Network Working Group                                 J. Alvarez-Hamelin
Internet-Draft                               Universidad de Buenos Aires
Updates: 2330 (if approved)                                    A. Morton
Intended status: Standards Track                               AT&T Labs
Expires: June 13, 2020                                         J. Fabini
                                                                 TU Wien
                                                            C. Pignataro
                                                     Cisco Systems, Inc.
                                                                 R. Geib
                                                        Deutsche Telekom
                                                       December 11, 2019

            Advanced Unidirectional Route Assessment (AURA)


   This memo introduces an advanced unidirectional route assessment
   (AURA) metric and associated measurement methodology, based on the IP
   Performance Metrics (IPPM) Framework RFC 2330.  This memo updates RFC
   2330 in the areas of path-related terminology and path description,
   primarily to include the possibility of parallel subpaths between a
   given Source and Destination pair, owing to the presence of multi-
   path technologies.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14[RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

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   This Internet-Draft will expire on June 13, 2020.

Copyright Notice

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   document authors.  All rights reserved.

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   ( in effect on the date of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Issues with Earlier Work to define Route  . . . . . . . .   3
   2.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Route Metric Terms and Definitions  . . . . . . . . . . . . .   5
     3.1.  Formal Name . . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Parameters  . . . . . . . . . . . . . . . . . . . . . . .   6
     3.3.  Metric Definitions  . . . . . . . . . . . . . . . . . . .   7
     3.4.  Related Round-Trip Delay and Loss Definitions . . . . . .   9
     3.5.  Discussion  . . . . . . . . . . . . . . . . . . . . . . .   9
     3.6.  Reporting the Metric  . . . . . . . . . . . . . . . . . .  10
   4.  Route Assessment Methodologies  . . . . . . . . . . . . . . .  10
     4.1.  Active Methodologies  . . . . . . . . . . . . . . . . . .  10
       4.1.1.  Temporal Composition for Route Metrics  . . . . . . .  12
       4.1.2.  Routing Class C Identification  . . . . . . . . . . .  13
       4.1.3.  Intermediate Observation Point Route Measurement  . .  14
     4.2.  Hybrid Methodologies  . . . . . . . . . . . . . . . . . .  15
     4.3.  Combining Different Methods . . . . . . . . . . . . . . .  15
   5.  Background on Round-Trip Delay Measurement Goals  . . . . . .  16
   6.  Tools to Measure Delays in the Internet . . . . . . . . . . .  17
   7.  RTD Measurements Statistics . . . . . . . . . . . . . . . . .  18
   8.  Conclusions . . . . . . . . . . . . . . . . . . . . . . . . .  20
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  21
   12. Appendix I MPLS Methods for Route Assessment  . . . . . . . .  21
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     13.2.  Informative References . . . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

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1.  Introduction

   The IETF IP Performance Metrics (IPPM) working group first created a
   framework for metric development in [RFC2330].  This framework has
   stood the test of time and enabled development of many fundamental
   metrics.  It has been updated in the area of metric composition
   [RFC5835], and in several areas related to active stream measurement
   of modern networks with reactive properties [RFC7312].

   The [RFC2330] framework motivated the development of "performance and
   reliability metrics for paths through the Internet," and Section 5 of
   [RFC2330] defines terms that support description of a path under
   test.  However, metrics for assessment of path components and related
   performance aspects had not been attempted in IPPM when the [RFC2330]
   framework was written.

   This memo takes-up the route measurement challenge and specifies a
   new route metric, two practical frameworks for methods of measurement
   (using either active or hybrid active-passive methods [RFC7799]), and
   Round-Trip Delay and link information discovery using the results of
   measurements.  All route measurements are limited by the willingness
   of hosts along the path to be discovered, to cooperate with the
   methods used, or to recognize that the measurement operation is
   taking place (such as when tunnels are present).

1.1.  Issues with Earlier Work to define Route

   Section 7 of [RFC2330] presented a simple example of a "route" metric
   along with several other examples.  The example is reproduced below
   (where the reference is to Section 5 of [RFC2330]):

   "route: The path, as defined in Section 5, from A to B at a given

   This example provides a starting point to develop a more complete
   definition of route.  Areas needing clarification include:

   Time:  In practice, the route will be assessed over a time interval,
      because active path detection methods like [PT] rely on TTL limits
      for their operation and cannot accomplish discovery of all hosts
      using a single packet.

   Type-P:  The legacy route definition lacks the option to cater for
      packet-dependent routing.  In this memo, we assess the route for a
      specific packet of Type-P, and reflect this in the metric
      definition.  The methods of measurement determine the specific
      Type-P used.

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   Parallel Paths:  Parallel paths are a reality of the Internet and a
      strength of advanced route assessment methods, so the metric must
      acknowledge this possibility.  Use of Equal Cost Multi-Path (ECMP)
      and Unequal Cost Multi-Path (UCMP) technologies are common sources
      of parallel subpaths.

   Cloud Subpath:  May contain hosts that do not decrement TTL or Hop
      Limit, but may have two or more exchange links connecting
      "discoverable" hosts or routers.  Parallel subpaths contained
      within clouds cannot be discovered.  The assessment methods only
      discover hosts or routers on the path that decrement TTL or Hop
      Count, or cooperate with interrogation protocols.  The presence of
      tunnels and nested tunnels further complicate assessment by hiding

   Hop:  Although the [RFC2330] definition of a hop was a link-host
      pair, only hosts are discoverable or have the capability to
      cooperate with interrogation protocols where link information may
      be exposed.

   The refined definition of Route metrics begins in the sections that

2.  Scope

   The purpose of this memo is to add new route metrics and methods of
   measurement to the existing set of IPPM metrics.

   The scope is to define route metrics that can identify the path taken
   by a packet or a flow traversing the Internet between two hosts.
   Although primarily intended for hosts communicating on the Internet
   with IP, the definitions and metrics are constructed to be applicable
   to other network domains, if desired.  The methods of measurement to
   assess the path may not be able to discover all hosts comprising the
   path, but such omissions are often deterministic and explainable
   sources of error.

