Network Working Group F. Templin
Internet-Draft Nokia
Expires: August 15, 2004 T. Gleeson
Cisco Systems K.K.
M. Talwar
D. Thaler
Microsoft Corporation
February 16, 2004
Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)
draft-ietf-ngtrans-isatap-20.txt
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of Section 10 of RFC2026.
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This Internet-Draft will expire on August 15, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
The Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) connects
IPv6 hosts/routers over IPv4 networks. ISATAP views the IPv4 network
as a link layer for IPv6 and views other nodes on the network as
potential IPv6 hosts/routers. ISATAP supports automatic tunneling and
a tunnel interface management abstraction similar to the Non-
Broadcast, Multiple Access (NBMA) and ATM Permanent/Switched Virtual
Circuit (PVC/SVC) models.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. ISATAP Conceptual Model . . . . . . . . . . . . . . . . . . . 5
5. Node Requirements . . . . . . . . . . . . . . . . . . . . . . 6
6. Addressing Requirements . . . . . . . . . . . . . . . . . . . 7
7. Configuration and Management Requirements . . . . . . . . . . 8
8. Automatic Tunneling . . . . . . . . . . . . . . . . . . . . . 12
9. Neighbor Discovery for ISATAP Interfaces . . . . . . . . . . . 17
10. Security considerations . . . . . . . . . . . . . . . . . . . 20
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
12. IAB Considerations . . . . . . . . . . . . . . . . . . . . . . 20
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22
A. Major Changes . . . . . . . . . . . . . . . . . . . . . . . . 23
B. The IPv6 Minimum MTU . . . . . . . . . . . . . . . . . . . . . 23
C. Modified EUI-64 Addresses in the IANA Ethernet Address Block . 24
D. Proposed ICMPv6 Code Field Types . . . . . . . . . . . . . . . 25
Normative References . . . . . . . . . . . . . . . . . . . . . 25
Informative References . . . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 28
Intellectual Property and Copyright Statements . . . . . . . . 29
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1. Introduction
This document specifies a simple mechanism called the Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP) that connects IPv6
[RFC2460] hosts/routers over IPv4 [STD5] networks. Dual-stack
(IPv6/IPv4) nodes use ISATAP to automatically tunnel IPv6 packets in
IPv4, i.e., ISATAP views the IPv4 network as a link layer for IPv6
and views other nodes on the network as potential IPv6 hosts/routers.
ISATAP enables automatic tunneling whether global or private IPv4
addresses are used, and supports a tunnel interface management
abstraction similar to the Non-Broadcast, Multiple Access (NBMA)
[RFC2491] and ATM Permanent/Switched Virtual Circuit (PVC/SVC)
[RFC2492] models.
The main objectives of this document are to: 1) describe the ISATAP
conceptual model, 2) specify addressing requirements, 3) discuss
configuration and management requirements, 4) specify automatic
tunneling using ISATAP, 5) specify operational aspects of IPv6
Neighbor Discovery, and 6) discuss IANA and Security considerations.
This document surveys all IETF v6ops WG documents current up to
February 16, 2004.
2. Requirements
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in [BCP14].
This document also makes use of internal conceptual variables to
describe protocol behavior and external variables that an
implementation must allow system administrators to change. The
specific variable names, how their values change, and how their
settings influence protocol behavior are provided to demonstrate
protocol behavior. An implementation is not required to have them in
the exact form described here, so long as its external behavior is
consistent with that described in this document.
3. Terminology
The terminology of [STD3][RFC2460][RFC2461][RFC3582] applies to this
document. The following additional terms are defined:
ISATAP node:
a node that implements the specifications in this document.
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ISATAP daemon:
an ISATAP node's server application that uses an API for control
plane signaling and tunnel interface configuration/management.
ISATAP driver:
an ISATAP node's network module that provides an API for control
plane signaling and tunnel interface configuration/management.
Also provides a packet encapsulation/decapsulation engine, and an
embedded gateway function (see: [STD3], section 3.3.4.2).
logical interface:
an IPv6 address or a configured tunnel interface associated with
an ISATAP interface (see: [STD3], section 3.3.4.1).
ISATAP interface:
an ISATAP node's point-to-multipoint interface that provides a
control plane interface for the ISATAP daemon and a forwarding
plane nexus for its associated logical interfaces.
ISATAP interface identifier:
an IPv6 interface identifier with an embedded IPv4 address
constructed as specified in section 6.1.
ISATAP address:
an IPv6 unicast address assigned on an ISATAP interface with an
on-link prefix and an ISATAP interface identifier.
locator:
an IPv4 address-to-interface mapping, i.e., a node's IPv4 address
and the index for it's associated interface.
locator set:
a set of locators associated with a tunnel interface, where each
locator in the set belongs to the same site.
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4. ISATAP Conceptual Model
ISATAP interfaces are advertising IPv6 interfaces that provide a
point-to-multipoint abstraction for IPv6-in-IPv4 tunneling. They
provide a forwarding plane nexus (used by the ISATAP driver) for
their associated logical interfaces. They also provide a control
plane interface (used by the ISATAP daemon) for tunnel configuration
signaling.
The ISATAP driver encapsulates packets for transmission according to
parameters associated with its logical interfaces. It also determines
the correct interface to receive each tunneled packet after
decapsulation, and provides an embedded gateway function.
The ISATAP daemon configures and manages tunnels via an API provided
by the ISATAP driver. Each such configured tunnel provides a nexus
for multiple applications using IPv6 addresses as application
identifiers. Each such application identifier provides a nexus for
multiple sessions. In summary, each configured tunnel provides a
point-to-point connection between peers that can support multiple
applications and multiple instances of each application.
