Network Working Group P. Nikander
Internet-Draft Ericsson Research Nomadic Lab
Expires: May 31, 2004 December 2003
Considerations on HIP based IPv6 multi-homing
draft-nikander-multi6-hip-00
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
The Host Identity Protocol implements the identifier locator
separation by introduing a new name space and a new layer to the IP
stack. The new structure insulates the transport layer protocols
from the internetworking layer, thereby allowing transport sessions
to remain unaffected even if the underlying IP addresses change.
That, in turn, seems to make it easier to solve the so called site
multi-homing problem than without introducing such an indirection
layer.
This document discusses how the proposed HIP mobility and
multi-homing solution, described separately, would fit to the IETF
multi6 working group requirements.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Current venues for HIP work . . . . . . . . . . . . . . . . 4
1.3 Baseline HIP multi-homing mechanism . . . . . . . . . . . . 4
2. HIP as a site-multi-homing solution . . . . . . . . . . . . 6
2.1 Hiding of underlying IP version . . . . . . . . . . . . . . 6
2.2 Integrated mobility . . . . . . . . . . . . . . . . . . . . 6
2.3 Architectural support for multi-realm connectivity . . . . . 6
2.4 Integrated, mandatory end-to-end security . . . . . . . . . 6
2.5 High state setup cost . . . . . . . . . . . . . . . . . . . 7
3. Using components of HIP or modified HIP instead of full
HIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1 Using HIP without IPsec ESP . . . . . . . . . . . . . . . . 8
3.2 Delaying HIP state setup . . . . . . . . . . . . . . . . . . 8
3.2.1 Securing LHIP state setup . . . . . . . . . . . . . . . . . 9
4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1 Default router and source address selection . . . . . . . . 11
4.2 Selecting primary destination address . . . . . . . . . . . 11
4.3 Reacting to addresses becoming unreachable . . . . . . . . . 11
5. Evaluation against of RFC 3582 and MULTI6 Solution
Questionaire . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1 Approach . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.2 Answers to MULTI6 Solution Questionaire . . . . . . . . . . 12
5.2.1 Routing . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.2.2 Identifiers and locators . . . . . . . . . . . . . . . . . . 13
5.2.3 On the wire . . . . . . . . . . . . . . . . . . . . . . . . 14
5.2.4 Names, Hosts, Endpoints, or no of the above? . . . . . . . . 16
5.3 RFC 3582 Section 3 considerations . . . . . . . . . . . . . 19
5.3.1 Multi-Homing capabilities . . . . . . . . . . . . . . . . . 19
5.3.2 Additional requirements . . . . . . . . . . . . . . . . . . 21
5.4 Security considerations . . . . . . . . . . . . . . . . . . 23
6. Security considerations . . . . . . . . . . . . . . . . . . 24
Informative references . . . . . . . . . . . . . . . . . . . 25
Author's Address . . . . . . . . . . . . . . . . . . . . . . 26
Intellectual Property and Copyright Statements . . . . . . . 27
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1. Introduction
The IETF multi6 working group is currently calling various
alternative solutions as components for an architectural analysis.
The aim of that work is to try to understand the architectural design
choices and their tradeoffs.
This document discusses how a Host Identity Protocol (HIP) based
approach could solve the multi6 site multi-homing problem. The draft
also presents some ideas on how the HIP architecture could be split
into components, some of which could be applied to the multi6 problem
without adopting all of the current HIP proposal.
1.1 Background
The Host Identity Protocol (HIP) is a proposal for changing the TCP/
IP stack architecture by a new name space and a new protocol layer to
the stack. The overall design is discussed in the HIP architecture
document [3]. The actual protocol details are defined in the HIP
protocol specification [2], and the mobility and multi-homing related
extensions in the HIP mobility and multi-homing specification [4].
It is expected through this document that the reader is at least
superficially familiar with the architecture document and the
protocol specifications.
The proposed HIP multi-homing mechanism [4] is primarily aimed to be
a host multi-homing solution. Basically, it allows two end hosts to
inform each other of their IP connectivity. That is, an end-host
sends a set of IP addresses to its peer, and the peer makes sure that
the end-host is reachable through (some of) these IP addresses.
In the baseline HIP solution, a HIP base exchange protocol is run
each time a new pair of hosts starts to communicate. This protocol is
a four-way handshake, requiring public key cryptographic operations.
While such a heavy exchange makes sense for applications where the
hosts have a fairly long term relationship, e.g. for e-mail, disk
access, etc., it may be too heavy for short term transactions, such
as some forms of web browsing etc. It is definitely unsuitable for
DNS (see Section 5.2.4.1). Therefore, the architecture has been
defined in such a way that each application can be configured either
to use HIP or to use legacy IP, without the HIP overhead (and, of
course, without any benefits from HIP).
