Network Working Group J. Mahdavi
Request for Comments: 2678 Pittsburgh Supercomputing Center
Obsoletes: 2498 V. Paxson
Category: Standards Track Lawrence Berkeley National Laboratory
September 1999
Network Working Group J. Mahdavi
Request for Comments: 2678 Pittsburgh Supercomputing Center
Obsoletes: 2498 V. Paxson
Category: Standards Track Lawrence Berkeley National Laboratory
September 1999
IPPM Metrics for Measuring Connectivity
IPPM度量连接性的指标
Status of this Memo
本备忘录的状况
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
本文件规定了互联网社区的互联网标准跟踪协议，并要求进行讨论和提出改进建议。有关本协议的标准化状态和状态，请参考当前版本的“互联网官方协议标准”（STD 1）。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (1999). All Rights Reserved.
版权所有（C）互联网协会（1999年）。版权所有。
Connectivity is the basic stuff from which the Internet is made. Therefore, metrics determining whether pairs of hosts (IP addresses) can reach each other must form the base of a measurement suite. We define several such metrics, some of which serve mainly as building blocks for the others.
连通性是构成互联网的基本要素。因此，确定主机对（IP地址）是否可以相互访问的指标必须构成度量套件的基础。我们定义了几个这样的度量，其中一些主要用作其他度量的构建块。
This memo defines a series of metrics for connectivity between a pair of Internet hosts. It builds on notions introduced and discussed in RFC 2330, the IPPM framework document. The reader is assumed to be familiar with that document.
此备忘录为一对Internet主机之间的连接定义了一系列指标。它以IPPM框架文件RFC 2330中介绍和讨论的概念为基础。假定读者熟悉该文档。
The structure of the memo is as follows:
备忘录的结构如下：
+ An analytic metric, called Type-P-Instantaneous-Unidirectional-Connectivity, will be introduced to define one-way connectivity at one moment in time. + Using this metric, another analytic metric, called Type-P-Instantaneous-Bidirectional-Connectivity, will be introduced to define two-way connectivity at one moment in time. + Using these metrics, corresponding one- and two-way analytic metrics are defined for connectivity over an interval of time.
+ 将引入一种称为类型-P-瞬时-单向-连通性的分析度量来定义某一时刻的单向连通性使用此度量，将引入另一个分析度量，称为Type-P-瞬时-双向-连通性，以定义某一时刻的双向连通性使用这些度量，为一段时间间隔内的连接性定义相应的单向和双向分析度量。
+ Using these metrics, an analytic metric, called Type-P1-P2- Interval-Temporal-Connectivity, will be introduced to define a useful notion of two-way connectivity between two hosts over an interval of time. + Methodologies are then presented and discussed for estimating Type-P1-P2-Interval-Temporal-Connectivity in a variety of settings.
+ 使用这些度量，将引入一个分析度量，称为Type-P1-P2-Interval Temporal Connectivity，以定义一个有用的概念，即在一段时间间隔内两台主机之间的双向连接然后介绍并讨论了在各种环境下估算P1-P2-区间-时间-连通性的方法。
Careful definition of Type-P1-P2-Interval-Temporal-Connectivity and the discussion of the metric and the methodologies for estimating it are the two chief contributions of the memo.
本备忘录的两个主要贡献是对P1-P2-区间-时间-连通性的仔细定义以及对度量和估算方法的讨论。
2.1. Metric Name:
2.1. 度量名称：
Type-P-Instantaneous-Unidirectional-Connectivity
P型瞬时单向连通性
2.2. Metric Parameters:
2.2. 公制参数：
+ Src, the IP address of a host + Dst, the IP address of a host + T, a time
+ Src，主机+Dst的IP地址，主机+T的IP地址，时间
2.3. Metric Units:
2.3. 公制单位：
Boolean.
布尔型。
2.4. Definition:
2.4. 定义：
Src has *Type-P-Instantaneous-Unidirectional-Connectivity* to Dst at time T if a type-P packet transmitted from Src to Dst at time T will arrive at Dst.
