TCP's Reaction to Soft Errors
RFC 5461

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Network Working Group                                            F. Gont
Request for Comments: 5461                                       UTN/FRH
Category: Informational                                    February 2009

                     TCP's Reaction to Soft Errors

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (c) 2009 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
   Provisions Relating to IETF Documents (http://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

Abstract

   This document describes a non-standard, but widely implemented,
   modification to TCP's handling of ICMP soft error messages that
   rejects pending connection-requests when those error messages are
   received.  This behavior reduces the likelihood of long delays
   between connection-establishment attempts that may arise in a number
   of scenarios, including one in which dual-stack nodes that have IPv6
   enabled by default are deployed in IPv4 or mixed IPv4 and IPv6
   environments.

Gont                         Informational                      [Page 1]
RFC 5461             TCP's Reaction to Soft Errors         February 2009

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Error Handling in TCP  . . . . . . . . . . . . . . . . . . . .  3
     2.1.  Reaction to ICMP Error Messages That Indicate Hard
           Errors . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.2.  Reaction to ICMP Error Messages That Indicate Soft
           Errors . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Problems That May Arise from TCP's Reaction to Soft Errors . .  5
     3.1.  General Discussion . . . . . . . . . . . . . . . . . . . .  5
     3.2.  Problems That May Arise with Dual-Stack IPv6 on by
           Default  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Deployed Workarounds for Long Delays between
       Connection-Establishment Attempts  . . . . . . . . . . . . . .  7
     4.1.  Context-Sensitive ICMP/TCP Interaction . . . . . . . . . .  7
     4.2.  Context-Sensitive ICMP/TCP Interaction with Repeated
           Confirmation . . . . . . . . . . . . . . . . . . . . . . .  8
   5.  Possible Drawbacks of Changing ICMP Semantics  . . . . . . . .  9
     5.1.  Non-Deterministic Transient Network Failures . . . . . . .  9
     5.2.  Deterministic Transient Network Failures . . . . . . . . . 10
     5.3.  Non-Compliant Network Address Translators (NATs) . . . . . 10
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   8.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 11
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 12
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 12

Gont                         Informational                      [Page 2]
RFC 5461             TCP's Reaction to Soft Errors         February 2009

1.  Introduction

   The handling of network failures can be separated into two different
   actions: fault isolation and fault recovery.  Fault isolation
   consists of the actions that hosts and routers take to determine that
   there is a network failure.  Fault recovery, on the other hand,
   consists of the actions that hosts and routers perform in an attempt
   to survive a network failure [RFC0816].

   In the Internet architecture, the Internet Control Message Protocol
   (ICMP) [RFC0792] is one fault isolation technique to report network
   error conditions to the hosts sending datagrams over the network.

   When a host is notified of a network error, its network stack will
   attempt to continue communications, if possible, in the presence of
   the network failure.  The fault recovery strategy may depend on the
   type of network failure taking place and the time at which the error
   condition is detected.

   This document analyzes the problems that may arise due to TCP's fault
   recovery reactions to ICMP soft errors.  It analyzes the problems
   that may arise when a host tries to establish a TCP connection with a
   multihomed host that has some unreachable addresses.  Additionally,
   it analyzes the problems that may arise in the specific scenario
   where dual-stack nodes that have IPv6 enabled by default are deployed
   in IPv4 or mixed IPv4 and IPv6 environments.

   Finally, we document a modification to TCP's reaction to ICMP