While the redundancy (Section 5.3.1.1) and especially transport layer
survivability (Section 5.3.1.6) make sense mostly for long term
transport sessions, where the state setup may be amortized over a
longer period of time, it would be benficial to avoid such a large
state setup cost. Therefore, in Section 3, we also describe how some
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components of HIP could be applied to the multi6 site-multihoming
problem without adopting all of HIP.
1.2 Current venues for HIP work
At the time of writing this version of this draft, a proposal to form
a HIP working group is being handled by the IESG. It is expected
that the working group charter will be approved in time so that the
working group will be able to meet at the 59th IETF meeting in Seoul.
The working group charter is expected to be very focused, addressing
the more practical aspects of the current HIP proposals.
At the same time, there are ongoing discussions about creating a
parallel IRTF research group. The charter of the research group
would be wider than that of the working group, looking at more
distant aspects of HIP, and also studying other proposals for
splitting identifiers and locators but HIP. Since the proposed
research group does not have a name nor an acronym yet, it is called
as the "IRTF XXX RG" in the rest of this document.
It is currently expected that if the HIP mobility and multi-homing
solution, or some aspects of it, are selected for further work at the
multi6 working group, then the resulting work will be chartered at
the multi6 WG. In that case some co-operation with the HIP WG and
the IRTF XXX RG.
1.3 Baseline HIP multi-homing mechanism
The baseline HIP multi-homing mechanism is specified in [4]. Here we
briefly summarize the mechanism, giving an outline to those
impatitient readers that don't have cycles to read the full HIP
specifications.
As mentioned above, when two HIP hosts start to communicate, they run
the HIP base exchange and create an HIP association. As a part of
this association, a multi-homed host MAY send a list of IP addresses
that it believes to belong to itself. The recipient of these
addresses stores them as potential addresses of the peer. Before
using any of new addresses, it MUST verify that the peer is indeed
reachable through the address. According the current specification,
an end-host MAY perform such reachability test at any time, subject
to its local policy. Such a reachability test requires only the
tested address to work, meaning that such a test can be delayed until
the other address(es) become unreachable.
The hosts are free to change the information about their addresses at
any time. However, note that especially in the case of site
multi-homing, one of the addresses may become unreachable while the
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other one still works. In the typical case, however, this does not
require the host to inform its peers about the situation, since even
the non-working address still logically exists.
Establishing the initial multi-addressing situation, and all changes
to that, are protected with strong cryptography. There are no known
vulnerabilities in the specified mechanisms. (Note, however, that
the fact that there are no _known_ vulnerabilities does not mean that
there are no unknown ones. There might be, and given the freshness
of the specifications, there probably are.)
The current specification outlines a method where one of the peer's
addresses is considered as a primary address. By default, all
traffic is sent using this address. This practise is similar to how
SCTP multi-addressing works, and is designed to work well with
current transport layer congestion control. However, the HIP
architecture itself would allow multiple addresses to be used in
parallel, even for one transport session. Experimentation of such
practise is assumed to take place at the IRTF XXX RG.
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2. HIP as a site-multi-homing solution
As mentioned above, HIP multi-homing is primarily designed as a
solution for multi-homed end-hosts. As such, it offers a
multi-address based baseline solution, similar to other proposed
multi-addressing based multi6 proposal. Efforts to adopt the
approach to site multi-homing, especially in the case where some
hosts within the site and outside of the site may be legacy non-HIP
hosts, has been fairly minimal.
It is expected that most of what applies to other multi-addressing
based multi6 proposals apply also to HIP.
Since the multi-homing aspects of HIP do note seem to considerably
differ from other multi-address based proposals, the focus in this
section is on the factors that differentiate HIP from the other
solutions. Multi-homing aspects are covered in Section 5.
2.1 Hiding of underlying IP version
HIP hides the underlying IP version from applications. That is, an
IPv4 legacy application can be run over IPv6, and vice versa, HIP
acting as an insulation layer. This also means that the HIP mobility
and multi-homing solution allows existing transport sessions to
change their underlying connectivityfrom IPv4 to IPv6 and vice versa,
as long as both end-hosts remain reachable (either directly or
through a gateway).
2.2 Integrated mobility
The HIP multi-homing mechanism is fully integrated with mobility. In
fact, the two mechanism are so integrated that it would be very hard
to make them separate.
