Network Working Group D. Thaler
Internet-Draft Microsoft
Expires: January 14, 2009 July 13, 2008
Evolution of the IP Model
draft-thaler-ip-model-evolution-01.txt
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Abstract
This draft attempts to document various aspects of the IP service
model and how it has evolved over time. In particular, it attempts
to document the properties of the IP layer as they are seen by upper-
layer protocols and applications, and especially properties which
were (and at times still are) incorrectly perceived to exist, as well
as properties that changing would cause problems.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The IP Service Model . . . . . . . . . . . . . . . . . . . . . 3
2.1. Links and Subnets . . . . . . . . . . . . . . . . . . . . 4
3. Common Application Assumptions . . . . . . . . . . . . . . . . 5
3.1. Assumptions about routing . . . . . . . . . . . . . . . . 5
3.1.1. Connectivity is symmetric . . . . . . . . . . . . . . 5
3.1.2. Connectivity is transitive . . . . . . . . . . . . . . 5
3.1.3. Multicast is supported within a link . . . . . . . . . 6
3.1.4. IPv4 broadcast is supported . . . . . . . . . . . . . 6
3.1.5. Multicast/broadcast is less expensive than
replicated unicast . . . . . . . . . . . . . . . . . . 7
3.1.6. Reordering is rare . . . . . . . . . . . . . . . . . . 7
3.1.7. Loss is rare and probabilistic, not deterministic . . 8
3.1.8. An end-to-end path exists at a single point in time . 8
3.2. Assumptions about addressing . . . . . . . . . . . . . . . 8
3.2.1. Addresses are stable over long periods of time . . . . 8
3.2.2. A non-multicast/broadcast address identifies a
single host over a long period of time . . . . . . . . 9
3.2.3. A host has only one address on one interface . . . . . 9
3.3. Assumptions about the relationship between routing and
addressing . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3.1. An address used by an application is the same as
the address used for routing . . . . . . . . . . . . . 10
3.3.2. A subnet is smaller than a link . . . . . . . . . . . 11
3.3.3. Selecting a local address selects the interface . . . 11
3.3.4. An address is part of an on-link subnet . . . . . . . 11
3.4. Assumptions about upper-layer extensibility . . . . . . . 11
3.4.1. New transport-layer protocols can work across the
Internet . . . . . . . . . . . . . . . . . . . . . . . 12
3.5. Assumptions about security . . . . . . . . . . . . . . . . 12
3.5.1. Packets are unmodified in transit . . . . . . . . . . 12
3.5.2. Packets are private . . . . . . . . . . . . . . . . . 12
3.5.3. Source addresses are not spoofed . . . . . . . . . . . 12
4. Impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5. Security Considerations . . . . . . . . . . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1. Normative References . . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 17
Intellectual Property and Copyright Statements . . . . . . . . . . 18
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1. Introduction
Since the Internet Protocol was first published as [IEN028] in 1978,
IP has provided a network-layer connectivity service to upper-layer
protocols and applications. The basic IP service model was
documented in the original IEN's (and subsequently the RFC's that
obsolete them). However, since the mantra has been "Everything Over
IP", the IP service model has evolved significantly over the past 30
years to enable new behaviors that the original definition did not
envision. For example, by 1989 there was already some confusion and
so [RFC1122] clarified many things and extended the model. In 2004,
[RFC3819] gave advice to link-layer protocol designers on a number of
things that affect upper layers and is the closest in intent to the
subject of this document. Today's IP service model is not well
documented in a single place, but is either implicit or discussed
piecemeal in many different RFCs. As a result, today's IP service
model is actually not well known, or at least is often misunderstood.
In the early days of IP, changing or extending the basic IP service
model was easier since it was not as widely deployed and there were
fewer implementations. Today, the ossification of the Internet makes
evolving the IP model even more difficult. Thus it is important to
understand the evolution of the IP model for two reasons:
1. To make it clear what upper-layer protocols and applications can
and cannot depend on. There are many myths (or at least beliefs
which are no longer true) applications may be based on which are
problematic.