   Also, to specify a framework for active methods of measurement which
   use the techniques described in [PT] at a minimum, and a framework
   for hybrid active-passive methods of measurement, such as the Hybrid
   Type I method [RFC7799] described in
   [I-D.ietf-ippm-ioam-data](intended only for single administrative
   domains), which do not rely on ICMP and provide a protocol for
   explicit interrogation of nodes on a path.  Combinations of active
   methods and hybrid active-passive methods are also in-scope.

   Further, this memo provides additional analysis of the round-trip
   delay measurements made possible by the methods, in an effort to

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   discover more details about the path, such as the link technology in

   This memo updates Section 5 of [RFC2330] in the areas of path-related
   terminology and path description, primarily to include the
   possibility of parallel subpaths between a given Source and
   Destination address pair (possibly resulting from Equal Cost Multi-
   Path (ECMP) and Unequal Cost Multi-Path (UCMP) technologies).

   There are several simple non-goals of this memo.  There is no attempt
   to assess the reverse path from any host on the path to the host
   attempting the path measurement.  The reverse path contribution to
   delay will be that experienced by ICMP packets (in active methods),
   and may be different from delays experienced by UDP or TCP packets.
   Also, the round trip delay will include an unknown contribution of
   processing time at the host that generates the ICMP response.
   Therefore, the ICMP-based active methods are not supposed to yield
   accurate, reproducible estimations of the Round-Trip Delay that UDP
   or TCP packets will experience.

3.  Route Metric Terms and Definitions

   This section sets requirements for the following components to
   support the Route Metric:

   Host  A Host as defined in [RFC2330] (a computer capable of IP
      communication, includes routers), a.k.a.  RFC 2330 Host.

   Node   A Node is any network function on the path capable of IP-layer
      Communication, includes RFC 2330 Hosts.

   Node Identity  The unique address for Nodes communicating within the
      network domain.  For Nodes communicating on the Internet with IP,
      it is the globally routable IP address(es) which the Node uses
      when communicating with other Nodes under normal or error
      conditions.  The Node Identity revealed (and its connection to a
      Node Name through reverse DNS) determines whether interfaces to
      parallel links can be associated with a single Node, or appear to
      identify unique Nodes.

   Discoverable Node  Nodes that convey their Node Identity according to
      the requirements of their network domain, such as when error
      conditions are detected by that Node.  For Nodes communicating
      with IP packets, compliance with Section of [RFC1122] when
      discarding a packet due to TTL or Hop Limit Exceeded condition,
      MUST result in sending the corresponding Time Exceeded message
      (containing a form of Node identity) to the source.  This

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      requirement is also consistent with section 5.3.1 of [RFC1812] for

   Cooperating Node  Nodes that MUST respond to direct queries for their
      Node identity as part of a previously agreed and established
      interrogation protocol.  Nodes SHOULD also provide information
      such as arrival/departure interface identification, arrival
      timestamp, and any relevant information about the Node or specific
      link which delivered the query to the Node.

   Hop  A Hop MUST contain a Node Identity, and MAY contain arrival and/
      or departure interface identification, round trip delay, and an
      arrival timestamp.

3.1.  Formal Name

   Type-P-Route-Ensemble-Method-Variant, abbreviated as Route Ensemble.

   Note that Type-P depends heavily on the chosen method and variant.

3.2.  Parameters

   This section lists the REQUIRED input factors to specify a Route

   o  Src, the address of a Node (such as the globally routable IP

   o  Dst, the address of a Node (such as the globally routable IP

   o  i, the limit on the number of Hops a specific packet may visit as
      it traverses from the Node at Src to the Node at Dst (such as the
      TTL or Hop Limit).

   o  MaxHops, the maximum value of i used, (i=1,2,3,...MaxHops).

   o  T0, a time (start of measurement interval)

   o  Tf, a time (end of measurement interval)

   o  MP(address), Measurement Point at address, such as Src or Dst,
      usually at the same node stack layer as "address".

   o  T, the Node time of a packet as measured at MP(Src), meaning
      Measurement Point at the Source.

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   o  Ta, the Node time of a reply packet's *arrival* as measured at
      MP(Src), assigned to packets that arrive within a "reasonable"
      time (see parameter below).

   o  Tmax, a maximum waiting time for reply packets to return to the
      source, set sufficiently long to disambiguate packets with long
      delays from packets that are discarded (lost), such that the
      distribution of Round-Trip Delay is not truncated.

   o  F, the number of different flows simulated by the method and

   o  flow, the stream of packets with the same n-tuple of designated
      header fields that (when held constant) result in identical
      treatment in a multi-path decision (such as the decision taken in
      load balancing).  Note: The IPv6 flow label MAY be included in the
      flow definition if the MP(Src) is a Tunnel End Point (TEP)
      complying with [RFC6438] guidelines.

   o  Type-P, the complete description of the packets for which this
      assessment applies (including the flow-defining fields).

3.3.  Metric Definitions

   This section defines the REQUIRED measurement components of the Route
   metrics (unless otherwise indicated):

   M, the total number of packets sent between T0 and Tf.

   N, the smallest value of i needed for a packet to be received at Dst
   (sent between T0 and Tf).

   Nmax, the largest value of i needed for a packet to be received at
   Dst (sent between T0 and Tf).  Nmax may be equal to N.

   Next, define a *singleton* definition for a Hop on the path, with
   sufficient indexes to identify all Hops identified in a measurement

   A Hop, designated h(i,j), the IP address and/or identity of one of j
   Discoverable Nodes (or Cooperating Nodes) that are i hops away from
   the Node with address = Src during the measurement interval, T0 to
   Tf.  As defined above, a Hop singleton measurement MUST contain a
   Node Identity, hid(i,j), and MAY contain one or more of the following

   o  a(i,j) Arrival Interface ID (e.g., when [RFC5837] is supported)

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   o  d(i,j) Departure Interface ID (e.g., when [RFC5837] is supported)

   o  t(i,j) Arrival Timestamp (where t(i,j) is ideally supplied by the
      Hop, or approximated from the sending time of the packet that
      revealed the Hop)

   o  Measurements of Round-Trip Delay (for each packet that reveals the
      same Node Identity and flow attributes, but not timestamp of
      course, see next section)

   Node Identities and related information can be ordered by their
   distance from the Node with address Src in Hops h(i,j).  Based on
   this, two forms of Routes are distinguished:

   A Route Ensemble is defined as the combination of all routes
   traversed by different flows from the Node at Src address to the Node
   at Dst address.  A single Route traversed by a single flow
   (determined by an unambiguous tuple of addresses Src and Dst, and
   other identical flow criteria) is a member of the Route Ensemble and
   called a Member Route.