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The following example diagram depicts the ISATAP conceptual model:
<-- IPv6-enabled applications -->
+----+ +---------------------------------------------+
|I D| | IPv6 Stack |
|S a| | |
|A e| | <-- IPv6 addresses --> |
|T m| | +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ |
|A o| | |v6| |v6| |v6| |v6| |v6| |v6| |v6| ... |v6| |
|P n| | +--+ +-++ ++-+ ++-+ ++++ ++-+ +-++ +-++ |
+-+--+ +---/---/----|----|---/-|--|-\----|--------|--+
| / / | | / | | \ | | <----+
x / / | | / | | \ | | I |
/ / +--++ +++-+ +--++ ++-++ +-+-+ S |
/ / |tun| |tun| |tun| |tun| ... |tun| A |
/ / +-+-+ +--++ +-+-+ ++--+ +-+-+ T |
/ / | \ | / | A |
x / / x | x \ | / x | P |
| / / | | | \ | / | | |
+--+---+---+ +------+---+ +-----+-+-++ +--------+-+ D |
|ISATAP I/F| |ISATAP I/F| |ISATAP I/F| .. |ISATAP I/F| r |
| (site 1) | | (site 1) | | (site 3) | | (site n) | i |
+---+----+++ +-++-----+-+ +-+-----+-++ +------+---+ v |
| | \ / | | | | \ | e |
| | \/ | | | | \ | r |
| | /\ | | | | \ | <----+
+---|----|-/--\-|-----|-----|-----|-----\ -------|---+
| +-+-+ +++-+ +++-+ +-+-+ +-+-+ +-+-+ +--++ +-+-+ |
| |loc| |loc| |loc| |loc| |loc| |loc| |loc| .. |loc| |
| +-+-+ +--++ +---+ +---+ +-+-+ +-+-+ +-+-+ +-+-+ |
| | / / / \ | / / |
| | / / +---+ \ | / / |
| | / / / \ | / / |
| | / / / IPv4 Stack \ | / / |
+-+-+-+--+-+--+--------+--+------+++------+-+------+-+
|IPv4 I/F| |IPv4 I/F| |IPv4 I/F| .... |IPv4 I/F|
|(site 1)| |(site 2)| |(site 3)| |(site n)|
+--------+ +--------+ +--------+ +--------+
5. Node Requirements
ISATAP nodes observe the common functionality requirements in
[NODEREQ] and the DNS requirements in ([MECH], section 2.2). They
also implement the additional features specified in this document.
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6. Addressing Requirements
ISATAP nodes implement the addressing requirements found in
([NODEREQ], section 4.5). [RFC2462][RFC3484][ADDR] MUST be supported,
and [RFC3041] SHOULD be supported (configurable on a per-connection
basis).
6.1 ISATAP Interface Identifiers
ISATAP interface identifiers are constructed in Modified EUI-64
format ([ADDR], appendix A). They are formed by concatenating the
24-bit IANA OUI (00-00-5E), the 8-bit hexadecimal value 0xFE, and a
32-bit IPv4 address in network byte order.
The format for ISATAP interface identifiers is given below (where 'u'
is the IEEE universal/local bit, 'g' is the IEEE group/individual
bit, and the 'm' bits represent the concatenated IPv4 address):
|0 1|1 3|3 4|4 6|
|0 5|6 1|2 7|8 3|
+----------------+----------------+----------------+----------------+
|000000ug00000000|0101111011111110|mmmmmmmmmmmmmmmm|mmmmmmmmmmmmmmmm|
+----------------+----------------+----------------+----------------+
When the IPv4 address is known to be globally unique, the 'u' bit is
set to 1; otherwise, the 'u' bit is set to 0 ([ADDR], section 2.5.1).
See: Appendix C for additional non-normative details.
6.2 ISATAP Addresses
Any IPv6 unicast address ([ADDR], section 2.5) that contains an
ISATAP interface identifier constructed as specified in section 6.1
and an on-link prefix on an ISATAP interface is considered an ISATAP
address.
6.3 Multicast/Anycast
ISATAP interfaces recognize a node's required IPv6 multicast/anycast
addresses ([ADDR], section 2.8).
For IPv6 multicast addresses of interest to local applications,
ISATAP nodes join the corresponding Organization-Local Scope IPv4
multicast groups ([RFC2529], section 6) on each interface that
appears in an ISATAP interface's locator set (see: section 7.2).
IPv6 multicast addresses of interest include a node's required
multicast addresses, and may also include e.g, the
'All_DHCP_Relay_Agents_and_Servers' and 'All_DHCP_Servers' multicast
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addresses (i.e., if the node is configured as a DHCPv6 server
[RFC3315][RFC3633]), etc.
Considerations for IPv6 anycast appear in [ANYCAST].
6.4 Source/Target Link Layer Address Options
Source/Target Link Layer Address Options ([RFC2461], section 4.6.1)
for ISATAP have the following format:
+-------+-------+-------+-------+-------+-------+-------+--------+
| Type |Length | 0 | 0 | IPv4 Address |
+-------+-------+-------+-------+-------+-------+-------+--------+
Type:
1 for Source Link-layer address. 2 for Target Link-layer address.
Length:
1 (in units of 8 octets).
IPv4 Address:
A 32 bit IPv4 address, in network byte order.
ISATAP nodes use the specifications in ([MECH], section 3.8) that
pertain to sending and receiving Source/Target Link Layer Address
Options.
7. Configuration and Management Requirements
7.1 Network Management
This document defines no new MIB tables, nor extensions to any
existing MIB tables. Objects found in [FTMIB][IPMIB][TUNMIB] are
supported as described in the following subsections.