如果在时间T从Src传输到Dst的P型数据包将到达Dst，则Src在时间T与Dst具有*P型瞬时单向连接*。
2.5. Discussion:
2.5. 讨论：
For most applications (e.g., any TCP connection) bidirectional connectivity is considerably more germane than unidirectional connectivity, although unidirectional connectivity can be of interest for some security applications (e.g., testing whether a firewall correctly filters out a "ping of death"). Most applications also require connectivity over an interval, while this metric is instantaneous, though, again, for some security applications instantaneous connectivity remains of interest. Finally, one might not have instantaneous connectivity due to a transient event such as a full queue at a router, even if at nearby instants in time one does have connectivity. These points are addressed below, with this metric serving as a building block.
对于大多数应用程序（例如，任何TCP连接），双向连接比单向连接密切得多，尽管单向连接可能对某些安全应用程序感兴趣（例如，测试防火墙是否正确过滤出“死亡ping”）。大多数应用程序还需要在一段时间间隔内进行连接，而此指标是瞬时的，不过，对于某些安全应用程序来说，瞬时连接仍然令人感兴趣。最后，由于一个瞬态事件，例如路由器上的一个完整队列，一个人可能没有即时连接，即使在时间上的附近时刻一个人确实有连接。下面将介绍这些要点，并将此指标作为构建模块。
Note also that we have not explicitly defined *when* the packet arrives at Dst. The TTL field in IP packets is meant to limit IP packet lifetimes to 255 seconds (RFC 791). In practice the TTL field can be strictly a hop count (RFC 1812), with most Internet hops being much shorter than one second. This means that most packets will have nowhere near the 255 second lifetime. In principle, however, it is also possible that packets might survive longer than 255 seconds. Consideration of packet lifetimes must be taken into account in attempts to measure the value of this metric.
还要注意，我们没有明确定义数据包到达Dst的时间。IP数据包中的TTL字段用于将IP数据包的生存时间限制为255秒（RFC 791）。在实践中，TTL字段可以严格地表示为跳数（RFC1812），大多数Internet跳数都比1秒短得多。这意味着大多数数据包的生存时间都不超过255秒。然而，原则上，数据包也可能存活超过255秒。在尝试测量此度量值时，必须考虑数据包的生存时间。
Finally, one might assume that unidirectional connectivity is difficult to measure in the absence of connectivity in the reverse direction. Consider, however, the possibility that a process on Dst's host notes when it receives packets from Src and reports this fact either using an external channel, or later in time when Dst does have connectivity to Src. Such a methodology could reliably measure the unidirectional connectivity defined in this metric.
最后，人们可能会假设，在没有反向连接的情况下，单向连接很难测量。然而，考虑到当DST主机从SRC接收分组时，一个进程的注释，并且使用外部信道报告这个事实，或者在Dst确实具有SRC连接的时间之后报告该事实。这种方法可以可靠地测量此度量中定义的单向连通性。
3.1. Metric Name:
3.1. 度量名称：
Type-P-Instantaneous-Bidirectional-Connectivity
P型瞬时双向连通性
3.2. Metric Parameters:
3.2. 公制参数：
+ A1, the IP address of a host + A2, the IP address of a host + T, a time
+ A1，主机的IP地址+A2，主机的IP地址+T，时间
3.3. Metric Units:
3.3. 公制单位：
Boolean.
布尔型。
3.4. Definition:
3.4. 定义：
Addresses A1 and A2 have *Type-P-Instantaneous-Bidirectional-Connectivity* at time T if address A1 has Type-P-Instantaneous-Unidirectional-Connectivity to address A2 and address A2 has Type-P-Instantaneous-Unidirectional-Connectivity to address A1.
