Internet Engineering Task Force I. Yamagata
Internet-Draft T. Nishitani
Intended status: Informational S. Miyakawa
Expires: September 9, 2010 NTT Communications
A. Nakagawa
KDDI CORPORATION
H. Ashida
iTSCOM
March 8, 2010
Common requirements for IP address sharing schemes
draft-nishitani-cgn-04
Abstract
This document defines common requirements of multiple types of Large
Scale Network Address Translation (NAT) that handles Unicast UDP, TCP
and ICMP.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on September 9, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Requirements for UDP . . . . . . . . . . . . . . . . . . . . . 5
4. Requirements for TCP . . . . . . . . . . . . . . . . . . . . . 9
5. Requirements for ICMP . . . . . . . . . . . . . . . . . . . . 12
6. LSN specified Requirements . . . . . . . . . . . . . . . . . . 16
7. Identifying particular users (BOTs, spammers, etc) . . . . . . 18
7.1. Store Translation Log . . . . . . . . . . . . . . . . . . 18
7.2. Fixed port assignment . . . . . . . . . . . . . . . . . . 19
8. Considerations about limiting the number of LSN external
ports . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
10. Security Considerations . . . . . . . . . . . . . . . . . . . 20
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
12.1. Normative References . . . . . . . . . . . . . . . . . . . 20
12.2. Informative Reference . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
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1. Introduction
Now there are several IPv4 address sharing schemes such as Large
Scale NAT (as known as NAT444[I-D.shirasaki-nat444-isp-shared-addr])
, DS-Lite[I-D.ietf-softwire-dual-stack-lite], A+P[I-D.ymbk-aplusp]
and so on under the discussion.
Those IPv4 address sharing schemes are intended to be used in the
middle of the ISP access network against IPv4 address shortage
problem by sharing one global IPv4 address by multiple users.
Authors believe that there are common requirements among all IPv4
address sharing schemes to make them "transparent" as much as
possible. At the BEHAVE working group of IETF, following RFCs have
already defined to achieve maximum transparency at the residential
CPE which has NAT function;
- RFC4787 : NAT Behavioral Requirements for Unicast UDP
- RFC5382 : NAT Behavioral Requirements for TCP
- RFC5508 : NAT Behavioral Requirements for ICMP
However so, because those RFCs are mainly aimed at residential CPE
and any IPv4 address sharing schemes are a bit different from it, we
believe that requirements for LSN and other schemes should be defined
alternatively to those RFCs.
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 an 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.
LSN external realm: The realm where IPv4 global addresses are
assigned
LSN internal realm: The realm placed between LSN and CPEs
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LSN external IP address: The IP address on LSN in LSN external
realm mapping to CPE IP address
LSN external port: The port on LSN in LSN external realm mapping
to CPE port
LSN external identifier: The identifier of ICMP on LSN in LSN
external realm mapping 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 (e.g. a single PC or NATBox)
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 an operator supplies various
services for CPE
Service Server (SS): The server placed in external realm
Service Provide Server (SPS): The server placed in external realm
and controlled by LSN administrators
++------++
| 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 |
++------++
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Figure 1. LSN network
3. Requirements for UDP
Based on RFC4787, we'd like to compile the list of the requirements
as follows.
Please note that UDP-REQ-8 is slightly different for original RFC.
And some of requirements have additional justification.
UDP-REQ-1: A NAT MUST have an "Endpoint-Independent Mapping"
behavior.
Status: Same as REQ-1 in RFC4787
Justification: This is needed to use UNilateral Self-Address
Fixing (UNSAF) which plays important role in STUN / TURN. More
detailed description can be found in the original RFC. But to be
more precise, in the LSN case, it may not be needed for some
specific protocol such as DNS query and response.
UDP-REQ-2: It is RECOMMENDED that a NAT have an "IP address pooling"
behavior of "Paired". Note that this requirement is not applicable
to NATs that do not support IP address pooling.
Status: Same as REQ-2 in RFC4787
Justification: This allows applications that use multiple ports
originating from the same internal IP address to also have the
same external IP address. More detailed description can be found
in original RFC.
