Network Working Group P. Thubert
Internet-Draft M. Molteni
Expires: April 12, 2004 Cisco Systems
October 13, 2003
IPv6 Reverse Routing Header and its application to Mobile Networks
draft-thubert-nemo-reverse-routing-header-03
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on April 12, 2004.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
Already existing proposals enable Mobile Networks by extending Mobile
IP to support Mobile Routers. In order to enable nested Mobile
Networks, some involve the overhead of nested tunnels between the
Mobile Routers and their Home Agents.
This proposal allows the building of a nested Mobile Network avoiding
the nested tunnel overhead. This is accomplished by using a new
routing header, called the reverse routing header, and by overlaying
a layer 3 tree topology on the evolving Mobile Network.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Recursive complexity . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Assumptions . . . . . . . . . . . . . . . 5
2.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Assumptions . . . . . . . . . . . . . . . . . . . . . . . 6
3. An Example . . . . . . . . . . . . . . . . . . . . . . . . 7
4. New Routing Headers . . . . . . . . . . . . . . . . . . . 11
4.1 Routing Header Type 2 (MIPv6 RH with extended semantics) . 11
4.2 Routing Header Type 4 (The Reverse Routing Header) . . . . 13
4.3 Extension Header order . . . . . . . . . . . . . . . . . . 15
5. ICMP . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6. Modifications to IPv6 Neighbor Discovery . . . . . . . . . 19
6.1 Modified Router Advertisement Message Format . . . . . . . 19
6.2 New Tree Information Option Format . . . . . . . . . . . . 20
7. Binding Cache Management . . . . . . . . . . . . . . . . . 23
7.1 Binding Updates . . . . . . . . . . . . . . . . . . . . . 23
7.2 RRH Heartbeat . . . . . . . . . . . . . . . . . . . . . . 23
8. Home Agent Operation . . . . . . . . . . . . . . . . . . . 24
9. Mobile Router Operation . . . . . . . . . . . . . . . . . 26
9.1 Processing of ICMP "RRH too small" . . . . . . . . . . . . 26
9.2 Processing of ICMP error . . . . . . . . . . . . . . . . . 27
9.3 Processing of RHH for Outbound Packets . . . . . . . . . . 27
9.4 Processing of Tree Information Option . . . . . . . . . . 28
9.5 Processing of the extended Routing Header Type 2 . . . . . 28
9.6 Decapsulation . . . . . . . . . . . . . . . . . . . . . . 30
10. Mobile Host Operation . . . . . . . . . . . . . . . . . . 30
11. Security Considerations . . . . . . . . . . . . . . . . . 30
11.1 IPsec Processing . . . . . . . . . . . . . . . . . . . . . 30
11.1.1 Routing Header type 2 . . . . . . . . . . . . . . . . . . 31
11.1.2 Routing Header type 4 . . . . . . . . . . . . . . . . . . 31
11.2 New Threats . . . . . . . . . . . . . . . . . . . . . . . 32
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 33
References . . . . . . . . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 35
A. Optimizations . . . . . . . . . . . . . . . . . . . . . . 36
A.1 Path Optimization with RRH . . . . . . . . . . . . . . . . 36
A.2 Packet Size Optimization . . . . . . . . . . . . . . . . . 37
A.2.1 Routing Header Type 3 (Home Address option replacement) . 38
B. Multi Homing . . . . . . . . . . . . . . . . . . . . . . . 40
B.1 Multi-Homed Mobile Network . . . . . . . . . . . . . . . . 40
B.2 Multihomed Mobile Router . . . . . . . . . . . . . . . . . 41
C. Changes from Previous Version of the Draft . . . . . . . . 42
Intellectual Property and Copyright Statements . . . . . . 43
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1. Introduction
This document assumes the reader is familiar with the Mobile Networks
terminology defined in [2] and with Mobile IPv6 defined in [1].
Generally a Mobile Network may be either simple (a network with one
mobile router) or nested, single or multi-homed. This proposal starts
from the assumption that nested Mobile Networks will be the norm, and
so presents a solution that avoids the tunnel within tunnel overhead
of already existing proposals.
The solution is based on a single bi-directional tunnel between the
first Mobile Router (MR) to forward a packet and its Home Agent (HA).
By using IPsec ESP on that tunnel, home equivalent privacy is
obtained without further encapsulation.
The solution uses a new Routing Header (RH), called the Reverse
Routing Header (RRH), to provide an optimized path for the single
tunnel. RRH is a variant of IPv4 Loose Source and Record Route (LSRR)
[6] adapted for IPv6. RRH records the route out of the nested Mobile
Network and can be trivially converted into a routing header for
packets destined to the Mobile Network.
This version focuses on single-homed Mobile Networks. Hints for
further optimizations and multi-homing are given in the appendixes.
Local Fixed Node (LFN) and Correspondent Node (CN) operations are
left unchanged as in Mobile IPv6 [1]. Specifically the CN can also be
a LFN.
Section 3 proposes an example to illustrate the operation of the
proposed solution, leaving detailed specifications to the remaining
chapters. The reader may refer to Section 2.1 for the specific
terminology.
1.1 Recursive complexity
A number of drafts and publications suggest -or can be extended to- a
model where the Home Agent and any arbitrary Correspondent would
actually get individual binding from the chain of nested Mobile
Routers, and form a routing header appropriately.
An intermediate MR would keep track of all the pending communications
between hosts in its subtree of Mobile Networks and their CNs, and a
binding message to each CN each time it changes its point of
attachment.
If this was done, then each CN, by receiving all the binding messages
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and processing them recursively, could infer a partial topology of
the nested Mobile Network, sufficient to build a multi-hop routing
header for packets sent to nodes inside the nested Mobile Network.