如果地址A1与地址A2具有P型瞬时单向连通性，且地址A2与地址A1具有P型瞬时单向连通性，则地址A1和A2在时间T具有*P型瞬时双向连通性*。
3.5. Discussion:
3.5. 讨论：
An alternative definition would be that A1 and A2 are fully connected if at time T address A1 has instantaneous connectivity to address A2, and at time T+dT address A2 has instantaneous connectivity to A1, where T+dT is when the packet sent from A1 arrives at A2. This definition is more useful for measurement, because the measurement
另一种定义是，如果在时间T时地址A1与地址A2具有瞬时连接性，并且在时间T+dT时地址A2与A1具有瞬时连接性，则A1和A2完全连接，其中T+dT是当从A1发送的分组到达A2时。此定义对于测量更有用，因为测量
can use a reply from A2 to A1 in order to assess full connectivity. It is a more complex definition, however, because it breaks the symmetry between A1 and A2, and requires a notion of quantifying how long a particular packet from A1 takes to reach A2. We postpone discussion of this distinction until the development of interval-connectivity metrics below.
可以使用A2到A1的回复来评估完整连接。然而，这是一个更复杂的定义，因为它打破了A1和A2之间的对称性，并且需要一个概念来量化从A1到A2的特定数据包需要多长时间。我们将这一区别的讨论推迟到下面的间隔连通性指标的开发。
4.1. Metric Name:
4.1. 度量名称：
Type-P-Interval-Unidirectional-Connectivity
P型区间单向连通性
4.2. Metric Parameters:
4.2. 公制参数：
+ Src, the IP address of a host + Dst, the IP address of a host + T, a time + dT, a duration {Comment: Thus, the closed interval [T, T+dT] denotes a time interval.}
+ Src，主机+Dst的IP地址，主机+T的IP地址，时间+dT，持续时间{注释：因此，闭合间隔[T，T+dT]表示时间间隔。}
4.3. Metric Units:
4.3. 公制单位：
Boolean.
布尔型。
4.4. Definition:
4.4. 定义：
Address Src has *Type-P-Interval-Unidirectional-Connectivity* to address Dst during the interval [T, T+dT] if for some T' within [T, T+dT] it has Type-P-instantaneous-connectivity to Dst.
地址Src在间隔[T，T+dT]期间对Dst具有*类型-P-间隔-单向-连接*，如果[T，T+dT]内的某些T'具有类型-P-瞬时-连接到Dst。
5.1. Metric Name:
5.1. 度量名称：
Type-P-Interval-Bidirectional-Connectivity
P型区间双向连通性
5.2. Metric Parameters:
5.2. 公制参数：
+ A1, the IP address of a host + A2, the IP address of a host + T, a time + dT, a duration {Comment: Thus, the closed interval [T, T+dT] denotes a time interval.}
+ A1，主机的IP地址+A2，主机的IP地址+T，时间+dT，持续时间{注释：因此，闭合间隔[T，T+dT]表示时间间隔。}
5.3. Metric Units:
5.3. 公制单位：
Boolean.
布尔型。
5.4. Definition:
5.4. 定义：
Addresses A1 and A2 have *Type-P-Interval-Bidirectional-Connectivity* between them during the interval [T, T+dT] if address A1 has Type-P-Interval-Unidirectional-Connectivity to address A2 during the interval and address A2 has Type-P-Interval-Unidirectional-Connectivity to address A1 during the interval.
如果地址A1在间隔[T，T+dT]期间具有与地址A2的P型间隔单向连通性，并且地址A2在间隔[T，T+dT]期间具有与地址A1的P型间隔单向连通性，则地址A1和A2在间隔[T，T+dT]期间具有*P型间隔双向连通性*。
5.5. Discussion:
5.5. 讨论：
This metric is not quite what's needed for defining "generally useful" connectivity - that requires the notion that a packet sent from A1 to A2 can elicit a response from A2 that will reach A1. With this definition, it could be that A1 and A2 have full-connectivity but only, for example, at time T1 early enough in the interval [T, T+dT] that A1 and A2 cannot reply to packets sent by the other. This deficiency motivates the next metric.