UDP-REQ-3: A NAT MUST NOT have a "Port assignment" behavior of "Port
overloading".
Status: Same as REQ-3 in RFC4787
Justification: This requirement must be met in order to enable two
applications on the internal side of the NAT both to use the same
port to try to communicate with the same destination. More
detailed description can be found in original RFC.
UDP-REQ-3-a: If the host's source port was in the range 0-1023, it is
RECOMMENDED the NAT's source port be in the same range. If the
host's source port was in the range 1024-65535, it is RECOMMENDED
that the NAT's source port be in that range.
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Status: Same as REQ-3-a in RFC4787
Justification: Certain applications expect the source UDP port to
be in the well-known range. More detailed description can be
found in original RFC. On the other hand, almost application
probably not use range 0-1023 for source port. Using ports as
many as possible, it may not be needed this requirement.
UDP-REQ-4: It is RECOMMENDED that a NAT have a "Port parity
preservation" behavior of "Yes".
Status: Same as REQ-4 in RFC4787
Justification: This is avoid breaking peer-to-peer applications
that do not explicitly and separately specify RTP and RTCP port
numbers and that follow the RFC 3550 rule to decrement an odd RTP
port to make it even. More detailed description can be found in
original RFC.
UDP-REQ-5: A NAT UDP mapping timer MUST NOT expire in less than two
minutes, unless REQ-5a applies.
UDP-REQ-5-a: For specific destination ports in the well-known port
range (ports 0-1023), a NAT MAY have shorter UDP mapping timers that
are specific to the IANA-registered application running over that
specific destination port.
UDP-REQ-5-b: The value of the NAT UDP mapping timer SHOULD be
configurable.
UDP-REQ-5-c: A default value of five minutes or more for the NAT UDP
mapping timer is RECOMMENDED.
Status: Same as REQ-5, REQ-5-a, REQ-5-b, REQ-5-c in RFC4787
UDP-REQ-6: The NAT mapping Refresh Direction MUST have a "NAT
Outbound refresh behavior" of "True".
Status: Same as REQ-6 in RFC4787
Justification: Outbound refresh is necessary for allowing the
client to keep the mapping alive. More detailed description can
be found in original RFC.
UDP-REQ-6-a: The NAT mapping Refresh Direction MAY have a "NAT
Inbound refresh behavior" of "True".
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Status: Same as REQ-6-a in RFC4787
Justification: Allowing inbound refresh may allow an external
attacker or misbehaving application to keep a mapping alive
indefinitely. Also, it the process is repeated with different
ports, over time, it could use up all the ports on the NAT. But
this requirement is maybe needed for some applications occurring
only incoming inbound traffic. In LSN, Making much of
transparency, this requirement is more necessary.
UDP-REQ-7: A NAT device whose external IP interface can be configured
dynamically MUST either
(1) Automatically ensure that its internal network uses IP
addresses that do not conflict with its external network, or
(2) Be able to translate and forward traffic between all internal
nodes and all external nodes whose IP addresses numerically
conflict with the internal network.
Status: Same as REQ-7 in RFC4787
UDP-REQ-8: It is RECOMMENDED that a NAT have "Endpoint-Independent
Filtering" behavior.
Status: "If application transparency is most important, it is
RECOMMENDED that a NAT have Endpoint-Independent Filtering
behavior. If a more stringent filtering behavior is most
important, it is RECOMMENDED that a NAT have Address-Dependent
Filtering behavior." is written at REQ-8 in RFC4787. In this
draft, we pick up only first requirement.
Justification: LSN which is placed at ISP/Carrier makes much of
transparency. In particular, for applications that receive media
simultaneously from multiple locations (e.g., gaming), or
applications that use rendezvous techniques. But to be more
precise, in the LSN case, it may not be needed for some specific
protocol such as DNS query and response.
UDP-REQ-8-a: The filtering behavior MAY be an option configurable by
the administrator of the NAT.
Status: Same as REQ-8-a in RFC4787
Justification: Having the filtering behavior being an option
configurable by the administrator of the NAT ensures that a NAT
can be used in the widest variety of deployment scenarios. More
detailed description can be found in original RFC.