However, this extension has a cost:
1. Binding Update storm
when one MR changes its point of attachment, it needs to send a
BU to all the CNs of each node behind him. When the Mobile
Network is nested, the number of nodes and relative CNs can be
huge, leading to congestions and drops.
2. Protocol Hacks
Also, in order to send the BUs, the MR has to keep track of all
the traffic it forwards to maintain his list of CNs. In case of
IPSec tunneled traffic, that CN information may not be available.
3. CN operation
The computation burden of the CN becomes heavy, because it has to
analyze each BU in a recursive fashion in order to infer nested
Mobile Network topology required to build a multi hop routing
header.
4. Missing BU
If a CN doesn't receive the full set of PSBU sent by the MR, it
will not be able to infer the full path to a node inside the
nested Mobile Network. The RH will be incomplete and the packet
may or may not be delivered.
5. Obsolete BU
If the Binding messages are sent asynchronously by each MR, then,
when the relative position of MRs and/or the TLMR point of
attachment change rapidly, the image of Mobile Network that the
CN maintains is highly unstable. If only one BU in the chain is
obsolete due to the movement of an intermediate MR, the
connectivity may be lost.
A conclusion is that the path information must be somehow aggregated
to provide the CN with consistent snapshots of the full path across
the Mobile Network. This can be achieved by an IPv6 form of loose
source / record route header, that we introduce here as a Reverse
Routing Header
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2. Terminology and Assumptions
2.1 Terminology
Simple Mobile Network
One or more IP subnets attached to a MR and mobile as a unit, with
respect to the rest of the Internet. A simple Mobile Network can
be either single or multi-homed.
The IP subnets may have any kind of topology and may contain fixed
routers. All the access points of the Mobile Network (to which
further MRs may attach) are on the same layer 2 link of the MR.
We like to represent a simple single-homed Mobile Network as an
hanger, because it has only one uplink hook and a bar to which
multiple hooks can be attached. Graphically we use the question
mark "?" to show the uplink hook (interface) connected to the MR,
and the "=" sign to represent the bar:
?
MR1
|
===============
Nested Mobile Network
A group of simple Mobile Networks recursively attached together
and implementing nested Mobility as defined in [2].
?
MR1
|
====?===============?====
MR2 MR3
| |
=========== ===?==========?===
MR4 MR5
| |
========== ============
IPv6 Mobile Host
A IPv6 Host, with support for MIPv6 MN, and the additional Nemo
capability described in this draft.
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Home prefix
Network prefix, which identifies the home link within the Internet
topology.
Mobile Network prefix
Network prefix, common to all IP addresses in the Mobile Network
when the MR is attached to the home link. It may or may not be a
subset of the Home subnet prefix.
Inbound direction:
direction from outside the Mobile Network to inside
Outbound direction:
direction from inside the Mobile Network to outside
2.2 Assumptions
We make the following assumptions:
1. A MR has one Home Agent and one Home Address -> one primary CoA.
2. A MR attaches to a single Attachment Router as default router.
3. A MR may have more than one uplink interface.
4. An interface can be either wired or wireless. The text assumes
that interfaces are wireless for generality.
5. Each simple Mobile Network may have more that one L2 Access
Point, all of them controlled by the same Attachment Router,
which we assume to be the Mobile Router.
Since an MR has only one primary CoA, only one uplink interface can
be used at a given point of time. Since the MR attaches to a single
attachment router, if due care is applied to avoid loops, then the
resulting topology is a tree.
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3. An Example
The nested Mobile Network in the following figure has a tree
topology, according to the assumptions in Section 2.2. In the tree
each node is a simple Mobile Network, represented by its MR.
+---------------------+
| Internet |---CN
+---------------|-----+
/ Access Router
MR3_HA |
======?======
MR1
|
====?=============?==============?===
MR5 MR2 MR6
| | |
=========== ===?========= =============
MR3
|
==|=========?== <-- Mobile Network3
LFN1 MR4
|
=========
An example nested Mobile Network
This example focuses on a Mobile Network node at depth 3 (Mobile
Network3) inside the tree, represented by its mobile router MR3. The
path to the Top Level Mobile Router (TLMR) MR1 and then the Internet
is
MR3 -> MR2 -> MR1 -> Internet
Consider the case where a LFN belonging to Mobile Network3 sends a
packet to a CN in the Internet, and the CN replies back. With the
tunnel within tunnel approach described by [3], we would have three
bi-directional nested tunnels:
-----------.
--------/ /-----------.
-------/ | | /-----------
CN ------( - - | - - - | - - - | - - - | - - - (-------- LFN
MR3_HA -------\ | | \----------- MR3
MR2_HA --------\ \----------- MR2
MR1_HA ----------- MR1
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Depending on the relative location of MR1_HA, MR2_HA and MR3_HA, this
may lead to a very inefficient "pinball" routing in the
Infrastructure.
On the other hand, with the RRH approach we would have only one
bi-directional tunnel:
--------------------------------- MR1 ---- MR2 ---- MR3
CN ------( - - - - - - - - - - - - - - - - (-------- LFN
MR3_HA --------------------------------- MR1 ---- MR2 ---- MR3
The first mobile router on the path, MR3, in addition to tunneling
the packet to its HA, adds a reverse routing header with N = 3
pre-allocated slots. Choosing the right value for N is discussed in
Section 6.2. The bottom slot is equivalent to the MIPv6 Home Address
option. MR3 inserts its home address MR3_HoA into slot 0.