7.2 The ifRcvAddressTable
The ISATAP driver maintains ifRcvAddressTable as a bidirectional
association of locators with tunnel interfaces. Each locator in the
table includes an IPv4 address-to-interface mapping (i.e., an IPv4
ipAddressEntry in the node's ipAddressTable) and a list of associated
tunnel interfaces. Each tunnel interface in the table has a
tunnelIfEntry and a list of associated locators, i.e., a "locator
set".
The ISATAP driver implements the following conceptual functions to
manage and search the ifRcvAddressTable:
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7.2.1 RcvTableAdd(locator, tunnel_interface)
Creates a bidirectional association in the ifRcvAddressTable between
the locator and tunnel interface, i.e., adds the locator to the
tunnel interface's locator set and adds the tunnel interface to the
locator's association list.
Returns success or failure.
7.2.2 RcvTableDel(locator, tunnel_interface)
Deletes ifRcvAddressTable entries according to the locator and tunnel
interface arguments as follows:
- if both arguments are NULL, garbage-collects the entire table.
- if both arguments are non-NULL, deletes the locator from the
tunnel interface's locator set and deletes the tunnel interface
from the locator's association list.
- if the locator is non-NULL and tunnel interface is NULL, deletes
the locator from the locator sets of all tunnel interfaces.
- if the locator is NULL and the tunnel interface is non-NULL,
deletes the tunnel interface from the association lists of all
locators.
Returns success or failure.
7.2.3 RcvTableLocate(packet)
Searches the ifRcvAddressTable to locate the correct tunnel interface
to decapsulate a packet. First, determines the locator that matches
the packet's IPv4 destination address and ifIndex for the interface
the packet arrived on. Next, checks each tunnel interface in the
locator's association list for exact matches of tunnelIfEncapsMethod
with the packet's encapsulation type and tunnelIfRemoteInetAddress
with the packet's IPv4 source address.
If there is no match on the packet's IPv4 source address, a tunnel
interface with a matching tunnelIfEncapsMethod and with
tunnelIfRemoteInetAddress set to 0.0.0.0 is selected. If there are
multiple matches, a tunnel interface with tunnelIfLocalInetAddress
that matches the packet's IPv4 destination address is preferred.
Returns a pointer to a tunnel interface if a match is found; else
NULL.
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7.3 ISATAP Driver API
The ISATAP driver implements an API used by, e.g., the ISATAP daemon,
startup scripts, manual command line entry, kernel processes, etc.
Access MUST be restricted to privileged users and applications.
ISATAP nodes implement the basic and advanced APIs for IPv6
[RFC3493][RFC3542].
7.4 ISATAP Interface Creation/Configuration
ISATAP interfaces are created via the tunnelIfConfigTable, which
results in simultaneous creation of a tunnelIfEntry and a companion
ipv6InterfaceEntry. Each ISATAP interface configures a locator set,
where each locator in the set represents an IPv4 address-to-interface
mapping for the same site (or, represents a mapping that is routable
on the global Internet). ISATAP interfaces MUST NOT configure a
locator set that spans multiple sites.
ISATAP interfaces configure the following values for objects in
tunnelIfEntry:
- tunnelIfEncapsMethod is set to an IANATunnelType for "isatap".
- tunnelIfLocalInetAddress is set to an IPv4 address from the
interface's locator set.
- tunnelIfRemoteInetAddress is set to 0.0.0.0 to denote wildcard
match for remote tunnel endpoints.
- other read-write objects in the tunnelIfEntry are configured as
for any tunnel interface.
ISATAP interfaces are configured as advertising IPv6 interfaces and
set the following values for objects in ipv6InterfaceEntry:
- ipv6InterfaceType is set to "tunnel".
- ipv6InterfacePhysicalAddress is set to an octet string of zero
length to indicate that this IPv6 interface does not have a
physical address.
- ipv6InterfaceForwarding and ip6Forwarding for the node are set to
"forwarding".
- other read-write objects in ipv6InterfaceEntry are configured as
for any IPv6 interface.
ISATAP interfaces create an ipv6RouterAdvertEntry and set its
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ipv6RouterAdvertIfIndex object to the same value as
ipv6InterfaceIfIndex. Other objects in ipv6RouterAdvertEntry are
configured as for any IPv6 router.
7.5 Configured Tunnel Creation/Configuration
Configured tunnels are normally created by the ISATAP daemon in
dynamic response to a tunnel creation request as an ISATAP
interface's associated logical interface; they inherit the locator
set of their associated ISATAP interface. Configured tunnels set the
following values for objects in tunnelIfEntry:
- tunnelIfEncapsMethod is set to an appropriate IANATunnelType
value.
- tunnelIfLocalInetAddress is set to an IPv4 address from the
interface's locator set.
- tunnelIfRemoteInetAddress is set to an IPv4 address for the node
at the far end of the tunnel.
- other read-write objects in the tunnelIfEntry are configured as
for any tunnel interface.
Configured tunnels set values for objects in ipv6InterfaceEntry as
follows:
- ipv6InterfaceType is set to "tunnel".
- ipv6InterfacePhysicalAddress is set to an octet string of zero
length to indicate that this IPv6 interface does not have a
physical address.
- other read-write objects in ipv6InterfaceEntry are configured as
for any IPv6 interface.
7.6 Reconfigurations Due to IPv4 Address Changes
When an IPv4 address is removed from an interface, its corresponding
locator SHOULD be removed from all locator sets via
RcvTableDel(locator, NULL); tunnelIfEntrys that used the IPv4 address
as tunnelIfLocalInetAddress SHOULD also configure a different local
IPv4 address from their remaining locator set.
When a new IPv4 address is added to an IPv4 interface, the node MAY
add the corresponding new locator to a tunnel interface's locator set
via RcvTableAdd(locator, tunnel_interface), and MAY also set
tunnelIfLocalInetAddress for its tunnelIfEntry to the new address.