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UDP-REQ-9: A NAT MUST support "Hairpinning".
UDP-REQ-9-a: A NAT Hairpinning behavior MUST be "External source IP
address and port".
Status: Same as REQ-9 in RFC4787
Justification: These requirements are to allow communications
between two endpoints behind the same NAT when they are trying
each other's external IP address. More detailed description can
be found in original RFC.
UDP-REQ-10: To eliminate interference with UNSAF NAT traversal
mechanisms and allow integrity protection of UDP communications, NAT
ALGs for UDP-based protocols SHOULD be turned off. Future standards
track specifications that define an ALG can update this to recommend
the ALGs on which they define default.
UDP-REQ-10-a: If a NAT includes ALGs, it is RECOMMENDED that the NAT
allow the NAT administrator to enable or disable each ALG separately.
Status: Same as REQ-10, REQ-10-a in RFC4787
Justification: NAT ALGs may interfere with UNSAF methods. More
detailed description can be found in original RFC.
UDP-REQ-11: A NAT MUST have deterministic behavior, i.e., it MUST NOT
change the NAT translation or the Filtering Behavior at any point in
time, or under any particular conditions.
Status: Same as REQ-11 in RFC4787
Justification: Non-deterministic NATs are very difficult to
troubleshoot. More detailed description can be found in original
RFC.
UDP-REQ-12: Receipt of any sort of ICMP message MUST NOT terminate
the NAT mapping.
UDP-REQ-12-a: The NAT's default configuration SHOULD NOT filter ICMP
messages based on their source IP address.
UDP-REQ-12-b: It is RECOMMENDED that a NAT support ICMP Destination
Unreachable messages.
Status: Same as REQ-12, REQ-12-a, REQ-12-b in RFC4787
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Justification: This is easy to do and is used for many things
including MTU discovery and rapid detection of error conditions,
and has no negative consequences. More detailed description can
be found in original RFC.
UDP-REQ-13: If the packet received on an internal IP address has
DF=1, the NAT MUST send back an ICMP message "Fragmentation needed
and DF set" to the host, as described in [RFC0792].
UDP-REQ-13-a: If the packet has DF=0, the NAT MUST fragment the
packet and SHOULD send the fragments in order.
Status: Same as REQ-13, REQ-13-a in RFC4787
Justification: This is the same function a router performs in a
similar situation. More detailed description can be found in
original RFC.
UDP-REQ-14: A NAT MUST support receiving in-order and out-of-order
fragments, so it MUST have "Received Fragment Out of Order" behavior.
UDP-REQ-14-a: A NAT's out-of-order fragment processing mechanism MUST
be designed so that fragmentation-based DoS attacks do not compromise
the NAT's ability to process in-order and unfragmented IP packets.
Status: Same as REQ-14, REQ-14-a in RFC4787
Justification: Since some networks deliver small packets ahead of
large ones, there can be many out-of order fragments. NATs that
are capable of delivering these out-of-order packets are possible,
but they need to store the out-of-order fragments which can open
up a Denial-of-Service (DoS) opportunity, if done incorrectly.
More detailed description can be found in original RFC.
4. Requirements for TCP
Based on RFC5382, we'd like to compile the list of the requirements
as follows.
Please note that TCP-REQ-3 is slightly different for original RFC.
And some of requirements have additional justification.
TCP-REQ-1: A NAT MUST have an "Endpoint Independent Mapping" behavior
for TCP.
Status: Same as REQ-1 in RFC5382
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Justification: This is needed to use UNilateral Self-Address
Fixing (UNSAF) which plays important role in STUN / TURN. More
detailed description can be found in the original RFC. But to be
more precise, in the LSN case, it may not be needed for some
specific protocols.
TCP-REQ-2: A NAT MUST support all valid sequences of TCP packets for
connections initiated both internally as well as externally when the
connection is permitted by the NAT.
TCP-REQ-2-a: In addition to handling the TCP 3-way handshake mode of
connection initiation, A NAT MUST handle the TCP simultaneous-open
mode of connection initiation.
