CDN Loop Prevention
draft-ietf-httpbis-cdn-loop-01

Document Type Active Internet-Draft (httpbis WG)
Last updated 2018-10-27 (latest revision 2018-10-23)
Replaces draft-cdn-loop-prevention
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HTTP Working Group                                              S. Ludin
Internet-Draft                                       Akamai Technologies
Intended status: Standards Track                           M. Nottingham
Expires: April 27, 2019                                           Fastly
                                                             N. Sullivan
                                                              Cloudflare
                                                        October 24, 2018

                          CDN Loop Prevention
                     draft-ietf-httpbis-cdn-loop-01

Abstract

   This specification defines the CDN-Loop request header field for
   HTTP.

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 https://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on April 27, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Relationship to Via . . . . . . . . . . . . . . . . . . .   2
     1.2.  Conventions and Definitions . . . . . . . . . . . . . . .   3
   2.  The CDN-Loop Request Header Field . . . . . . . . . . . . . .   3
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   In modern deployments of HTTP servers, it is common to interpose
   Content Delivery Networks (CDNs) in front of origin servers to
   improve end-user perceived latency, reduce operational costs, and
   improve scalability and reliability of services.

   Often, more than one CDN is in use by a given origin.  This happens
   for a variety of reasons, such as cost savings, arranging for
   failover should one CDN have issues, or to directly compare their
   services.

   As a result, it is not unknown for forwarding CDNs to be configured
   in a "loop" accidentally; because routing is achieved through a
   combination of DNS and forwarding rules, and site configurations are
   sometimes complex and managed by several parties.

   When this happens, it is difficult to debug.  Additionally, it
   sometimes isn't accidental; loops between multiple CDNs be used as an
   attack vector (e.g., see [loop-attack]), especially if one CDN
   unintentionally strips the loop detection headers of another.

   This specification defines the CDN-Loop request header field for HTTP
   to enable secure interoperability of forwarding CDNs.  Having a
   header that is guaranteed not to be modified by other CDNs that are
   used by a shared customer helps give each CDN additional confidence
   that any purpose (debugging, data gathering, enforcement) that they
   use this header for is free from tampering due to how that customer
   configured the other CDNs.

1.1.  Relationship to Via

   HTTP defines the Via header field in [RFC7230], Section 5.7.1 for
   "tracking message forwards, avoiding request loops, and identifying

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   the protocol capabilities of senders along the request/response
   chain."

   In theory, Via could be used to identify these loops.  However, in
   practice it is not used in this fashion, because some HTTP servers
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