Internet DRAFT - draft-kitamura-tcp-sharp-close
draft-kitamura-tcp-sharp-close
Network Working Group H. Kitamura
Internet-Draft NEC Corporation
Intended status: Standards Track S. Ata
Expires: April 2016 Osaka City University
M. Murata
Osaka University
October 16, 2015
"Sharp Close": Elimination of TIME-WAIT state of TCP connections
<draft-kitamura-tcp-sharp-close-02.txt>
Abstract
This document describes an idea "Sharp Close" that eliminates or
minimizes TIME-WAIT state of TCP connections.
In the current TCP specification ([RFC0793]), there are some
inappropriate or not up-to-date functions. Here we focus and
discuss on TCP TIME-WAIT state function.
TIME-WAIT is the last state of TCP connections of Active Close side
nodes. After TCP connections are effectively closed, state of them
move to TIME-WAIT state. After TIME-WAIT state is finished,
resources of connections are released. This means that even if
connections are effectively finished, resources of connections are
NOT released. The TIME-WAIT state prevents from releasing them.
From the viewpoints of current high-speed and high-multiplicity
communication styles, it is thought that TIME-WAIT state is one of
evil functions.
In order to provide efficient communications that match current
styles, an idea "Sharp Close" that eliminates or minimizes TIME-
WAIT state of TCP connections is proposed.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Analysis of current TIME-WAIT state . . . . . . . . . . . . . . 3
3. Why TIME-WAIT state is needed? . . . . . . . . . . . . . . . . 5
4. Design of "Sharp Close" (elimination of TIME-WAIT state) . . . 6
5. Eliminate TIME-WAIT state by setsockopt() . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
Appendix A. Implementations . . . . . . . . . . . . . . . . . . . 8
1. Introduction
This document describes an idea "Sharp Close" that eliminates or
minimizes TIME-WAIT state of TCP connections.
In the current TCP specification ([RFC0793]), there are some
inappropriate or not up-to-date functions. Here we focus and
discuss on TCP TIME-WAIT state function.
TIME-WAIT is the last state of TCP connections of Active Close side
nodes. After TCP connections are effectively closed, state of them
move to TIME-WAIT state. [RFC0793] defines that the connections
stay there 2MSL(Maximum Segment Lifetime) seconds. (2MSL = 240
sec.)
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After TIME-WAIT state is finished, resources of connections are
released. This means that even if connections are effectively
finished, resources of connections are NOT released. The TIME-WAIT
state prevents from releasing them.
From the viewpoints of current high-speed and high-multiplicity
communication styles that require highly resource recycling, it is
thought that TIME-WAIT state is one of evil functions.
In order to provide efficient communications that match current
styles, an idea "Sharp Close" that eliminates or minimizes TIME-
WAIT state of TCP connections is proposed.
In the following sections, analysis of current TIME-WAIT state and
design of "Sharp Close" etc. are described.
2. Analysis of current TIME-WAIT state
ACTIVE CLOSE PASSIVE CLOSE
side side
| |
ESTABLISH | | ESTABLISH
_________________|_ FIN |
| \__ |
| \__ |
| \__ |
FIN-WAIT-1 | \_|__________________
| __/ |
| __/ACK | CLOSE-WAIT
| __/ _|__________________
_________________|_/ __/ |
| __/FIN |
FIN-WAIT-2 | __/ |
_________________|_/ | LAST-ACK
| | \_ACK |
| | \__ |
| | \__ |
2MSL TIME-WAIT | \_|__________________
| | |
| | |
| | | CLOSED
__V______________| |
| |
CLOSED | |
| |
Fig. 1 Current ACTIVE-PASSIVE Close Sequence
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ACTIVE CLOSE ACTIVE CLOSE
side side
| |
ESTABLISH | | ESTABLISH
_________________|_ FIN |
| \__ FIN_|__________________
| \__ __/ |
FIN-WAIT-1 | __X__ | FIN-WAIT-1
| __/ \_|__________________
_________________|_/ __/ |
| \_ACK_/ACK |
CLOSING | __\/_ | CLOSING
_________________|_/ \__ |
| | \_|__________________
| | | |
| | | |
2MSL TIME-WAIT | | |
| | | TIME-WAIT 2MSL
| | | |
| | | |
__V______________| | |
| |_______________V__
CLOSED | |
| | CLOSED
| |
Fig. 2 Current ACTIVE-ACTIVE Close Sequence
Fig. 1 and Fig. 2 show Close Sequence that is defined by current
specification [RFC0793]. TCP connections on ACTIVE CLOSE node (that
initiates sending FIN) side reach TIME-WAIT as a last state. They
stay there 2MSL seconds.