Status: Same as REQ-2,REQ-2-a in RFC5382
Justification: This is to allow standards compliant TCP stacks to
traverse NATs. More detailed description can be found in original
RFC.
TCP-REQ-3: It is RECOMMENDED that a NAT have an "Endpoint independent
filtering" behavior for TCP.
Status: "If application transparency is most important, it is
RECOMMENDED that a NAT have an "Endpoint independent filtering"
behavior for TCP. If a more stringent filtering behavior is most
important, it is RECOMMENDED that a NAT have an "Address dependent
filtering" behavior." is REQ-3 in RFC5382. In this draft, we pick
up only first requirement.
Justification: LSN which is placed at ISP/Carrier makes much of
transparency. But to be more precise, in the LSN case, it may not
be needed for some specific protocols.
TCP-REQ-3-a: The filtering behavior MAY be an option configurable by
the administrator of the NAT.
TCP-REQ-3-b: The filtering behavior for TCP MAY be independent of the
filtering behavior for UDP.
Status: Same as REQ-3-a, REQ-3-b in RFC5382
TCP-REQ-4: A NAT MUST NOT respond to an unsolicited inbound SYN
packet for at least 6 seconds after the packet is received. If
during this interval the NAT receives and translates an outbound SYN
for the connection the NAT MUST silently drop the original
unsolicited inbound SYN packet. Otherwise the NAT SHOULD send an
ICMP Port Unreachable error (Type 3, Code 3) for the original SYN,
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unless REQ-4a applies.
TCP-REQ-4-a: The NAT MUST silently drop the original SYN packet if
sending a response violates the security policy of the NAT.
Status: Same as REQ-4, REQ-4-a in RFC5382
Justification: This intent of this requirement is to allow
simultaneous-open to work reliably in the presence of NATs. More
detailed description can be found in original RFC.
TCP-REQ-5: If a NAT cannot determine whether the endpoints of a TCP
connection are active, it MAY abandon the session if it has been idle
for some time. In such cases, the value of the "established
connection idle-timeout" MUST NOT be less than 2 hours 4 minutes.
The value of the "transitory connection idle-timeout" MUST NOT be
less than 4 minutes.
TCP-REQ-5-a: The value of the NAT idle-timeouts MAY be configurable.
Status: Same as REQ-5, REQ-5-a in RFC5382
Justification: The intent of this requirement is to minimize the
cases where a NAT abandons session state for a live connection.
More detailed description can be found in original RFC.
TCP-REQ-6: If a NAT includes ALGs that affect TCP, it is RECOMMENDED
that all of those ALGs (except for FTP) be disabled by default.
Status: Same as REQ-6 in RFC5382
Justification: The intent of this requirement is to prevent ALGs
from interfering with UNSAF methods. More detailed description
can be found in original RFC.
TCP-REQ-7: A NAT MUST NOT have a "Port assignment" behavior of "Port
overloading" for TCP.
Status: Same as REQ-7 in RFC5382
Justification: This requirement allows two applications on the
internal side of the NAT to consistently communicate with the same
destination.
TCP-REQ-8: A NAT MUST support "Hairpinning" for TCP.
TCP-REQ-8-a: A NAT's Hairpinning behavior MUST be of type "External
source IP address and port".
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Status: Same as REQ-8, REQ-8-a in RFC5382
Justification: This requirement allows two applications behind the
same NAT that are trying to communicate with each other using
their external addresses. More detailed description can be found
in original RFC.
TCP-REQ-9: If a NAT translates TCP, it SHOULD translate ICMP
Destination Unreachable (Type 3) messages.
Status: Same as REQ-9 in RFC5382
Justification: Translating ICMP Destination Unreachable messages
avoids communication failures. More detailed description can be
found in original RFC.
TCP-REQ-10: Receipt of any sort of ICMP message MUST NOT terminate
the NAT mapping or TCP connection for which the ICMP was generated.
Status: Same as REQ-10 in RFC5382
Justification: This is necessary for reliably performing TCP
simultaneous-open where a remote NAT may temporarily signal an
ICMP error. More detailed description can be found in original
RFC.
5. Requirements for ICMP
Based on RFC5508, we'd like to compile the list of the requirements
as follows.
