Internet Engineering Task Force T. Nishitani
Internet-Draft S. Miyakawa
Intended status: BCP NTT Communications
Expires: May 23, 2009 A. Nakagawa
KDDI CORPORATION
H. Ashida
iTSCOM
November 19, 2008
Common Functions of Large Scale NAT (LSN)
draft-nishitani-cgn-01
Status of this Memo
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This Internet-Draft will expire on May 23, 2009.
Abstract
This document defines common functions of multiple types of Large
Scale Network Address Translation (NAT) that handles Unicast UDP, TCP
and ICMP.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The policy of assignment of LSN external IP address, port
and identifier . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Requirements for protocol handling . . . . . . . . . . . . . . 8
4.1. Unicast UDP Requirements . . . . . . . . . . . . . . . . . 8
4.2. TCP Requirements . . . . . . . . . . . . . . . . . . . . . 9
4.3. ICMP Requirements . . . . . . . . . . . . . . . . . . . . 10
4.4. Summary of Requirements . . . . . . . . . . . . . . . . . 10
5. Identifying particular users (BOTs, spammers, etc) . . . . . . 12
5.1. Store Translation Log . . . . . . . . . . . . . . . . . . 12
5.2. Fixed port assignment . . . . . . . . . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . . 13
9.2. Informative Reference . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 16
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1. Introduction
Global IPv4 address from the IANA pool will run out in a few years,
thus network operators such as ISPs, carriers, large enterprises,
universities need to shift from IPv4 services to IPv6 ones. However,
IPv6 deployment seems to take a long time.
NAT [RFC3022] is a key technology to utilize IPv4 global address
effectively in current practice. Operators may have to place NAT
devices between end-users and the public Internet to suppress global
IPv4 address consumption.
In this document, we call big NAT device Large Scale NAT (LSN).
Variety of LSN (Large Scale NAT) have been proposed. Some of them
are proposed for business continuity after the exhaustion, and some
of them are proposed to access from IPv6 network to IPv4 Internet.
- NAT444 [I-D.shirasaki-nat444-isp-shared-addr]
- DS-Lite (NAT464) [I-D.durand-v6ops-natv4v6v4]
- NAT-64 [I-D.bagnulo-behave-nat64]
Each types of Large Scale NAT are shared by plural users and forward
huge traffic. Because a demand is common, many of necessary
functions are common.
By defining the common function in this document, developers of Large
Scale NAT can put their development resource into their maker
specific function. On the other hand, operator can introduce the
Large Scale NAT that meets their requirement.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Readers are expected to be familiar with [RFC4787] and the terms
defined there. The following term are used in this document:
Large-Scale NAT(LSN): NAT devices placed between CPE and public
Internet by a operator. LSN converts CPE IP Address, CPE Port,
and CPE Identifier into LSN external IP Address, LSN external Port
and LSN external Identifier in communication between CPE and GGN
external.
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LSN external realm: The realm where IPv4 global addresses are
assigned
LSN internal realm: The realm placed between LSN and CPEs
LSN external IP address: The IP address on LSN in LSN external
realm corresponding to CPE IP address
LSN external port: The port on LSN in LSN external realm
corresponding to CPE port
LSN external identifier: The identifier of ICMP on LSN in LSN
external realm corresponding to CPE identifier
Customer Premises Equipment(CPE): The terminal which is placed in
LSN internal realm and may establish TCP sessions to LSN external
realm
CPE IP address: The IP address on CPE in LSN internal realm
CPE port: The port on CPE in LSN internal realm
CPE identifier: CPE's identifier of ICMP in LSN internal realm
CPE 3-tuple: The tuple of TCP/UDP, CPE IP address, and CPE Port
Service Server (SS) The server a operator supplies various
services for CPE
Service Server (SS): The server a operator supplies various
services for CPE
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++------++
| SS |
++------++
|
|
|
LSN external IP address Y1 |
LSN external port y1 |
++------++ LSN external realm
........... | LSN |...............
++------++ LSN internal realm
|
CPE IP address X1 |
CPE port x1 |
++------++
| CPE |
++------++
LSN network
3. The policy of assignment of LSN external IP address, port and
identifier
A LSN has a pool of LSN external IP addresses, ports and identifiers.