The outer packet has source MR3's Care of Address, MR3_CoA, and
destination MR3's Home Agent, MR3_HA:
<-------------- outer IPv6 header -------------------->
+-------+-------++ -- ++----+-------+-------+---------+ +-------
|oSRC |oDST |: :|oRRH| slot2 | slot1 | slot0 | |
|MR3_CoA|MR3_HA |:oEXT:|type| | |MR3_HoA | |iPACKET
| | |: :| 4 | | | | |
+-------+-------++ -- ++----+-------+-------+---------+ +-------
The second router on the path, MR2, notices that the packet already
contains an RRH, and so it overwrites the source address of the
packet with its own address, MR2_CoA, putting the old source address,
MR3_CoA, in the first free slot of the RRH.
The outer packet now has source MR2_CoA and destination MR3_HA; the
RRH from top to bottom is MR3_CoA | MR3_HoA:
<-------------- outer IPv6 header -------------------->
+-------+-------++ -- ++----+-------+-------+---------+ +-------
|oSRC |oDST |: :|oRRH| slot2 | slot1 | slot0 | |
|MR2_CoA|MR3_HA |:oEXT:|type| |MR3_CoA|MR3_HoA | |iPACKET
| | |: :| 4 | | | | |
+-------+-------++ -- ++----+-------+-------+---------+ +-------
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In general the process followed by the second router is repeated by
all the routers on the path, including the TLMR (in this example
MR1). When the packet leaves MR1 the source address is MR1_CoA and
the RRH is MR2_CoA | MR3_CoA | MR3_HoA:
<-------------- outer IPv6 header -------------------->
+-------+-------++ -- ++----+-------+-------+---------+ +-------
|oSRC |oDST |: :|oRRH| slot2 | slot1 | slot0 | |
|MR1_CoA|MR3_HA |:oEXT:|type|MR2_CoA|MR3_CoA|MR3_HoA | |iPACKET
| | |: :| 4 | | | | |
+-------+-------++ -- ++----+-------+-------+---------+ +-------
In a colloquial way we may say that while the packet travels from MR3
to MR3_HA, the Mobile Network tunnel end point "telescopes" from MR3
to MR2 to MR1.
When the home agent MR3_HA receives the packet it notices that it
contains a RRH and it looks at the bottom entry, MR3_HoA. This entry
is used as if it were a MIPv6 Home Address destination option, i.e.
as an index into the Binding Cache. When decapsulating the inner
packet the home agent performs the checks described in Section 8, and
if successful it forwards the inner packet to CN.
MR3_HA stores two items in the Bind Cache Entry associated with MR3:
the address entries from RRH, to be used to build the RH, and the
packet source address MR1_CoA, to be used as the first hop.
Further packets from the CN to the LFN are plain IPv6 packets.
Destination is LFN, and so the packet reaches MR3's home network.
MR3_HA intercepts it, does a Bind Cache prefix lookup and obtains as
match the MR3 entry, containing the first hop and the information
required to build the RH. It then puts the packet in the tunnel
MR3_HA -- MR3 as follows: source address MR3_HA and destination
address the first hop, MR1_CoA. The RH is trivially built out of the
previous RRH: MR2_CoA | MR3_CoA | MR3_HoA:
<-------------- outer IPv6 header -------------------->
+-------+-------++ -- ++----+-------+-------+---------+ +-------
|oSRC |oDST |: :|oRH | | | | |
|MR3_HA |MR1_CoA|:oEXT:|type|MR2_CoA|MR3_CoA|MR3_HoA | |iPACKET
| | |: :| 2 | | | | |
+-------+-------++ -- ++----+-------+-------+---------+ +-------
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The packet is routed with plain IP routing up to the first
destination MR1_CoA.
The RH of the outer packet is type 2 as in MIPv6 [1], but has
additional semantics inherited from type 0: it contains the path
information to traverse the nested Mobile Network from the TLMR to
the tunnel endpoint MR3. Each intermediate destination forwards the
packet to the following destination in the routing header. The
security aspects of this are treated in Section 11.2.
MR1, which is the initial destination in the IP header, looks at the
RH and processes it according to Section 9, updating the RH and the
destination and sending it to MR2_CoA. MR2 does the same and so on
until the packet reaches the tunnel endpoint, MR3.
When the packet reaches MR3, the source address in the IP header is
MR3_HA, the destination is MR3_CoA and in the RH there is one segment
left, MR3_HoA. As a consequence the packet belongs to the MR3_HA --
MR3 tunnel. MR3 decapsulates the inner packet, applying the rules
described in Section 9 and sends it to LFN. The packet that reaches
LFN is the plain IPv6 packet that was sent by CN.
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4. New Routing Headers
This draft modifies the MIPv6 Routing Header type 2 and introduces
two new Routing Headers, type 3 and 4. Type 3, which is an
optimization of type 4 will be discussed in Appendix A.2.1. The draft
presents their operation in the context of Mobile Routers although
the formats are not tied to Mobile IP and could be used in other
situations.
4.1 Routing Header Type 2 (MIPv6 RH with extended semantics)
Mobile IPv6 uses a Routing header to carry the Home Address for
packets sent from a Correspondent Node to a Mobile Node. In [1], this
Routing header (Type 2) is restricted to carry only one IPv6 address.
The format proposed here extends the Routing Header type 2 to be
multi-hop.
The processing of the multi-hop RH type 2 inherits from the RH type 0
described in IPv6 [10]. Specifically: the restriction on multicast
addresses is the same; a RH type 2 is not examined or processed until
it reaches the node identified in the Destination Address field of
the IPv6 header; in that node, the RH type 0 algorithm applies, with
added security checks.