   Using h(i,j) and components and parameters, further define:

   When considering the set of Hops in the context of a single flow, a
   Member Route j is an ordered list {h(1,j), ... h(Nj, j)} where h(i-1,
   j) and h(i, j) are by 1 hop away from each other and Nj satisfying
   h(Nj,j)=Dst is the minimum count of Hops needed by the packet on
   Member Route j to reach Dst. Member Routes must be unique.  The
   uniqueness property requires that any two Member routes j and k that
   are part of the same Route Ensemble differ either in terms of minimum
   hop count Nj and Nk to reach the destination Dst, or, in the case of
   identical hop count Nj=Nk, they have at least one distinct Hop:
   h(i,j) != h(i, k) for at least one i (i=1..Nj).

   All the optional information collected to describe a Member Route,
   such as the arrival interface, departure interface, and Round Trip
   Delay at each Hop, turns each list item into a rich structure.  There
   may be information on the links between Hops, possibly information on
   the routing (arrival interface and departure interface), an estimate
   of distance between Hops based on Round-Trip Delay measurements and
   calculations, and a time stamp indicating when all these additional
   details were valid.

   The Route Ensemble from Src to Dst, during the measurement interval
   T0 to Tf, is the aggregate of all m distinct Member Routes discovered
   between the two Nodes with Src and Dst addresses.  More formally,
   with the Node having address Src omitted:

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   Route Ensemble = {
   {h(1,1), h(2,1), h(3,1), ... h(N1,1)=Dst},
   {h(1,2), h(2,2), h(3,2),..., h(N2,2)=Dst},
   {h(1,m), h(2,m), h(3,m), ....h(Nm,m)=Dst}

   where the following conditions apply: i <= Nj <= Nmax (j=1..m)

   Note that some h(i,j) may be empty (null) in the case that systems do
   not reply (not discoverable, or not cooperating).

   h(i-1,j) and h(i,j) are the Hops on the same Member Route one hop
   away from each other.

   Hop h(i,j) may be identical with h(k,l) for i!=k and j!=l ; which
   means there may be portions shared among different Member Routes
   (parts of Member Routes may overlap).

3.4.  Related Round-Trip Delay and Loss Definitions

   RTD(i,j,T) is defined as a singleton of the [RFC2681] Round-Trip
   Delay between the Node with address = Src and the Node at Hop h(i,j)
   at time T.

   RTL(i,j,T) is defined as a singleton of the [RFC6673] Round-trip Loss
   between the Node with address = Src and the Node at Hop h(i,j) at
   time T.

3.5.  Discussion

   Depending on the way that Node Identity is revealed, it may be
   difficult to determine parallel subpaths between the same pair of
   Nodes (i.e. multiple parallel links).  It is easier to detect
   parallel subpaths involving different Nodes.

   o  If a pair of discovered Nodes identify two different addresses,
      then they will appear to be different Nodes.

   o  If a pair of discovered Nodes identify two different IP addresses,
      and the IP addresses resolve to the same Node name (in the DNS),
      then they will appear to be the same Nodes.

   o  If a discovered Node always replies using the same network
      address, regardless of the interface a packet arrives on, then
      multiple parallel links cannot be detected in that network domain.
      This condition may apply to traceroute-style methods, but may not

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      apply to other hybrid methods based on In-situ Operations,
      Administration, and Maintenance (IOAM).

   o  If parallel links between routers are aggregated below the IP
      layer, then from Node point of view, all these links share the
      same pair of IP addresses.  The existence of these parallel links
      can't be detected at IP layer.  This applies to other network
      domains with layers below them, as well.  This condition may apply
      to traceroute-style methods, but may not apply to other hybrid
      methods based on IOAM.

   When a route assessment employs IP packets (for example), the reality
   of flow assignment to parallel subpaths involves layers above IP.
   Thus, the measured Route Ensemble is applicable to IP and higher
   layers (as described in the methodology's packet of Type-P and flow

3.6.  Reporting the Metric

   An Information Model and an XML Data Model for Storing Traceroute
   Measurements is available in [RFC5388].  The measured information at
   each hop includes four pieces of information: a one-dimensional hop
   index, Node symbolic address, Node IP address, and RTD for each

   The description of Hop information that may be collected according to
   this memo covers more dimensions, as defined in Section 3.3 above.
   For example, the Hop index is two-dimensional to capture the
   complexity of a Route Ensemble, and it contains corresponding Node
   identities at a minimum.  The models need to be expanded to include
   these features, as well as Arrival Interface ID, Departure Interface
   ID, and Arrival Timestamp, when available.  The original sending
   Timestamp from the Src Node anchors a particular measurement in time.

4.  Route Assessment Methodologies

   There are two classes of methods described in this section, active
   methods relying on the reaction to TTL or Hop Limit Exceeded
   condition to discover Nodes on a path, and Hybrid active-passive
   methods that involve direct interrogation of cooperating Nodes
   (usually within a single domain).  Description of these methods

4.1.  Active Methodologies

   This section describes the method employed by current open source
   tools, thereby providing a practical framework for further advanced

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   techniques to be included as method variants.  This method is
   applicable for use across multiple administrative domains.

   Paris-traceroute [PT] provides some measure of protection from path
   variation generated by ECMP load balancing, and it ensures traceroute
   packets will follow the same path in 98% of cases according to
   [SCAMPER].  If it is necessary to find every usable path between two
   Nodes, Paris-traceroute provides "exhaustive" mode while scamper
   provides "tracelb" (stands for traceroute load balance).