2.3 Architectural support for multi-realm connectivity
The HIP architecture allows HIP associations to be router through
layer 3.5 middle boxes, thereby extending the associations across
multiple IP realms. In other words, HIP would allow controlled
NAT-traversal that have not the ill effects of the current NAT
practise. However, fully realising such service requires more work,
and is subject to study at the IRTF XXX RG.
2.4 Integrated, mandatory end-to-end security
HIP has its origin as a security solution, aiming to simplify IPsec
administration and address mobility at the same time. Hence, HIP as
defined today, requires that all payload traffic is protected with
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IPsec ESP. By default, this adds the overhead of carrying the ESP
header and trailer in all packets. Additionally, the current IPsec
specifications mandate that either encryption or integrity protection
of ESP MUST be used, i.e., it is not allowed to use IPsec without
encryption and without integrity protection. Hence, all HIP packets
are subject to the cost of symmetric crypto processing on both
sending and receiving ends. While this cost is fairly minor in most
modern architectures, it may have negative effects on small devices,
such as PDAs, and large scale servers.
In addition to the header overhead and computational cost, ESP breaks
some middle box functionality by making it impossible to inspect and/
or modify the packet contents.
It should be noted that when end-to-end security is desirable, HIP
adds no additional overhead compared to using standard IPsec
mechanisms. Hence, for applications were IPsec based security is
adequate and desirable, HIP looks like an optimal or near-optimal
multi-homing solution.
In Section 3.1, below, we discuss how ESP could be replaced with
other mechanisms for the case where end-to-end security is not needed
for payload traffic.
2.5 High state setup cost
The HIP base exchange is a four-way cryptographic authentication
protocol, implementing a sigma [10] authenticated Diffie-Hellman
exchange, with state-space and CPU-exhaustion denial-of-service
protection. A single protocol run requires a few long integer
exponentiations, taking a fraction of a second on modern CPU
architectures.
Compared to other multi6 proposals, the state setup cost of HIP seems
to be largest. In Section 3.2 we discuss how this state setup cost
might be delayed to a later moment, allowing two hosts to start
communicating and creating the state only if they later determine
that they want security or want change active IP addresses. In
Section 3.2.1 we discuss how the security properties of such delayed
state setup might be improved with hash chains.
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3. Using components of HIP or modified HIP instead of full HIP
In this section, we first briefly describe how HIP could be modified
so that it would impose less computational overhead, and then how
some HIP-like ideas could relate to other multi6 proposals, and vice
versa.
3.1 Using HIP without IPsec ESP
As mentioned above, some applications may have long lasting
connections that would benefit from redundancy and transport layer
survivability, but would not need end-to-end security. For example,
DRM protected video streams using application level encryption might
be one such example. In cases like that, it would be beneficial to
use HIP without ESP.
There seems at least to be two different ways how HIP could possibly
be used without ESP:
One possibility is to replace the ESP header with a simple header
that carries the SPI, similar to the M6 header proposed in the SIM
proposal [8]. In the HIP case, the context tag would be the SPI.
Another possibility would be to allocate a single bit in the IP
header, indicating whether in the receiving end the source and
destination locators should be rewritten into identifiers or not.
This would be somewhat similar to the NOID proposal [7]. When ESP
is not used, there is no replay protection, and therefore there is
no need for multiple parallel SAs.
Adding support for non-ESP communication would add a need for policy
into HIP. For each connection, the end-points would need to decide
whether to use ESP or not. Since one of the current HIP goals has
been and still is simplicity, this feature has not been added to the
current HIP specifications. From a functional point of view, the
possibility of not using ESP is a mere performance optimization.
3.2 Delaying HIP state setup
It might be possible to delay the actual HIP state setup. However, it
would not be possible to use ESP before the state has been
established. The main benefit from this kind of optimization is to
initially avoid the computational cost.
This variant is tentatively called LHIP, for Lightweight HIP.
The idea goes as follows:
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1. The Initiator sends an I1, just like in the current
specification. However, the I1 packet would contain an extension
to indicate that it wants to delay state setup. It could also
piggyback the initial payload, e.g., TCP SYN.
2. The Responder checks if it already has a state established with
the given HITs. If it does, it replies with an R1 as usually,
and forgets about the packet.
3. The Responder checks it policy to see if it allows delayed state
setup for the HITs and IP addresses in I1. If it doesn't, it
sends an R1 as usually, and forgets about the packet. On the
other hand, if it does allow delayed state setup, and generates a
new nonce for lightweight state set up. The lightweight state
will consist of the HITs, the IP addresses, and the nonce. The
recipient will remember these, either by storing them or
algorithmically, for a limited delta period. The Responder
replies with a new packet (LR1), which contains the HITs and the
nonce. A TCP SYN ACK may be piggypacked on the LR1.