The construction of the multi-hop RH type 2 by the HA is described in
Section 8; the processing by the MRs is described in Section 9.5; and
the security aspects are treated in Section 11.2.
The destination node of a packet containing a RH type 2 can be a MR
or some other kind of node. If it is a MR it will perform the
algorithm described in Section 9.5, otherwise it will operate as
prescribed by IPv6 [10] when the routing type is unrecognized.
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The multi-hop Routing Header type 2, as extended by this draft, has
the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type=2| Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Address[1] +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Address[2] +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. . .
. . .
. . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Address[n] +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header
8-bit selector. Identifies the type of header immediately
following the Routing header. Uses the same values as the IPv4
Protocol field [13].
Hdr Ext Len
8-bit unsigned integer. Length of the Routing header in 8-octet
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units, not including the first 8 octets. For the Type 2 Routing
header, Hdr Ext Len is equal to two times the number of addresses
in the header.
Routing Type
8-bit unsigned integer. Set to 2.
Segments Left
8-bit unsigned integer. Number of route segments remaining, i.e.,
number of explicitly listed intermediate nodes still to be visited
before reaching the final destination.
Reserved
32-bit reserved field. Initialized to zero for transmission;
ignored on reception.
Address[1..n]
Vector of 128-bit addresses, numbered 1 to n.
4.2 Routing Header Type 4 (The Reverse Routing Header)
The Routing Header type 4, or Reverse Routing Header (RRH), is a
variant of IPv4 loose source and record route (LSRR) [6] adapted for
IPv6.
Addresses are added from bottom to top (0 to n-1 in the picture). The
RRH is designed to help the destination build an RH for the return
path.
When a RRH is present in a packet, the rule for upper-layer checksum
computing is that the source address used in the pseudo-header is
that of the original source, located in the slot 0 of the RRH, unless
the RRH slot 0 is empty, in which case the source in the IP header of
the packet is used.
As the 'segment left' field of the generic RH is reassigned to the
number of segments used, an IPv6 node that does not support RRH will
discard the packet, unless the RRH is empty.
The RRH contains n pre-allocated address slots, to be filled by each
MR in the path. It is possible to optimize the number of slots using
the Tree Information Option described in Section 6.2.
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The Type 4 Routing Header has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type=4| Segments Used |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Slot[n-1] +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. . .
. . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Slot[1] (1st MR CoA) +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Slot[0] (Home address) +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header
8-bit selector. Identifies the type of header immediately
following the Routing header. Uses the same values as the IPv4
Protocol field [13].
Hdr Ext Len
8-bit unsigned integer. Length of the Routing header in 8-octet
units, not including the first 8 octets. For the Type 4 Routing
header, Hdr Ext Len is equal to two times the number of addresses
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in the header.
Routing Type
8-bit unsigned integer. Set to 4.
Segments Used
8-bit unsigned integer. Number of slots used. Initially set to 1
by the MR when only the Home Address is there. Incremented by the
MRs on the way as they add the packets source addresses to the
RRH.
Sequence Number
32-bit unsigned integer. The Sequence Number starts at 0, and is
incremented by the source upon each individual packet. Using the
Radia Perlman's lollipop algorithm, values between 0 and 255 are
'negative', left to indicate a reboot or the loss of HA
connectivity, and are skipped when wrapping and upon positive
Binding Ack. The sequence number is used to check the freshness of
the RRH; anti-replay protection is left to IPsec AH.
Slot[n-1..0]
Vector of 128-bit addresses, numbered n-1 to 0.
When applied to the Nemo problem, the RRH can be used to update the
HA on the actual location of the MR. Only MRs forwarding packets on
an egress interface while not at home update it on the fly.
A RRH is inserted by the first MR on the Mobile Network outbound
path, as part of the reverse tunnel encapsulation; it is removed by
the associated HA when the tunneled packet is decapsulated.
4.3 Extension Header order
The RH type 2 is to be placed as any RH as described in [10] section
4.1. If a RH type 0 is present in the packet, then the RH type 2 is
placed immediately after the RH type 0, and the RH type 0 MUST be
consumed before the RH type 2.
RH type 3 and 4 are mutually exclusive. They are to be placed right
after the Hop-by-Hop Options header if any, or else right after the
IPv6 header.
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As a result, the order prescribed in section 4.1 of RFC 2460 becomes:
IPv6 header
Hop-by-Hop Options header
Routing header type 3 or 4
Destination Options header (note 1)
Routing header type 0
Routing header type 2
Fragment header
Authentication header (note 2)
Encapsulating Security Payload header (note 2)
Destination Options header (note 3)
upper-layer header
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5. ICMP
The RRH could have fewer slots than the number of MRs in the path
because either the nested Mobile Network topology is changing too
quickly or the MR that inserted the RRH could have a wrong
representation of the topology.
To solve this problem a new ICMP message is introduced, "RRH
Warning", type 64. Note that this ICMP message creates a new class of
warning messages besides the error messages and the control messages
of ICMP.
This message allows a MR on the path to propose a larger number of
slots to the MR that creates the RRH. The Proposed Size MUST be
larger than the current size and MUST NOT be larger than 8.
The originating MR must rate-limit the ICMP messages to avoid
excessive ICMP traffic in the case of the source failing to operate
as requested.
The originating MR must insert an RH type 2 based on the RRH in the
associated IP header, in order to route the ICMP message back to the
source of the reverse tunnel. A MR that receives this ICMP message is
the actual destination and it MUST NOT forward it to the (LFN) source
of the tunneled packet.
A MR on the path that finds no more space in the RRH SHOULD send an
ICMP "RRH warning" back to the MR that inserted the RRH. On the other
hand, a MR should always be able, by receiving TI option with up to
date tree depth (see Section Section 6.2). to correctly size the RRH
to insert in an outgoing packet.