   The Type-P of packets used could be ICMP (as in the original
   traceroute), UDP or TCP.  The latter are used when a particular
   characteristic needs to be to verified, such as filtering or traffic
   shaping on specific ports (i.e., services).  [SCAMPER] supports IPv6
   traceroute measurements, keeping the FlowLabel constant in all

   The advanced route assessment methods used in Paris-traceroute [PT]
   keep the critical fields constant for every packet to maintain the
   appearance of the same flow.  Since route assessment can be conducted
   using TCP, UDP or ICMP packets, this method REQUIRES the Diffserv
   field, the protocol number, IP source and destination addresses, and
   the port settings for TCP or UDP to be kept constant.  For ICMP
   probes, the method additionally REQUIRES keeping the type, code, and
   ICMP checksum constant (the latter occupy the corresponding positions
   in the header of an IP packet, e.g., bytes 20 to 23 when the header
   IP has no options).

   Maintaining a constant checksum in ICMP is most challenging because
   the ICMP Sequence Number is part of the calculation.  The advanced
   traceroute method requires calculations using the IP Sequence Number
   Field and the Identifier Field, yielding a constant ICMP checksum in
   successive packets.  For an example of calculations to maintain a
   constant checksum, see Appendix A of [RFC7820], where revision of a
   timestamp field is complemented by modifying the 2 octet checksum
   complement field (these fields take the roles of the ICMP Sequence
   Number and Identifier Fields, respectively).

   For TCP and UDP packets, the checksum must also be kept constant.
   Therefore, the first four bytes of UDP (or TCP) data field are
   modified to compensate for fields that change from packet to packet.

   Finally, the return path is also important to check.  Taking into
   account that it is an ICMP time exceeded (during transit) packet, the
   source and destination IP are constant for every reply.  Then, we
   should consider the fields in the first 32 bits of the protocol on
   the top of IP: the type and code of ICMP packet, and its checksum.
   Again, to keep the ICMP checksum constant for the returning packets,

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   we need to consider the whole ICMP message.  It contains the IP
   header of the discarded packet plus the first 8 bytes of the IP
   payload; that is some of the fields of the TCP header, the UDP header
   plus four data bytes, the ICMP header plus four bytes.  Therefore,
   for the UDP case the data field is used to maintain the ICMP checksum
   constant in the returning packet.  For the ICMP case, the identifier
   and sequence fields of the sent ICMP probe are manipulated to be
   constant.  The TCP case presents no problem because its first eight
   bytes will be the same for every packet probe.

   Formally, to maintain the same flow in the measurements to a certain
   hop, the Type-P-Route-Ensemble-Method-Variant packets should be[PT]:

   o  TCP case: Fields Src, Dst, port-Src, port_Dst, and Diffserv Field
      should be the same.

   o  UDP case: Fields Src, Dst, port-Src, port-Dst, and Diffserv Field
      should be the same, the UDP-checksum should change to keep the IP
      checksum of the ICMP time exceeded reply constant.  Then, the data
      length should be fixed, and the data field is used to fixing it
      (consider that ICMP checksum uses its data field, which contains
      the original IP header plus 8 bytes of UDP, where TTL or Hop
      Limit, IP identification, IP checksum, and UDP checksum changes).

   o  ICMP case: The Data field should compensate variations on TTL or
      Hop Limit, IP identification, and IP checksum for every packet.

   Then, the way to identify different hops and attempts of the same
   flow is:

   o  TCP case: The IP identification field.

   o  UDP case: The IP identification field.

   o  ICMP case: The IP identification field, and ICMP Sequence number.

4.1.1.  Temporal Composition for Route Metrics

   The Active Route Assessment Methods described above have the ability
   to discover portions of a path where ECMP load balancing is present,
   observed as two or more unique Member Routes having one or more
   distinct Hops which are part of the Route Ensemble.  Likewise,
   attempts to deliberately vary the flow characteristics to discover
   all Member Routes will reveal portions of the path which are flow-

   Section 9.2 of [RFC2330] describes Temporal Composition of metrics,
   and introduces the possibility of a relationship between earlier

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   measurement results and the results for measurement at the current
   time (for a given metric).  There is value in establishing a Temporal
   Composition relationship for Route Metrics.  However, this
   relationship does not represent a forecast of future route conditions
   in any way.

   For Route Metric measurements, the value of Temporal Composition is
   to reduce the measurement iterations required with repeated
   measurements.  Reduced iterations are possible by inferring that
   current measurements using fixed and previously measured flow

   o  will have many common hops with previous measurements.

   o  will have relatively time-stable results at the ingress and egress
      portions of the path when measured from user locations, as opposed
      to measurements of backbone networks and across inter-domain

   o  may have greater potential for time-variation in path portions
      where ECMP load balancing is observed (because increasing or
      decreasing the pool of links changes the hash calculations).

   Optionally, measurement systems may take advantage of the inferences
   above when seeking to reduce measurement iterations, after exhaustive
   measurements indicate that the time-stable properties are present.
   Repetitive Active Route measurement systems:

   1.  SHOULD occasionally check path portions which have exhibited
       stable results over time, particularly ingress and egress
       portions of the path.

   2.  SHOULD continue testing portions of the path that have previously
       exhibited ECMP load balancing.

   3.  SHALL trigger re-assessment of the complete path and Route
       Ensemble, if any change in hops is observed for a specific (and
       previously tested) flow.

4.1.2.  Routing Class C Identification

   There is an opportunity to apply the [RFC2330] notion of equal
   treatment for a class of packets, "...very useful to know if a given
   Internet component treats equally a class C of different types of
   packets", as it applies to Route measurements.  Knowledge of "class
   C" parameters (unrelated to address classes of the past) on a path
   potentially reduces the number of flows required for a given method
   to assess a Route Ensemble over time.

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   First, recognize that each Member Route of a Route Ensemble will have
   a corresponding Routing Class C.  Class C can be discovered by
   testing with multiple flows, all of which traverse the unique set of
   hops that comprise a specific Member Route.

   Second, recognize that the different Routing Classes depend primarily
   on the hash functions used at each instance of ECMP load balancing on
   the path.

   Third, recognize the synergy with Temporal Composition methods
   (described above) where evaluation intends to discover time-stable
   portions of each Member Route so that more emphasis can be placed on
   ECMP portions that also determine Class C.