2. To document lessons for future evolution to take into account.
It is important that the service model remain consistent, rather
than evolving in two opposing directions. It is sometimes the
case in IETF Working Groups today that directions are considered
or even taken which would change the IP service model. Doing
this without understanding the implications on applications can
be dangerous.
This draft attempts to document various aspects of the IP service
model and how it has evolved over time. In particular, it attempts
to document the properties of the IP layer as they are seen by upper-
layer protocols and applications, and especially properties which
were (and at times still are) incorrectly perceived to exist, as well
as properties that changing would cause problems.
2. The IP Service Model
In this document, we use the term "IP Service Model" to refer to the
model exposed by IP to higher-layer protocols and applications. This
is depicted in Figure 1 by the horizontal line.
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+-------------+ +-------------+
| Application | | Application |
+------+------+ +------+------+
| |
+------+------+ +------+------+
| Upper-Layer | | Upper-Layer |
| Protocol | | Protocol |
+------+------+ +------+------+
| |
------------------------------------------------------------------
| |
+--+--+ +-----+ +--+--+
| IP | | IP | | IP |
+--+--+ +--+--+ +--+--+
| | |
+-----+------+ +-----+------+ +-----+------+
| Link Layer | | Link Layer | | Link Layer |
+-----+------+ +--+-----+---+ +-----+------+
| | | |
+---------------------+ +--------------------+
Source Destination
IP Service Model
Figure 1
The foundation of the IP service model today is documented in
[RFC0791] section 2.2. Generally speaking, IP provides a
connectionless delivery service for variable size packets, which does
not guarantee ordering, delivery, or lack of duplication, but is
merely best effort. Senders can send to a destination address
without signaling a priori, and receivers just listen on an already
provisioned address, without signaling a priori.
2.1. Links and Subnets
Section 2.1 of [RFC4903] discusses the terms "link" and "subnet" with
respect to the IP model.
A "link" in the IP service model refers to the topological area
within which a packet with IPv4 TTL or IPv6 Hop Limit of 1 can be
delivered. That is, where no IP-layer forwarding (which entails a
TTL/Hop Limit decrement) occurs between two nodes.
A "subnet" in the IP service model refers to the topological area
within which addresses from the same subnet prefix are assigned to
interfaces.
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3. Common Application Assumptions
Below is a list of properties which are often assumed by applications
and upper-layer protocol, but which have become less true over time.
3.1. Assumptions about routing
3.1.1. Connectivity is symmetric
Many applications assume that if a host A can contact a host B, then
the reverse is also true. Examples of this behavior include request-
response patterns, which only requires that reverse connectivity
exists after forward connectivity, and callbacks (e.g., as used by
the File Transfer Protocol (FTP) [RFC0959]).
Originally it was the case that connectivity was symmetric (although
the path taken may not be), both within a link and across the
Internet. With the advent of technologies such as NATs and
firewalls, this can no longer be assumed. However, it is still the
case that if a request can be sent, then a reply to that request can
generally be received, but an unsolicited request in the other
direction may not be received. [RFC2993] discusses this in more
detail.
There are also links (e.g., satellite) which were defined as
unidirectional links and hence an address on such a link results in
asymmetric connectivity. [RFC3077] explicitly addresses this problem
for multi-homed hosts by tunneling packets over another interface in
order to restore symmetric connectivity.
Finally, even with common wireless networks such as 802.11, this
assumption may not be true, as discussed in [WIRELESS] section 5.5.
3.1.2. Connectivity is transitive
Many applications assume that if a host A can contact host B, and B
can contact C, then host A can contact C. An example of this behavior
is applications and protocols that use referrals.
Originally it was the case that connectivity was transitive, both
within a link and across the Internet. With the advent of
technologies such as NATs, and firewalls, this can no longer be
assumed across the Internet, but it is often still true within a
link. As a result, upper-layer protocols and applications may be
relying on transitivity within a link. However, radio technologies
such as 802.11 ad-hoc mode violate this assumption.