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The type 64 ICMP has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 64 | Code = 0 | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Current Size | Proposed Size | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| As much of invoking packet |
+ as will fit without the ICMPv6 packet +
| exceeding the minimum IPv6 MTU |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
64 [To Be Assigned]
Code 0: RRH too small
The originating MR requires the source to set the RRH size to a
larger value. The packet that triggered the ICMP will still be
forwarded by the MR, but the path cannot be totally optimized (see
Section 9.3).
Checksum
The ICMP checksum [12].
Current Size
RRH size of the invoking packet, as a reference.
Proposed Size
The new value, expressed as a number of IPv6 addresses that can
fit in the RRH.
Reserved
16-bit reserved field. Initialized to zero for transmission;
ignored on reception.
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6. Modifications to IPv6 Neighbor Discovery
6.1 Modified Router Advertisement Message Format
Mobile IPv6 [1] modifies the format of the Router Advertisement
message [11] by the addition of a single flag bit (H) to indicate
that the router sending the Advertisement message is serving as a
home agent on this link.
This draft adds another single flag bit (N) to indicate that the
router sending the advertisement message is a MR. This means that the
link on which the message is sent is a Mobile Network, which may or
may not be at home.
The Router Advertisement message has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cur Hop Limit |M|O|H|N|Reservd| Router Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reachable Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Retrans Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
This format represents the following changes over that originally
specified for Neighbor Discovery [11]:
Home Agent (H)
The Home Agent (H) bit is set in a Router Advertisement to
indicate that the router sending this Router Advertisement is also
functioning as a Mobile IP home agent on this link.
NEMO Capable (N)
The NEMO Capable (N) bit is set in a Router Advertisement to
indicate that the router sending this Router Advertisement is also
functioning as a Mobile Router on this link, so that the link is a
Mobile Network, possibly away from home.
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6.2 New Tree Information Option Format
This draft defines a new Tree Information option, used in Router
Advertisement messages. Fields set by the TLMR are propagated
transparently by the MRs. Mobile Routers SHOULD add that option to
the Router Advertisement messages sent over the ingress interfaces.
The Tree Information option has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length = 6 | TreePreference| TreeDepth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|H| Reserved | Bandwidth | DelayTime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MRPreference | BootTimeRandom |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PathCRC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Tree TLMR Identifier +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Tree Group +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
8-bit unsigned integer set to 10 by the TLMR.
Length
8-bit unsigned integer set to 6 by the TLMR. The length of the
option (including the type and length fields) in units of 8
octets.
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TreePreference
8-bit unsigned integer set by the TLMR to its configured
preference. Range from 0 = lowest to 255 = highest.
TreeDepth
8-bit unsigned integer set to 0 by the TLMR and incremented by 1
by each MR down the tree.
Fixed (F)
1-bit flag. Set by the TLMR to indicate that it is either attached
to a fixed network or at home.
Home (H)
1-bit flag. Set by the TLMR to indicate that it is also
functioning as a HA, for re-homing purposes.
Reserved
6-bit unsigned integer, set to 0 by the TLMR.
Bandwidth
8-bit unsigned integer set by the TLMR and decremented by MRs with
lower egress bandwidth. This is a power of 2 so that the available
egress bandwidth in bps is between 2^Bandwidth and
2^(Bandwidth+1). 0 means 'unspecified' and can not be modified
down the tree.
DelayTime
16-bit unsigned integer set by the TLMR. Tree time constant in
milliseconds.
MRPreference
8-bit signed integer. Set by each MR to its configured preference.
Range from 0 = lowest to 255 = highest.
BootTimeRandom
24-bit unsigned integer set by each MR to a random value that the
MR generates at boot time.
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PathCRC
32-bit unsigned integer CRC, updated by each MR. This is the
result of a CRC-32c computation on a bit string obtained by
appending the received value and the MR CareOf Address. TLMRs use
a 'previous value' of zeroes to initially set the pathCRC.
Tree TLMR Identifier
IPv6 global address, set by the TLMR. Identifier of the tree.
Tree Group
IPv6 global address, set by the TLMR. Identifier of the tree
group. A MR may use the Tree Group in its tree selection
algorithm.
The TLMR MUST include this option in its Router Advertisements.
A MR receiving this option from its Attachment Router MUST update the
TreeDepth, MRPreference, BootTimeRandom and PathCRC fields, and MUST
propagate it on its ingress interface(s), as described in Section
9.4.
The alignment requirement of the Tree Information option is 8n.
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7. Binding Cache Management
7.1 Binding Updates
Binding Updates are still used as described in MIPv6 [1] for Home
Registration and de-registration, but only when the MR registers for
the first time with its HA.
Since the BU doesn't contain the full NEMO path to the MR, it cannot
be used in this design of nested Mobile Networks.
7.2 RRH Heartbeat
Subsequent updates (or just refreshes) to the CoA binding are
obtained as one of the results of processing the RRH by the HA.
When the MR becomes aware of a topology change in the tree (for
examples it changes point of attachment, it obtains a new CoA, it
receives a Tree Information Option in an RA message that indicates a
change in the attachment tree) or in the absence of traffic (detected
by a timeout) to the HA, it must send an RRH Heartbeat (IP packet
with the RRH and empty payload).
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8. Home Agent Operation
This section inherits from chapter 10 of MIPv6 [1], which is kept
unmodified except for parts 10.5 and 10.6 which are extended. This
draft mostly adds the opportunity for a MN to update the Binding
Cache of its Home Agent using RRH, though it does not change the fact
that MNs still need to select a home agent, register and deregister
to it, using the MIP Bind Update.
