--- 1/draft-ietf-ippm-connectivity-03.txt 2006-02-04 23:45:15.000000000 +0100 +++ 2/draft-ietf-ippm-connectivity-04.txt 2006-02-04 23:45:15.000000000 +0100 @@ -1,17 +1,17 @@ Network Working Group J. Mahdavi, Pittsburgh Supercomputer Center Internet Draft V. Paxson, Lawrence Berkeley National Laboratory -Expiration Date: April 1999 October 1998 +Expiration Date: May 1999 November 1998 IPPM Metrics for Measuring Connectivity - + 1. Status of this Memo This document is an Internet Draft. Internet Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet Drafts. Internet Drafts are draft documents valid for a maximum of six months, and may be updated, replaced, or obsoleted by other documents @@ -36,21 +36,21 @@ define several such metrics, some of which serve mainly as building blocks for the others. 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. The structure of the memo is as follows: -ID IPPM Metrics for Measuring Connectivity October 1998 +ID IPPM Metrics for Measuring Connectivity November 1998 + 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. + Using these metrics, an analytic metric, called Type-P1-P2- @@ -78,21 +78,21 @@ 3.3. Metric Units: Boolean. 3.4. Definition: 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. -ID IPPM Metrics for Measuring Connectivity October 1998 +ID IPPM Metrics for Measuring Connectivity November 1998 3.5. Discussion: 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 @@ -121,61 +121,61 @@ the unidirectional connectivity defined in this metric. 4. Instantaneous Two-way Connectivity 4.1. Metric Name: Type-P-Instantaneous-Bidirectional-Connectivity 4.2. Metric Parameters: -ID IPPM Metrics for Measuring Connectivity October 1998 +ID IPPM Metrics for Measuring Connectivity November 1998 + A1, the IP address of a host + A2, the IP address of a host + T, a time 4.3. Metric Units: Boolean. 4.4. Definition: 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. 4.5. Discussion: - An alternative definition would be that at 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 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. + 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 + 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. 5. One-way Connectivity 5.1. Metric Name: Type-P-Interval-Unidirectional-Connectivity 5.2. Metric Parameters: + Src, the IP address of a host -ID IPPM Metrics for Measuring Connectivity October 1998 +ID IPPM Metrics for Measuring Connectivity November 1998 + 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.} 5.3. Metric Units: Boolean. @@ -205,29 +205,29 @@ Boolean. 6.4. Definition: 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. -ID IPPM Metrics for Measuring Connectivity October 1998 +ID IPPM Metrics for Measuring Connectivity November 1998 6.5. Discussion: 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 at time T1 early enough in the interval [T, + 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. 7. Two-way Temporal Connectivity 7.1. Metric Name: Type-P1-P2-Interval-Temporal-Connectivity 7.2. Metric Parameters: @@ -247,21 +247,21 @@ 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: + 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. -ID IPPM Metrics for Measuring Connectivity October 1998 +ID IPPM Metrics for Measuring Connectivity November 1998 + dT2 is the time taken for a Type-P2 packet sent by Dst at time T2 to arrive at Src. 7.5. Discussion: 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 @@ -288,28 +288,29 @@ dT = 60 seconds. W = 10 seconds. N = 20 packets. 7.6.3. Algorithm: + Compute N *sending-times* that are randomly, uniformly distributed over [T, T+dT-W]. -ID IPPM Metrics for Measuring Connectivity October 1998 +ID IPPM Metrics for Measuring Connectivity November 1998 + 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 a successful - reply is received, the value of the measurement is "true". + 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". 7.6.4. Discussion: 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 @@ -332,21 +333,21 @@ 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.} -ID IPPM Metrics for Measuring Connectivity October 1998 +ID IPPM Metrics for Measuring Connectivity November 1998 + 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 @@ -370,32 +371,36 @@ 9. Security Considerations 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. 10. References - F. Baker, "Requirements for IP Version 4 Routers", RFC 1812, June - 1995. + [RFC1812] + F. Baker, "Requirements for IP Version 4 Routers", June 1995. - R. Braden, "Requirements for Internet hosts - communication layers", - RFC 1122, October 1989. + [RFC1122] + R. Braden, Editor, "Requirements for Internet Hosts -- Communi- + cation Layers," Oct. 1989. - V. Paxson, G. Almes, J. Mahdavi, and M. Mathis, Paxson, "Framework - for IP Performance Metrics", RFC 2330, May 1998. + [RFC2330] -ID IPPM Metrics for Measuring Connectivity October 1998 +ID IPPM Metrics for Measuring Connectivity November 1998 - J. Postel, "Internet Protocol", RFC 791, September 1981. + V. Paxson, G. Almes, J. Mahdavi, and M. Mathis, "Framework for + IP Performance Metrics", May 1998. + + [RFC791] + J. Postel, "Internet Protocol", September 1981. 11. Authors' Addresses Jamshid Mahdavi Pittsburgh Supercomputing Center 4400 5th Avenue Pittsburgh, PA 15213 USA Vern Paxson