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3.1.3. Multicast is supported within a link
[RFC1112] introduced multicast to the IP service model. In this
evolution, senders still just send to a destination address without
signaling a priori, but in contrast to the original IP model,
receivers must signal to the network before they can receive traffic
to a multicast address.
Today, many applications and protocols are defined to use multicast
addresses, including protocols for address configuration, service
discovery, etc. (See [MCAST4] and [MCAST6] for those that use well-
known addresses.)
Most of these assume that multicast works within a link, but may or
may not function across a wider area. While network-layer multicast
works over most link types, there are Non-Broadcast Multi-Access
(NBMA) links over which multicast does not work (e.g., X.25, ATM,
frame relay, 6to4, ISATAP, Teredo) and this can interfere with some
protocols and applications. Similarly, there are links such as
802.11 ad-hoc mode where multicast packets may not get delivered to
all receivers on the link. [RFC2461] and its successor [RFC4861]
both state:
"Note that all link types (including NBMA) are expected to provide
multicast service for applications that need it (e.g., using
multicast servers)."
However, not all link types today do meet this expectation.
3.1.4. IPv4 broadcast is supported
IPv4 broadcast support was originally defined on a link, across a
network, and for subnet directed broadcast, and is used by many
applications and protocols. For security reasons, however, [RFC2644]
deprecated forwarding of broadcast packets, and hence since 1999
broadcast can only be relied on within a link. Still, there exist
NBMA links over which broadcast does not work, and there exist some
"semi-broadcast" links (e.g., 802.11 ad-hoc mode) where broadcast
packets may not get delivered to all nodes on the link. Another case
where broadcast fails to work is when a /32 or /31 is assigned to a
point-to-point interface (e.g., [RFC3021]), leaving no broadcast
address available.
In addition, the addition of link-scoped multicast to the IP service
model to a large extent obsoleted the need for broadcast. It is also
worth noting that the broadcast API model used by most platforms
allows receivers to just listen on an already provisioned address,
without signaling a priori, but in contrast to the unicast API model,
senders must signal to the local IP stack (SO_BROADCAST) before they
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can send traffic to a broadcast address. However, from the network's
perspective, the host still sends without signaling a priori.
3.1.5. Multicast/broadcast is less expensive than replicated unicast
Some applications and upper-layer protocols use multicast or
broadcast do so not because they do not know the addresses of
receivers, but simply to avoid sending multiple copies of the same
packet over the same link.
In wired networks, sending a single multicast packet on a link is
generally less expensive than sending multiple unicast packets. This
may not be true for wireless networks, where implementations can only
send multicast at the basic rate, regardless of the negotiated rates
of potential receivers. As a result, replicated unicast may achieve
much higher throughput across such links than multicast/broadcast
traffic.
3.1.6. Reordering is rare
As discussed in [REORDER], [RFC2991], and [RFC3819] section 15, there
are a number of effects of reordering. For example, reordering
increases buffering requirements (and jitter) in many applications,
and in devices that do packet reassembly. TCP [RFC0793] in
particular is adversely affected by reordering since it enters fast-
retransmit when three packets are received before a late packet,
which drastically lowers throughput.
Today there are number of things that cause reordering. First, some
routers do per-packet round-robin load balancing, which, depending on
the topology, can result in a great deal of reordering. Second,
protocols such as Protocol Independent Multicast - Sparse Mode
(PIM-SM) [RFC4601], the Multicast Source Discovery Protocol (MSDP)
[RFC3618], and Mobile IPv6 [RFC3775] send packets on one path, and
then allow immediately switching to a shorter path, resulting in
deterministic reordering within the first burst of packets. There
are various proposals currently being evaluated by the IETF Routing
Research Group that result in similar reordering.
An undesirable effect of reordering among initial packets is that
some applications choose a destination address by sending a message
to each of a number of candidates, picking the first one to respond,
and then using that destination for subsequent communication. A high
degree of reordering can result in a highly non-optimal destination
being chosen, with much longer paths (and hence load on the Internet)
and lower throughput.