   The methods to assess the various Routing Class C characteristics
   benefit from the following measurement capabilities:

   o  flows designed to determine which n-tuple header fields are
      considered by a given hash function and ECMP hop on the path, and
      which are not.  This operation immediately narrows the search
      space, where possible, and partially defines a Routing Class C.

   o  a priori knowledge of the possible types of hash functions in use
      also helps to design the flows for testing (major router vendors
      publish information about these hash functions, examples are here

   o  ability to direct the emphasis of current measurements on ECMP
      portions of the path, based on recent past measurement results
      (the Routing Class C of some portions of the path is essentially
      "all packets").

4.1.3.  Intermediate Observation Point Route Measurement

   There are many examples where passive monitoring of a flow at an
   Observation Point within the network can detect unexpected Round Trip
   Delay or Delay Variation.  But how can the cause of the anomalous
   delay be investigated further --from the Observation Point --
   possibly located at an intermediate point on the path?

   In this case, knowledge that the flow of interest belongs to a
   specific Routing Class C will enable measurement of the route where
   anomalous delay has been observed.  Specifically, Round-Trip Delay
   assessment to each Hop on the path between the Observation Point and
   the Destination for the flow of interest may discover high or
   variable delay on a specific link and Hop combination.

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   The determination of a Routing Class C which includes the flow of
   interest is as described in the section above, aided by computation
   of the relevant hash function output as the target.

4.2.  Hybrid Methodologies

   The Hybrid Type I methods provide an alternative method for Route
   Member assessment.  As mentioned in the Scope section,
   [I-D.ietf-ippm-ioam-data] provides a possible set of data fields that
   would support route identification.

   In general, nodes in the measured domain would be equipped with
   specific abilities:

   o  Support of the "Loopback" Flag (L-bit), where a copy of the packet
      is returned to the encapsulating node, and the packet is processed
      like any other IOAM packet on the return transfer.

   In addition to node identity, nodes may also identify the ingress and
   egress interfaces utilized by the tracing packet, the time of day
   when the packet was processed, and other generic data (as described
   in section 4 of [I-D.ietf-ippm-ioam-data]).  Interface identification
   isn't necessarily limited to IP, i.e. different links in a bundle
   (LACP) could be identified.  Equally well, links without explicit IP
   addresses can be identified (like with unnumbered interfaces in an
   IGP deployment).

   Note that Type-P packet specification for this method will likely be
   a partial specification, because most of the packet fields are
   determined by the user traffic.  The packet header(s) added by the
   Hybrid method can certainly be specified in Type-P.

4.3.  Combining Different Methods

   In principle, there are advantages if the entity conducting Route
   measurements can utilize both forms of advanced methods (active and
   hybrid), and combine the results.  For example, if there are Nodes
   involved in the path that qualify as Cooperating Nodes, but not as
   Discoverable Nodes, then a more complete view of Hops on the path is
   possible when a hybrid method (or interrogation protocol) is applied
   and the results are combined with the active method results collected
   across all other domains.

   In order to combine the results of active and hybrid/interrogation
   methods, the network Nodes that are part of a domain supporting an
   interrogation protocol have the following attributes:

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   1.  Nodes at the ingress to the domain SHOULD be both Discoverable
       and Cooperating, and SHOULD reveal the same Node Identity in
       response to both active and hybrid methods.

   2.  Any Nodes within the domain that are both Discoverable and
       Cooperating SHOULD reveal the same Node Identity in response to
       both active and hybrid methods.

   3.  Nodes at the egress to the domain SHOULD be both Discoverable and
       Cooperating, and SHOULD reveal the same Node Identity in response
       to both active and hybrid methods.

   When Nodes follow these requirements, it becomes a simple matter to
   match single domain measurements with the overlapping results from a
   multidomain measurement.

   In practice, Internet users do not typically have the ability to
   utilize the OAM capabilities of networks that their packets traverse,
   so the results from a remote domain supporting an interrogation
   protocol would not normally be accessible.  However, a network
   operator could combine interrogation results from their access domain
   with other measurements revealing the path outside their domain.

5.  Background on Round-Trip Delay Measurement Goals

   The aim of this method is to use packet probes to unveil the paths
   between any two end-Nodes of the network.  Moreover, information
   derived from RTD measurements might be meaningful to identify:

   1.  Intercontinental submarine links

   2.  Satellite communications

   3.  Congestion

   4.  Inter-domain paths

   This categorization is widely accepted in the literature and among
   operators alike, and it can be trusted with empirical data and
   several sources as ground of truth (e.g., [RTTSub] ) but it is an
   inference measurement nonetheless [bdrmap][IDCong].

   The first two categories correspond to the physical distance
   dependency on Round-Trip Delay (RTD) while the last one binds RTD
   with queueing delay on routers.  Due to the significant contribution
   of propagation delay in long distance hops, RTD will be on the order
   of 100ms on transatlantic hops, depending on the geolocation of the
   vantage points.  Moreover, RTD is typically greater than 480ms when

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   two hops are connected using geostationary satellite technology
   (i.e., their orbit is at 36000km).  Detecting congestion with latency
   implies deeper mathematical understanding since network traffic load
   is not stationary.  Nonetheless, as the first approach, a link seems
   to be congested if after sending several traceroute probes, it is
   possible to detect congestion observing different statistics
   parameters (e.g., see [IDCong]).

6.  Tools to Measure Delays in the Internet

   Internet routing is complex because it depends on the policies of
   thousands Autonomous Systems (AS).  While most of the routers perform
   load balancing on flows using Equal Cost Multiple Path (ECMP), a few
   still divide the workload through packet-based techniques.  The
   former scenario is defined according to [RFC2991] while the latter
   generates a round-robin scheme to deliver every new outgoing packet.
   ECMP uses a hashing function to ensure that every packet of a flow is
   delivered by the same path, and this avoids increasing the packet
   delay variation and possibly producing overwhelming packet reordering
   in TCP flows.