这个指标并不是定义“一般有用”连接性所需要的——这需要一个概念，即从A1发送到A2的数据包可以引发A2的响应，该响应将到达A1。根据该定义，可以是A1和A2具有完全连接性，但仅在间隔[T，T+dT]足够早的时间T1处，A1和A2不能回复由另一方发送的分组。这一缺陷激发了下一个指标。
6.1. Metric Name:
6.1. 度量名称：
Type-P1-P2-Interval-Temporal-Connectivity
类型-P1-P2-区间-时间-连通性
6.2. Metric Parameters:
6.2. 公制参数：
+ Src, the IP address of a host + Dst, the IP address of a host + T, a time + dT, a duration {Comment: Thus, the closed interval [T, T+dT] denotes a time interval.}
+ Src，主机+Dst的IP地址，主机+T的IP地址，时间+dT，持续时间{注释：因此，闭合间隔[T，T+dT]表示时间间隔。}
6.3. Metric Units:
6.3. 公制单位：
Boolean.
布尔型。
6.4. Definition:
6.4. 定义：
Address Src has *Type-P1-P2-Interval-Temporal-Connectivity* to address Dst during the interval [T, T+dT] if there exist times T1 and T2, and time intervals dT1 and dT2, such that:
如果存在时间T1和T2以及时间间隔dT1和dT2，则地址Src在间隔[T，T+dT]期间具有*Type-P1-P2-Interval-Temporal-Connectivity*，以寻址Dst，从而：
+ T1, T1+dT1, T2, T2+dT2 are all in [T, T+dT]. + T1+dT1 <= T2. + At time T1, Src has Type-P1 instantanous connectivity to Dst. + At time T2, Dst has Type-P2 instantanous connectivity to Src. + dT1 is the time taken for a Type-P1 packet sent by Src at time T1 to arrive at Dst. + dT2 is the time taken for a Type-P2 packet sent by Dst at time T2 to arrive at Src.
+ T1，T1+dT1，T2，T2+dT2都在[T，T+dT]。+T1+dT1<=T2+在时间T1，Src具有与Dst+的P1型瞬时连接在时间T2，Dst具有与Src+的P2型瞬时连接dT1是Src在时间T1发送的P1型数据包到达Dst所用的时间dT2是Dst在时间T2发送的P2型数据包到达Src所用的时间。
6.5. Discussion:
6.5. 讨论：
This metric defines "generally useful" connectivity -- Src can send a packet to Dst that elicits a response. Because many applications utilize different types of packets for forward and reverse traffic, it is possible (and likely) that the desired responses to a Type-P1 packet will be of a different type Type-P2. Therefore, in this metric we allow for different types of packets in the forward and reverse directions.
这个指标定义了“通常有用”的连接性——Src可以向Dst发送一个数据包，以获得响应。由于许多应用程序利用不同类型的分组进行前向和反向通信，因此对类型P1分组的期望响应可能（并且很可能）是不同类型P2。因此，在这个度量中，我们允许在正向和反向上使用不同类型的数据包。
6.6. Methodologies:
6.6. 方法：
Here we sketch a class of methodologies for estimating Type-P1-P2- Interval-Temporal-Connectivity. It is a class rather than a single methodology because the particulars will depend on the types P1 and P2.
这里，我们概述了一类用于估计P1-P2型时间间隔连通性的方法。它是一个类而不是一个单一的方法，因为细节将取决于类型P1和P2。
6.6.1. Inputs:
6.6.1. 投入：
+ Types P1 and P2, addresses A1 and A2, interval [T, T+dT]. + N, the number of packets to send as probes for determining connectivity. + W, the "waiting time", which bounds for how long it is useful to wait for a reply to a packet. Required: W <= 255, dT > W.
+ P1和P2类型，地址A1和A2，间隔[T，T+dT]。+N、 作为探测器发送以确定连接性的数据包数。+W、 “等待时间”，它限定了等待数据包回复的有效时间。所需：W<=255，dT>W。
6.6.2. Recommended values:
6.6.2. 建议值：
dT = 60 seconds. W = 10 seconds. N = 20 packets.
dT=60秒。W=10秒。N=20个数据包。
6.6.3. Algorithm:
6.6.3. 算法：
+ Compute N *sending-times* that are randomly, uniformly distributed over [T, T+dT-W]. + At each sending time, transmit from A1 a well-formed packet of type P1 to A2. + Inspect incoming network traffic to A1 to determine if a successful reply is received. The particulars of doing so are dependent on types P1 & P2, discussed below. If any successful reply is received, the value of the measurement is "true". At this point, the measurement can terminate. + If no successful replies are received by time T+dT, the value of the measurement is "false".