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Methods for triggering the above changes are out of scope.
8. Automatic Tunneling
ISATAP nodes use the basic tunneling mechanisms specified in [MECH].
The following additional specifications are also used:
8.1 Encapsulation
The ISATAP driver encapsulates IPv6 packets using various
encapsulation methods, including ip-protocol-41 (e.g., 6over4
[RFC2529], 6to4 [RFC3056], IPv6-in-IPv4 configured tunnels [MECH],
isatap, etc.), UDP [STD6] port 3544, and others.
Security processing (e.g., [RFC2402][RFC2406], etc.), upper layer
fragmentation [RFC3542] and header compression for the packet's inner
headers are performed prior to encapsulation.
8.1.1 NAT Traversal
Native IPv6 and/or ip-protocol-41 encapsulation provides sufficient
functionality to support communications between peers that reside
within the same site (i.e., the same enterprise network). When the
remote peer is in a different site, NAT traversal via UDP/IPv4
encapsulation MAY be necessary.
When an ISATAP node determines that NAT traversal is necessary to
reach a particular peer, it encapsulates IPv6 packets using UDP/IPv4
port 3544 encapsulation. This determination may come through, e.g.,
first attempting communications via ip-protocol-41 then failing over
to UDP/IPv4 port 3544 encapsulation, administrative knowledge that a
NAT is on the path, etc.
8.1.2 Multicast
ISATAP interfaces encapsulate packets with IPv6 multicast destination
addresses using a mapped Organization-Local Scope IPv4 multicast
address ([RFC2529], section 6) as the destination address in the
encapsulating IPv4 header.
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8.2 Tunnel MTU and Fragmentation
Encapsulated packets sent by the ISATAP driver may require host-based
IPv4 fragmentation in order to satisfy the 1280 byte IPv6 minimum
MTU, e.g., when the underlying link has a small IPv4 MTU [BCP48].
While this intentional fragmentation is not considered harmful,
unmitigated IPv4 fragmentation caused by the network can cause poor
performance [FRAG]. For example, since the minimum IPv4 fragment
size is only 8 bytes [STD5], a single 1280 byte encapsulated packet
could be shredded by the network into as many as 160 IPv4 fragments
with obvious negative performance implications.
ISATAP uses the MTU and fragmentation specifications in ([MECH],
section 3.2) and the Maximum Reassembly Unit (MRU) specifications in
([MECH], section 3.6), which provide sufficient measures for avoiding
excessive IPv4 fragmentation in certain controlled environments
(e.g., 3GPP operator networks, enterprise networks, etc). To minimize
IPv4 fragmentation and improve performance in general use case
scenarios, ISATAP nodes SHOULD add the following simple
instrumentation to the IPv4 reassembly cache:
When the initial fragment of an encapsulated packet arrives, the
packet's IPv4 reassembly timer is set to 1 second (i.e., the worst
case store-and-forward delay budget for a 1280 byte packet). If an
encapsulated packet's IPv4 reassembly timer expires:
- If enough contiguous leading bytes of the packet have arrived
(see: section 8.6), reassemble the packet using zero-filled or
heuristically-chosen replacement data bytes in place of any
missing fragments. (Otherwise, garbage-collect the reassembly
buffer and return from processing.)
- Mark the packet as "INCOMPLETE", and also mark it with an
"ACTUAL_BYTES" length that encodes the actual number of data bytes
in fragments that arrived.
- Deliver the packet to the ISATAP driver, and do not send an ICMPv4
"time exceeded" message [STD5].
Appendix B provides informative text on the derivation of the 1280
byte IPv6 minimum MTU.
8.3 Handling ICMPv4 Errors
ISATAP interfaces SHOULD process ARP failures and persistent ICMPv4
errors as link-specific information indicating that a path to a
neighbor may have failed ([RFC2461], section 7.3.3).
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8.4 Link-Local Addresses
ISATAP interfaces use link local addresses constructed as specified
in section 6.1 of this document.
8.5 Neighbor Discovery over Tunnels
The specification in ([MECH], section 3.8) is used; the additional
specification for neighbor discovery in section 9 of this document
are also used.
8.6 Decapsulation/Filtering
ISATAP nodes typically arrange for the ISATAP driver to receive all
IPv4-encapsulated IPv6 packets that are addressed to one of the
node's IPv4 addresses. Examples include ip-protocol-41 (e.g., 6to4,
6over4, configured tunnels, isatap, etc.), UDP/IPv4 port 3544, and
others. The ISATAP driver uses the decapsulation and filtering
specifications in ([MECH], section 3.6), and processes each packet
according to the following steps:
1. Locate the correct tunnel interface to receive the packet (see:
section 7.2.3). If not found, silently discard the packet and
return from processing.
2. If the tunnel uses header compression, reconstitute headers. If
header reconstitution fails, silently discard the packet and
return from processing.
3. Verify that the packet's IPv4 source address is correct for the
encapsulated IPv6 source address. For packets received on a
configured tunnel interface, verification is exactly as specified
in ([MECH], section 3.6).
For packets received on an ISATAP interface, the IPv4 source
address is correct if:
- the IPv6 source address is an ISATAP address that embeds the
IPv4 source address in its interface identifier, or:
- the IPv6 source address is the address of an IPv6 neighbor on
an ISATAP interface associated with the locator that matched
the packet (see: section 7.2.3), or:
- the IPv4 source address is a member of the Potential Router
List (see: section 9.1).
If the IPv4 source address is incorrect, silently discard the
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packet and return from processing.
4. Perform IPv4 ingress filtering (optional; disabled by default)
then decapsulate the packet but do not discard encapsulating
headers. If the IPv6 source address is invalid (see: [MECH],
section 3.6), silently discard the packet and return from
processing.