   Taking into account that Internet protocol was designed under the
   "end-to-end" principle, the IP payload and its header do not provide
   any information about the routes or path necessary to reach some
   destination.  For this reason, the well-known tool traceroute was
   developed to gather the IP addresses of each hop along a path using
   the ICMP protocol [RFC0792].  Besides, traceroute adds the measured
   RTD from each hop.  However, the growing complexity of the Internet
   makes it more challenging to develop an accurate traceroute
   implementation.  For instance, the early traceroute tools would be
   inaccurate in the current network, mainly because they were not
   designed to retain flow state.  However, evolved traceroute tools,
   such as Paris-traceroute [PT] [MLB] and Scamper [SCAMPER], expect to
   encounter ECMP and achieve more accurate results when they do.

   Paris-traceroute-like tools operate in the following way: every
   packet should follow the same path because the sensitive fields of
   the header are controlled to appear as the same flow.  This means
   that source and destination IP addresses, source and destination port
   numbers are the same in every packet.  Additionally, Differentiated
   Services Code Point (DSCP), checksum and ICMP code should remain
   constant since they may affect the path selection.

   Today's traceroute tools can send either UDP, TCP or ICMP packet
   probes.  Since ICMP header does not include transport layer
   information, there are no fields for source and destination port
   numbers.  For this reason, these tools keep constant ICMP type, code,
   and checksum fields to generate a kind of flow.  However, the

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   checksum may vary in every packet, therefore when probes use ICMP
   packets, ICMP Identifier and sequence number are manipulated to
   maintain constant checksum in every packet.  On the other hand, when
   UDP probes are generated, the expected variation in the checksum of
   each packet is again compensated by manipulating the payload.

   Paris-traceroute allows its users to measure RTD in every hop of the
   path for a particular flow.  Furthermore, either Paris-traceroute or
   Scamper is capable of unveiling the many available paths between a
   source and destination (which are visible to this method).  This task
   is accomplished by repeating complete traceroute measurements with
   different flow parameters for each measurement.  The Framework for IP
   Performance Metrics (IPPM) ([RFC2330] updated by [RFC7312]) has the
   flexibility to require that the Round-Trip Delay measurement
   [RFC2681] uses packets with the constraints to assure that all
   packets in a single measurement appear as the same flow.  This
   flexibility covers ICMP, UDP, and TCP.  The accompanying methodology
   of [RFC2681] needs to be expanded to report the sequential hop
   identifiers along with RTD measurements, but no new metric definition
   is needed.

7.  RTD Measurements Statistics

   Several articles have shown that network traffic presents a self-
   similar nature [SSNT] [MLRM] which is accountable for filling the
   queues of the routers.  Moreover, router queues are designed to
   handle traffic bursts, which is one of the most remarkable features
   of self-similarity.  Naturally, while queue length increases, the
   delay to traverse the queue increases as well and leads to an
   increase on RTD.  Due to traffic bursts generate short-term overflow
   on buffers (spiky patterns), every RTD only depicts the queueing
   status on the instant when that packet probe was in transit.  For
   this reason, several RTD measurements during a time window could
   begin to describe the random behavior of latency.  Loss must also be
   accounted for in the methodology.

   To understand the ongoing process, examining the quartiles provides a
   non-parametric way of analysis.  Quartiles are defined by five
   values: minimum RTD (m), RTD value of the 25% of the Empirical
   Cumulative Distribution Function (ECDF) (Q1), the median value (Q2),
   the RTD value of the 75% of the ECDF (Q3) and the maximum RTD (M).
   Congestion can be inferred when RTD measurements are spread apart,
   and consequently, the Inter-Quartile Range (IQR), the distance
   between Q3 and Q1, increases its value.

   This procedure requires to compute quartile values "on the fly" using
   the algorithm presented in [P2].

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   This procedure allows us to update the quartiles value whenever a new
   measurement arrives, which is radically different from classic
   methods of computing quartiles because they need to use the whole
   dataset to compute the values.  This way of calculus provides savings
   in memory and computing time.

   To sum up, the proposed measurement procedure consists in performing
   traceroutes several times to obtain samples of the RTD in every hop
   from a path, during a time window (W) and compute the quantiles for
   every hop.  This could be done for a single Member Route flow or for
   every detected Route Ensemble flow.

   The identification of a specific Hop in traceroute is based on the IP
   origin address of the returned ICMP Time Exceeded packet, and on the
   distance identified by the value set in the TTL field inserted by
   traceroute.  As this specific Hop can be reached by different paths,
   also the IP source and destination addresses of the traceroute packet
   need to be recorded.  Finally, different return paths are
   distinguished by evaluating the ICMP Time Exceeded TTL (of the reply
   message): if this TTL is constant for different paths containing the
   same Hop, the return paths have the same distance.  Moreover, this
   distance can be estimated considering that the TTL value is normally
   initialized with values 64, 128, or 255.  The 5-tuple (origin IP,
   destination IP, reply IP, distance, response TTL) univocally
   identifies every measurement.

   This algorithm below runs in the origin of the traceroute.  It
   returns the Qs quartiles for every Hop and Alt (alternative paths
   because of balancing).  The following parameters are used: W window
   time of the measurement, i_t time between two measurements, Dst
   destination IP address.

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   1  input:   W (window time of the measurement)
   2           i_t (time between two measurements)
   3           E (True: exhaustive, False: a single path)
   4           Dst (destination IP address)
   5  output:  Qs (quartiles for every Hop and Alt)
   6  T := start_timer(W)
   7  while T is not finished do:
   8  |       start_timer(i_t)
   9  |       RTD(Hop,Alt) = advanced-traceroute(Dst,E)
   10 |       for each Hop and Alt in RTD do:
   11 |       |     Qs[Dst,Hop,Alt] := ComputeQs(RTD(Hop,Alt))
   12 |       done
   13 |       wait until i_t timer is expired
   14 done
   15  return (Qs)

   During the time W, lines 6 and 7 assure that the measurement loop is
   made.  Line 8 and 13 set a timer for each cycle of measurements.  A
   cycle comprises the traceroutes packets, considering every possible
   Hop and the alternatives paths in the Alt variable (ensured in lines
   9-12).  In line 9 the advance-traceroute could be either Paris-
   traceroute or Scamper, which will use "exhaustive" mode or "tracelb"
   option if E is set True, respectively.  The procedure returns a list
   of tuples (m,Q1,Q2,Q3,M) for each intermediate hop in the path
   towards the Dst. Additionally, it could also return path variations
   using "alt" variable.Finally, lines 10 and 12 stores each measurement
   into the real-time quartiles computation.