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3.1.7. Loss is rare and probabilistic, not deterministic
In the original IP model, senders just send, without signaling the
network a priori. This works to a degree. In practice, the last hop
(and in rare cases, other hops) of the path needs to resolve next hop
information (e.g., the link-layer address of the destination) on
demand which results in queuing traffic, and if the queue fills up,
some traffic gets dropped. This means that bursty sources can be
problematic (and indeed a single large packet that gets fragmented
becomes such a burst at the last hop). The problem is rarely
observed in practice today, either because the resolution within the
last hop happens very quickly, or because bursty applications are
rarer. However, any protocol that significantly increases such
delays or adds new resolutions would be a change to the classic IP
model and may adversely impact upper-layer protocols and applications
that result in bursts of packets.
In addition, mechanisms that simply drop the first packet, rather
than queuing it, also break this assumption. Similar to the result
of reordering, they can result in a highly non-optional destination
being chosen by applications that use the first one to respond. Two
examples of mechanisms that appear to do this are network interface
cards that support a "Wake-on-LAN" capability where any packet that
matches a specified pattern will wake up a machine in a power-
conserving mode, but only after dropping the matching packet, and
MSDP (since encapsulating data packets is optional).
3.1.8. An end-to-end path exists at a single point in time
In classic IP, applications assume that an end-to-end path either
exists to a destination, or that the packet will be dropped. In
addition, IP today tends to assume that the packet delay is
relatively short (since the "Time"-to-live is just a hop count, since
each hop is assumed to be less than a second), whereas earlier the
TTL field was expected to be decremented each second (not just each
hop). The IRTF Delay Tolerant Networking Research Group
investigating changing this assumption.
3.2. Assumptions about addressing
3.2.1. Addresses are stable over long periods of time
Originally addresses were manually configured on fixed machines, and
hence addresses were very stable. With the advent of technologies
such as DHCP, roaming, and wireless, addresses can no longer be
assumed to be stable for long periods of time. However, the APIs
provided to applications today typically still assume stable
addresses (e.g., address lifetimes are not exposed to applications
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that get addresses). This can cause problems today when addresses
become stale.
For example, many applications resolve names to addresses and then
cache them without any notion of lifetime. In fact, the classic name
resolution APIs do not even provide applications with the lifetime of
entries.
Proxy Mobile IPv6 [I-D.ietf-netlmm-proxymip6] tries to restore this
assumption to some extent by preserving the same address while
roaming around a local area. The issue of roaming between different
networks has been known since at least 1980 when [IEN135] proposed a
mobility solution that attempted to restore this assumption by adding
an additional address that can be used by applications which is
stable while roaming anywhere with Internet connectivity. More
recent protocols such as Mobile IPv6 (MIP6) [RFC3775] and the Host
Identity Protocol (HIP) [RFC4423] follow in this same vein.
3.2.2. A non-multicast/broadcast address identifies a single host over
a long period of time
Many applications and upper-layer protocols maintain a communication
session with a destination over some period of time. If that address
is reassigned to another host, or if that address is assigned to
multiple hosts and the host at which packets arrive changes, such
applications can have problems.
[RFC1546] introduced the notion of anycast to the IP service model.
It states:
Because anycasting is stateless and does not guarantee delivery of
multiple anycast datagrams to the same system, an application
cannot be sure that it is communicating with the same peer in two
successive UDP transmissions or in two successive TCP connections
to the same anycast address.
The obvious solutions to these issues are to require applications
which wish to maintain state to learn the unicast address of their
peer on the first exchange of UDP datagrams or during the first
TCP connection and use the unicast address in future
conversations.
The issues with anycast are further discussed in [RFC4786].
3.2.3. A host has only one address on one interface
Although many applications assume this (e.g., by calling a name
resolution function such as gethostbyname and then just using the
first address returned), it was never really true to begin with, even
if it was the common case. Even [RFC0791] states:
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"provision must be made for a host to have several physical
interfaces to the network with each having several logical
internet addresses".