+ 计算在[T，T+dT-W]上随机均匀分布的N*发送时间*。+在每次发送时，从A1向A2+发送P1类型的格式良好的数据包检查A1的传入网络流量，以确定是否收到了成功的回复。这样做的细节取决于下面讨论的类型P1和P2。如果收到任何成功的回复，则测量值为“真”。此时，测量可以终止如果在时间T+dT之前没有收到成功的回复，则测量值为“假”。
6.6.4. Discussion:
6.6.4. 讨论：
The algorithm is inexact because it does not (and cannot) probe temporal connectivity at every instant in time between [T, T+dT]. The value of N trades off measurement precision against network measurement load. The state-of-the-art in Internet research does not yet offer solid guidance for picking N. The values given above are just guidelines.
该算法是不精确的，因为它不会（也不能）在[T，T+dT]之间的每一时刻探测时间连通性。N值将测量精度与网络测量负载进行权衡。互联网研究的最新进展还不能为选择N提供可靠的指导。上面给出的值只是指导。
6.6.5. Specific methodology for TCP:
6.6.5. TCP的具体方法：
A TCP-port-N1-port-N2 methodology sends TCP SYN packets with source port N1 and dest port N2 at address A2. Network traffic incoming to A1 is interpreted as follows:
TCP-port-N1-port-N2方法在地址A2处发送源端口N1和目的端口N2的TCP SYN数据包。传入A1的网络流量解释如下：
+ A SYN-ack packet from A2 to A1 with the proper acknowledgement fields and ports indicates temporal connectivity. The measurement terminates immediately with a value of "true". {Comment: if, as a side effect of the methodology, a full TCP connection has been established between A1 and A2 -- that is, if A1's TCP stack acknowledges A2's SYN-ack packet, completing the three-way handshake -- then the connection now established between A1 and A2 is best torn down using the usual FIN handshake, and not using a RST packet, because RST packets are not reliably delivered. If the three-way handshake is not completed, however, which will occur if the measurement tool on A1 synthesizes its own initial SYN packet rather than going through A1's TCP stack, then A1's TCP stack will automatically terminate the connection in a reliable fashion as A2 continues transmitting the SYN-ack in an attempt to establish the connection. Finally, we note that using A1's TCP stack to conduct the measurement complicates the methodology in that the stack may retransmit the initial SYN packet, altering the number of probe packets sent.}
+ 从A2到A1的带有正确确认字段和端口的SYN ack数据包表示临时连接。测量立即终止，值为“真”。{注释：作为该方法的一个副作用，如果A1和A2之间建立了完整的TCP连接——也就是说，如果A1的TCP堆栈确认A2的SYN ack数据包，完成了三次握手——那么现在在A1和A2之间建立的连接最好使用通常的FIN握手，而不是使用RST数据包，because RST数据包不能可靠地传递。但是，如果三方握手没有完成，如果A1上的测量工具合成其自己的初始SYN数据包而不是通过A1的TCP堆栈，则A1的TCP堆栈将在A2继续传输SYN时以可靠的方式自动终止连接-最后，我们注意到，使用A1的TCP堆栈进行测量会使方法复杂化，因为堆栈可能会重新传输初始SYN数据包，从而改变发送的探测数据包的数量。}
+ A RST packet from A2 to A1 with the proper ports indicates temporal connectivity between the addresses (and a *lack* of service connectivity for TCP-port-N1-port-N2 - something that probably should be addressed with another metric). + An ICMP port-unreachable from A2 to A1 indicates temporal connectivity between the addresses (and again a *lack* of service connectivity for TCP-port-N1-port-N2). {Comment: TCP implementations generally do not need to send ICMP port-unreachable messages because a separate mechanism is available (sending a RST). However, RFC 1122 states that a TCP receiving an ICMP port-unreachable MUST treat it the same as the equivalent transport-level mechanism (for TCP, a RST).} + An ICMP host-unreachable or network-unreachable to A1 (not necessarily from A2) with an enclosed IP header matching that sent from A1 to A2 *suggests* a lack of temporal connectivity. If by time T+dT no evidence of temporal connectivity has been gathered, then the receipt of the ICMP can be used as additional information to the measurement value of "false".