For UDP port 3544 packets received on an ISATAP interface, if the
IPv6 source address is an ISATAP link local address with the 'u'
bit set to 0 and an embedded IPv4 address that does not match the
IPv4 source address, rewrite the IPv6 source address to inform
upper layers of the sender's mapped UDP port number and IPv4
source address. Specific rules for rewriting the IPv6 source
address are established during ISATAP interface configuration.
5. Perform ingress filtering on the IPv6 source address (see:
[MECH], section 3.6). Next, determine the correct transport
protocol listener [FLOW] if the packet is destined to the
localhost; otherwise, perform an IPv6 forwarding table lookup and
site border/firewall filtering (see: [UNIQUE], section 6).
If the packet cannot be delivered, the driver SHOULD send an
ICMPv6 Destination Unreachable message ([RFC2463], section 3.2)
to the packet's source. The message SHOULD select as its source
address an IPv6 address from the outgoing interface (if the
packet was destined to the localhost) or an ingress-wise correct
IPv6 address from the interface that would have forwarded the
packet had it not been filtered.
The Code field of the message is set as follows:
- if there is no route to the destination, the Code field is set
to 0 (see: [RFC2463], section 3.1).
- if communication with the destination is administratively
prohibited, the Code field is set to 1 ([RFC2463], section
3.1).
- if the packet is destined to the localhost, but the transport
protocol has no listener, the Code field is set to 4
([RFC2463], section 3.1).
- if the packet's destination is beyond the scope of the source
address, the Code field is set to 2 (see: IANA
Considerations).
- if the packet was dropped due to ingress filtering policies,
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the Code field is set to 5 (see: IANA Considerations).
- if the packet is dropped due to a reject route, the Code field
is set to 6 (see: IANA Considerations).
- if the packet was received on a point-to-point link and
destined to an address within a subnet assigned to that same
link, or if the reason for the failure to deliver cannot be
mapped to any of the specific conditions listed above, the
Code field is set to 3 ([RFC2463], section 3.2).
After sending the ICMPv6 Destination Unreachable message, discard
the packet and return from processing.
6. If the packet is "INCOMPLETE" (see section 8.2) prepare an
authenticated, unsolicited Router Advertisement message
([RFC2461], section 6.2.4) with an MTU option that encodes the
maximum of "ACTUAL_BYTES" and (68 bytes minus the size of
encapsulating headers.)
The IPv6 destination address in the Router Advertisement message
is set to the packet's IPv6 source address, and the message is
reverse-encapsulated and returned to the node that sent the
"INCOMPLETE" packet, i.e., it is NOT presented to the native IPv6
stack for transmission.
The 68 byte minimum MTU is due to the requirement that every
Internet module must be able to forward a datagram of 68 octets
without further fragmentation ([STD5], Internet Protocol, section
3.2).
7. Discard encapsulating headers. If the packet was destined to a
remote host, forward the packet and return from processing.
Otherwise, apply security processing (e.g., [RFC2402][RFC2406],
etc.), and place the packet in a buffer for upper layers. The
buffer may be, e.g., the IPv6 reassembly cache, an application's
mapped data buffer [RFC3542], etc.
If there is clear evidence that upper layer reassembly has
stalled, an ICMPv6 Packet Too Big message [RFC1981] MAY be sent
to the packet's source address with an MTU value likely to incur
successful reassembly. Some applications may realize greater
efficiency by accepting partial information from "INCOMPLETE"
packets (see: section 8.2) and requesting selective
retransmission of missing portions.
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9. Neighbor Discovery for ISATAP Interfaces
ISATAP nodes use the neighbor discovery mechanisms specified in
[RFC2461] to create/change neighbor cache entries and to provide
control plane signaling for automatic tunnel configuration. Securing
mechanisms for neighbor discovery messages (e.g., [RFC2402], [SEND])
are used according to the trust model appropriate for the given
deployment scenario [SENDPS]. ISATAP interfaces also implement the
following specifications:
9.1 Conceptual Model Of A Host
To the list of Conceptual Data Structures ([RFC2461], section 5.1),
ISATAP interfaces add:
Potential Router List
A set of entries about potential routers; used to support the
mechanisms specified in section 9.2.2.1. Each entry ("PRL(i)")
has an associated timer ("TIMER(i)"), and an IPv4 address
("V4ADDR(i)") that represents a router's advertising ISATAP
interface.
9.2 Router and Prefix Discovery
9.2.1 Router Specification
Solicited Router Advertisements sent on ISATAP interfaces are sent
directly to the soliciting node, i.e., they might not be received by
other nodes on the link.
Router Advertisements sent on ISATAP interfaces MAY include
information delegated via DHCPv6 [RFC3633].
Router Advertisements sent on ISATAP interfaces MUST NOT include a
prefix option containing a preferred lifetime greater than the valid
lifetime.
9.2.2 Host Specification
The Host Specification in ([RFC2461], section 6.3) is used. ISATAP
interfaces add the following specifications:
9.2.2.1 Host Variables
To the list of host variables ([RFC2461], section 6.3.2), ISATAP
interfaces add:
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PrlRefreshInterval
Time in seconds between successive refreshments of the PRL after
initialization. The designated value of all 1's (0xffffffff)
represents infinity.
Default: 3600 seconds
MinRouterSolicitInterval
Minimum time in seconds between successive solicitations of the
same advertising ISATAP interface. The designated value of all 1's
(0xffffffff) represents infinity.
9.2.2.2 Potential Router List Initialization
ISATAP nodes provision an ISATAP interface's PRL with IPv4 addresses
discovered via a DNS fully-qualified domain name (FQDN) [STD13],
manual configuration, a DHCPv4 option, a DHCPv4 vendor-specific
option, or an unspecified alternate method.