However today this assumption is increasingly less true, with the
advent of multiple interfaces (e.g., wired and wireless), dual-IPv4/
IPv6 nodes, multiple IPv6 addresses on the same interface (e.g.,
link-local and global), etc. Similarly, many protocol specifications
such as DHCP only describe operations for a single interface, whereas
obtaining host-wide configuration from multiple interfaces presents a
merging problem for nodes in practice. Too often this problem is
simply ignored by Working Groups, and applications and users suffer
as a result from poor merging algorithms.
One use of protocols such as MIP6 and HIP is to make this assumption
somewhat more true by adding an additional "address" that can be the
one used by such applications, and the protocol will deal with the
complexity of multiple physical interfaces and addresses.
3.3. Assumptions about the relationship between routing and addressing
3.3.1. An address used by an application is the same as the address
used for routing
Some applications assume that the address the application uses is the
same as that used by routing. For example, some applications use raw
sockets to read/write packet headers, including the source and
destination addresses in the IP header. As another example, some
applications make assumptions about locality (e.g., whether the
destination is on the same subnet) by comparing addresses.
Protocols such as Mobile IPv6 and HIP specifically break this
assumption (in an attempt to restore other assumptions as discussed
above). Recently, the IRTF Routing Research Group has been
evaluating a number of possible mechanisms, some of which would also
break this assumption, while others preserve this assumption near the
edges of the network and only break it in the core of the Internet.
Breaking this assumption is sometimes referred to as an "identifier/
locator" split. As originally defined in 1978 ([IEN019], [IEN023]),
however, an address was originally defined as only a locator, whereas
names were defined to be the identifiers. However, the TCP protocol
then used addresses as identifiers.
Finally, in a liberal sense, any tunneling mechanism might be said to
break this assumption, although in practice applications that make
this assumption will continue to work. Since the address of the
inside of the tunnel is still used for routing as expected.
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3.3.2. A subnet is smaller than a link
In the classic IP model, a "subnet" is smaller than, or equal to, a
"link". Destinations with addresses in the same subnet can be
reached with TTL (or Hop Count) = 1. Link-scoped multicast packets,
and all-ones broadcast packets will be delivered (in a best effort
fashion) to all listening nodes on the link. Subnet broadcast
packets will be delivered (in a best effort fashion) to all listening
nodes in the subnet. There have been some efforts in the past (e.g.,
[RFC0925], [RFC3069]) to allow multi-link subnets and change the
above service model, but the adverse impact on applications that have
such assumptions recommend against changing this assumption.
[RFC4903] discusses this topic in more detail and surveys a number of
protocols and applications that depend on this assumption.
3.3.3. Selecting a local address selects the interface
Some applications assume that binding to a given local address
constrains traffic reception to the interface with that address, and
that traffic from that address will go out on that address's
interface. However, [RFC1122] section 3.3.4.2 defines two models:
the Strong End System (or Strong host) model where this is true, and
the Weak End System (or Weak host) model where this is not true. In
fact any router is inherently a weak host implementation, since
packets can be forwarded between interfaces.
3.3.4. An address is part of an on-link subnet
To some extent, this was never true, in that there were cases in IPv4
where the "mask" was 255.255.255.255, such as on a point-to-point
link where the two endpoints had addresses out of unrelated address
spaces. However, this didn't stop many platforms and applications
from assuming that every address had a "mask" (or prefix) that was
on-link. The assumption of whether a subnet is on-link (in which
case one can send directly to the destination after using ARP/ND) or
off-link (in which case one just sends to a router) has evolved over
the years, and it can no longer be assumed that an address has an on-
link prefix. In 1998, [RFC2461] introduced the distinction as part
of the core IPv6 protocol suite. This topic is discussed further in
[I-D.wbeebee-on-link-and-off-link-determination], and [RFC4903] also
touches on this topic with respect to the service model seen by
applications.