+ 从A2到A1的带有适当端口的RST数据包表示地址之间的暂时连接（以及TCP-port-N1-port-N2的*缺乏*服务连接-可能应该使用另一个度量来解决这一问题）。+从A2到A1无法访问的ICMP端口表示地址之间的暂时连接（以及TCP-port-N1-port-N2的“缺少”服务连接）。{注释：TCP实现通常不需要发送ICMP端口不可访问的消息，因为有单独的机制可用（发送RST）。但是，RFC 1122指出，接收ICMP端口不可访问的TCP必须将其视为等效的传输级别机制（对于TCP，RST）。}+如果A1无法访问ICMP主机或无法访问网络（不一定来自A2），且从A1发送到A2的封闭IP报头匹配*表明*缺乏临时连接。如果到T+dT时没有收集到时间连通性的证据，则ICMP的接收可用作“假”测量值的附加信息。
{Comment: Similar methodologies are needed for ICMP Echo, UDP, etc.}
{Comment: Similar methodologies are needed for ICMP Echo, UDP, etc.}
The comments of Guy Almes, Martin Horneffer, Jeff Sedayao, and Sean Shapira are appreciated.
感谢盖伊·阿尔姆斯、马丁·霍内弗、杰夫·塞达尧和肖恩·沙皮拉的评论。
As noted in RFC 2330, active measurement techniques, such as those defined in this document, can be abused for denial-of-service attacks disguised as legitimate measurement activity. Furthermore, testing for connectivity can be used to probe firewalls and other security mechnisms for weak spots.
如RFC 2330所述，主动测量技术（如本文档中定义的技术）可被滥用，用于伪装为合法测量活动的拒绝服务攻击。此外，连通性测试可用于探测防火墙和其他安全机制的薄弱点。
[RFC1812] Baker, F., "Requirements for IP Version 4 Routers", RFC 1812, June 1995.
[RFC1812]Baker，F.，“IP版本4路由器的要求”，RFC1812，1995年6月。
[RFC1122] Braden, R., Editor, "Requirements for Internet Hosts -- Communication Layers", STD, 3, RFC 1122, October 1989.
[RFC1122]Braden，R.，编辑，“互联网主机的要求——通信层”，STD，3，RFC 1122，1989年10月。
[RFC2330] Paxson, V., Almes, G., Mahdavi, J. and M. Mathis, "Framework for IP Performance Metrics", RFC 2330, May 1998.
[RFC2330]Paxson，V.，Almes，G.，Mahdavi，J.和M.Mathis，“IP性能度量框架”，RFC 2330，1998年5月。
[RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.
[RFC791]Postel，J.，“互联网协议”，标准5，RFC7911981年9月。
Jamshid Mahdavi Pittsburgh Supercomputing Center 4400 5th Avenue Pittsburgh, PA 15213 USA
美国宾夕法尼亚州匹兹堡第五大道4400号杰姆希德·马赫达维匹兹堡超级计算中心，邮编15213
EMail: mahdavi@psc.edu
EMail: mahdavi@psc.edu
Vern Paxson MS 50A-3111 Lawrence Berkeley National Laboratory University of California Berkeley, CA 94720 USA
Vern Paxson MS 50A—31 11劳伦斯伯克利国家实验室加利福尼亚大学伯克利，CA 94720美国
Phone: +1 510/486-7504
EMail: vern@ee.lbl.gov
Phone: +1 510/486-7504
EMail: vern@ee.lbl.gov
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Acknowledgement
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