draft-ietf-tcpm-tcp-soft-errors-09.txt   rfc5461.txt 
TCP Maintenance and Minor F. Gont Network Working Group F. Gont
Extensions (tcpm) UTN/FRH Request for Comments: 5461 UTN/FRH
Category: Informational February 2009
Intended status: Informational
Expires: June 3, 2009
TCP's Reaction to Soft Errors TCP's Reaction to Soft Errors
draft-ietf-tcpm-tcp-soft-errors-09.txt
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Abstract Abstract
This document describes a non-standard, but widely implemented, This document describes a non-standard, but widely implemented,
modification to TCP's handling of ICMP soft error messages, that modification to TCP's handling of ICMP soft error messages that
rejects pending connection-requests when those error messages are rejects pending connection-requests when those error messages are
received. This behavior reduces the likelihood of long delays received. This behavior reduces the likelihood of long delays
between connection establishment attempts that may arise in a number between connection-establishment attempts that may arise in a number
of scenarios, including one in which dual stack nodes that have IPv6 of scenarios, including one in which dual-stack nodes that have IPv6
enabled by default are deployed in IPv4 or mixed IPv4 and IPv6 enabled by default are deployed in IPv4 or mixed IPv4 and IPv6
environments. environments.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Error Handling in TCP . . . . . . . . . . . . . . . . . . . . 3 2. Error Handling in TCP . . . . . . . . . . . . . . . . . . . . 3
2.1. Reaction to ICMP error messages that indicate hard 2.1. Reaction to ICMP Error Messages That Indicate Hard
errors . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Errors . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Reaction to ICMP error messages that indicate soft 2.2. Reaction to ICMP Error Messages That Indicate Soft
errors . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Errors . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Problems that may arise from TCP's reaction to soft errors . . 5 3. Problems That May Arise from TCP's Reaction to Soft Errors . . 5
3.1. General Discussion . . . . . . . . . . . . . . . . . . . . 5 3.1. General Discussion . . . . . . . . . . . . . . . . . . . . 5
3.2. Problems that may arise with Dual Stack IPv6 on by 3.2. Problems That May Arise with Dual-Stack IPv6 on by
Default . . . . . . . . . . . . . . . . . . . . . . . . . 6 Default . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Deployed workarounds for long delays between 4. Deployed Workarounds for Long Delays between
connection-establishment attempts . . . . . . . . . . . . . . 7 Connection-Establishment Attempts . . . . . . . . . . . . . . 7
4.1. Context-sensitive ICMP/TCP interaction . . . . . . . . . . 7 4.1. Context-Sensitive ICMP/TCP Interaction . . . . . . . . . . 7
4.2. Context-sensitive ICMP/TCP interaction with repeated 4.2. Context-Sensitive ICMP/TCP Interaction with Repeated
confirmation . . . . . . . . . . . . . . . . . . . . . . . 8 Confirmation . . . . . . . . . . . . . . . . . . . . . . . 8
5. Possible drawbacks of changing ICMP semantics . . . . . . . . 9 5. Possible Drawbacks of Changing ICMP Semantics . . . . . . . . 9
5.1. Non-deterministic transient network failures . . . . . . . 9 5.1. Non-Deterministic Transient Network Failures . . . . . . . 9
5.2. Deterministic transient network failures . . . . . . . . . 10 5.2. Deterministic Transient Network Failures . . . . . . . . . 10
5.3. Non-compliant Network Address Translators (NATs) . . . . . 10 5.3. Non-Compliant Network Address Translators (NATs) . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 11
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 12 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 9.1. Normative References . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . . 12 9.2. Informative References . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . . 12
Appendix A. Change log (to be removed before publication of
the document as an RFC) . . . . . . . . . . . . . . . 13
A.1. Changes from draft-ietf-tcpm-tcp-soft-errors-08 . . . . . 13
A.2. Changes from draft-ietf-tcpm-tcp-soft-errors-07 . . . . . 14
A.3. Changes from draft-ietf-tcpm-tcp-soft-errors-06 . . . . . 14
A.4. Changes from draft-ietf-tcpm-tcp-soft-errors-05 . . . . . 14
A.5. Changes from draft-ietf-tcpm-tcp-soft-errors-04 . . . . . 15
A.6. Changes from draft-ietf-tcpm-tcp-soft-errors-03 . . . . . 15
A.7. Changes from draft-ietf-tcpm-tcp-soft-errors-02 . . . . . 15
A.8. Changes from draft-ietf-tcpm-tcp-soft-errors-01 . . . . . 15
A.9. Changes from draft-ietf-tcpm-tcp-soft-errors-00 . . . . . 15
A.10. Changes from draft-gont-tcpm-tcp-soft-errors-02 . . . . . 15
A.11. Changes from draft-gont-tcpm-tcp-soft-errors-01 . . . . . 15
A.12. Changes from draft-gont-tcpm-tcp-soft-errors-00 . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . . . . 17
1. Introduction 1. Introduction
The handling of network failures can be separated into two different The handling of network failures can be separated into two different
actions: fault isolation and fault recovery. Fault isolation actions: fault isolation and fault recovery. Fault isolation
consists of the actions that hosts and routers take to determine that consists of the actions that hosts and routers take to determine that
there is a network failure. Fault recovery, on the other hand, there is a network failure. Fault recovery, on the other hand,
consists of the actions that hosts and routers perform in an attempt consists of the actions that hosts and routers perform in an attempt
to survive a network failure [RFC0816]. to survive a network failure [RFC0816].
In the Internet architecture, the Internet Control Message Protocol In the Internet architecture, the Internet Control Message Protocol
(ICMP) [RFC0792] is one fault isolation technique to report network (ICMP) [RFC0792] is one fault isolation technique to report network
error conditions to the hosts sending datagrams over the network. error conditions to the hosts sending datagrams over the network.
When a host is notified of a network error, its network stack will When a host is notified of a network error, its network stack will
attempt to continue communications, if possible, in the presence of attempt to continue communications, if possible, in the presence of
the network failure. The fault recovery strategy may depend on the the network failure. The fault recovery strategy may depend on the
type of network failure taking place, and the time the error type of network failure taking place and the time at which the error
condition is detected. condition is detected.
