Network Working Group                                      M. Nottingham
Intended status: Informational                             July 04, 2014
Expires: January 05, 2015

                  Granular Information about Networks


   Protocol endpoints often want to adapt their behavior based upon the
   current properties of the network path, but have limited information
   available to aid these decisions.  This document motivates discussion
   of protocol work to make this information available.

Status of This Memo

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   This Internet-Draft will expire on January 05, 2015.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Granular Information about Networks: Straw-Men  . . . . . . .   4
     3.1.  DNS . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  HTTP  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.3.  TLS . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.4.  TCP . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Protocol endpoints often want to adapt their behavior based upon the
   current properties of the network path.

   For example, it has become common practice for HTTP [RFC7230] servers
   to adapt the responses they give based upon the IP address of the
   client, client "fingerprinting" (e.g., using the User-Agent request
   header field), and other properties.

   Likewise, client using HTTP sometimes adapt their behavior in a
   similar fashion; for example, a mobile client on a 3G network might
   download a different video file then if it were on a wifi network.
   Often, the goal of these adaptations is to improve user experience by
   making content more suitable for the properties of the network it is
   traversing, whilst utilizing the network resources more optimally.

   There are currently a number of sources of information to inform
   these decisions, but they share a few limitations.  For example, it
   is possible to measure delay to a given server using ICMP, but the
   results are ephemeral, and may change if a different server has

   There have also been attempts to provide relevant information in
   APIs; for example, [netinfo].  Doing so has proven to be difficult,
   because of the limited information available to the client.

   To address these issues, network operators have been deploying
   infrastructure that uses the information available to them to modify
   content; e.g., [bytemobile], [verizon], [syniverse], [flashnet].

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   However, at the same time, encryption has become more prevalent on
   the Internet, with many prominent (and heavily traffic'd) Web sites
   going HTTPS-only.  This frustrates attempts to adapt content in the

   This document proposes an alternative approach.  By making the
   information that the network operators have available to the
   endpoints, it allows them to make more informed choices about
   content, thereby allowing the user experience to be improved and the
   network to be used more optimally without requiring that the end-to-
   end nature of encryption (e.g., in HTTPS) to be compromised.

1.1.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.  Requirements

   To be useful to endpoints, the information a network exposes needs to

   o  Specific to the client - General information about network
      properties is often an improvement over current practice, but to
      be truly useful, it should be able to be tailored to a specific
      client IP address.

   o  Reasonably current - Information from fifteen minutes ago is often
      useless; when necessary, an endpoint ought to be able to get
      information that is fresh (on the granularity of a few seconds).

   o  Scalable - The overhead of conveying information to clients ought
      to be minimal, and it needs to be usable on the scale of a large
      Web site.

   o  Private - The protocol ought not expose details of private
      networks, or any personally identifying information beyond that
      already available.

   A protocol for exposing this information necessarily must choose the
   scope of its applicability.  Due to the nature of the Internet, it is
   not practical to meet the goals above for the end-to-end path(s)
   between any given pair of IP addresses; the permutations are
   impractical, and discovering meaningful information on this scale is
   likewise unlikely.

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   However, it is comparatively easy for a network operator to expose
   what it considers to be the "last mile" properties of an IP address.
   For example, an ISP providing ADSL access to its subscribers could
   advertise the properties of those end links, whereas a mobile
   operator could use the information available to advertise the
   properties of individual subscriber handset IP addresses (whether
   they be globally routable, or behind NAT).

   This partial information is not a complete picture, of course, but it
   is information that's difficul to aquire now, and often has a
   disproprionate impact upon the delivery of content.

   A protocol for such information ought to expose a minimum of:

   o  Bandwidth - an approximation of the bandwidth currently unused on
      the "last mile" connection, in bits per second.

   o  Delay - an approximation of delay seen on the "last mile"
      connection, in milliseconds.

   o  Packet Loss - the current packet loss seen on "last mile"
      connections from the client, expressed as a percentage.

   Additional metrics (including some that are operator-specific) might
   also be useful, and ought to be accommodated.

   This information, in turn, could be used by Web servers, browsers and
   other tools to optimize both the responses and requests made.  For
   example, MPEG-DASH clients could use the information about their own
   address to better choose an encoding; servers could re-encode images
   and HTML to account for slow networks, based upon the requesting
   client's IP address.

3.  Granular Information about Networks: Straw-Men

   NOTE: the technical mechanisms discussed are straw-men, and might not
   be the "real" approach.  Readers are encouraged to consider and
   discuss the overall viability of the idea expressed above before
   focusing too much upon the details below.

3.1.  DNS

   One approach would be to using DNS [RFC1035] to convey this
   information.  This has several advantages:

   o  DNS works at the granularity of an IP address

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   o  Reverse DNS for a public IP address is often administered by the
      access network that provisions it

   o  DNS is lightweight and has a built-in caching mechanism

   Potential disadvantages include:

   o  Servers receiving requests from clients that are unknown (or where
      there is only stale information available) will need to either
      wait for the lookup, or act without information for such requests

   o  Additional load on DNS infrastructure may be considerable

   This would require a new RRTYPE to be defined to carry the
   information outlined above.

3.2.  HTTP

   It might be possible to provide such information with a lightweight
   HTTP [RFC7230] service exposed by the network operator.  However,
   discovery of that service would still need to be established; this
   might be possible through DNS.

   This approach's advantages include:

   o  Built-in caching and scaling mechanisms

   o  Rich extensibility

   o  Familiarity for developers and ops

   Potential disadvantages include:

   o  Servers receiving requests from clients that are unknown (or where
      there is only stale information available) will need to either
      wait for the lookup, or act without information for such requests

   o  Comparatively high overhead

3.3.  TLS

   Another approach would be to add another channel in TLS [RFC5246]
   that does not form part of teh encrypted session, to allow the
   network to annotate connections directly.

   This has a few advantages:

   o  Immediate availability of network information in-channel

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   o  Direct binding to a single connection

   o  Annotations could be added on subsequent hops


   o  Doing so is likely to be technically invasive, my have interop
      problems with deployed infrastructure

   o  May be seen as a layering violation / security issue

3.4.  TCP

   Yet another approach would be to define simliar side-channel
   mechanisms in TCP [RFC0793].

   The advantages and disadvantages of this approach are similar to
   those around TLS; however, there is an additional disadvantage, in
   that TCP extensibility is even more constrained than TLS'.

4.  Security Considerations

   This document is only exploratory now, but there are already clearly
   evident security and privacy implications, including:

   o  Whether the information exposed can be used to identify a user

   o  Whether denial of service attacks are possible using this

5.  References

5.1.  Normative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

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

   [RFC7230]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Message Syntax and Routing", RFC 7230, June

5.2.  Informative References

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7, RFC
              793, September 1981.

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   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

              Citrix, "ByteMobile Adaptive Traffic Management", 2014,

              Flash Networks, "Optimization Overview", 2014,

   [netinfo]  W3C, "The Network Information API", 2014,

              Syniverse, "Hosted Data Optimization", 2014, <http://

              2014, <

Author's Address

   Mark Nottingham


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