3.4. Assumptions about upper-layer extensibility
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3.4.1. New transport-layer protocols can work across the Internet
IP was originally designed to support the addition of new transport-
layer protocols, and [PROTOCOLS] lists many such protocols.
However, as discussed in [I-D.rosenberg-internet-waist-hourglass],
NATs and firewalls today break this assumption and often only allow
UDP and TCP (or even just HTTP).
3.5. Assumptions about security
3.5.1. Packets are unmodified in transit
Some applications and upper-layer protocols assume that a packet is
unmodified in transit, except for a few well-defined fields (e.g.,
TTL). Examples of this behavior include protocols that define their
own integrity protection mechanism such as a checksum.
This assumption is broken by NATs as discussed in [RFC2993] and other
middleboxes that modify the contents of packets. There are many
tunneling technologies (e.g., [RFC4380]) that attempt to restore this
assumption to some extent.
The IPsec architecture [RFC4301] added security to the IP model,
providing a way to address this problem without changing
applications, although it is not currently widely used over the
Internet.
3.5.2. Packets are private
The assumption that data is private has never really been true.
However, many old applications and protocols (e.g., FTP) transmit
passwords or other sensitive data in the clear.
IPsec provides a way to address this problem without changing
applications, although it is not yet widely deployed, and doing
encryption/decryption for all packets can be computationally
expensive.
3.5.3. Source addresses are not spoofed
Most applications and protocols use the source address of some
incoming packet when generating a response, and hence assume that it
has not been spoofed (and as a result can often be vulnerable to
reflection attachs).
Various mechanisms that restore this assumption include, for example,
IPsec and Cryptographically Generated Addresses (CGAs) [RFC3972].
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4. Impact
Because a huge number of applications already exist that use TCP/IP
for business-critical operations, any changes to the service model
need to be done with extreme care. Extensions that merely add
additional optional functionality without impacting any existing
applications are much safer than extensions which change one or more
of the core assumptions discussed above. Any changes to the above
assumptions should only be done in accordance with some mechanism to
minimize or mitigate the risks of breaking mission-critical
applications. Historically, changes have been done without regard to
such considerations and as a result the situation for applications
today is already problematic. Key to maintaining an interoperable
Internet is documenting and maintaining invariants that higher layers
can depend on, and being very judicious with changes.
5. Security Considerations
This document discusses assumptions about the IP service model made
by many applications and upper-layer protocols. Whenever these
assumptions are broken, if the application or upper-layer protocol
has some security-related behavior that is based on the assumption,
then security can be affected.
For example, if an application assumes that binding to the IP address
of a "trusted" interface means that it will never receive traffic
from an "untrusted" interface, and that assumption is broken (as
discussed in Section 3.3.3) then an attacker could get access to
private information.
As a result, great care should be taken when expanding the extent to
which an assumption is false. On the other hand, application and
upper-layer protocol developers should carefully consider the impact
of basing their security on any of the assumptions enumerated in this
document.
It is also worth noting that many of the changes that have occurred
over time (e.g., firewalls, dropping directed broadcasts, etc.) that
are discussed in this document were done in the interest of improving
security at the expense of breaking some applications.
6. IANA Considerations
This document has no IANA Actions.
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7. Acknowledgements
Bernard Aboba, Chris Hopps, Kurtis Lindqvist, Danny McPherson, Dow
Street, and others provided helpful discussion on various points that
led to this document.
8. References
8.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, August 1989.
[RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989.
[RFC1546] Partridge, C., Mendez, T., and W. Milliken, "Host
Anycasting Service", RFC 1546, November 1993.
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998.
[RFC2644] Senie, D., "Changing the Default for Directed Broadcasts
in Routers", BCP 34, RFC 2644, August 1999.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
8.2. Informative References
[I-D.ietf-netlmm-proxymip6]
Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6",
draft-ietf-netlmm-proxymip6-18 (work in progress),
May 2008.