FQDNs are established via manual configuration or an unspecified
alternate method. FQDNs are resolved into IPv4 addresses through
querying the DNS service, querying a site-specific name service,
static host file lookup, or an unspecified alternate method.
When the node provisions an ISATAP interface's PRL with IPv4
addresses, it sets a timer for the interface (e.g.,
PrlRefreshIntervalTimer) to PrlRefreshInterval seconds. The node re-
initializes the PRL as specified above when PrlRefreshIntervalTimer
expires, or when an asynchronous re-initialization event occurs. When
the node re-initializes the PRL, it resets PrlRefreshIntervalTimer to
PrlRefreshInterval seconds.
9.2.2.3 Processing Received Router Advertisements
To the list of checks for validating Router Advertisement messages
([RFC2461], section 6.1.1), ISATAP interfaces add:
- IP Source Address is an ISATAP link-local address that embeds
V4ADDR(i) for some PRL(i).
Valid Router Advertisements received on an ISATAP interface are
processed exactly as specified in ([RFC2461], section 6.3.4).
[RFC3315] and [RFC3633] are stateful mechanisms associated with the M
and O bits.
For Router Advertisements that include an MTU option, the MTU value
does not alter the ISATAP interface LinkMTU. Instead, the MTU value
is recorded, e.g., in the IPv6 forwarding table. If the IPv6
destination address is one of the node's own unicast addresses, the
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MTU value is recorded such that upper layer fragmentation [RFC3542]
will be used to reduce the size of the encapsulated packets sent via
the router. The recorded value is aged as for IPv6 path MTU
information [RFC1981].
9.2.2.4 Sending Router Solicitations
To the list of events after which Router Solicitation messages may be
sent ([RFC2461], section 6.3.7), ISATAP interfaces add:
- TIMER(i) for some PRL(i) expires.
Since unsolicited Router Advertisements may be incomplete and/or
absent, TIMER(i) MAY be used to schedule periodic Router Solicitation
events for certain PRL(i)'s.
When used, TIMER(i) SHOULD be set such that the next Router
Solicitation event will refresh remaining lifetimes stored for the
PRL(i), including Router Lifetime, Valid Lifetimes received in Prefix
Information Options, and Route Lifetimes received in Route
Information Options [DEFLT]. TIMER(i) MUST be set to no less than
MinRouterSolicitInterval seconds, where MinRouterSolicitInterval is
configurable for the node (or, for each PRL(i)) with a conservative
default value.
When TIMER(i) expires, Router Solicitation messages are sent as
specified in ([RFC2461], section 6.3.7) except that the messages are
sent directly to PRL(i), i.e., they might not be received by other
nodes on the link. While the node continues to use PRL(i) as a router
(and, while PRL(i) continues to act as a router), the node resets
TIMER(i) after each expiration as described above.
9.3 Address Resolution and Neighbor Unreachability Detection
9.3.1 Address Resolution
The specification in ([RFC2461], section 7.2) is used. ISATAP
addresses for which the neighbor's link-layer address cannot
otherwise be determined (e.g., from a neighbor cache entry) are
resolved to link-layer addresses by a static computation, i.e., the
last four octets are treated as an IPv4 address.
Hosts SHOULD perform an initial reachability confirmation by sending
Neighbor Solicitation message(s) and receiving a Neighbor
Advertisement message. Routers MAY perform this initial reachability
confirmation, but this might not scale in all environments.
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9.3.2 Neighbor Unreachability Detection
Hosts SHOULD perform Neighbor Unreachability Detection ([RFC2461],
section 7.3). Routers MAY perform neighbor unreachability detection,
but this might not scale in all environments.
10. Security considerations
The Security Considerations in the normative references, and in
([NODEREQ], section 8) apply. Also:
- ISATAP nodes observe the security considerations outlined in
[SENDPS]; use of IPsec (e.g., [RFC2402][RFC2406], etc.) is not
always feasible.
- site border routers SHOULD install a reject route for the IPv6
prefix FC00::/7 [UNIQUE] to insure that packets with local IPv6
destination addresses will not be forwarded outside of the site
via a default route.
- administrators MUST ensure that lists of IPv4 addresses
representing the advertising ISATAP interfaces of PRL members are
well maintained.
11. IANA Considerations
The IANA is instructed to specify the format for Modified EUI-64
address construction ([ADDR], Appendix A) in the IANA Ethernet
Address Block. The text in Appendix C of this document is offered as
an example specification. The current version of the IANA registry
for Ether Types can be accessed at:
http://www.iana.org/assignments/ethernet-numbers.
The IANA is instructed to assign the new ICMPv6 code field types
found in Appendix D of this document for the ICMPv6 Destination
Unreachable message. The policy for assigning new ICMPv6 code field
types is First Come First Served, as defined in [BCP26]. The current
version of the IANA registry for ICMPv6 type numbers can be accessed
at:
http://www.iana.org/assignments/icmpv6-parameters.
12. IAB Considerations
[RFC3424] ("IAB Considerations for UNilateral Self-Address Fixing
(UNSAF) Across Network Address Translation") section 4 requires that
any proposal supporting NAT traversal must explicitly address the
following considerations:
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12.1 Problem Definition
The specific problem being solved is enabling IPv6 connectivity for
ISATAP nodes that are unable to communicate via ip-protocol-41 or
native IPv6.
12.2 Exit Strategy
ISATAP nodes use UDP/IPv4 encapsulation for NAT traversal as a last
resort. As soon as native IPv6 or ip-protocol-41 support becomes
available, ISATAP nodes will naturally cease using UDP/IPv4
encapsulation.