4. When the Initiator receives the LR1, it stores the nonce, and and
sends and LI2, containing just the HITs and the nonce.
5. When the Responder receives the LI2, it knows that some node is
reachable at the given IP address. However, it has no assurance
that the host is actually the one identified by the HIT. Hence,
the HIT cannot be used for access control or any other security
purposes -- any node might have claimed to be identified by the
HIT.
If the Initiator later wants to move or use ESP, it must update the
lightweight state to a full HIP association. Similarily, if the
Recipient later wants to move, use ESP, or open a new transport
session in the reverse direction, it must update the state. Note
that the notion is asymmetric here: the Recipient must update the
state also in the case of opening new transport sessions, since it
has no assurance that the other host actually "owns" the given HIT.
It is noteworthy that this lightweight setup is completely insecure,
allowing the initator to use any HIT as an identifier for itself. On
the other hand, it adds very little overhead to the setup of an
initial connection, allowing the TCP three-way handshake to be
piggybacked on the protocol.
3.2.1 Securing LHIP state setup
Based on some initial discussions, it may be feasible to bring some
security to the LHIP state setup using hash chains. However, futher
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analysis would be needed. For an example of how hash chains could be
used for securing multi6 related state setup, see [11].
If such hash chains (or something similar) was added to the creation
of the lightweight state, the state could probably be used for
securing changes in the mobility and multi-homing state of the hosts.
However, it would not be sufficient for creating ESP SAs.
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4. Discussion
4.1 Default router and source address selection
Source address selection must be based on first selecting the
outgoing router, based on the current reachability state, and then
source address to be used, not vice versa.
4.2 Selecting primary destination address
Section 8.4 of [4] briefly discusses how the hosts should select the
primary destination address to use for their peers. It should be
noted that the currently presented discussion is probably not the
optimal way of solving the problem. Further engineering and maybe
some research is required on the topic.
4.3 Reacting to addresses becoming unreachable
In the case of site multi-homing one of the addresses may become
unreachablewhile the other one still works. In the typical case,
however, this does not require the host to inform its peers about the
situation, since even the non-working address still logically exists.
Brian Carpenter: It's just as well you don't require this
notification. The last node to know that an address is unreachable is
the node that address belongs to. Unreachability is discovered at the
other end of the multihomed session.
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5. Evaluation against of RFC 3582 and MULTI6 Solution Questionaire
5.1 Approach
5.2 Answers to MULTI6 Solution Questionaire
5.2.1 Routing
As HIP is implemented on the top of IP, it does not directly affect
basic IP routing. Routing within any UP realm is performed just as
today. The end-hosts maintain a binding table that maps Host
Identifiers into a set of IP addresses, and the HIP mobility and
multi-homing protocol [4] is used to update these bindings.
5.2.1.1 Primary multi-homing solution idea
The HIP mobility and multi-homing protocol [4] allows an end-host to
send information about all of its IP addresses, both IPv4 and IPv6,
to its peers. The peers have to check reachability of these
addresses prior to using them for sending large amount of traffic.
This mechanism allows interacting HIP hosts to establish
multi-addressing based multi-homing state.
The exact mechanisms on how a host is supposed to perform address and
path selection are not defined in the current HIP specifications.
However, the required practise is assumed to be similar to any other
multi-addressing based multi-homing solutions. Hence, it is expected
that the multi6 WG (instead of the HIP WG) will define the required
mechanisms.
Some of the above described variations of HIP allow delayed
establishment of the multi-addressing state. However, the details
such practise are currently undefined and there is no implementation
experience on the aspect.
5.2.1.2 Uniqueness
[I don't understand what the title of this section refers to.]
5.2.1.2.1 Mobility
HIP addresses mobility. A mobile host sends HIP readdressing
information to all of its peer hosts, allowing them to update
addressing information.
Initial rendezvous is planned to be started with DNS. An initiating
host that wants to contact a mobile host is supposed to look up the
Host Identifier and a set of current IP addresses from the DNS. The
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set of current IP addresses may include real active addresses of the
mobile host, addresses of a Rendezvous server, or both.
Once the initiating host has a tentative set of addresses, it sends
an HIP I1 packet to an address. If the address is a real address of
the mobile host, the mobile host will directly answer with an R1
packet, and the rest of the HIP base exchange is run between the
used addresses. At the end the hosts inform each other about their
multi-addressing state.
If the I1 destination address ia an address of a Rendezvous server,
the Rendezvous server will forward the packet to the currently
registered address of the mobile host. The mobile host will send an
R1 directly back to the initiating host, and the rest of the HIP base
exchange is run directly between the mobile host and the initiating
host.