This document analyzes the problems that may arise due to TCP's fault This document analyzes the problems that may arise due to TCP's fault
recovery reactions to ICMP soft errors. It analyzes the problems recovery reactions to ICMP soft errors. It analyzes the problems
that may arise when a host tries to establish a TCP connection with a that may arise when a host tries to establish a TCP connection with a
multihomed host for which some of its addresses are unreachable. multihomed host that has some unreachable addresses. Additionally,
Additionally, it analyzes the problems that may arise in the specific it analyzes the problems that may arise in the specific scenario
scenario where dual stack nodes that have IPv6 enabled by default are where dual-stack nodes that have IPv6 enabled by default are deployed
deployed in IPv4 or mixed IPv4 and IPv6 environments. in IPv4 or mixed IPv4 and IPv6 environments.
Finally, we document a modification to TCP's reaction to ICMP Finally, we document a modification to TCP's reaction to ICMP
messages indicating soft errors during connection startup, that has messages indicating soft errors during connection startup that has
been implemented in a variety of TCP/IP stacks to help overcome the been implemented in a variety of TCP/IP stacks to help overcome the
problems outlined below. We stress that this modification runs problems outlined below. We stress that this modification runs
contrary to the standard behavior and this document unambiguously contrary to the standard behavior and this document unambiguously
does not change the standard reaction. does not change the standard reaction.
[Gont] describes alternative approaches for dealing with the problem [Gont] describes alternative approaches for dealing with the problem
of long delays between connection-establishment attempts in TCP. of long delays between connection-establishment attempts in TCP.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Error Handling in TCP 2. Error Handling in TCP
Network errors can be divided into soft and hard errors. Soft errors Network errors can be divided into soft and hard errors. Soft errors
are considered to be transient network failures, which are likely to are considered to be transient network failures that are likely to be
be solved in the near term. Hard errors, on the other hand, are solved in the near term. Hard errors, on the other hand, are
considered to reflect network error conditions that are unlikely to considered to reflect network error conditions that are unlikely to
be solved in the near future. be solved in the near future.
The Host Requirements RFC [RFC1122] states, in Section 4.2.3.9., that The Host Requirements RFC [RFC1122] states, in Section 4.2.3.9, that
the ICMP messages that indicate soft errors are ICMP "Destination the ICMP messages that indicate soft errors are ICMP "Destination
Unreachable" codes 0 (network unreachable), 1 (host unreachable), and Unreachable" codes 0 (network unreachable), 1 (host unreachable), and
5 (source route failed), ICMP "Time Exceeded" codes 0 (time to live 5 (source route failed); ICMP "Time Exceeded" codes 0 (time to live
exceeded in transit) and 1 (fragment reassembly time exceeded), and exceeded in transit) and 1 (fragment reassembly time exceeded); and
ICMP "Parameter Problem". Even though ICMPv6 did not exist when ICMP "Parameter Problem". Even though ICMPv6 did not exist when
[RFC1122] was written, one could extrapolate the concept of soft [RFC1122] was written, one could extrapolate the concept of soft
errors to ICMPv6 "Destination Unreachable" codes 0 (no route to errors to ICMPv6 "Destination Unreachable" codes 0 (no route to
destination) and 3 (address unreachable), ICMPv6 "Time Exceeded" destination) and 3 (address unreachable); ICMPv6 "Time Exceeded"
codes 0 (Hop limit exceeded in transit) and 1 (Fragment reassembly codes 0 (hop limit exceeded in transit) and 1 (fragment reassembly
time exceeded), and ICMPv6 "Parameter Problem" codes 0 (Erroneous time exceeded); and ICMPv6 "Parameter Problem" codes 0 (erroneous
header field encountered), 1 (Unrecognized Next Header type header field encountered), 1 (unrecognized Next Header type
encountered) and 2 (Unrecognized IPv6 option encountered) [RFC4443]. encountered), and 2 (unrecognized IPv6 option encountered) [RFC4443].
+----------------------------------+--------------------------------+ +----------------------------------+--------------------------------+
| ICMP | ICMPv6 | | ICMP | ICMPv6 |
+----------------------------------+--------------------------------+ +----------------------------------+--------------------------------+
| Destination Unreachable (codes | Destination Unreachable (codes | | Destination Unreachable (codes | Destination Unreachable (codes |
| 0, 1, and 5) | 0 and 3) | | 0, 1, and 5) | 0 and 3) |
+----------------------------------+--------------------------------+ +----------------------------------+--------------------------------+
| Time Exceeded (codes 0 and 1) | Time exceeded (codes 0 and 1) | | Time Exceeded (codes 0 and 1) | Time Exceeded (codes 0 and 1) |
+----------------------------------+--------------------------------+ +----------------------------------+--------------------------------+
| Parameter Problem | Parameter Problem (codes 0, 1, | | Parameter Problem | Parameter Problem (codes 0, 1, |
| | and 2) | | | and 2) |
+----------------------------------+--------------------------------+ +----------------------------------+--------------------------------+
Table 1: Extrapolating the concept of soft errors to ICMPv6 Table 1: Extrapolating the concept of soft errors to ICMPv6
When there is a network failure that is not signaled to the sending When there is a network failure that is not signaled to the sending
host, such as a gateway corrupting packets, TCP's fault recovery host, such as a gateway corrupting packets, TCP's fault recovery
action is to repeatedly retransmit the segment until either it gets action is to repeatedly retransmit the corresponding data until
acknowledged, or the connection times out. either they get acknowledged or the connection times out.
In the case that a host does receive an ICMP error message referring In the case that a host does receive an ICMP error message referring
to an ongoing TCP connection, the IP layer will pass this message up to an ongoing TCP connection, the IP layer will pass this message up
to the corresponding TCP instance to raise awareness of the network to the corresponding TCP instance to raise awareness of the network
failure [RFC1122]. TCP's reaction to ICMP messages will depend on failure [RFC1122]. TCP's reaction to ICMP messages will depend on
the type of error being signaled. the type of error being signaled.
