播的程度。
It is unclear that such measures would result in substantial longer term changes to the scaling and convergence properties of BGP4. Taking the requirement set enumerated in section 6 of this document, one approach to the longer term requirements may be to preserve a number of attributes of the current BGP protocol, while refine other aspects of the protocol to improve its scaling and convergence properties. A minimal set of alterations could retain the Autonomous System concept to allow for boundaries of information summarization, as well as retaining the approach of associating each prefix advertisement with an originating AS. The concept of policy opaqueness would also be retained in such an approach, implying that each AS accepts a set of route advertisements, applies local policy constraints, and re-advertises those advertisements permitted by the local policy constraints. It could be feasible to consider alterations to the distance vector path selection algorithm, particularly as it relates to intermediate states during processing of a route withdrawal. It is also feasible to consider the use of compound route attributes, allowing a route object to include an
目前尚不清楚这些措施是否会导致BGP4的标度和收敛特性发生实质性的长期变化。考虑到本文件第6节中列举的需求集，解决长期需求的一种方法可能是保留当前BGP协议的一些属性，同时改进协议的其他方面，以改进其伸缩性和收敛性。一组最小的变更可以保留自主系统概念，以允许信息摘要的边界，并且保留将每个前缀广告与源as关联的方法。这种方法也将保留政策不透明的概念，这意味着每个AS都接受一组路线广告，应用当地政策约束，并重新发布当地政策约束允许的广告。考虑距离矢量路径选择算法的改变是可行的，特别是在路由撤回处理过程中涉及到中间状态。考虑使用复合路由属性也是可行的，允许路由对象包括
aggregate route, and a number of specifics of the aggregate route, and attach attributes that may apply to the aggregate or a specific address prefix. Such route attributes could be used to support multi-homing and inter-domain traffic engineering mechanisms. The overall intent of this approach is to address the major requirements in the inter-domain routing space without using an increasing set of globally propagated specific route objects.
聚合路由和聚合路由的许多细节，并附加可能应用于聚合或特定地址前缀的属性。这种路由属性可用于支持多归属和域间流量工程机制。这种方法的总体目的是解决域间路由空间中的主要需求，而不使用越来越多的全局传播的特定路由对象。
A potential applied research topic is to consider the feasibility of de-coupling the requirements of inter-domain connectivity management with the applications of policy constraints and the issues of sender-and/or receiver-managed traffic engineering requirements. Such an approach may use a link-state protocol as a means of maintaining a consistent view of the topology of inter-domain network, and then use some form of overlay protocol to negotiate policy requirements of each AS, and use a further overlay to support inter-domain traffic engineering requirements. The underlying assumption of such an approach is that by dividing up the functional role of inter-domain routing into distinct components each component will have superior scaling and convergence properties which in turn to result in superior properties for the entire routing system. Obviously, this assumption requires some testing.
一个潜在的应用研究课题是考虑域间连通性管理的需求与策略约束的应用以及发送者和/或接收者管理的流量工程需求的问题的可行性。这种方法可以使用链路状态协议作为维护域间网络拓扑的一致视图的手段，然后使用某种形式的覆盖协议来协商每个as的策略需求，并使用进一步的覆盖来支持域间流量工程需求。这种方法的基本假设是，通过将域间路由的功能角色划分为不同的组件，每个组件都将具有优越的可伸缩性和收敛性，从而使整个路由系统具有优越的性能。显然，这一假设需要一些测试。
Research topics with potential longer term application include the approach of drawing a distinction between a network's identity, a network's location relative to other networks, and a feasible path between a source and destination network that satisfies various policy and traffic engineering constraints. Again the intent of such an approach would be to divide the current routing function into a number of distinct scalable components.
具有潜在长期应用的研究主题包括区分网络身份、网络相对于其他网络的位置以及满足各种策略和流量工程约束的源和目标网络之间的可行路径的方法。同样，这种方法的目的是将当前路由功能划分为若干不同的可伸缩组件。
Any adopted inter-domain routing protocol needs to be secure against disruption. Disruption comes from two primary sources:
任何采用的域间路由协议都需要安全，以防中断。中断来自两个主要来源：
- Accidental misconfiguration - Malicious attacks
- 意外配置错误-恶意攻击
Given past experience with routing protocols, both can be significant sources of harm.
鉴于过去在路由协议方面的经验，两者都可能是重大的危害源。
Given that it is not reasonable to guarantee the security of all the routers involved in the global Internet inter-domain routing system, there is also every reason to believe that malicious attacks may come from peer routers, in addition to coming from external sources.