If a mobile host changes its active address while the HIP base
exchange is going on, there will be a timeout and the initating host
needs to start again, either using another address from the set of
addresses received from the DNS, or remaking the DNS query if
necessary.
All hosts that use rendezvous servers are assumed to include the
rendezvous server address in their active address sets. Hence, if
two interacting mobile hosts move at the same time so that the
readdressing indications cross each other in the network and get
lost, the host will fall back to the rendezvous server address after
a timeout. (The length of the timeout is currently unspecified, and
subject to local policy of the hosts.) Hence, provided that the
hosts have updated their current location to the rendezvous server,
the hosts will be able to continue communications.
The HIP mobility mechanism is expected to replace Mobile IP for all
communication taking place between HIP enabled hosts. When a HIP
host is communicating with a legacy host, it may use Mobile IP,
provided that the host stack includes both HIP and Mobile IP
implementaitons.
5.2.2 Identifiers and locators
5.2.2.1 Split identifiers and locators
HIP is based on the idea of splitting identifiers and locators.
Public cryptographic keys are used as identifiers. IP addresses are
used as locators. From the routing point-of-view, IP addresses are
used just like today. From the applications and transport layer
point of view, identifiers (in the form of HITs and LSIs [3]) replace
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IP addresses.
5.2.2.2 Binding lifetime
The lifetime of the binding from an identifier to a locator is
defined in the protocol messages. Typically it is equal to the
lifetime of the locator. The host creating the binding state simply
accepts the lifetime from the sending host.
5.2.2.3 Update of bindings
The bindings are updated by a host sending HIP readdressing
paramters, typically in a HIP UPDATE packet. A single packet may
update several sets of bindings.
Whenever a new address is associated with an identifier, the hosts
must verify the reachability of the address before using the address
for payload traffic. This procedure is required in order to block
flooding attacks [6].
Updating the bindings have no direct effect on transport connections,
which will remain up. Changes in the actual paths may have effects
on transport connections, such as changes in QoS.
5.2.3 On the wire
HIP, as currently defined, consists of two protocols. One is a new
protocol, the HIP protocol, run directly on the the top of IP. The
other one is IPsec ESP. Using telecom terminology, the HIP protocol
forms a control plane, and all user plane traffic is encapsulated in
ESP.
As discussed above, it might be possible to use HIP without requiring
all user plane traffic to be ESP encapsulated. However, such
practise has not been defined in detail and there are no
implementation experience.
5.2.3.1 Solution layer
HIP can be consider to be a layer 3.5 solution.
HIP is applied to every packet, in the form of encapsulating them
into ESP envelopes. The ESP SPI field is used to associate the
packet with the right end-point identifiers in the receiving end.
As described above in Section 3.1, it ESP was not used, a single bit
in the IP header might suffice to allow the receiving host to
associate HIP and non-HIP traffic with the appropriate sockets. In
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that case the source and destination IP addresses would be used to
associate the packet with the right end-points. This practice has the
drawback that does not allow multiple host identifiers to be hosted
on a single node.
If the single bit approach is deemed infeasible, it would be possible
to create a new extension header that would contain a new
demultiplexing field. From the HIP demultiplexing point of view, the
contents of the field would be similar to ESP SPI.
5.2.3.2 Correctness of the selected layer
Multi-homing is a phenomenon that clearly appears between hosts.
Hence, a multi-homing solution should be located at a layer that has
host granularity, and not any finer granularity. This leaves out
transport and higher layer solutions.
Multi-homing can be considered to be either as an end-to-end or a
routing level phenomenon. In the case of end-host multi-homing,
where a single host has multiple accesses to the Internet, the
situation seems to be best modelled as an end-to-end one.
Respectively, the case of intra-transit-provider connectivity, an
extreme form of site multi-homing, is probably best modeled as a part
of the overall routing topology. Various types of end-site
multi-homing (soho...multinational) fall on different locations on
this axis.
The IP layer contains both end-to-end and routing functions. Hence,
IP layer could implement both end-to-end and routing based
multi-homing solutions.
Since HIP introduces a new name space, Host Identifiers, it is best
described as a shim or 3.5 layer solution [9]. In other words, it is
end-to-end in nature, affecting some of the current IP layer
end-to-end functionality, but relies clearly below the transport
layer.
A layer 3.5 solution has a number of good proporties:
It is possible to continue using unmodified TCP and UDP.
It would become possible to move much of the SCTP and DCCP
multi-addressing functionality into the new layer. Such
functionality would then be shared between them and the legacy
transport protocols, TCP and UDP.