2.1. Reaction to ICMP error messages that indicate hard errors 2.1. Reaction to ICMP Error Messages That Indicate Hard Errors
When receiving an ICMP error message that indicates a hard error When receiving an ICMP error message that indicates a hard error
condition, compliant TCP implementations will simply abort the condition, compliant TCP implementations will simply abort the
corresponding connection, regardless of the connection state. corresponding connection, regardless of the connection state.
The Host Requirements RFC [RFC1122] states, in Section 4.2.3.9, that The Host Requirements RFC [RFC1122] states, in Section 4.2.3.9, that
TCP SHOULD abort connections when receiving ICMP error messages that TCP SHOULD abort connections when receiving ICMP error messages that
indicate hard errors. This policy is based on the premise that, as indicate hard errors. This policy is based on the premise that, as
hard errors indicate network error conditions that will not change in hard errors indicate network error conditions that will not change in
the near term, it will not be possible for TCP to usefully recover the near term, it will not be possible for TCP to usefully recover
from this type of network failure. from this type of network failure.
It should be noted that virtually all current TCP implementations do It should be noted that virtually none of the current TCP
not follow the advice in [RFC1122], and do not abort the implementations follow the advice in [RFC1122], and they do not abort
corresponding connection when an ICMP hard error is received for the corresponding connection when an ICMP hard error is received for
connection that is in any of the synchronized states a connection that is in any of the synchronized states
[I-D.ietf-tcpm-icmp-attacks]. [ICMP-ATTACKS].
2.2. Reaction to ICMP error messages that indicate soft errors 2.2. Reaction to ICMP Error Messages That Indicate Soft Errors
If an ICMP error message is received that indicates a soft error, TCP If an ICMP error message is received that indicates a soft error, TCP
will repeatedly retransmit the segment until it either gets will repeatedly retransmit the corresponding data until either they
acknowledged or the connection times out. In addition, the TCP get acknowledged or the connection times out. In addition, the TCP
sender may record the information for possible later use [Stevens] sender may record the information for possible later use (see
(pp. 317-319). [Stevens], pp. 317-319).
The Host Requirements RFC [RFC1122] states, in Section 4.2.3.9, that The Host Requirements RFC [RFC1122] states, in Section 4.2.3.9, that
TCP MUST NOT abort connections when receiving ICMP error messages TCP MUST NOT abort connections when receiving ICMP error messages
that indicate soft errors. This policy is based on the premise that, that indicate soft errors. This policy is based on the premise that,
as soft errors are transient network failures that will hopefully be as soft errors are transient network failures that will hopefully be
solved in the near term, one of the retransmissions will succeed. solved in the near term, one of the retransmissions will succeed.
When the connection timer expires, and an ICMP soft error message has When the connection timer expires and an ICMP soft error message has
been received before the timeout, TCP can use this information to been received before the timeout, TCP can use this information to
provide the user with a more specific error message [Stevens] (pp. provide the user with a more specific error message (see [Stevens],
317-319). pp. 317-319).
This reaction to soft errors exploits the valuable feature of the This reaction to soft errors exploits a valuable feature of the
Internet that for many network failures, the network can be Internet -- that, for many network failures, the network can be
dynamically reconstructed without any disruption of the endpoints. dynamically reconstructed without any disruption of the endpoints.
3. Problems that may arise from TCP's reaction to soft errors 3. Problems That May Arise from TCP's Reaction to Soft Errors
3.1. General Discussion 3.1. General Discussion
Even though TCP's fault recovery strategy in the presence of soft Even though TCP's fault recovery strategy in the presence of soft
errors allows for TCP connections to survive transient network errors allows for TCP connections to survive transient network
failures, there are scenarios in which this policy may cause failures, there are scenarios in which this policy may cause
undesirable effects. undesirable effects.
For example, consider a scenario in which an application on a local For example, consider a scenario in which an application on a local
host is trying to communicate with a destination whose name resolves host is trying to communicate with a destination whose name resolves
to several IP addresses. The application on the local host will try to several IP addresses. The application on the local host will try
to establish a connection with the destination host, usually cycling to establish a connection with the destination host, usually cycling
through the list of IP addresses, until one succeeds [RFC1123]. through the list of IP addresses until one succeeds [RFC1123].
Suppose that some (but not all) of the addresses in the returned list Suppose that some (but not all) of the addresses in the returned list
are permanently unreachable. If such a permanently unreachable are permanently unreachable. If such a permanently unreachable
address is the first in the list, the application will likely try to address is the first in the list, the application will likely try to
use the permanently unreachable address first and block waiting for a use it first and block waiting for a timeout before trying an
timeout before trying an alternate address. alternate address.
As discussed in Section 2, this unreachability condition may or may As discussed in Section 2, this unreachability condition may or may
not be signaled to the sending host. If the local TCP is not not be signaled to the sending host. If the local TCP is not
signaled concerning the error condition, there is very little that signaled concerning the error condition, there is very little that
can be done other than repeatedly retransmit the SYN segment, and can be done other than to repeatedly retransmit the SYN segment and
wait for the existing timeout mechanism in TCP, or an application wait for the existing timeout mechanism in TCP, or an application
timeout, to be triggered. However, even if unreachability is timeout, to be triggered. However, even if unreachability is
signaled by some intermediate router to the local TCP by means of an signaled by some intermediate router to the local TCP by means of an
ICMP soft error message, the local TCP will still repeatedly ICMP soft error message, the local TCP will still repeatedly
retransmit the SYN segment until the connection timer expires (in the retransmit the SYN segment until the connection timer expires (in the
hopes that the error is transient). The Host Requirements RFC hopes that the error is transient). The Host Requirements RFC
[RFC1122] states that this timer MUST be large enough to provide [RFC1122] states that this timer MUST be large enough to provide
retransmission of the SYN segment for at least 3 minutes. This would retransmission of the SYN segment for at least 3 minutes. This would
mean that the application on the local host would spend several mean that the application on the local host would spend several
minutes for each unreachable address it uses for trying to establish minutes for each unreachable address with which it tries to establish
the TCP connection. These long delays between connection the TCP connection. These long delays between connection-
establishment attempts would be inappropriate for many interactive establishment attempts would be inappropriate for many interactive
applications such as the web. [Shneiderman] and [Thadani] offer some applications, such as the Web. [Shneiderman] and [Thadani] offer some
insight into interactive systems (e.g., how the response time affects insight into interactive systems (e.g., how the response time affects
the usability of an application). This highlights that there is no the usability of an application). This highlights that there is no
one definition of a "transient error" and that the level of one definition of a "transient error" and that the level of
persistence in the face of failure represents a tradeoff. persistence in the face of failure represents a tradeoff.