CPEs share LSN external IP addresses. Each LSN occupies combination
of LSN external IP address and LSN external port exclusively. For a
fair use of limited resources, LSN has a limitation for the number of
the LSN external ports per CPE. LSNs need to keep high transparency
to continue existing services after LSN is introduced. Requirement
of high transparency for LSN leads to high scalability of LSN. High
transparency means LSN basically keeps communications among CPEs
except effect of limitations of the number of LSN external ports and
TCP sessions.
A CPE MAY apply UDP hole punching or TCP hole punching for
interactive services among CPEs like Voice over IP and P2P. LSN
SHOLUD NOT interfere in services using UDP hole punching or TCP hole
punching.
REQ-1: A LSN MUST allocate one external IP address to each CPE.
a) LSN external IP address of the UDP, TCP and ICMP MUST be same.
Justification: If a LSN allocates multiple LSN external IP addresses
to each CPE, some applications might not work.
REQ-2: A LSN MUST allocate LSN external ports corresponding to CPE
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ports of UDP.
a) A LSN MUST NOT overload LSN external port while a NAT UDP
mapping timer does not expire.
b) A LSN MAY overload LSN external port after a NAT UDP mapping
timer expires.
c) A LSN SHOULD limit the number of the LSN external ports of UDP
per CPE.
d) The number of the LSN external ports of UDP per CPE which LSN
can allocate SHOULD be configurable for the administrator of LSN.
e) A LSN SHOULD NOT allocate well-known ports as LSN external
ports.
Justification: CPEs can communicate to CPE external realm fairly by
limiting the number of LSN external ports per CPE.
REQ-3: A LSN MUST allocate LSN external ports corresponding to CPE
ports of TCP.
a) A LSN MUST NOT overload LSN external port while the port is
allocated for one or more TCP sessions originated by another CPE.
b) A LSN MAY reuse LSN external port while the port is allocated
for no session originated by any CPE.
c) A LSN SHOULD limit the number of the LSN external ports of TCP
per CPE.
d) The number of the LSN external ports of TCP per CPE SHOULD be
an administratively configurable option.
e) A LSN SHOULD limit the number of the new sessions of TCP per
time unit and per CPE.
f) A LSN SHOULD NOT allocate well-known ports as LSN external
ports.
Justification: CPEs can communicate to CPE external realm fairly by
limiting the number of LSN external ports per CPE. In addition, TCP
LSN external port MAY have TCP sessions, and therefore the TCP
session timer is necessary for every 5-Tuple. LSN can have not only
the limitations of the number of LSN external ports but also TCP
sessions per CPE. Thus a LSN can prevent denial of service attacks
with the tons of TCP open and close by malicious CPEs.
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REQ-4: A LSN MUST allocate LSN external identifiers corresponding to
CPE identifiers.
a) A LSN MUST NOT overload LSN external identifier before an ICMP
Query session timer expires.
b) A LSN MAY overload LSN external identifier after an ICMP Query
session timer expires.
c) A LSN SHOULD limit the number of the LSN external identifier
allocated per CPE.
d) The number of the LSN external identifiers per CPE which LSN
can allocate SHOULD be an administratively configurable option.
Justification: CPEs can communicate to CPE external realm fairly by
limiting the number of LSN external identifiers every CPE.
When a LSN limits the number of LSN external ports and TCP sessions,
CPE may not use TCP services during using web and P2P services. For
example, some services using Ajax demand few dozens of TCP sessions.
P2P software like BitTorrent demands also TCP sessions more than few
dozens. Some CPEs MAY use E-mail services like POP3 and SMTP even
though CPE uses the services which demand many TCP sessions at the
same time. Therefore it is important to reserve LSN external ports
for such administratively configured services.
REQ-5: Reserving LSN external ports per CPE for the always-available
services are RECOMENDED.
a) The destination port which is used for reservation of LSN
external ports SHOULD be administratively configurable.
Justification: To reserve the LSN external ports for specific
services, CPE can avoid the effect of the limitation of LSN external
ports by LSN.
In addition, it MAY not be necessary to set a limit to the number of
LSN external ports for the communications between CPEs and SS. The
reason is because LSN should pass-through the communications between
CPEs and SS.
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X1:x1 X1':x1' X2:x2
+---+from X1:x1 +---+fromX1:x1 +---+
| |to X2:x2 | | to X2:x2 | |
| C |>>>>>>>>>>>>| L |>>>>>>>>>>>>>>| S |
| P | | S | | S |
| E |<<<<<<<<<<<<| N |<<<<<<<<<<<<<<| |
| |from X2:x2 | |fromX2:x2 | |
+---+ to X1:x1 +---+ to X1:x1 +---+
pass-through
REQ-6: A LSN SHOULD pass-through the communication between CPEs and
SS.