Some of requirements have additional justification.
ICMP-REQ-1: Unless explicitly overridden by local policy, a NAT
device MUST permit ICMP Queries and their associated responses, when
the Query is initiated from a private host to the external hosts.
ICMP-REQ-1-a: NAT mapping of ICMP Query Identifiers SHOULD be
external host independent.
Status: Same as REQ-1 in RFC5508
Justification: ICMP Query mapping by NAT devices is necessary for
current ICMP-Query-based applications to work. More detailed
description can be found in original RFC.
ICMP-REQ-2: An ICMP Query session timer MUST NOT expire in less than
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60 seconds.
ICMP-REQ-2-a: It is RECOMMENDED that the ICMP Query session timer be
made configurable.
Status: Same as REQ-2, REQ-2-a in RFC5508
Justification: Setting the ICMP NAT session timeout to a very
large duration ( say, 240 seconds) could potentially tie up
precious NAT resources for the whole duration. On the other hand,
setting the timeout very low can result in premature freeing of
NAT resources and applications failing to complete gracefully. A
60-second timeout is a balance between the two extremes. More
detailed description can be found in original RFC.
ICMP-REQ-3: When an ICMP Error packet is received, if the ICMP
checksum fails to validate, the NAT SHOULD silently drop the ICMP
Error packet. If the ICMP checksum is valid, do the following.
a. If the IP checksum of the embedded packet fails to validate, the
NAT SHOULD silently drop the Error packet; and
b. If the embedded packet includes IP options, the NAT device MUST
traverse past the IP options to locate the start of transport
header for the embedded packet; and
c. The NAT device SHOULD NOT validate the transport checksum of the
embedded packet within an ICMP Error message, even when it is
possible to do so; and
d. If the ICMP Error payload contains ICMP extensions, the NAT
device MUST exclude the optional zero-padding and the ICMP
extensions when evaluating transport checksum for the embedded
packet.
Status: Same as REQ-3 in RFC5508
Justification: An ICMP Error message checksum covers the entire
ICMP message, including the payload. NAT uses the embedded IP and
transport headers for forwarding and translating the ICMP Error
message. More detailed description can be found in original RFC.
ICMP-REQ-4: If a NAT device receives an ICMP Error packet from
external realm, and the NAT device does not have an active mapping
for the embedded payload, the NAT SHOULD silently drop the ICMP Error
packet. If the NAT has active mapping for the embedded payload, then
the NAT MUST do the following prior to forwarding the packet, unless
local policy explicitly overridden by local policy:
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a. Revert the IP and transport headers of the embedded IP packet to
their original form, using the matching mapping; and
b. Leave the ICMP Error type and code unchanged; and
c. Modify the destination IP address of the outer IP header to be
same as the source IP address of the embedded packet after
translation.
Status: Same as REQ-4 in RFC5508
ICMP-REQ-5: If a NAT device receives an ICMP Error packet from the
private realm, and the NAT does not have an active mapping for the
embedded payload, the NAT SHOULD silently drop the ICMP Error packet.
If the NAT has active mapping for the embedded payload, then the NAT
MUST do the following prior to forwarding the packet, unless
explicitly overridden by local policy.
a. Revert the IP and transport headers of the embedded IP packet to
their original form, using the matching mapping; and
b. Leave the ICMP Error type and code unchanged; and
c. If the NAT enforces Basic NAT function, and the NAT has active
mapping for the IP address that sent the ICMP Error, translate
the source IP address of the ICMP Error packet with the public IP
address in the mapping. In all other cases, translate the source
IP address of the ICMP Error packet with its own public IP
address.
Status: Same as REQ-5 in RFC5508
ICMP-REQ-6: While processing an ICMP Error packet pertaining to an
ICMP Query or Query response message, a NAT device MUST NOT refresh
or delete the NAT Session that pertains to the embedded payload
within the ICMP Error packet.
Status: Same as REQ-6 in RFC5508
Justification: This requirement ensures that the NAT Session will
not be modified if someone is able to spoof ICMP Error messages
for the session. More detailed description can be found in
original RFC.