It is worth noting that while most applications try the addresses It is worth noting that while most applications try the addresses
returned by the name-to-address function in serial, this is certainly returned by the name-to-address function in serial, this is certainly
not the only possible approach. For example, applications could try not the only possible approach. For example, applications could try
multiple addresses in parallel until one succeeds, possibly avoiding multiple addresses in parallel until one succeeds, possibly avoiding
the problem of long delays between connection establishment attempts the problem of long delays between connection-establishment attempts
described in this document. described in this document [Gont].
3.2. Problems that may arise with Dual Stack IPv6 on by Default 3.2. Problems That May Arise with Dual-Stack IPv6 on by Default
A particular scenario in which the above sketched type of problem may A particular scenario in which the above type of problem may occur
occur regularly is that where dual stack nodes that have IPv6 enabled regularly is that where dual-stack nodes that have IPv6 enabled by
by default are deployed in IPv4 or mixed IPv4 and IPv6 environments, default are deployed in IPv4 or mixed IPv4 and IPv6 environments and
and the IPv6 connectivity is non-existent [RFC4943]. the IPv6 connectivity is non-existent [RFC4943].
As discussed in [RFC4943], there are two possible variants of this As discussed in [RFC4943], there are two possible variants of this
scenario, which differ in whether the lack of connectivity is scenario, which differ in whether or not the lack of connectivity is
signaled to the sending node, or not. signaled to the sending node.
In those scenarios in which packets sent to a destination are In those scenarios in which packets sent to a destination are
silently dropped and no ICMPv6 [RFC4443] errors are generated, there silently dropped and no ICMPv6 [RFC4443] errors are generated, there
is little that can be done other than waiting for the existing is little that can be done other than to wait for the existing
connection timeout mechanism in TCP, or an application timeout, to be connection-timeout mechanism in TCP, or an application timeout, to be
triggered. triggered.
In scenarios where a legacy node has no default routers and Neighbor In scenarios where a legacy node has no default routers and Neighbor
Unreachability Detection (NUD) [RFC4861] fails for destinations Unreachability Detection (NUD) [RFC4861] fails for destinations
assumed to be on-link, or where firewalls or other systems that assumed to be on-link, or where firewalls or other systems that
enforce scope boundaries send ICMPv6 errors, the sending node will be enforce scope boundaries send ICMPv6 errors, the sending node will be
signaled of the unreachability problem. However, as discussed in signaled of the unreachability problem. However, as discussed in
Section 2.2, standard TCP implementations will not abort connections Section 2.2, compliant TCP implementations will not abort connections
when receiving ICMP error messages that indicate soft errors. when receiving ICMP error messages that indicate soft errors.
4. Deployed workarounds for long delays between connection- 4. Deployed Workarounds for Long Delays between Connection-
establishment attempts Establishment Attempts
The following subsections describe a number of workarounds for the The following subsections describe a number of workarounds for the
problem of long delays between connection-establishment attempts that problem of long delays between connection-establishment attempts that
have been implemented in a variety of TCP/IP stacks. We note that have been implemented in a variety of TCP/IP stacks. We note that
treating soft errors as hard errors during connection establishment, treating soft errors as hard errors during connection establishment,
while widespread, is not part of standard TCP behavior and this while widespread, is not part of standard TCP behavior and this
document does not change that state of affairs. The TCPM WG (TCP document does not change that state of affairs. The consensus of the
Maintenance and Minor Extensions Working Group) consensus was to TCPM WG (TCP Maintenance and Minor Extensions Working Group) was to
document this widespread implementation of nonstandard TCP behavior, document this widespread implementation of nonstandard TCP behavior
but to not change the TCP standard. but to not change the TCP standard.
4.1. Context-sensitive ICMP/TCP interaction 4.1. Context-Sensitive ICMP/TCP Interaction
As discussed in Section 1, it may make sense for the fault recovery As discussed in Section 1, it may make sense for the fault recovery
action to depend not only on the type of error being reported, but action to depend not only on the type of error being reported but
also on the state of the connection against which the error is also on the state of the connection against which the error is
reported. For example, one could infer that when an error arrives in reported. For example, one could infer that when an error arrives in
response to opening a new connection, it is probably caused by response to opening a new connection, it is probably caused by
opening the connection improperly, rather than by a transient network opening the connection improperly, rather than by a transient network
failure [RFC0816]. failure [RFC0816].
A number of TCP implementations have modified their reaction to all A number of TCP implementations have modified their reaction to all
ICMP soft errors, to treat them as hard errors when they are received ICMP soft errors and treat them as hard errors when they are received
for connections in the SYN-SENT or SYN-RECEIVED states. For example, for connections in the SYN-SENT or SYN-RECEIVED states. For example,
this workaround has been implemented in the Linux kernel since this workaround has been implemented in the Linux kernel since
version 2.0.0 (released in 1996) [Linux]. However, it should be version 2.0.0 (released in 1996) [Linux]. However, it should be
noted that this change violates section 4.2.3.9 of [RFC1122], which noted that this change violates section 4.2.3.9 of [RFC1122], which
states that these ICMP error messages indicate soft error conditions states that these ICMP error messages indicate soft error conditions
and therefore TCP MUST NOT abort the corresponding connection. and that, therefore, TCP MUST NOT abort the corresponding connection.