12.3 Brittleness
UDP/IPv4 encapsulation with ISATAP introduces brittleness into the
system in several ways: the discovery process assumes a certain
classification of devices based on their treatment of UDP; the
mappings need to be continuously refreshed, and addressing structure
may cause some hosts located beyond a common NAT to be unreachable
from each other.
ISATAP assumes a certain classification of devices based on their
treatment of UDP. There could be devices that would not fit into one
of these molds, and hence would be improperly classified by ISATAP.
The bindings allocated from the NAT need to be continuously
refreshed. Since the timeouts for these bindings is very
implementation specific, the refresh interval cannot easily be
determined. When the binding is not being actively used to receive
traffic, but to wait for an incoming message, the binding refresh
will needlessly consume network bandwidth.
12.4 Requirements for a Long Term Solution
The devices that implement the IPv4 NAT service should in the future
also become IPv6 routers.
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13. Acknowledgments
The ideas in this document are not original, and the authors
acknowledge the original architects. Portions of this work were
sponsored through SRI International internal projects and government
contracts. Government sponsors include Monica Farah-Stapleton and
Russell Langan (U.S. Army CECOM ASEO), and Dr. Allen Moshfegh (U.S.
Office of Naval Research). SRI International sponsors include Dr.
Mike Frankel, J. Peter Marcotullio, Lou Rodriguez, and Dr. Ambatipudi
Sastry.
The following are acknowledged for providing peer review input: Jim
Bound, Rich Draves, Cyndi Jung, Ambatipudi Sastry, Aaron Schrader,
Ole Troan, Vlad Yasevich.
The following are acknowledged for their significant contributions:
Alain Durand, Hannu Flinck, Jason Goldschmidt, Nathan Lutchansky,
Karen Nielsen, Mohan Parthasarathy, Chirayu Patel, Art Shelest, Pekka
Savola, Margaret Wasserman, Brian Zill.
The authors acknowledge the work of Quang Nguyen on "Virtual
Ethernet" under the guidance of Dr. Lixia Zhang that proposed very
similar ideas to those that appear in this document. This work was
first brought to the authors' attention on September 20, 2002.
IAB considerations are the same as for Teredo. The diagram in section
4 was inspired by a similar diagram in RFC 3371.
The following individuals are acknowledged for their helpful insights
on path MTU discovery: Jari Arkko, Iljitsch van Beijnum, Jim Bound,
Ralph Droms, Alain Durand, Jun-ichiro itojun Hagino, Brian Haberman,
Bob Hinden, Christian Huitema, Kevin Lahey, Hakgoo Lee, Matt Mathis,
Jeff Mogul, Erik Nordmark, Soohong Daniel Park, Chirayu Patel,
Michael Richardson, Pekka Savola, Hesham Soliman, Mark Smith, Dave
Thaler, Michael Welzl, Lixia Zhang and the members of the Nokia NRC/
COM Mountain View team.
"...and I'm one step ahead of the shoe shine,
Two steps away from the county line,
Just trying to keep my customers satisfied,
Satisfi-i-ied!" - Paul Simon, 1969
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Appendix A. Major Changes
Major changes from earlier versions to version 17:
- new section on configuration/management.
- new appendices on IPv6 minimum MTU; IANA considerations.
- expanded section on MTU and fragmentation.
- expanded sections on encapsulation/decapsulation.
- specified relation to IPv6 Node Requirements.
- introduced distinction between control; forwarding planes.
- specified multicast mappings.
- revised neighbor discovery, address autoconfiguration, IANA
considerations and security considerations sections.
Appendix B. The IPv6 minimum MTU
The 1280 byte IPv6 minimum MTU was proposed by Steve Deering and
agreed through working group consensus in November 1997 discussions
on the IPv6 mailing list. The size was chosen to allow extra room for
link layer encapsulations without exceeding the Ethernet MTU of 1500
bytes, i.e., the practical physical cell size of the Internet. The
1280 byte MTU also provides a fixed upper bound for the size of IPv6
packets/fragments with a maximum store-and-forward delay budget of ~1
second assuming worst-case link speeds of ~10Kbps [BCP48], thus
providing a convenient value for use in reassembly buffer timer
settings. Finally, the 1280 byte MTU allows transport connections
(e.g., TCP) to configure a large-enough maximum segment size for
improved performance even if the IPv4 interface that will send the
tunneled packets uses a smaller MTU.
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Appendix C. Modified EUI-64 Addresses in the IANA Ethernet Address Block
Modified EUI-64 addresses ([ADDR], Appendix A) in the IANA Ethernet
Address Block are formed as the concatenation of the 24-bit IANA OUI
(00-00-5E) with a 40-bit extension identifier. They have the
following appearance in memory (bits transmitted right-to-left within
octets, octets transmitted left-to-right):
0 23 63
| OUI | extension identifier |
000000ug00000000 01011110xxxxxxxx xxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxx
When the first two octets of the extension identifier encode the
hexadecimal value 0xFFFE, the remainder of the extension identifier
encodes a 24-bit vendor-supplied id as follows:
0 23 39 63
| OUI | 0xFFFE | vendor-supplied id |
000000ug00000000 0101111011111111 11111110xxxxxxxx xxxxxxxxxxxxxxxx
When the first octet of the extension identifier encodes the
hexadecimal value 0xFE, the remainder of the extension identifier
encodes a 32-bit IPv4 address as follows:
0 23 31 63
| OUI | 0xFE | IPv4 address |
000000ug00000000 0101111011111110 xxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxx
Modified EUI-64 format interface identifiers are formed by inverting
the "u" bit, i.e., the "u" bit is set to one (1) to indicate
universal scope and it is set to zero (0) to indicate local scope
([ADDR], section 2.5.1).