ICMP-REQ-7: LSN devices MUST support the traversal of hairpinned ICMP
Query sessions and Error messages.
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a. When forwarding a hairpinned ICMP Error message, the NAT device
MUST translate the destination IP address of the outer IP header
to be same as the source IP address of the embedded IP packet
after the translation
Status: "NAT devices enforcing Basic NAT MUST support the
traversal of hairpinned ICMP Query sessions. All NAT devices
(i.e., Basic NAT as well as NAPT devices) MUST support the
traversal of hairpinned ICMP Error messages." is REQ-7 in RFC5508.
LSN is kind of Basic NATs, and is enforced Basic NAT behavior, so
LSN MUST support ICMP Query and Error messages.
Justification: This requirement is necessary for current
applications to work correctly. More detailed description can be
found in original RFC.
ICMP-REQ-8: When a NAT device is unable to establish a NAT Session
for a new transport-layer (TCP, UDP, ICMP, etc.) flow due to resource
constraints or administrative restrictions, the NAT device SHOULD
send an ICMP destination unreachable message, with a code of 13
(Communication administratively prohibited) to the sender, and drop
the original packet.
Status: Same as REQ-8 in RFC5508
Justification: LSN, limiting the number of the LSN external ports
of UDP/TCP per CPE, often unable to establish new NAT session for
a CPE, because the CPE use many sessions. In this case, LSN
SHOULD send an ICMP destination unreachable message or some
applications maybe not work well.
ICMP-REQ-9: A NAT device MAY implement a policy control that prevents
ICMP messages being generated toward certain interface(s).
Implementation of such a policy control overrides the MUSTs and
SHOULDs in REQ-10.
ICMP-REQ-10: Unless overridden by REQ-9's policy, a NAT device needs
to support ICMP messages as below, some conforming to Section 4.3 of
[RFC1812] and some superseding the requirements of Section 4.3 of
[RFC1812]:
a) MUST support:
1. Destination Unreachable Message
2. Time Exceeded Message
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3. Echo Request/Reply Messages
b) MAY support:
1. Redirect Message
2. Timestamp and Timestamp Reply Messages
3. Source Route Options
4. Address Mask Request/Reply Message
5. Parameter Problem Message
6. Router Advertisement and Solicitations
c) SHOULD NOT support
1. Source Quench Message
2. Information Request/reply
In addition, a NAT device is RECOMMENDED to conform to the following
implementation considerations:
a. d) DS Field Usage
b. e) When Not to Send ICMP Errors
c. f) Rate Limiting
Status: Same as REQ-9, REQ-10 in RFC5508
Justification: These are for conformance to RFC 1812.
ICMP-REQ-11: A NAT MAY drop or appropriately handle Non-QueryError
ICMP messages.
Status: Same as REQ-11 in RFC5508
Justification: NAT devices may handle of Non-QueryError ICMP
messages.
6. LSN specified Requirements
ORIG-REQ-1: A LSN MUST allocate one external IP address to each CPE.
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a) LSN external IP address allocated to the CPE MUST be same for
the UDP, TCP and ICMP.
Justification: If a LSN allocates multiple LSN external IP addresses
to each CPE, some applications might not work.
ORIG-REQ-2: A LSN MUST allocate LSN external ports which is mapped
for CPE ports of UDP.
a) A LSN MAY reuse LSN external port after a NAT UDP mapping timer
expires.
b) A LSN SHOULD limit the number of the LSN external ports of UDP
per CPE.
c) The number of the LSN external ports of UDP per CPE which LSN
can allocate SHOULD be configurable for the administrator of LSN.
Justification: CPEs can communicate to CPE external realm fairly by
limiting the number of LSN external ports per CPE.
ORIG-REQ-3: A LSN MUST allocate LSN external ports which is mapped
for CPE ports of TCP.
a) A LSN MAY reuse LSN external port while the port is allocated
for no session originated by any CPE.
b) A LSN SHOULD limit the number of the LSN external ports of TCP
per CPE.
c) 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.
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.
ORIG-REQ-4: A LSN MUST allocate LSN external identifiers which is
mapped for CPE identifiers of ICMP.