[RFC3168] states that a host that receives a RST in response to the [RFC3168] states that a host that receives a RST in response to the
transmission of an ECN-setup SYN packet MAY resend a SYN with CWR and transmission of an ECN (Explicit Congestion Notification)-setup SYN
ECE cleared. This is meant to deal with faulty middle-boxes that packet MAY resend a SYN with the CWR (Congestion Window Reduced) and
reject connections when a SYN segment has the ECE and CWR bits set. ECE (ECN-Echo) bits cleared. This is meant to deal with faulty
Some faulty middle-boxes (e.g., firewalls) may reject connections middle-boxes that reject connections when a SYN segment has the ECE
with an ICMP soft error of type 3 (Destination Unreachable), code 0 and CWR bits set. Some faulty middle-boxes (e.g., firewalls) may
(net unreachable) or 1 (host unreachable), instead of an RST. reject these connection requests with an ICMP soft error of type 3
Therefore a system that processes ICMP error messages as hard errors (Destination Unreachable), code 0 (net unreachable) or 1 (host
when they are received for a connection in any of the non- unreachable), instead of a RST. Therefore, a system that processes
synchronized states could resend the SYN segment with the ECE and CWR ICMP soft error messages as hard errors when they are received for a
bits cleared when an ICMP "net unreachable" (type 3, code 0) or "host connection in any of the non-synchronized states could resend the SYN
unreachable" (type 3, code 1) error message is received in response segment with the ECE and CWR bits cleared when an ICMP "net
to a SYN segment that had these bits set. unreachable" (type 3, code 0) or "host unreachable" (type 3, code 1)
error message is received in response to a SYN segment that had these
bits set.
Section 4.2 discusses a more conservative approach than that sketched Section 4.2 discusses a more conservative approach than that sketched
above, that is implemented in FreeBSD. above, which is implemented in FreeBSD.
4.2. Context-sensitive ICMP/TCP interaction with repeated confirmation 4.2. Context-Sensitive ICMP/TCP Interaction with Repeated Confirmation
A more conservative approach than simply treating soft errors as hard A more conservative approach than simply treating soft errors as hard
errors as described above would be to abort a connection in the SYN- errors (as described above) would be to abort a connection in the
SENT or SYN-RECEIVED states only after an ICMP soft error has been SYN-SENT or SYN-RECEIVED states only after an ICMP soft error has
received a specified number of times, and the SYN segment has been been received a specified number of times and the SYN segment has
retransmitted more than some specified number of times. been retransmitted more than some specified number of times.
Two new parameters would have to be introduced to TCP, to be used Two new parameters would have to be introduced to TCP, to be used
only during the connection-establishment phase: MAXSYNREXMIT and only during the connection-establishment phase: MAXSYNREXMIT and
MAXSOFTERROR. MAXSYNREXMIT would specify the number of times the SYN MAXSOFTERROR. MAXSYNREXMIT would specify the number of times the SYN
segment would have to be retransmitted before a connection is segment would have to be retransmitted before a connection is
aborted. MAXSOFTERROR would specify the number of ICMP messages aborted. MAXSOFTERROR would specify the number of ICMP messages
indicating soft errors that would have to be received before a indicating soft errors that would have to be received before a
connection is aborted. connection is aborted.
Two additional state variables would need to be introduced to store Two additional state variables would need to be introduced to store
skipping to change at page 8, line 49 skipping to change at page 9, line 6
zero when a connection attempt is initiated, with "nsynrexmit" being zero when a connection attempt is initiated, with "nsynrexmit" being
incremented by one every time the SYN segment is retransmitted and incremented by one every time the SYN segment is retransmitted and
"nsofterror" being incremented by one every time an ICMP message that "nsofterror" being incremented by one every time an ICMP message that
indicates a soft error is received. indicates a soft error is received.
A connection in the SYN-SENT or SYN-RECEIVED states would be aborted A connection in the SYN-SENT or SYN-RECEIVED states would be aborted
if "nsynrexmit" was greater than MAXSYNREXMIT and "nsofterror" was if "nsynrexmit" was greater than MAXSYNREXMIT and "nsofterror" was
simultaneously greater than MAXSOFTERROR. simultaneously greater than MAXSOFTERROR.
This approach would give the network more time to solve the This approach would give the network more time to solve the
connectivity problem than simply aborting a connection attempt upon connectivity problem than does simply aborting a connection attempt
reception of the first soft error. However, it should be noted that upon reception of the first soft error. However, it should be noted
depending on the values chosen for the MAXSYNREXMIT and MAXSOFTERROR that, depending on the values chosen for the MAXSYNREXMIT and
parameters, this approach could still lead to long delays between MAXSOFTERROR parameters, this approach could still lead to long
connection establishment attempts, thus not solving the problem. For delays between connection-establishment attempts, thus not solving
example, BSD systems abort connections in the SYN-SENT or the SYN- the problem. For example, BSD systems abort connections in the SYN-
RECEIVED state when a second ICMP error is received, and the SYN SENT or the SYN-RECEIVED state when a second ICMP error is received
segment has been retransmitted more than three times. They also set and the SYN segment has been retransmitted more than three times.
up a "connection-establishment timer" that imposes an upper limit on They also set up a "connection-establishment timer" that imposes an
the time the connection establishment attempt has to succeed, which upper limit on the time the connection-establishment attempt has to
expires after 75 seconds [Stevens2] (pp. 828-829). Even when this succeed, which expires after 75 seconds (see [Stevens2], pp. 828-
policy may be better than the three-minutes timeout policy specified 829). Even when this policy may be better than the three-minute
in [RFC1122], it may still be inappropriate for handling the timeout policy specified in [RFC1122], it may still be inappropriate
potential problems described in this document. This more for handling the potential problems described in this document. This
conservative approach has been implemented in BSD systems for more more conservative approach has been implemented in BSD systems for
than ten years [Stevens2]. more than ten years [Stevens2].
We also note that the approach given in this section is a generalized We also note that the approach given in this section is a generalized
version of the approach sketched in the previous section. In version of the approach sketched in the previous section. In
particular, with MAXSOFTERROR set to 1 and MAXSYNREXMIT set to zero particular, with MAXSOFTERROR set to 1 and MAXSYNREXMIT set to zero,
the schemes are identical. the schemes are identical.
5. Possible drawbacks of changing ICMP semantics 5. Possible Drawbacks of Changing ICMP Semantics
The following subsections discuss some of the possible drawbacks The following subsections discuss some possible drawbacks that could
arising from the use of the non-standard modifications to TCP's arise from use of the non-standard modifications to TCP's reaction to
reaction to soft errors described in Section 4.1 and Section 4.2. soft errors, which are described in Section 4.1 and Section 4.2.