This draft extends [1] section 10.6 as follows:
o The entry point of the tunnel is now checked against the TLMR as
opposed to the primary CoA.
o The Binding Cache can be updated based on RRH with proper AH
authentication.
As further explained in Section 7.1, this specification modifies MIP
so that the HA can rely on the RH type 4 (RRH) to update its Bind
Cache Entry (BCE), when the Mobile Node moves. The conceptual content
of the BCE is extended to contain a sequence counter, and the
sequence of hops within the --potentially nested-- Mobile Network to
a given Mobile Node. The sequence counter is initially set to 0.
When the HA receives a packet destined to itself, it checks for the
presence of a Routing Header of type 3 or 4. Both contain as least
the entry for the home address of the MN in slot 0; this replaces the
MIP Home Address Option and allows the HA to determine the actual
source of the packet, to access the corresponding security
association.
As explained in Section 11.2, the HA MUST verify the authenticity of
the packet using IPSEC AH and drop packets that were not issued by
the proper Mobile Node. An RRH is considered only if the packet is
authenticated and if its sequence number is higher than the one saved
in the BCE.
Also, an RRH is considered only if an initial Bind Update exchange
has been successfully completed between the Mobile Node and its Home
Agent for Home Registration. If the RRH is valid, then the Bind Cache
Entry is revalidated for a lifetime as configured from the initial
Bind Update.
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The BCE abstract data is updated as follows:
The first hop for the return path is the last hop on the path of
the incoming packet, that is between the HA and the Top Level
Mobile Router (TLMR) of the Mobile Network. The HA saves the IP
address of the TLMR from the source field in the IP header.
The rest of the path to the MN is found in the RRH.
The sequence counter semantics is changed as described in Section
4.2
This draft extends [1] section 10.5 as follows:
A Home Agent advertises the prefixes of its registered Mobile
Routers, during the registration period, on the local Interior
Gateway Protocol (IGP).
The Routing Header type 2 is extended to be multi-hop.
The Home Agent is extended to support routes to prefixes that are
owned by Mobile Routers. This can be configured statically, or can be
exchanged using a routing protocol as in [3], which is out of the
scope of this document. As a consequence of this process, the Home
Agent which is selected by a Mobile Router advertises reachability of
the MR prefixes for the duration of the registration over the local
IGP.
When a HA gets a packet for which the destination is a node behind a
Mobile Router, it places the packet in the tunnel to the associated
MR. This ends up with a packet which destination address in the IP
Header is the TLMR, and with a Routing Header of type 2 for the rest
of the way to the Mobile Router, which may be multi-hop.
To build the RH type 2 from the RRH, the HA sets the type to 2, and
clears the bits 32-63 (byte 4 to 7).
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9. Mobile Router Operation
This section inherits from chapter 11 of [1], which is extended to
support Mobile Networks and Mobile Routers as a specific case of
Mobile Node.
This draft extends section 11.2.1 of MIPv6 [1] as follows:
o When not at home, an MR uses a reverse tunnel with its HA for all
the traffic that is sourced in its mobile network(s); traffic
originated further down a nested network is not tunneled twice but
for exception cases.
o The full path to and within the Mobile Network is piggy-backed
with the traffic on a per-packet basis to cope with rapid
movement. This makes the packet construction different from MIPv6.
The MR when not at home sets up a bi-directional tunnel with its HA.
The reverse direction MR -> HA is needed to assure transparent
topological correctness to LFNs, as in [3]. But, as opposed to that
solution, nested tunnels are generally avoided.
9.1 Processing of ICMP "RRH too small"
The New ICMP message "RRH too Small" is presented in Section 5. This
message is addressed to the MR which performs the tunnel
encapsulation and generates the RRH.
Hence, a MR that receives the ICMP "RRH too small" MUST NOT propagate
it to the originating LFN or inner tunnel source, but MUST process it
for itself.
If the Current Size in the ICMP messages matches the actual current
number of slots in RRH, and if the ICMP passes some safety checks as
described in Section 5, then the MR MAY adapt the number of slots to
the Proposed Size.
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9.2 Processing of ICMP error
ICMP back {
if RRH is present {
compute RH type 2 based on RRH
get packet source from IP header
send ICMP error to source including RH type 2.
}
else {
get packet source from IP header
send ICMP error to source with no RH.
}
}
When the MR receives an ICMP error message, it checks whether it is
the final destination of the packet by looking at the included
packet. If the included packet has an RRH, then the MR will use the
RRH to forward the ICMP to the original source of the packet.
9.3 Processing of RHH for Outbound Packets
if no RRH in outer header /* First Mobile Router specific */
or RRH present but saturated { /* Need a nested encapsulation */
if RRH is saturated {
do ICMP back (RRH too small)
}
/* put packet in sliding reverse tunnel */
insert new IP header plus RRH
set source address to the MR Home Address
set destination address to the MR Home Agent Address
add an RRH with all slots zeroed out
compute IPsec AH on the resulting packet
}
/* All MRs including first */
if packet size <= MTU {
select first free slot in RRH bottom up
set it to source address from IP header
overwrite source address in IP header with MR CareOf
transmit packet
} else {
do ICMP back (Packet too Big)
}
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If the packet already contains an RRH in the outer header, and has a
spare slot, the MR adds the source address from the packet IP header
to the RRH and overwrites the source address in the IP header with
its CoA. As a result, the packets are always topologically correct.
Else, if the RRH is present but is saturated, and therefore the
source IP can not be added, the MR sends a ICMP 'RRH too small' to
the tunnel endpoint which originated the outer packet, using the RRH
info to route it back. The ICMP message is a warning, and the packet
is not discarded. Rather, the MR does a nested encapsulation of the
packet in its own reverse tunnel home with an additional RRH.