[I-D.rosenberg-internet-waist-hourglass]
Rosenberg, J., "UDP and TCP as the New Waist of the
Internet Hourglass",
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draft-rosenberg-internet-waist-hourglass-00 (work in
progress), February 2008.
[I-D.wbeebee-on-link-and-off-link-determination]
Singh, H., Beebee, W., and E. Nordmark, "IPv6 Subnet
Model",
draft-wbeebee-on-link-and-off-link-determination-02 (work
in progress), February 2008.
[IEN019] Shoch, J., "A note on Inter-Network Naming, Addressing,
and Routing", IEN 19, January 1978,
<ftp://ftp.rfc-editor.org/in-notes/ien/ien19.txt>.
[IEN023] Cohen, D., "On Names, Addresses and Routings", IEN 23,
January 1978,
<ftp://ftp.rfc-editor.org/in-notes/ien/ien23.txt>.
[IEN028] Postel, J., "Draft Internetwork Protocol Specification",
IEN 28, February 1978,
<ftp://ftp.rfc-editor.org/in-notes/ien/ien-index.html>.
[IEN135] Sunshine, C. and J. Postel, "Addressing Mobile Hosts in
the ARPA Internet Environment", IEN 135, March 1980,
<ftp://ftp.rfc-editor.org/in-notes/ien/ien135.txt>.
[MCAST4] Internet Assigned Numbers Authority, "IPv4 Multicast
Addresses",
<http://www.iana.org/assignments/multicast-addresses>.
[MCAST6] Internet Assigned Numbers Authority, "INTERNET PROTOCOL
VERSION 6 MULTICAST ADDRESSES",
<http://www.iana.org/assignments/
ipv6-multicast-addresses>.
[PROTOCOLS]
Internet Assigned Numbers Authority, "Protocol Numbers",
<http://www.iana.org/assignments/protocol-numbers>.
[REORDER] Bennett, J., Partridge, C., and N. Shectman, "Packet
reordering is not pathological network behavior", IEEE/ACM
Transactions on Networking, Vol. 7, No. 6, December 1999.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
[RFC0925] Postel, J., "Multi-LAN address resolution", RFC 925,
October 1984.
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[RFC0959] Postel, J. and J. Reynolds, "File Transfer Protocol",
STD 9, RFC 959, October 1985.
[RFC2991] Thaler, D. and C. Hopps, "Multipath Issues in Unicast and
Multicast Next-Hop Selection", RFC 2991, November 2000.
[RFC2993] Hain, T., "Architectural Implications of NAT", RFC 2993,
November 2000.
[RFC3021] Retana, A., White, R., Fuller, V., and D. McPherson,
"Using 31-Bit Prefixes on IPv4 Point-to-Point Links",
RFC 3021, December 2000.
[RFC3069] McPherson, D. and B. Dykes, "VLAN Aggregation for
Efficient IP Address Allocation", RFC 3069, February 2001.
[RFC3077] Duros, E., Dabbous, W., Izumiyama, H., Fujii, N., and Y.
Zhang, "A Link-Layer Tunneling Mechanism for
Unidirectional Links", RFC 3077, March 2001.
[RFC3618] Fenner, B. and D. Meyer, "Multicast Source Discovery
Protocol (MSDP)", RFC 3618, October 2003.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
[RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, July 2004.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380,
February 2006.
[RFC4423] Moskowitz, R. and P. Nikander, "Host Identity Protocol
(HIP) Architecture", RFC 4423, May 2006.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
[RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast
Services", BCP 126, RFC 4786, December 2006.
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[RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
June 2007.
[WIRELESS]
Kotz, D., Newport, C., and C. Elliott, "The mistaken
axioms of wireless-network research", Dartmouth College
Computer Science Technical Report TR2003-467, July 2003,
<http://pdos.csail.mit.edu/decouto/papers/kotz03.pdf>.
Author's Address
Dave Thaler
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
USA
Phone: +1 425 703 8835
Email: dthaler@microsoft.com
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