5.1. Non-deterministic transient network failures 5.1. Non-Deterministic Transient Network Failures
In scenarios where a transient network failure affects all of the In scenarios where a transient network failure affects all of the
addresses returned by the name-to-address translation function, all addresses returned by the name-to-address translation function, all
destinations could be unreachable for some short period of time. For destinations could be unreachable for some short period of time. For
example, a mobile system consisting of a cell and a repeater may pass example, a mobile system consisting of a cell and a repeater may pass
through a tunnel, leading to a loss of connectivity at the repeater, through a tunnel, leading to a loss of connectivity at the repeater,
with the repeater sending ICMP soft errors back to the cell. Also, with the repeater sending ICMP soft errors back to the cell. Also, a
transient routing problem might lead some intervening router to drop transient routing problem might lead some intervening router to drop
a SYN segment that was meaning to establish a TCP connection and send a SYN segment that was meaning to establish a TCP connection and send
an ICMP soft error back to the host. Finally, a SYN segment carrying an ICMP soft error back to the host. Finally, a SYN segment carrying
data might get fragmented and some of the resulting fragments might data might get fragmented and some of the resulting fragments might
get lost, with the destination host timing out the reassembly process get lost, with the destination host timing out the reassembly process
and sending an ICMP soft error back to the sending host (although and sending an ICMP soft error back to the sending host (although
this particular scenario is unlikely because, while the [RFC0793] this particular scenario is unlikely because, while [RFC0793] allows
allows SYN segments to carry data, in practice they do not). In such SYN segments to carry data, in practice they do not). In such
scenarios, the application could quickly cycle through all the IP scenarios, the application could quickly cycle through all the IP
addresses in the list and return an error, when it could have let TCP addresses in the list and return an error, when it could have let TCP
retry a destination a few seconds later, when the transient problem retry a destination a few seconds later, when the transient problem
could have disappeared. In this case, the modifications described could have disappeared. In this case, the modifications described
here make TCP less robust than a standards-compliant implementation. here make TCP less robust than a standards-compliant implementation.
Additionally, in many cases a domain name maps to a single IP Additionally, in many cases a domain name maps to a single IP
address. In such a case, it might be better to try that address address. In such a case, it might be better to try that address
persistently according to normal TCP rules, instead of just aborting persistently according to normal TCP rules, instead of just aborting
the pending connection upon receipt of an ICMP soft error. the pending connection upon receipt of an ICMP soft error.
5.2. Deterministic transient network failures 5.2. Deterministic Transient Network Failures
There are some scenarios in which transient network failures could be There are some scenarios in which transient network failures could be
deterministic. For example, consider a scenario in which upstream deterministic. For example, consider a scenario in which upstream
network connectivity is triggered by network use. That is, network network connectivity is triggered by network use. That is, network
connectivity is instantiated only on an "as needed" basis. In this connectivity is instantiated only on an "as needed" basis. In this
scenario, the connection triggering the upstream connectivity could scenario, the connection triggering the upstream connectivity could
deterministically receive ICMP Destination Unreachables while the deterministically receive ICMP Destination Unreachables while the
upstream connectivity is being activated, and thus would be aborted. upstream connectivity is being activated, and thus would be aborted.
Again, in this case, the modifications described here make TCP less Again, in this case, the modifications described here make TCP less
robust than a standards-compliant implementation. robust than a standards-compliant implementation.
5.3. Non-compliant Network Address Translators (NATs) 5.3. Non-Compliant Network Address Translators (NATs)
Some NATs respond to an unsolicited inbound SYN segment with an ICMP Some NATs respond to an unsolicited inbound SYN segment with an ICMP
soft error message. If the system sending the unsolicited SYN soft error message. If the system sending the unsolicited SYN
segment implements the workaround described in this document, it will segment implements the workaround described in this document, it will
abort the connection upon receipt of the ICMP error message, thus abort the connection upon receipt of the ICMP error message, thus
probably preventing TCP's simultaneous open through the NAT from probably preventing TCP's simultaneous open from succeeding through
succeeding. However, it must be stressed that those NATs described the NAT. However, it must be stressed that those NATs described in
in this section are not BEHAVE-compliant, and therefore should this section are not BEHAVE-compliant and therefore should implement
implement REQ-4 of [RFC5382] instead. REQ-4 of [RFC5382] instead.
In those scenarios in which such a non-BEHAVE-compliant NAT is In those scenarios in which such a non-BEHAVE-compliant NAT is
deployed, TCP simultaneous open could fail. While undesirable, this deployed, TCP simultaneous opens could fail. While undesirable, this
is tolerable in many situations. For instance, a number of host is tolerable in many situations. For instance, a number of host
implementations of TCP do not support TCP simultaneous opens implementations of TCP do not support TCP simultaneous opens
[Zuquete]. [Zuquete].
6. Security Considerations 6. Security Considerations
This document describes a non-standard modification to TCP's reaction This document describes a non-standard modification to TCP's reaction
to soft errors that has been implemented in a variety of TCP to soft errors that has been implemented in a variety of TCP
implementations. This modification makes TCP abort a connection in implementations. This modification makes TCP abort a connection in
the SYN-SENT or the SYN-RECEIVED states when it receives an ICMP the SYN-SENT or the SYN-RECEIVED states when it receives an ICMP
skipping to change at page 11, line 12 skipping to change at page 11, line 16
vulnerable to attack, even if only slightly. However, we note that vulnerable to attack, even if only slightly. However, we note that
an attacker wishing to reset ongoing TCP connections could send any an attacker wishing to reset ongoing TCP connections could send any
of the ICMP hard error messages in any connection state. of the ICMP hard error messages in any connection state.
Generally, TCP backs off its retransmission timer each time it Generally, TCP backs off its retransmission timer each time it
retransmits the SYN segment for the same connection. If a TCP retransmits the SYN segment for the same connection. If a TCP
implements the modification described in this document, that is, implements the modification described in this document, that is,
tries the next address in the list upon receipt of an ICMP error tries the next address in the list upon receipt of an ICMP error
message, it might end up injecting more packets into the network than message, it might end up injecting more packets into the network than
if it had simply retried the same address a number of times. if it had simply retried the same address a number of times.