Else, if the packet does not have an RRH, the MR puts it in its
reverse tunnel, sourced at the CoA, with an RRH indicating in slot 0
the Home Address of the MR, and with proper IPsec AH as described
further in Section 11.1.
9.4 Processing of Tree Information Option
The Tree Information option in Router Advertisement messages allows
the Mobile Router to select a tree and learn about its capabilities.
The treeDepth can be used to compute the optimum number of slots in
the RRH.
The RRH contains an entry for the home address in slot 0, and one for
every CareOf on the way but that of the last Mobile Router (TLMR). As
the TLMR sets the treeDepth to 0 and each MR increments it on the way
down the tree, the optimum number of slots is normally (treeDepth+1),
where treeDepth is the depth advertised by the MR over its Mobile
Networks.
9.5 Processing of the extended Routing Header Type 2
if Segments Left = 0 {
/* new check: packet must be looped back internally */
if packet doesn't come from a loopback interface {
discard the packet
return
}
proceed to process the next header in the packet, whose type is
identified by the Next Header field in the Routing header
}
else if Hdr Ext Len is odd {
send an ICMP Parameter Problem, Code 0, message to the Source
Address, pointing to the Hdr Ext Len field, and discard the
packet
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}
else {
compute n, the number of addresses in the Routing header, by
dividing Hdr Ext Len by 2
if Segments Left is greater than n {
send an ICMP Parameter Problem, Code 0, message to the Source
Address, pointing to the Segments Left field, and discard the
packet
}
else {
decrement Segments Left by 1;
compute i, the index of the next address to be visited in
the address vector, by subtracting Segments Left from n
if Address [i] or the IPv6 Destination Address is multicast {
discard the packet
}
else {
/* new security check */
if Address [i] doesn't belong to one of the Mobile Network prefixes {
discard the packet
return
}
/* new check: keep MIPv6 behavior: prevent packets from being
* forwarded outside the node.
*/
if Segments Left equals 0 and Address[i] isn't the node's own
home address {
discard the packet
return
}
swap the IPv6 Destination Address and Address[i]
if the IPv6 Hop Limit is less than or equal to 1 {
send an ICMP Time Exceeded -- Hop Limit Exceeded in
Transit message to the Source Address and discard the
packet
}
else {
decrement the Hop Limit by 1
resubmit the packet to the IPv6 module for transmission
to the new destination;
}
}
}
}
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9.6 Decapsulation
A MR when decapsulating a packet from its HA must perform the
following checks
1. Destination address
The destination address of the inner packet must belong to one of
the Mobile Network prefixes.
10. Mobile Host Operation
When it is at Home, a Mobile Host issues packets with source set to
its home address and with destination set to its CN, in a plain IPv6
format.
When a MH is not at home but is attached to a foreign link in the
Fixed Infrastructure, it SHOULD use MIPv6 as opposed to this draft to
manage its mobility.
When a MH is visiting a foreign Mobile Network, it forwards its
outbound packets over the reverse tunnel (including RRH) to its HA.
One can view that operation as a first MR process applied on a plain
IPv6 packet issued by a LFN.
As a result, the encapsulating header include:
with source set to the MH COA and destination set to the MH HA
with slot 0 set to the MH Home Address
The inner packet is the plain IPv6 packet from the MH Home Address to
the CN.
11. Security Considerations
This section is not complete; further work is needed to analyse and
solve the security problems of record and source route.
Compared to MIPv6, the main security problem seems to be the fact
that the RRH can be modified in transit by an attacker on the path.
It has to be noted that such an attacker (for example any MR in the
Mobile Network) can perform more effective attacks than modifying the
RRH.
11.1 IPsec Processing
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The IPsec [7] AH [8] and ESP [9] can be used in tunnel mode to
provide different security services to the tunnel between a MR and
its HA. ESP tunnel mode SHOULD be used to provide confidentiality and
authentication to the inner packet. AH tunnel mode MUST be used to
provide authentication of the outer IP header fields, especially the
Routing Headers.
11.1.1 Routing Header type 2
Due to the possible usage of Doors [5] to enable IPv4 traversal, the
Routing Header type 2 cannot be treated as type 0 for the purpose of
IPsec processing (i.e. it cannot be included in its intierity in the
Integrity Check Value (ICV) computation, because NAT/PAT may mangle
one of the MR care-of-addresses along the HA-MR path.
The sender (the HA) will put the slot 0 entry (the MR Home Address)
of the RH as destination of the outer packet, will zero out
completely the Routing Header and will perform the ICV computation.
The receiver (the MR) will put the slot 0 entry as destination of the
outer packet, will zero out the Routing Header and will perform the
ICV verification.
11.1.2 Routing Header type 4
The Routing Header type 4 is "partially mutable", and as such can be
included in the Authentication Data calculation. Given the way type 4
is processed, the sender cannot order the field so that it appears as
it will at the receiver; this means the receiver will have to shuffle
the fields.
The sender (the MR) will zero out all the slots and the Segment Used
field of the RRH, and will put as source address of the outer packet
its Home Address, and then will perform the ICV computation.
The receiver (the HA) will put the entry in slot 0 (the MR Home
Address) in the source address and will zero out all the slots and
the Segment Used field of the RRH, and then will perform the ICV
verification.
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11.2 New Threats
The RH type 4 is used to construct a MIPv6 RH type 2 with additional
semantics, as described in Section 4.1. Since RH type 2 becomes a
multi hop option like RH type 0, care must be applied to avoid the
spoofing attack that can be performed with the IPv4 source route
option. This is why IPv6 [10] takes special care in responding to
packets carrying Routing Headers.