Table 1 Actual 2MSL values used by major OS implementation.
+-------------+-----------+
| RFC/OS | 2MSL value|
+=============+===========+
| [RFC0793] | 240 sec.|
+-------------+-----------+
| Windows2000 | 240 sec.|
+-------------+-----------+
| Windows | |
|(after Win2K)| 120 sec.|
+-------------+-----------+
| Unix/Linux | 60 sec.|
+-------------+-----------+
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Table 1 shows actual 2MSL values that are surveyed by authors.
[RFC0793] says "For this specification the MSL is taken to be 2
minutes."
Since 240 sec. ([RFC0793]) is long time, recent major OSes adopt
rather shorter time.
However, from the viewpoints of current communication styles that
require highly resource recycling, TIME-WAIT time is still too
long.
Now, it is almost thought that staying at TIME-WAIT state is waste
of time.
3. Why TIME-WAIT state is needed?
Basically, TIME-WAIT state is designed for !fail-safe! purpose.
If it is assumed that packets transferring order is not changed,
all of !data! packets from a corresponding node are received when
FIN-WAIT-2 state is finished (responding FIN packet is received)
and no !data! packets will not be received after that.
At TIME-WAIT state, an ACTIVE CLOSE node waits for a 'resending'
!control! packet FIN only from the corresponding node for the case
of the sent ACK (for the FIN) is lost. (No !data! packets are
waited for.)
Only when the last sent ACK from the ACTIVE CLOSE node is lost,
'resending' control packet FIN from the corresponding node is
issued.
It is rare case to happen this event at current stable network
environment.
Since all data from the corresponding node is received by the
ACTIVE CLOSE node, it is less significant issue to wait for
'resending' FIN packet.
If 'resending' FIN is NOT waited at ACTIVE CLOSE node and
'resending' FIN is issued from the corresponding node, significant
problem will NOT be happened, only RST packet (to notify receiving
unexpected packet) will be issued from the ACTIVE CLOSE node.
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4. Design of "Sharp Close" (elimination of TIME-WAIT state)
ACTIVE CLOSE PASSIVE CLOSE
side side
| |
ESTABLISH | | ESTABLISH
_________________|_ FIN |
| \__ |
| \__ |
| \__ |
FIN-WAIT-1 | \_|__________________
| __/ |
| __/ACK | CLOSE-WAIT
| __/ _|__________________
_________________|_/ __/ |
| __/FIN |
FIN-WAIT-2 | __/ |
_________________|_/ | LAST-ACK
(NO) TIME-WAIT | \_ACK |
| \__ |
CLOSED | \__ |
| \_|__________________
| |
| | CLOSED
| |
Fig. 3 (Proposed) Sharp ACTIVE-PASSIVE Close Sequence
ACTIVE CLOSE ACTIVE CLOSE
side side
| |
ESTABLISH | | ESTABLISH
_________________|_ FIN |
| \__ FIN_|__________________
| \__ __/ |
FIN-WAIT-1 | __X__ | FIN-WAIT-1
| __/ \_|__________________
_________________|_/ __/ |
| \_ACK_/ACK |
CLOSING | __\/_ | CLOSING
_________________|_/ \__ |
(NO) TIME-WAIT | \_|__________________
| | (NO) TIME-WAIT
CLOSED | |
| | CLOSED
Fig. 4 (Proposed) Sharp ACTIVE-ACTIVE Close Sequence
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It is easy to design "Sharp Close" function. "Sharp Close" function
is achieved by eliminating or minimizing TIME-WAIT state of TCP
connections.