However, compliant TCP implementations might already incur into this However, compliant TCP implementations might already incur this
behaviour (e.g., as a result of cycling through the list of IP behavior (e.g., as a result of cycling through the list of IP
addressses in response to RST segments) as there are currently no addresses in response to RST segments) as there are currently no
recommendations on methods for limiting the rate at which SYN recommendations on methods for limiting the rate at which SYN
segments are sent for connecting to a specific destination. segments are sent for connecting to a specific destination.
A discussion of the use of ICMP to perform a variety of attacks A discussion of the use of ICMP to perform a variety of attacks
against TCP, and a number of counter-measures that minimize the against TCP, and a number of counter-measures that minimize the
impact of these attacks can be found in [I-D.ietf-tcpm-icmp-attacks]. impact of these attacks, can be found in [ICMP-ATTACKS].
A discussion of the security issues arising from the use of ICMPv6 A discussion of the security issues arising from the use of ICMPv6
can be found in [RFC4443]. can be found in [RFC4443].
7. IANA Considerations 7. Acknowledgements
This document has no actions for IANA.
8. Acknowledgements
The author wishes to thank Mark Allman, Jari Arkko, David Black, Ron The author wishes to thank Mark Allman, Jari Arkko, David Black, Ron
Bonica, Ted Faber, Gorry Fairhurst, Sally Floyd, Tomohiro Fujisaki, Bonica, Ted Faber, Gorry Fairhurst, Sally Floyd, Juan Fraschini,
Guillermo Gont, Saikat Guha, Alfred Hoenes, Michael Kerrisk, Eddie Tomohiro Fujisaki, Guillermo Gont, Saikat Guha, Alfred Hoenes,
Kohler, Mika Liljeberg, Arifumi Matsumoto, Sandy Murphy, Carlos Michael Kerrisk, Eddie Kohler, Mika Liljeberg, Arifumi Matsumoto,
Pignataro, Pasi Sarolahti, Pekka Savola, Pyda Srisuresh, Jinmei Sandy Murphy, Carlos Pignataro, Pasi Sarolahti, Pekka Savola, Pyda
Tatuya, and Joe Touch, for contributing many valuable comments on Srisuresh, Jinmei Tatuya, and Joe Touch for contributing many
earlier versions of this document. valuable comments on earlier versions of this document.
The author wishes to thank Secretaria de Extension Universitaria at The author wishes to thank Secretaria de Extension Universitaria at
Universidad Tecnologica Nacional, and Universidad Tecnologica Universidad Tecnologica Nacional and Universidad Tecnologica
Nacional/Facultad Regional Haedo, for their support in this work. Nacional/Facultad Regional Haedo for their support in this work.
Finally, the author wishes to express deep and heartfelt gratitude to Finally, the author wishes to express deep and heartfelt gratitude to
Jorge Oscar Gont and Nelida Garcia, for their precious motivation and Jorge Oscar Gont and Nelida Garcia for their precious motivation and
guidance. guidance.
9. Contributors 8. Contributors
Mika Liljeberg was the first to describe how their implementation Mika Liljeberg was the first to describe how their implementation
treated soft errors. Based on that, the solution discussed in treated soft errors. Based on that, the solution discussed in
Section 4.1 was documented in [I-D.ietf-v6ops-v6onbydefault] by Section 4.1 was documented in [v6-ON] by Sebastien Roy, Alain Durand,
Sebastien Roy, Alain Durand and James Paugh. and James Paugh.
10. References 9. References
10.1. Normative References 9.1. Normative References
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, [RFC0792] Postel, J., "Internet Control Message Protocol",
RFC 792, September 1981. STD 5, RFC 792, September 1981.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981. RFC 793, September 1981.
[RFC1122] Braden, R., "Requirements for Internet Hosts - [RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989. Communication Layers", STD 3, RFC 1122, October 1989.
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application [RFC1123] Braden, R., "Requirements for Internet Hosts -
and Support", STD 3, RFC 1123, October 1989. Application and Support", STD 3, RFC 1123,
October 1989.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The
of Explicit Congestion Notification (ECN) to IP", Addition of Explicit Congestion Notification (ECN) to
RFC 3168, September 2001. IP", RFC 3168, September 2001.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet
Message Protocol (ICMPv6) for the Internet Protocol Control Message Protocol (ICMPv6) for the Internet
Version 6 (IPv6) Specification", RFC 4443, March 2006. Protocol Version 6 (IPv6) Specification", RFC 4443,
March 2006.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H.
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, Soliman, "Neighbor Discovery for IP version 6
September 2007. (IPv6)", RFC 4861, September 2007.
10.2. Informative References 9.2. Informative References
[Gont] Gont, F., "On the problem of long delays between [Gont] Gont, F., "On the problem of long delays between
connection-establishment attempts in TCP", http:// connection-establishment attempts in TCP", Work
www.gont.com.ar/papers/connection-delays/ in Progress, January 2009.
fgont-alt-solutions-connection-delays.pdf , 2008.
[I-D.ietf-tcpm-icmp-attacks]
Gont, F., "ICMP attacks against TCP",
draft-ietf-tcpm-icmp-attacks-04 (work in progress),
October 2008.
[I-D.ietf-v6ops-v6onbydefault] [ICMP-ATTACKS] Gont, F., "ICMP attacks against TCP", Work
Roy, S., Durand, A., and J. Paugh, "Issues with Dual Stack in Progress, October 2008.
IPv6 on by Default", draft-ietf-v6ops-v6onbydefault-03
(work in progress), July 2004.
[Linux] The Linux Project, "http://www.kernel.org". [Linux] The Linux Project, "http://www.kernel.org".
[RFC0816] Clark, D., "Fault isolation and recovery", RFC 816, [RFC0816] Clark, D., "Fault isolation and recovery", RFC 816,
July 1982. July 1982.