8.  Conclusions

   Combining the method proposed in Section 4 and statistics in
   Section 7, we can measure the performance of paths interconnecting
   two endpoints in Internet, and attempt the categorization of link
   types and congestion presence based on RTD.

9.  Security Considerations

   The security considerations that apply to any active measurement of
   live paths are relevant here as well.  See [RFC4656] and [RFC5357].

   The active measurement process of "changing several fields to keep
   the checksum of different packets identical" does not require special
   security considerations because it is part of synthetic traffic
   generation, and is designed to have minimal to zero impact on network
   processing (to process the packets for ECMP).

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   For applicable Hybrid methods, the security considerations
   in[I-D.ietf-ippm-ioam-data] apply.

   When considering privacy of those involved in measurement or those
   whose traffic is measured, the sensitive information available to
   potential observers is greatly reduced when using active techniques
   which are within this scope of work.  Passive observations of user
   traffic for measurement purposes raise many privacy issues.  We refer
   the reader to the privacy considerations described in the Large Scale
   Measurement of Broadband Performance (LMAP) Framework [RFC7594],
   which covers active and passive techniques.

10.  IANA Considerations

   This memo makes no requests of IANA.  We thank the good folks at IANA
   for having checked this section anyway.

11.  Acknowledgements

   The original 3 authors acknowledge Ruediger Geib, for his penetrating
   comments on the initial draft, and his initial text for the
   Appendix on MPLS.  Carlos Pignataro challenged the authors to
   consider a wider scope, and applied his substantial expertise with
   many technologies and their measurement features in his extensive
   comments.  Frank Brockners also shared useful comments, so did Footer
   Foote.  We thank them all!

12.  Appendix I MPLS Methods for Route Assessment

   A Node assessing an MPLS path must be part of the MPLS domain where
   the path is implemented.  When this condition is met, RFC 8029
   provides a powerful set of mechanisms to detect "correct operation of
   the data plane, as well as a mechanism to verify the data plane
   against the control plane" [RFC8029].

   MPLS routing is based on the presence of a Forwarding Equivalence
   Class (FEC) Stack in all visited Nodes.  Selecting one of several
   Equal Cost Multi Path (ECMP) is however based on information hidden
   deeper in the stack.  Early deployments may support a so called
   "Entropy label" for this purpose.  State of the art deployments base
   their choice of an ECMP member based on the IP addresses (see
   Section 2.4 of [RFC7325]).  Both methods allow load sharing
   information to be decoupled from routing information.  Thus, an MPLS
   traceroute is able to check how packets with a contiguous number of
   ECMP relevant addresses (and the same destination) are routed by a
   particular router.  The minimum number of MPLS paths traceable at a
   router should be 32.  Implementations supporting more paths are

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   The MPLS echo request and reply messages offering this feature must
   support the Downstream Detailed Mapping TLV (was Downstream Mapping
   initially, but the latter has been deprecated).  The MPLS echo
   response includes the incoming interface where a router received the
   MPLS Echo request.  The MPLS Echo reply further informs which of the
   n addresses relevant for the load sharing decision results in a
   particular next hop interface and contains the next hop's interface
   address (if available).  This ensures that the next hop will receive
   a properly coded MPLS Echo request in the next step route of

   [RFC8403] explains how a central Path Monitoring System could be used
   to detect arbitrary MPLS paths between any routers within a single
   MPLS domain.  The combination of MPLS forwarding, Segment Routing and
   MPLS traceroute offers a simple architecture and a powerful mechanism
   to detect and validate (segment routed) MPLS paths.

13.  References

13.1.  Normative References

              Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
              Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
              P.,, r.,,
              d., and J. Lemon, "Data Fields for In-situ OAM", draft-
              ietf-ippm-ioam-data-08 (work in progress), October 2019.

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, DOI 10.17487/RFC0792, September 1981,

   [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122,
              DOI 10.17487/RFC1122, October 1989,

   [RFC1812]  Baker, F., Ed., "Requirements for IP Version 4 Routers",
              RFC 1812, DOI 10.17487/RFC1812, June 1995,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

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   [RFC2330]  Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
              "Framework for IP Performance Metrics", RFC 2330,
              DOI 10.17487/RFC2330, May 1998,

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <>.

   [RFC2675]  Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms",
              RFC 2675, DOI 10.17487/RFC2675, August 1999,

   [RFC2681]  Almes, G., Kalidindi, S., and M. Zekauskas, "A Round-trip
              Delay Metric for IPPM", RFC 2681, DOI 10.17487/RFC2681,
              September 1999, <>.

   [RFC2991]  Thaler, D. and C. Hopps, "Multipath Issues in Unicast and
              Multicast Next-Hop Selection", RFC 2991,
              DOI 10.17487/RFC2991, November 2000,

   [RFC4494]  Song, JH., Poovendran, R., and J. Lee, "The AES-CMAC-96
              Algorithm and Its Use with IPsec", RFC 4494,
              DOI 10.17487/RFC4494, June 2006,

   [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
              Zekauskas, "A One-way Active Measurement Protocol
              (OWAMP)", RFC 4656, DOI 10.17487/RFC4656, September 2006,

   [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
              Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
              RFC 5357, DOI 10.17487/RFC5357, October 2008,

   [RFC5388]  Niccolini, S., Tartarelli, S., Quittek, J., Dietz, T., and
              M. Swany, "Information Model and XML Data Model for
              Traceroute Measurements", RFC 5388, DOI 10.17487/RFC5388,
              December 2008, <>.

   [RFC5644]  Stephan, E., Liang, L., and A. Morton, "IP Performance
              Metrics (IPPM): Spatial and Multicast", RFC 5644,
              DOI 10.17487/RFC5644, October 2009,

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   [RFC5835]  Morton, A., Ed. and S. Van den Berghe, Ed., "Framework for
              Metric Composition", RFC 5835, DOI 10.17487/RFC5835, April
              2010, <>.