The approach would make it easier to collect per-path MTU and RTT
information, if seen approapriate from the transport
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point-of-view.
The approach does not require any changes to the IP layer or the
pseudo header. (But see also Section 3.1.)
5.2.3.3 Expansion of packet size
The solution does not cause any expansion of packet size of than that
caused by ESP. If ESP is not used, the single-bit solution, outlined
above, would allow HIP to be used without any expansion of packet
size.
5.2.3.4 Fragmentation
It is expected that HIP solutions report a reduced MTU to upper
layer, similar to current ESP practise. Other than that, the
standard ESP fragmentation practise is used. The current
implementations seem to work, but no-one has performed a detailed
analysis.
5.2.3.5 Changes to ICMP error semantics
The current HIP specifications do not create any new ICMP error
messages. However, a detailed analysis is needed to see if there are
any subtle changes to the current semantics. Such an analysis has
not been made.
5.2.4 Names, Hosts, Endpoints, or no of the above?
5.2.4.1 Relationship with DNS
It is expected that the HIT (or the HI) of each HIP host is stored
into the DNS, in addition to the IP address(es). When a HIP host
starts to connect to another HIP hosts, it queries for both the HIT/
HI and the addresses. If a HIT/HI is received, the initiating host
creates a piece of local state, attempts to create a HIP association
with the peer upon first connection request. If the association is
created, the hosts establish their multi-addressing state directly.
The addresses stored in the DNS are not used beyond building the HIP
association. If no HIT/HI are received, the initiating host falls
back to using legacy IP.
Defining the required new RR type is a working item for the HIP WG.
5.2.4.2 Interactions with 2-faced DNS
Interactions with 2-faced DNS have not been fully analyzed. However,
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as HIP reduced the applications' dependency on IP addresses, it looks
like that HIP would easily allow 2-faced DNS to be used.
Furthermore, if there is a proper HIP aware security gateway between
the two domains, it should be possible to fully control the creation
of HIP associations between the domains.
5.2.4.3 (Non)need for centralized registration
HIP does not require centralized registration. The identifiers are
public keys, and typically self-generated.
It is expected that the IRTF XXX RG will study how to provide a
service similar to reverse mapping for the public keys.
5.2.4.4 (No) Circular dependencies with DNS
DNS is not expected to use HIP. In a typical implementation, this is
accomplised by configuring the DNS proxies and servers to bind/
connect to IP addresses, not HITs.
5.2.4.5 Multihomed DNS servers
Multi-homed DNS servers are expected to continue direct utilization
of multiple IP addresses.
5.2.4.6 Application/API changes
Most old code will just work. Multi-party applications doing
IP-address-based referrals will break.
the IRTF XXX RG will study how to support such multi-party
applications.
To gain full benefit from HIP, extensions to the current socket API
are expected to be needed. However, using such extensions is not
required to benefit from the multi-addressing properties of HIP.
5.2.4.7 Backward compatibility and incremental deployment with current
IPv6
The current implementations allow full compatibility with the current
IPv6, with the exception of using a large but unused part of the IPv6
address space to represent HITs internally. No requirements are
placed on non-multihomed, non-mobile legacy hosts.
HIP is designed to be incrementally deployed. It is expected that
HIP capable servers announce their capability to run HIP by listing
the new resource record in the DNS. Possibilities to run HIP
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opportunistically, without DNS, is being studied at the IRTF XXX RG.
5.2.4.8 Backward compatibility with IPv4
HIP works with both IPv4 and IPv6, even allowing simultaneous use of
both IPv4 and IPv6 connections.
It has not been analyzed how HIP interacts with existing 6to4
gateways. Such work is not on the HIP WG charter, but may be pursued
at the IRTF XXX RG.
5.2.4.9 Interaction with middleboxes
Firewalls Since HIP introduces a new control protocol to be run
directly over IP, and uses IPsec to secure payload traffic, HIP
would break most current firewalls. However, the HIP base
exchange and the rest of the control protocol has been carefully
designed to be friendly towards future firewalls, allowing HIP
aware firewalls to control HIP traffic.
NAT HIP, as currently defined, does not work with IP-multiplexing NAT
boxes. On the other hand, it would be fairly trivial to build HIP
aware NAT devices that would allow multiple Host Identities to be
NATed behind one IP address.
Web caches Since HIP encrypts by default all traffic, HIP does not
work with existing web caches or other application level middle
boxes. If HIP was to be used without IPsec (see Section 3.1), Web
proxies, and transparent application layer middle boxes might
work. However, that hasn't been analyzed.