[RFC4943] Roy, S., Durand, A., and J. Paugh, "IPv6 Neighbor [RFC4943] Roy, S., Durand, A., and J. Paugh, "IPv6 Neighbor
Discovery On-Link Assumption Considered Harmful", Discovery On-Link Assumption Considered Harmful",
RFC 4943, September 2007. RFC 4943, September 2007.
[RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P. [RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.
Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142, Srisuresh, "NAT Behavioral Requirements for TCP",
RFC 5382, October 2008. BCP 142, RFC 5382, October 2008.
[Shneiderman] [Shneiderman] Shneiderman, B., "Response Time and Display Rate in
Shneiderman, B., "Response Time and Display Rate in Human Human Performance with Computers", ACM
Performance with Computers", ACM Computing Surveys , 1984. Computing Surveys, 1984.
[Stevens] Stevens, W., "TCP/IP Illustrated, Volume 1: The [Stevens] Stevens, W., "TCP/IP Illustrated, Volume 1: The
Protocols", Addison-Wesley , 1994. Protocols", Addison-Wesley , 1994.
[Stevens2] [Stevens2] Wright, G. and W. Stevens, "TCP/IP Illustrated,
Wright, G. and W. Stevens, "TCP/IP Illustrated, Volume 2: Volume 2: The Implementation", Addison-Wesley, 1994.
The Implementation", Addison-Wesley , 1994.
[Thadani] Thadani, A., "Interactive User Productivity", IBM Systems
Journal No. 1, 1981.
[Zuquete] Zuquete, A., "Improving the functionality of SYN cookies",
6th IFIP Communications and Multimedia Security Conference
(CMS 2002) , 2002.
Appendix A. Change log (to be removed before publication of the
document as an RFC)
A.1. Changes from draft-ietf-tcpm-tcp-soft-errors-08
o Addresses Last Call feedback from David Black: Minor tweaks in the
Section 1, Section 5.3, and Section 4.1 (ECN).
o Addresses Last Call feedback from Jinmei Tatuya: (on-link
assumption has been deprecated)
o Addresses Last Call feedback from Sandy Murphy: clarifies that
reaction to ICMP soft errors applies to all ICMP soft errors,
expands Section 5.1, and clarifies Section 4.1 (ECN).
o Minor editorial changes
A.2. Changes from draft-ietf-tcpm-tcp-soft-errors-07
o Fixes id nits.
A.3. Changes from draft-ietf-tcpm-tcp-soft-errors-06
o Added a paragraph (in Section 4.1) about the interaction of the
described modification with ECN-enabled connections
o Added a paragraph (in Section 6) about the possible scenario in
which a host injects SYN segments into the network at a high rate,
in response to ICMP soft errors.
o Miscellaneous editorial changes
A.4. Changes from draft-ietf-tcpm-tcp-soft-errors-05
o Miscellaneous edits, clarifications, and reorganization of both
workarounds into a single top-level section, as suggested by Pasi
Sarolahti.
o Added note on non-compliant NATs, as suggested by Ted Faber and
Saikat Guha
o Miscellaneous edits suggested by Gorry Fairhurst
o Added a table to clarify how to extrapolate the concept of ICMPv4
"soft errors" to ICMPv6 (as suggested by Arifumi Matsumoto and
Gorry Fairhurst).
o Miscellaneous edits, clarification on alternative approach by
sending connection requests in parallel, example of mobile system
(for non-deterministic errors), and note on the possible impact of
the workarounds on TCP's robusteness (as suggested by Joe Touch)
A.5. Changes from draft-ietf-tcpm-tcp-soft-errors-04
o Addresses feedback sent by Carlos Pignataro (adds missing error
codes in Section 2, and fixes a number of typos/writeos).
A.6. Changes from draft-ietf-tcpm-tcp-soft-errors-03
o Addresses feedback sent by Ted Faber and Gorry Fairhurst
(miscellaneous editorial changes).
A.7. Changes from draft-ietf-tcpm-tcp-soft-errors-02
o Moved appendix on FreeBSD's approach to the body of the draft.
o Removed rest of the appendix, as suggested by Ron Bonica and Mark
Allman.
o Reworded some parts of the document to make the text more neutral.
o Miscellaneous editorial changes.
A.8. Changes from draft-ietf-tcpm-tcp-soft-errors-01
o Addressed feedback posted by Sally Floyd (remove sentence in
Section 2.1 regarding processing of RST segments)
A.9. Changes from draft-ietf-tcpm-tcp-soft-errors-00
o Miscellaneous editorial changes
A.10. Changes from draft-gont-tcpm-tcp-soft-errors-02
o Draft resubmitted as draft-ietf.
o Miscellaneous editorial changes
A.11. Changes from draft-gont-tcpm-tcp-soft-errors-01
o Changed wording to describe the mechanism, rather than proposing
it
o Miscellaneous editorial changes
A.12. Changes from draft-gont-tcpm-tcp-soft-errors-00
o Added reference to the Linux implementation in Section 4.1
o Added Section 5
o Added section on Higher-Level API
o Added Section 4.2
o Moved section "Asynchronous Application Notification" to Appendix [Thadani] Thadani, A., "Interactive User Productivity", IBM
Systems Journal, No. 1, 1981.
o Added section on parallel connection requests [Zuquete] Zuquete, A., "Improving the functionality of SYN
cookies", 6th IFIP Communications and Multimedia
Security Conference (CMS 2002), 2002.
o Miscellaneous editorial changes [v6-ON] Roy, S., Durand, A., and J. Paugh, "Issues with Dual
Stack IPv6 on by Default", Work in Progress,
July 2004.
Author's Address Author's Address
Fernando Gont Fernando Gont
Universidad Tecnologica Nacional / Facultad Regional Haedo Universidad Tecnologica Nacional / Facultad Regional Haedo
Evaristo Carriego 2644 Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706 Haedo, Provincia de Buenos Aires 1706
Argentina Argentina
Phone: +54 11 4650 8472 Phone: +54 11 4650 8472
Email: fernando@gont.com.ar EMail: fernando@gont.com.ar
URI: http://www.gont.com.ar URI: http://www.gont.com.ar
Full Copyright Statement
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contained in BCP 78, and except as set forth therein, the authors
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