   [RFC5837]  Atlas, A., Ed., Bonica, R., Ed., Pignataro, C., Ed., Shen,
              N., and JR. Rivers, "Extending ICMP for Interface and
              Next-Hop Identification", RFC 5837, DOI 10.17487/RFC5837,
              April 2010, <>.

   [RFC6282]  Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
              Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
              DOI 10.17487/RFC6282, September 2011,

   [RFC6437]  Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
              "IPv6 Flow Label Specification", RFC 6437,
              DOI 10.17487/RFC6437, November 2011,

   [RFC6438]  Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
              for Equal Cost Multipath Routing and Link Aggregation in
              Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,

   [RFC6564]  Krishnan, S., Woodyatt, J., Kline, E., Hoagland, J., and
              M. Bhatia, "A Uniform Format for IPv6 Extension Headers",
              RFC 6564, DOI 10.17487/RFC6564, April 2012,

   [RFC6673]  Morton, A., "Round-Trip Packet Loss Metrics", RFC 6673,
              DOI 10.17487/RFC6673, August 2012,

   [RFC7045]  Carpenter, B. and S. Jiang, "Transmission and Processing
              of IPv6 Extension Headers", RFC 7045,
              DOI 10.17487/RFC7045, December 2013,

   [RFC7312]  Fabini, J. and A. Morton, "Advanced Stream and Sampling
              Framework for IP Performance Metrics (IPPM)", RFC 7312,
              DOI 10.17487/RFC7312, August 2014,

   [RFC7799]  Morton, A., "Active and Passive Metrics and Methods (with
              Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
              May 2016, <>.

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   [RFC7820]  Mizrahi, T., "UDP Checksum Complement in the One-Way
              Active Measurement Protocol (OWAMP) and Two-Way Active
              Measurement Protocol (TWAMP)", RFC 7820,
              DOI 10.17487/RFC7820, March 2016,

   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
              Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029,
              DOI 10.17487/RFC8029, March 2017,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

13.2.  Informative References

   [bdrmap]   Luckie, M., Dhamdhere, A., Huffaker, B., Clark, D., and
              KC. Claffy, "bdrmap: Inference of Borders Between IP
              Networks",  In Proceedings of the 2016 ACM on Internet
              Measurement Conference, pp. 381-396. ACM, 2016.

   [IDCong]   Luckie, M., Dhamdhere, A., Clark, D., and B. Huffaker,
              "Challenges in inferring Internet interdomain
              congestion",  In Proceedings of the 2014 Conference on
              Internet Measurement Conference, pp. 15-22. ACM, 2014.

   [MLB]      Augustin, B., Friedman, T., and R. Teixeira, "Measuring
              load-balanced paths in the Internet",   Proceedings of the
              7th ACM SIGCOMM conference on Internet measurement, pp.
              149-160. ACM, 2007., 2007.

   [MLRM]     Fontugne, R., Mazel, J., and K. Fukuda, "An empirical
              mixture model for large-scale RTT measurements",  2015
              IEEE Conference on Computer Communications (INFOCOM), pp.
              2470-2478. IEEE, 2015., 2015.

   [P2]       Jain, R. and I. Chlamtac, "The P 2 algorithm for dynamic
              calculation of quantiles and histograms without storing
              observations",  Communications of the ACM 28.10 (1985):
              1076-1085, 2015.

   [PT]       Augustin, B., Cuvellier, X., Orgogozo, B., Viger, F.,
              Friedman, T., Latapy, M., Magnien, C., and R. Teixeira,
              "Avoiding traceroute anomalies with Paris traceroute",
              Proceedings of the 6th ACM SIGCOMM conference on Internet
              measurement, pp. 153-158. ACM, 2006., 2006.

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   [RFC7325]  Villamizar, C., Ed., Kompella, K., Amante, S., Malis, A.,
              and C. Pignataro, "MPLS Forwarding Compliance and
              Performance Requirements", RFC 7325, DOI 10.17487/RFC7325,
              August 2014, <>.

   [RFC7594]  Eardley, P., Morton, A., Bagnulo, M., Burbridge, T.,
              Aitken, P., and A. Akhter, "A Framework for Large-Scale
              Measurement of Broadband Performance (LMAP)", RFC 7594,
              DOI 10.17487/RFC7594, September 2015,

   [RFC8403]  Geib, R., Ed., Filsfils, C., Pignataro, C., Ed., and N.
              Kumar, "A Scalable and Topology-Aware MPLS Data-Plane
              Monitoring System", RFC 8403, DOI 10.17487/RFC8403, July
              2018, <>.

   [RTTSub]   Bischof, Z., Rula, J., and F. Bustamante, "In and out of
              Cuba: Characterizing Cuba's connectivity",  In Proceedings
              of the 2015 ACM Conference on Internet Measurement
              Conference, pp. 487-493. ACM, 2015.

   [SCAMPER]  Matthew Luckie, M., "Scamper: a scalable and extensible
              packet prober for active measurement of the
              Internet",  Proceedings of the 10th ACM SIGCOMM conference
              on Internet measurement, pp. 239-245. ACM, 2010., 2010.

   [SSNT]     Park, K. and W. Willinger, "Self-Similar Network Traffic
              and Performance Evaluation (1st ed.)",  John Wiley & Sons,
              Inc., New York, NY, USA, 2000.

Authors' Addresses

   J. Ignacio Alvarez-Hamelin
   Universidad de Buenos Aires
   Av. Paseo Colon 850
   Buenos Aires  C1063ACV

   Phone: +54 11 5285-0716

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   Al Morton
   AT&T Labs
   200 Laurel Avenue South
   Middletown, NJ  07748

   Phone: +1 732 420 1571
   Fax:   +1 732 368 1192

   Joachim Fabini
   TU Wien
   Gusshausstrasse 25/E389
   Vienna  1040

   Phone: +43 1 58801 38813
   Fax:   +43 1 58801 38898

   Carlos Pignataro
   Cisco Systems, Inc.
   7200-11 Kit Creek Road
   Research Triangle Park, NC  27709


   Ruediger Geib
   Deutsche Telekom
   Heinrich Hertz Str. 3-7
   Darmstadt  64295

   Phone: +49 6151 5812747

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