Justification: Using pass-through, LSN does not have to assign LSN
external IP address, ports, and identifiers and limit to the number
of ports and TCP sessions for the services that an operator manages.
4. Requirements for protocol handling
4.1. Unicast UDP Requirements
[RFC4787] describes requirements of the Unicast UDP of a NAT, and the
behavior of "Endpoint-Independent Filtering "is RECOMMNEDED, and a
NAT MUST have an "Endpoint-Independent Mapping" behavior to ensure
transparency of LSN.
To have "Endpoint-Independent Filtering" and "Endpoint-Independent
Mapping" behaviors for LSNs, LSNs help to establish UDP Hole Punching
among CPEs. In other words, the possibility of the establishment of
UDP Hole Punching among CPEs which have LSN is equal to the
possibility among CPEs which don's t have LSN. If LSNs have an
"Address-Dependent Mapping" or "Address and Port-Dependent Mapping"
behavior, the possibility that establishment of UDP Hole Punching is
less than when LSNs have an "Endpoint-Independent Mapping" behavior.
And if LSNs have an "Address and Port-Dependent Filtering" behavior,
the possibility that establishment of UDP Hole Punching is less than
when LSNs have an "Endpoint-Independent Filtering" or "Address
Dependent Filtering" behavior. Because a SS is placed external LSN
realm, the source IP address and port of the communication from CPE
to SS is LSN external IP address and port. It is RECOMMENDED to use
STUN[I-D.ietf-behave-rfc3489bis] if CPEs check the LSN external IP
address and port for CPE.
An operator MAY introduce TURN [I-D.ietf-behave-turn] to support
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communications among CPEs. If LSN supports "Hairpinning", LSN can
hairpin the communications between CPEs in the same LSN. Therefore
the requirements of Hairpinning for LSN MAY reduce requirements for
the performance of TURN servers. When CPEs decide the course of UDP
between CPEs, CPE MAY use [I-D.ietf-mmusic-ice] .
X1:x1
+------+ from X1:x1 to X2':x2'
| CPE1 |>>>>>>>>>>>>>>>>>>>>>>>>>>>>++----++X1':x1'
+------+ | L |
| S |
| N |
X2:x2 | |
+------+ from X1':x1' to X2:x2 | |
| CPE2 |<<<<<<<<<<<<<<<<<<<<<<<<<<<<++----++X2':x2'
+------+
Hairpinning
REQ-7: A LSN SHOULD comply with [RFC4787] for unicast UDP.
Justification: LSN SHOULD have to keep high transparency for unicast
UDP communications. And CPE MAY use P2P and interactive services
between CPEs after a LSN is introduced.
4.2. TCP Requirements
[I-D.ietf-behave-tcp] describes requirements of TCP of a NAT, and the
behavior of "Endpoint-Independent Filtering" is RECOMMNEDED, and a
NAT MUST have an "Endpoint-Independent Mapping" behavior to ensure
transparency of LSN
To have "Endpoint-Independent Filtering" and "Endpoint-Independent
Mapping" behaviors for LSNs, LSNs help to establish TCP Hole Punching
among CPEs. In other words, the possibility of the establishment of
TCP Hole Punching among CPEs which have LSN is equal to the
possibility among CPEs which don's t have LSN. If LSNs have an
"Address-Dependent Mapping" or "Address and Port-Dependent Mapping"
behavior, the possibility that establishment of TCP Hole Punching is
less than when LSNs have an "Endpoint-Independent Mapping" behavior.
And if LSNs have an "Address and Port-Dependent Filtering" behavior,
the possibility that establishment of TCP Hole Punching is less than
when LSNs have an "Endpoint-Independent Filtering" or "Address
Dependent Filtering" behavior. Because a SS is placed external LSN
realm, the source of IP address and port of the communication from
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CPE to SS is LSN external IP address and port. It is RECOMMENDED to
use STUN[I-D.ietf-behave-rfc3489bis] if CPEs want to check the LSN
external IP address and port for CPE.