Fig. 3 and Fig. 4. show Close Sequence that is defined by "Sharp
Close" function.
5. Eliminate TIME-WAIT state by setsockopt()
Under current implementation, TIME-WAIT (close()) action can be
controlled by setsockopt() function.
SO_LINGER option of setsockopt() can eliminate TIME-WAIT state and
close connections immediately.
Concrete procedures how to eliminate TIME-WAIT:
Fig. 5 shows struct socket in <sys/socket.h>
struct linger {
int l_onoff; /* linger active */
int l_linger; /* how many seconds to linger for */
};
Fig. 5. struct linger
By using the following shown procedures, TIME-WAIT state is
eliminated and connections are closed immediately.
1: makes linger active(on)
l_onoff = on;
2: sets linger time to 0
l_linger = 0 ;
It is possible to eliminate TIME-WAIT state by these procedures.
However, this behavior is "NOT default" operation. In order to
utilize this feature, it is necessary to modify huge number of
communication applications.
Furthermore, this feature is not implemented on every existing OSes
and it is not always possible to eliminate TIME-WAIT state on every
OSes.
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6. Security Considerations
Goals of the proposed idea ("Sharp Close") are to eliminate or
minimize TIME-WAIT state by default on OS kernel level. From
functional viewpoints, the same concept to eliminate TIME-WAIT
state is already implemented by using LINGER option of setsockopt()
function. It is not default operation, however it has already
implemented and worked.
So, there are no new Security Consideration issues that should be
discussed here.
7. IANA Considerations
This document does not require any resource assignments to IANA.
Acknowledgment
A part of this work is supported by the program: SCOPE (Strategic
Information and Communications R&D Promotion Programme) operated by
Ministry of Internal Affairs and Communications of JAPAN.
Appendix A. Implementations
Currently, above described "Sharp Close" functions have been
implemented and verified under the following OS.
Ubuntu 13.04 (kernel 3.8.13.8)
References
Normative References
[RFC0793] "Transmission Control Protocol", RFC 0793, September 1981
[RFC3513] R. Hinden and S.Deering, "Internet Protocol Version 6
(IPv6) Addressing Architecture", RFC 3513, April 2003
[RFC3493] R. Gilligan, S. Thomson, J. Bound, J. McCann and W.
Stevens, "Basic Socket Interface Extensions for IPv6",
RFC3493, February 2003
Informative References
[RFC3542] W. Stevens, M. Thomas, E. Nordmark and T. Jinmei,
"Advanced Sockets Application Program Interface (API)
for IPv6", RFC 3542, May 2003
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Authors' Addresses
Hiroshi Kitamura
Cyber Security Strategy Division / Cloud System Research Laboratories,
NEC Corporation
7-1, Shiba 5-chome, Minato-ku, Tokyo 108-8001, JAPAN
Phone: +81 3 3798 0563
Email: kitamura@da.jp.nec.com
Shingo Ata
Graduate School of Engineering, Osaka City University
3-3-138, Sugimoto, Sumiyoshi-Ku, Osaka 558-8585, JAPAN
Phone: +81 6 6605 2191
Fax: +81 6 6605 2191
Email: ata@info.eng.osaka-cu.ac.jp
Masayuki Murata
Graduate School of Information Science and Technology, Osaka Univ.
1-5 Yamadaoka, Suita, Osaka 565-0871, JAPAN
Phone: +81 6 6879 4542
Fax: +81 6 6879 4544
Email: murata@ist.osaka-u.ac.jp
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