考虑到保证全球互联网域间路由系统中涉及的所有路由器的安全是不合理的，因此有充分的理由相信恶意攻击除了来自外部来源外，还可能来自对等路由器。
A protocol design should therefore consider how to minimize the damage to the overall routing computation that can be caused by a single or small set of misbehaving routers.
因此，协议设计应该考虑如何最小化由单个或小组不当路由器引起的整体路由计算的损坏。
The routing system itself needs to be resilient against accidental or malicious advertisements of a route object by a route server not entitled to generate such an advertisement. This implies several things, including the need for cryptographic validation of announcements, cryptographic protection of various critical routing messages and an accurate and trusted database of routing assignments via which authorization can be checked.
路由系统本身需要能够抵抗路由服务器对路由对象的意外或恶意广告，该路由服务器无权生成此类广告。这意味着几件事，包括需要对公告进行加密验证，对各种关键路由消息进行加密保护，以及建立一个准确可靠的路由分配数据库，通过该数据库可以检查授权。
[1] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996.
[1] Bradner，S.，“互联网标准过程——第3版”，BCP 9，RFC 2026，1996年10月。
[2] Clark, D., Chapin, L., Cerf, V., Braden, R. and R. Hobby, "Towards the Future Internet Architecture", RFC 1287, December 1991.
[2] Clark，D.，Chapin，L.，Cerf，V.，Braden，R.和R.Hobby，“走向未来的互联网架构”，RFC 12871991年12月。
[3] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification, RFC 2460, December 1998.
[3] Deering，S.和R.Hinden，“互联网协议，第6版（IPv6）规范，RFC 2460，1998年12月。
[4] Srisuresh, P. and K. Egevang, "Traditional IP Network Address Translator (Traditional NAT)", RFC 3022, January 2001.
[4] Srisuresh，P.和K.Egevang，“传统IP网络地址转换器（传统NAT）”，RFC 3022，2001年1月。
[5] Fuller, V., Li, T., Yu, J. and K. Varadhan, "Classless Inter-Domain Routing (CIDR): an Address Assignment and Aggregation Strategy", RFC 1519, September 1993.
[5] Fuller，V.，Li，T.，Yu，J.和K.Varadhan，“无类域间路由（CIDR）：地址分配和聚合策略”，RFC 1519，1993年9月。
[6] Huston, G., "The BGP Routing Table", The Internet Protocol Journal, vol. 4, No. 1, March 2001.
[6] Huston，G.，“BGP路由表”，《互联网协议杂志》，第4卷，第1期，2001年3月。
[7] Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 (BGP-4)", RFC 1771, March 1995.
[7] Rekhter，Y.和T.Li，“边境网关协议4（BGP-4）”，RFC 17711995年3月。
[8] Vohara, Q. and E. Chen, "BGP support for four-octet AS number space", Work in Progress.
[8] Vohara，Q.和E.Chen，“BGP支持四个八位组作为数字空间”，工作正在进行中。
[9] Hain, T., "Architectural Implications of NAT", RFC 2993, November 2000.
[9] Hain，T.，“NAT的建筑含义”，RFC 2993，2000年11月。
[10] Labovitz, C., Ahuja, A., Bose, A. and J. Jahanian, "Delayed Internet Routing Convergence", Proceedings ACM SIGCOMM 2000, August 2000.
[10] Labovitz，C.，Ahuja，A.，Bose，A.和J.Jahanian，“延迟互联网路由收敛”，ACM SIGCOMM 2000年论文集，2000年8月。
[11] Lothberg, P., personal communication, December 2000.
[11] Lothberg，P.，个人通讯，2000年12月。
This document is the outcome of a collaborative effort of the IAB, and the editor acknowledges the contributions of the members of the IAB in the preparation of the document. The contributions of John Leslie, Thomas Narten and Abha Ahuja in reviewing this document are also acknowledged.
本文件是IAB合作的成果，编辑承认IAB成员在编写本文件过程中所做的贡献。我们还感谢John Leslie、Thomas Narten和Abha Ahuja在审查本文件时所作的贡献。
Internet Architecture Board Email: iab@ietf.org
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Geoff Huston Telstra 5/490 Northbourne Ave Dickson ACT 2602 Australia
Geoff Huston Telstra 5/490 Northbourne Ave Dickson ACT 2602澳大利亚
EMail: gih@telstra.net
EMail: gih@telstra.net
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