5.2.4.10 Implications on scoped addressing
It has not been analyzed how HIP would effect scoped addressing.
Multicast Not analyzed.
Link local HIP should not have any effects on link local addresses or
using them.
Son-of-Sitelocal It looks like that HIP might reduce need for site
local kind of addresses.
5.2.4.11 Layer 2 implications
HIP, as such, does not seem to have any direct implications on layer
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2 or neighbor discovery. However, given that HIP introduces a public
key per host, it might be possible to further simplify ND and layer 2
security mechanisms.
5.2.4.12 Referrals
As HIP replaces IP addresses with HITs in application data
structures, and since HITs cannot be currently resolved into IP
addresses, multi-party applications doing IP-address-based referrals
will not work. The IRTF XXX RG will study the support of such
multi-party applications.
5.2.4.13 Legal stuff / trade marks and name space management
Public keys or their hashes are not mnemonic. The name space does
not need to be managed.
5.3 RFC 3582 Section 3 considerations
5.3.1 Multi-Homing capabilities
5.3.1.1 Redundancy
Path redundancy is fully supported, similar to other solutions based
on multi-addressing. More specifically, as soon as the hosts have
established multi-addressing state by exchanging REA payloads, the
hosts may use the different transit providers interchangeably. The
current HIP specifications do not specify how a host detects a path
failure; such a mechanism is expected to be specified in the multi6
WG.
If a failure occurs before the multi-addressing state has been
established, e.g., before the HIP base exchange has been completed,
the hosts may try to re-create the HIP state using different IP
addresses, if available, e.g., from the DNS. However, the HIP
specifications do not currently discuss such a situation, and the
actual behaviour depends on local implementation.
5.3.1.2 Load sharing
Load sharing is supported, in the sense that the hosts may use
different transit providers interchangeably, similar to other
solutiosn based on multi-addressing.
The current specification does include a feature that allows a host
to control the primary address that it wants its peer to use. If
more fine grained control is required, suitable policy mechanisms
could be developed on the top of HIP.
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5.3.1.3 Performance
By default, HIP based multi-homing does not require
intra-transit-provider links to be used. This is similar to other
multi-addressing based solutions.
As HIP insulates the transport sessions from the IP addresses, HIP
allows more freedom in source or destination address based policy
routing.
The baseline HIP solution adds a small delay before the first
transport sessions between a pair of hosts is established. The
duration of the delay depends on latency and available CPU resources,
consisting of two round trips of latency and requiring both hosts to
compute Diffie-Hellman shared key, one DSA signature, and verify one
DSA signature. Using short keys is allowed by the protocol, subject
to local policy considerations.
5.3.1.4 Policy
As of today, HIP does not contain any policy control mechanisms.
However, adding such mechanisms seems to be fairly straightforward,
not differing from other multi-addressing based solutions.
5.3.1.5 Simplicity
HIP requires both end hosts to be changed. Most applications do not
require any changes; applications that use explicit referral may need
to be made HIP aware. Incremental deployment is fully supported.
Legacy IPv6 (and IPv4) hosts can be used at a multi-homed site either
as such, in which case they do not benefit from multi-homing, or
through a HIP proxy, located at the site. If a multi-homed site
wants to benefit from multi-homing when communicating with legacy
hosts outside of the site, a HIP proxy must be deployed somewhere
close to the core network.
The exact details of HIP proxies have not been defined yet.
The current HIP implementations, with limited multi-homing support,
have aroudn 10 000 lines of C code. Adding full multi-homing support,
as defined in [4] is expected to add less than 3 000 lines of code.
5.3.1.6 Transport layer survivability
The solution provides full re-homing transparency for all transport
layer sessions, similar to other multi-addressing based solutions.
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Most of the known current implementations do not support transparency
for raw IP, as raw IP is considered to be located the host identity
layer.
5.3.1.7 Impact on DNS
HIP adds a new DNS resource record for each HIP capable host. The
details are to be defined in the HIP WG. This new resource record
will be queried along with the IP addresses, thereby adding little
overhead.
For redundancy in initial connections, a HIP capable host should list
multiple IP addresses in the DNS. However, these addresses are used
only for the initial connection. Once the multi-addressing state has
been established, the hosts are independent of DNS.
5.3.1.8 Packet filtering
HIP is similar to other multi-addressing based solutions.
5.3.2 Additional requirements
5.3.2.1 Scalability
The solution does not impose new requirements on the routing system.
From a multi-homing point of view, the only required piece of new
infrastructure is the new DNS resource record. Adding such records
scales approximately as well as the DNS does today.