An operator MAY introduce TURN [I-D.ietf-behave-turn] to support
communications among CPEs. If LSN supports "Hairpinning", LSN can
hairpin the communications between CPEs in the same LSN. Therefore
the requirements of Hairpinning for LSN MAY reduce requirements for
the performance of TURN servers. When CPEs decide the course of TCP
between CPEs, CPE MAY use [I-D.ietf-mmusic-ice] .
REQ-8: A LSN SHOULD comply with [I-D.ietf-behave-tcp] for TCP.
Justification: LSN SHOULD have to keep high transparency for TCP
communications. And CPE MAY use P2P and interactive services between
CPEs after a LSN is introduced.
4.3. ICMP Requirements
[I-D.ietf-behave-nat-icmp] describes requirements of ICMP of a NAT.
And there MAY be a case that CPE cannot establish communication from
CPEs to LSN external realm because LSN limits the number of LSN
external ports, identifiers and TCP sessions per CPE. It is useful
if CPE can distinguish an error to occur by the limitation of the LSN
external ports, identifiers and TCP sessions from other errors.
REQ-9: A LSN SHOULD comply with [I-D.ietf-behave-nat-icmp] for ICMP.
a) When a LSN can't establish new session of TCP/UDP by limiting
of TCP/UDP ports per user, the LSN sends an ICMP destination
unreachable message, with code of 13 (Communication
administratively prohibited) to the sender.
Justification: LSN SHOULD have to keep high transparency for ICMP.
And CPE MAY use P2P and interactive services between CPEs after a LSN
is introduced. And it is necessary to be able to distinguish an
error to occur by the limitation of the LSN external ports and TCP
sessions from a network error.
4.4. Summary of Requirements
REQ-1: A LSN MUST allocate one external IP address to each CPE.
a) LSN external IP address of the UDP, TCP and ICMP MUST be same.
REQ-2: A LSN MUST allocate LSN external ports corresponding to CPE
ports of UDP.
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a) A LSN MUST NOT overload LSN external port while a NAT UDP
mapping timer does not expire.
b) A LSN MAY overload LSN external port after a NAT UDP mapping
timer expires.
c) A LSN SHOULD limit the number of the LSN external ports of UDP
per CPE.
d) The number of the LSN external ports of UDP per CPE which LSN
can allocate SHOULD be configurable for the administrator of LSN.
e) A LSN SHOULD NOT allocate well-known ports as LSN external
ports.
REQ-3: A LSN MUST allocate LSN external ports corresponding to CPE
ports of TCP.
a) A LSN MUST NOT overload LSN external port while the port is
allocated for one or more TCP sessions originated by another CPE.
b) A LSN MAY reuse LSN external port while the port is allocated
for no session originated by any CPE.
c) A LSN SHOULD limit the number of the LSN external ports of TCP
per CPE.
d) The number of the LSN external ports of TCP per CPE SHOULD be
an administratively configurable option.
e) A LSN SHOULD limit the number of the new sessions of TCP per
time unit and per CPE.
f) A LSN SHOULD NOT allocate well-known ports as LSN external
ports.
REQ-4: A LSN MUST allocate LSN external identifiers corresponding to
CPE identifiers.
a) A LSN MUST NOT overload LSN external identifier before an ICMP
Query session timer expires.
b) A LSN MAY overload LSN external identifier after an ICMP Query
session timer expires.
c) A LSN SHOULD limit the number of the LSN external identifier
allocated per CPE.
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d) The number of the LSN external identifiers per CPE which LSN
can allocate SHOULD be an administratively configurable option.
REQ-5: Reserving LSN external ports per CPE for the always-available
services are RECOMENDED.
a) The destination port which is used for reservation of LSN
external ports SHOULD be administratively configurable.
REQ-6: A LSN SHOULD pass-through the communication between CPEs and
SS.
REQ-7: A LSN SHOULD comply with [RFC4787] for unicast UDP.
REQ-8: A LSN SHOULD comply with [I-D.ietf-behave-tcp] for TCP.
REQ-9: A LSN SHOULD comply with [I-D.ietf-behave-nat-icmp] for ICMP.
a) When a LSN can't establish new session of TCP/UDP by limiting
of TCP/UDP ports per user, the LSN sends an ICMP destination
unreachable message, with code of 13 (Communication
administratively prohibited) to the sender.
5. Identifying particular users (BOTs, spammers, etc)
It is necessary for network administrators to identify a user from an
IP address and a timestamp in order to deal with abuse and lawful
intercept. When multiple users share one external address at LSN,
the source address and the source port that are visible at the
destination host are translated ones. The following mechanisms can
be used to identify the user that transmitted a certain packet.