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a) A LSN MAY reuse LSN external identifier after an ICMP Query
session timer expires.
b) A LSN SHOULD limit the number of the LSN external identifier
allocated per CPE.
c) 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.
If a CPE has already consumed many LSN external ports, the CPE might
not use new ports because LSNs limit the number of ports.
ORIG-REQ-5: A LSN MAY have implementations that some specific
applications can work well even if each CPE's usable number of LSN
external ports have already consumed.
Justification: Some specific applications don't work well due to
limitation of number of number of ports by LSN, therefore other
applications might be affected in the same CPE.
In Section 7 we discuss in detail.
7. 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.
7.1. Store Translation Log
One mechanism stores the following information at LSN.
- destination address
- destination port
- translated source address
- translated source port
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- untranslated source address
- 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.
7.2. 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.
8. Considerations about limiting the number of LSN external ports
As discussed in section 3, LSN limits the number of LSN external
ports and identifier per CPE. Therefore some important applications
like DNS might not work well due to applications consuming many LSN
external ports.
There are two ways to solve this issue. The one is that particular
applications are out of the targets for the number of port limitation
for LSN. In the case, the applications should be configurable for
the administrator of LSN.
The other is that LSN doesn't translate address or port for some
specific applications, moreover it doesn't limit the number of LSN
external ports.(we call "LSN pass-through") Therefore, LSN behave as
a router. In this case, some specific applications are out of
limitation for the number of LSN external ports. Some applications,
which don't work well due to address translation like FTP, is
effective. Reducing costs of translation is also effective. As a
condition, administrators of LSN can control SPS which become a
target of LSN pass-through.
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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 | | P |
| E |<<<<<<<<<<<<| N |<<<<<<<<<<<<<<| S |
| |from X2:x2 | |fromX2:x2 | |
+---+ to X1:x1 +---+ to X1:x1 +---+
Figure 3. LSN pass-through
No matter which solutions you choose, you should consider which
applications you are out of limitation target for the number of LSN
external ports. When you choose too many applications, this might
cause LSNs large load.
9. IANA Considerations
There are no IANA considerations.
10. 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.
11. Acknowledgements
Thanks for the input and review by Yasuhiro Shirasaki, Takeshi
Tomochika, Kousuke Shishikura, Dai Kuwabara, Tomoya Yoshida, Takanori
Mizuguchi, Arifumi Matsumoto, Tomohiro Fujisaki
12. References
12.1. 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.
[RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.
Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
RFC 5382, October 2008.
[RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT
Behavioral Requirements for ICMP", BCP 148, RFC 5508,
April 2009.
[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-02 (work in
progress), September 2009.
12.2. Informative Reference
[I-D.ietf-softwire-dual-stack-lite]
Durand, A., Droms, R., Haberman, B., Woodyatt, J., Lee,
Y., and R. Bush, "Dual-stack lite broadband deployments
post IPv4 exhaustion",
draft-ietf-softwire-dual-stack-lite-03 (work in progress),
February 2010.
[I-D.ymbk-aplusp]
Bush, R., "The A+P Approach to the IPv4 Address Shortage",
draft-ymbk-aplusp-05 (work in progress), October 2009.
Authors' Addresses
Ikuhei Yamagata
NTT Communications Corporation
Gran Park Tower 17F, 3-4-1 Shibaura, Minato-ku
Tokyo 108-8118
Japan
Phone: +81 50 3812 4704
Email: ikuhei@nttv6.jp
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Tomohiro Nishitani
NTT Communications Corporation
Gran Park Tower 17F, 3-4-1 Shibaura, Minato-ku
Tokyo 108-8118
Japan
Phone: +81 50 3812 4742
Email: tomohiro.nishitani@ntt.com
Shin Miyakawa
NTT Communications Corporation
Gran Park Tower 17F, 3-4-1 Shibaura, Minato-ku
Tokyo 108-8118
Japan
Phone: +81 50 3812 4695
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.
541-1 Ichigao-cho Aoba-ku
Yokohama 225-0024
Japan
Email: ashida@itscom.ad.jp
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