--- 1/draft-ietf-ippm-connectivity-02.txt 2006-02-04 23:45:14.000000000 +0100 +++ 2/draft-ietf-ippm-connectivity-03.txt 2006-02-04 23:45:14.000000000 +0100 @@ -1,17 +1,17 @@ Network Working Group J. Mahdavi, Pittsburgh Supercomputer Center Internet Draft V. Paxson, Lawrence Berkeley National Laboratory -Expiration Date: February 1999 August 1998 +Expiration Date: April 1999 October 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 August 1998 +ID IPPM Metrics for Measuring Connectivity October 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 August 1998 +ID IPPM Metrics for Measuring Connectivity October 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 @@ -121,21 +121,21 @@ 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 August 1998 +ID IPPM Metrics for Measuring Connectivity October 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: @@ -161,21 +161,21 @@ 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 August 1998 +ID IPPM Metrics for Measuring Connectivity October 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. @@ -205,21 +205,21 @@ 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 August 1998 +ID IPPM Metrics for Measuring Connectivity October 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, T+dT] that A1 and A2 cannot reply to packets sent by the other. This deficiency motivates the next metric. @@ -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 August 1998 +ID IPPM Metrics for Measuring Connectivity October 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 @@ -288,21 +288,21 @@ 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 August 1998 +ID IPPM Metrics for Measuring Connectivity October 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". + If no successful replies are received by time T+dT, the value of the measurement is "false". @@ -315,77 +315,93 @@ yet offer solid guidance for picking N. The values given above are just guidelines. 7.6.5. Specific methodology for TCP: 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: + 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: the - connection now established between A1 and A2 should be properly - torn down using the usual FIN handshake (not by using a RST - packet, as these are not transmitted reliably).} + 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.} + +ID IPPM Metrics for Measuring Connectivity October 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 (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).} - -ID IPPM Metrics for Measuring Connectivity August 1998 - + 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". {Comment: Similar methodologies are needed for ICMP Echo, UDP, etc.} -8. Security Considerations +8. Acknowledgments + + The comments of Guy Almes, Martin Horneffer, Jeff Sedayao, and Sean + Shapira are appreciated. + +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. -9. References +10. References F. Baker, "Requirements for IP Version 4 Routers", RFC 1812, June 1995. R. Braden, "Requirements for Internet hosts - communication layers", RFC 1122, October 1989. V. Paxson, G. Almes, J. Mahdavi, and M. Mathis, Paxson, "Framework for IP Performance Metrics", RFC 2330, May 1998. +ID IPPM Metrics for Measuring Connectivity October 1998 + J. Postel, "Internet Protocol", RFC 791, September 1981. -10. Authors' Addresses +11. Authors' Addresses Jamshid Mahdavi Pittsburgh Supercomputing Center 4400 5th Avenue Pittsburgh, PA 15213 USA Vern Paxson MS 50A-3111 Lawrence Berkeley National Laboratory University of California Berkeley, CA 94720 - -ID IPPM Metrics for Measuring Connectivity August 1998 - USA Phone: +1 510/486-7504