5.1. Store Translation Log
One mechanism stores the following information at LSN.
- destination address
- destination port
- translated source address
- translated source port
- untranslated source address
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- untranslated source port
- timestamp
In such environment that one LSN accommodates a lot of users or
processes large amount of traffic, the amount of log will be so large
and the operator has to prepare large volume of storage.
5.2. Fixed port assignment
To save costs for storage, one can adopt this port assignment
mechanism at LSN. By fixing the range of external port per user/CPE,
and having the mapping of internal IP address to external IP address
and port, there will be no need to store per session log. Note that
this mechanism is possible only if the source port is known as well
as the source address, the destination address and the destination
port.
6. IANA Considerations
There are no IANA considerations.
7. Security Considerations
If malicious CPE can camouflage CPE 3-Tuple, the malicious CPE MAY
prevent a normal CPE from sending data to external realm. Therefore,
an operator SHOULD make policies to prevent a spoofing of CPE
3-tuple.
8. Acknowledgements
Thanks for the input and review by Yasuhiro Shirasaki, Takeshi
Tomochika, Kousuke Shishikura, Dai Kuwabara, Tomoya Yoshida, Takanori
Mizuguchi, Arifumi Matsumoto, Tomohiro Fujisaki
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022,
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January 2001.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation
(NAT) Behavioral Requirements for Unicast UDP", BCP 127,
RFC 4787, January 2007.
[I-D.shirasaki-nat444-isp-shared-addr]
Shirasaki, Y., Miyakawa, S., Nakagawa, A., Yamaguchi, J.,
and H. Ashida, "NAT444 with ISP Shared Address",
draft-shirasaki-nat444-isp-shared-addr-00 (work in
progress), October 2008.
[I-D.ietf-behave-tcp]
Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.
Srisuresh, "NAT Behavioral Requirements for TCP",
draft-ietf-behave-tcp-08 (work in progress),
September 2008.
[I-D.ietf-behave-nat-icmp]
Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT
Behavioral Requirements for ICMP protocol",
draft-ietf-behave-nat-icmp-10 (work in progress),
October 2008.
[I-D.ietf-behave-rfc3489bis]
Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for (NAT) (STUN)",
draft-ietf-behave-rfc3489bis-18 (work in progress),
July 2008.
[I-D.ietf-mmusic-ice]
Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols",
draft-ietf-mmusic-ice-19 (work in progress), October 2007.
[I-D.ietf-behave-turn]
Rosenberg, J., Mahy, R., and P. Matthews, "Traversal Using
Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN)",
draft-ietf-behave-turn-11 (work in progress),
October 2008.
9.2. Informative Reference
[I-D.durand-v6ops-natv4v6v4]
Durand, A., "Distributed NAT for broadband deployments
post IPv4 exhaustion", draft-durand-v6ops-natv4v6v4-01
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(work in progress), February 2008.
[I-D.bagnulo-behave-nat64]
Bagnulo, M., Matthews, P., and I. Beijnum, "NAT64: Network
Address and Protocol Translation from IPv6 Clients to IPv4
Servers", draft-bagnulo-behave-nat64-02 (work in
progress), November 2008.
Authors' Addresses
Tomohiro Nishitani
NTT Communications Corporation
Tokyo Opera City Tower 21F, 3-20-2 Nishi-Shinjuku, Shinjuku-ku
Tokyo 163-1421
Japan
Phone: +81 3 6800 3214
Email: tomohiro.nishitani@ntt.com
Shin Miyakawa
NTT Communications Corporation
Tokyo Opera City Tower 21F, 3-20-2 Nishi-Shinjuku, Shinjuku-ku
Tokyo 163-1421
Japan
Phone: +81 3 6800 3262
Email: miyakawa@nttv6.jp
Akira Nakagawa
KDDI CORPORATION
GARDEN AIR TOWER, 3-10-10, Iidabashi, Chiyoda-ku
Tokyo 102-8460
Japan
Email: ai-nakagawa@kddi.com
Hiroyuki Ashida
its communications Inc.
3-5-7 Hisamoto Takatsu-ku
Kawasaki 213-0011
Japan
Email: ashida@itscom.ad.jp
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The IETF invites any interested party to bring to its attention any
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Nishitani, et al. Expires May 23, 2009 [Page 16]