HIP uses approximately 120 bit pseudo-random identifiers for
identifying hosts. According to the birthday paradigm, as long as
the total number of hosts remains considerably lower than sqrt(2^120)
= 2^60, the probability of identifier collisions remains low. If the
number of hosts is expected to grow larger, the length of the
identifier can be doubled with minor modifications to the solution.
5.3.2.2 Impact on routers
The solution does not require changes to IPv6 routers, other than
what the multi6 wg has already determined useful for all
multi-addressing based solutions.
5.3.2.3 Impact on hosts
HIP provides full backwards compatibility with legacy hosts.
Whenever one of the two communicating hosts is not HIP aware, the
applications fall back to levacy IP.
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HIP does require changes to the host stack. These changes can be
classified into two classes:
Basic packet processing must be changed to recognize HITs on
outgoing packets, and incoming ESP protected HIP packets must
replace the IP addresses with HITs. This change is minor, and can
be implemented either integral to IPsec, or separate. In a
typical implementation, the number of changed and/or added lines
is a few hundred.
A HIP protocol implementation must be added to the stack. This
change is a logically separate function. In a typical
implementation, the number of lines required is in order of 10
000.
The solution does not _require_ changes to the socket API or
transport layer. However, it is _expected_ that the socket API and
the transport layer will be changed in order to gain full benefit
from HIP.
As it is currently defined, HIP breaks some multi-party applications
that use IP addresses for referral. Solutions to this problem is a
research topic, being studied at the IRTF XXX RG.
5.3.2.4 Interactions between hosts and the routing system
HIP does not require interaction between hosts and the routing
system, other than what the multi6 wg has already determined for
other multi-addressing based solutions.
5.3.2.5 Operations and management
HIP implementations are expected to include a facility that allows an
administrator to view HIT to address mapping. There is no HIP MIB or
PIB, but it can be expected to be added as a working item for the HIP
working group in the future.
5.3.2.6 Co-operationg between transit providers
HIP does not require any co-operation between transit providers. If
such co-operation is available, HIP would benefit form it similar to
other multi-addressing based solutions.
5.3.2.7 Multiple solutions
HIP should work well with multi-homing solutions that are located
solely at the IP layer, i.e., below HIP.
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Interoperability with other multi-addressing based solutions depend
on many details, and need to be analyzed case-by-case.
5.4 Security considerations
HIP attempts to raise the security baseline in the Internet by
employing IPsec ESP protection by default.
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6. Security considerations
HIP security has been extensively discussed in [3] and [2]. Mobility
and multicast related security issues have been briefly discussed in
[4]. As this draft is more a discussion draft and not a protocol
specification, security considerations related to using HIP
components instead of full HIP are currently not discussed anywhere.
Such a discussion is planned to be added at a later stage, if this
draft goes forward.
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Informative references
[1] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[2] Moskowitz, R., Nikander, P. and P. Jokela, "Host Identity
Protocol", draft-moskowitz-hip-08 (work in progress), October
2003.
[3] Moskowitz, R., "Host Identity Protocol Architecture",
draft-moskowitz-hip-arch-05 (work in progress), October 2003.
[4] Nikander, P., "End-Host Mobility and Multi-Homing with Host
Identity Protocol", draft-nikander-hip-mm-01 (work in
progress), January 2004.
[5] Nikander, P., "Mobile IP version 6 Route Optimization Security
Design Background", draft-nikander-mobileip-v6-ro-sec-02 (work
in progress), December 2003.
[6] Nordmark, E. and T. Li, "Threats relating to IPv6 multihoming
solutions", draft-nordmark-multi6-threats-00 (work in
progress), October 2003.
[7] Nordmark, E., "Multihoming without IP Identifiers",
draft-nordmark-multi6-noid-01 (work in progress), October 2003.
[8] Nordmark, E., "Strong Identity Multihoming using 128 bit
Identifiers (SIM/CBID128)", draft-nordmark-multi6-sim-01 (work
in progress), October 2003.
[9] Crocker, D., "CHOICES FOR MULTIADDRESSING",
draft-crocker-mast-analysis-01 (work in progress), October
2003.
[10] Krawczyk, H., "The SIGMA family of key-exchange protocols",
2003.
[11] Ylitalo, J., "Multihoming using Reverse Hash Chains and
Splitted Secrets", draft-ylitalo-multi6-hc-00 (work in
progress), January 2004.
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Author's Address
Pekka Nikander
Ericsson Research Nomadic Lab
JORVAS FIN-02420
FINLAND
Phone: +358 9 299 1
EMail: pekka.nikander@nomadiclab.com
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