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Appendix D. Proposed ICMPv6 Code Field Types
Three new ICMPv6 Code Field Type definitions are proposed for the
ICMPv6 Destination Unreachable message. The first proposes a new
definition for a currently-unassigned code type (2) in the ICMPv6
Type Numbers registry; the others propose new definitions for code
types (5) and (6). The code type field definition proposals appear
below:
Type Name Reference
---- ------------------------- ---------
1 Destination Unreachable [RFC2463]
Code 2 - beyond the scope of source address
5 - source address failed ingress policy
6 - reject route to destination
Normative References
[BCP14] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[BCP26] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
[STD3] Braden, R., "Requirements for Internet Hosts - Communication
Layers", STD 3, RFC 1122, October 1989.
[STD5] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
[STD6] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August
1980.
[RFC1981] McCann, J., Deering, S. and J. Mogul, "Path MTU Discovery for
IP version 6", RFC 1981, August 1996.
[RFC2402] Kent, S. and R. Atkinson, "IP Authentication Header", RFC
2402, November 1998.
[RFC2406] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
(ESP)", RFC 2406, November 1998.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2461] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998.
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[RFC2462] Thomson, S., and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[RFC2463] Conta, A., and S. Deering, "Internet Control Message Protocol
(ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification",
RFC 2463, December 1998.
[RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529, March 1999.
[RFC3041] Narten, T. and R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6", RFC 3041, January, 2001.
[RFC3424] Daigle, L. and IAB, "IAB Considerations for UNilateral Self-
Address Fixing (UNSAF) Across Network Address Translation", RFC 3424,
November 2002.
[RFC3484] Draves, R., "Default Address Selection for Internet Protocol
version 6 (IPv6)", RFC 3484, February 2003.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
Stevens, "Basic Socket Interface Extensions for IPv6", RFC 3493,
February 2003.
[RFC3542] Stevens, W., Thomas, M., Nordmark, E. and T. Jinmei,
"Advanced Sockets Application Program Interface (API) for IPv6", RFC
3542, May 2003.
[RFC3582] Abley, J., Black, B. and V. Gill, "Goals for IPv6 Site-
Multihoming Architectures", RFC 3582, August 2003.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host
Configuration Protocol (DHCP) version 6", RFC 3633, December 2003.
[ADDR] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", draft-ietf-ipv6-addr-arch-v4, Work in Progress,
October 2003.
[DEFLT] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", draft-ietf-ipv6-router-selection, Work in
Progress, December 2003.
[MECH] Gilligan, R. and E. Nordmark, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", draft-ietf-v6ops-mech-v2, Work in
Progress, February 2003.
[NODEREQ] Loughney, J., "IPv6 Node Requirements", draft-ietf-ipv6-node-
requirements, Work in Progress, October 2003.
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[UNIQUE] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", draft-ietf-ipv6-unique-local-addr, Work in Progress,
January 2004.
Informative References
[BCP48] Dawkins, S., Montenegro, G., Kojo, M. and V. Magret, "End-
to-end Performance Implications of Slow Links", BCP 48, RFC 3150,
July 2001.
[STD13] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2491] Armitage, G., Schulter, P., Jork, M. and G. Harter, "IPv6
over Non-Broadcast Multiple Access (NBMA) networks", RFC 2491,
January 1999.
[RFC2492] Armitage, G., Schulter, P. and M. Jork, "IPv6 over ATM
Networks", RFC 2492, January 1999.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via
IPv4 Clouds", RFC 3056, February 2001.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M.
Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC
3315, July 2003.
[ANYCAST] Hagino, J. and K. Ettikan, "An Analysis of IPv6 Anycast",
draft-ietf-ipngwg-ipv6-anycast-analysis, Work in Progress, June 2003.
[FLOW] Rajahalme, J., Conta, A., Carpenter, B. and S. Deering,
"IPv6 Flow Label Specification", draft-ietf-ipv6-flow-label, Work in
Progress, December 2003.
[FRAG] Mogul, J. and C. Kent, "Fragmentation Considered Harmful", In
Proc. SIGCOMM '87 Workshop on Frontiers in Computer Communications
Technology. August, 1987.
[FTMIB] Haberman, B. and M. Wasserman, "IP Forwarding Table MIB",
draft-ietf-ipv6-rfc2096-update, Work in Progress, August 2003.
[IPMIB] Routhier, S., "Management Information Base for the Internet
Protocol (IP)", draft-ietf-ipv6-rfc2011-update, Work in Progress,
September 2003.
[SEND] Arkko, J., Kempf, J., Sommerfield, B., Zill, B. and P.
Nikander, "Secure Neighbor Discovery (SEND)", draft-ietf-send-ndopt,
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Work in Progress, October 2003.
[SENDPS] Nikander, P., Kempf, J. and E. Nordmark, "IPv6 Neighbor
Discovery Trust Models and Threats", draft-ietf-send-psreq, Work in
Progress, October 2003.
[TUNMIB] Thaler, D., "IP Tunnel MIB", draft-ietf-ipv6-inet-tunnel-mib,
Work in Progress, January 2004.
Authors' Addresses
Fred L. Templin
Nokia
313 Fairchild Drive
Mountain View, CA 94110
US
Phone: +1 650 625 2331
EMail: ftemplin@iprg.nokia.com
Tim Gleeson
Cisco Systems K.K.
Shinjuku Mitsu Building
2-1-1 Nishishinjuku, Shinjuku-ku
Tokyo 163-0409
Japan
EMail: tgleeson@cisco.com
Mohit Talwar
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
US
Phone: +1 425 705 3131
EMail: mohitt@microsoft.com
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Dave Thaler
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
US
Phone: +1 425 703 8835
EMail: dthaler@microsoft.com
Full Copyright Statement
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Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
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