AH authenticates the MR Home Address identity and the RRH sequence
number. The RRH sequence number is to be used to check the freshness
of the RRH; anti-replay protection can be obtained if the receiver
enables the anti-replay service of AH [8].
In particular, if IPSec is being used, the content is protected and
can not be read or modified, so there is no point in redirecting the
traffic just to screen it.
Say a MR in a nested structure modifies the RRH in order to bomb a
target outside of the tree. If that MR forwards the packet with
itself as source address, the MR above it will make sure that the
response packets come back to the attacker first, since that source
is prepended to the RRH. If it forges the source address, then the
ingress filtering at the MR above it should detect the irregularity
and drop the packet. Same if the attacker is actually TLMR. The
conclusion is that ingress filtering is recommended at MR and AR.
Say that an attacker in the infrastructure and on the path of the
MRHA tunnel modifies the RRH in order to redirect the response
packets and bomb a target. Considering the position of the attacker -
a compromised access or core router - there's a lot more it could do
to send perturbations to the traffic, like changing source and
destinations of packets on the fly or eventually polute the routing
protocols.
Say a MR in a nested structure modifies the RH 2 in order to attack a
target outside of the tree. The RH type 2 forwarding rules make sure
that the packet can only go down a tree. So unless the attacker is
TLMR, the packet will not be forwarded. In any case, the attacker
will be bombed first.
Say that an attacker on the path of the MRHA tunnel modifies the RRH
in order to black out the MR. The result could actually be
accomplished by changing any bit in the packet since the IPSec
signature would fail, or scrambling the radio waves in the case of
wireless.
Selecting the tree to attach to is a security critical operation
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outside of the scope of this draft. Note that the MR should not
select a path based on trust but rather on measured service. If a
better bandwidth is obtained via an untrusted access using IPSec,
isn't it better than a good willing low bandwidth trusted access?
12. Acknowledgements
The authors wish to thank David Auerbach, Fred Baker, Dana Blair,
Steve Deering, Dave Forster, Thomas Fossati, Francois Le Faucheur,
Kent Leung, Massimo Lucchina, Vincent Ribiere, Dan Shell and Patrick
Wetterwald -last but not least :)-.
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References
[1] Johnson, D., Perkins, C. and J. Arkko, "Mobility Support in
IPv6", draft-ietf-mobileip-ipv6-24 (work in progress), July
2003.
[2] Ernst, T. and H. Lach, "Network Mobility Support Terminology",
draft-ietf-nemo-terminology-00 (work in progress), May 2003.
[3] Kniveton, T., "Mobile Router Tunneling Protocol",
draft-kniveton-mobrtr-03 (work in progress), November 2002.
[4] Deering, S. and B. Zill, "Redundant Address Deletion when
Encapsulating IPv6 in IPv6",
draft-deering-ipv6-encap-addr-deletion-00 (work in progress),
November 2001.
[5] Thubert, P., Molteni, M. and P. Wetterwald, "IPv4 traversal for
MIPv6 based Mobile Routers",
draft-thubert-nemo-ipv4-traversal-01 (work in progress), May
2003.
[6] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
[7] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[8] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
November 1998.
[9] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
(ESP)", RFC 2406, November 1998.
[10] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
[11] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998.
[12] Conta, A. and S. Deering, "Internet Control Message Protocol
(ICMPv6) for the Internet Protocol Version 6 (IPv6)
Specification", RFC 2463, December 1998.
[13] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by an
On-line Database", RFC 3232, January 2002.
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Authors' Addresses
Pascal Thubert
Cisco Systems Technology Center
Village d'Entreprises Green Side
400, Avenue Roumanille
Biot - Sophia Antipolis 06410
FRANCE
EMail: pthubert@cisco.com
Marco Molteni
Cisco Systems Technology Center
Village d'Entreprises Green Side
400, Avenue Roumanille
Biot - Sophia Antipolis 06410
FRANCE
EMail: mmolteni@cisco.com
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Appendix A. Optimizations
A.1 Path Optimization with RRH
The body of the draft presents RRH as a header that circulates in the
reverse tunnel exclusively. The RRH format by itself has no such
limitation. This section illustrates a potential optimization for
end-to-end traffic between a Mobile Network Node and its
Correspondent Node.
The MNN determines that it is part of a Mobile Network by screening
the Tree Information option in the RA messages from its Attachment
Router. In particular, the MNN knows the TreeDepth as advertised by
the AR. An initial test phase could be derived from MIPv6 to decide
whether optimization with a given CN is possible.
When an MNN performs end-to-end optimization with a CN, the MNN
inserts an empty RRH inside its packets, as opposed to tunneling them
home, which is the default behavior of a Mobile Host as described in
Section 10.
The number of slots in the RRH is initially the AR treeDepth plus 1,
but all slots are clear as opposed to the MR process as described in
Section 9. The source address in the header is the MNN address, and
the destination is the CN.
The AR of the MNN is by definition an MR. Since an RRH is already
present in the packet, the MR does not put the packets from the MNN
on its reverse tunnel, but acts as an intermediate MR; it adds the
source address of the packet (the MNN's address) in the RRH (in slot
0) and stamps its careOf instead in the IP header source address
field. Recursively, all the MRs on a nested network trace in path in
the RRH and take over the source IP.
The support required on the CN side extends MIPv6 in a way similar to
the extension that this draft proposes for the HA side. The CN is
required to parse the RRH when it is valid, refresh its BCE
accordingly, and include an RH type 2 with the full path to its
packets to the MNN.
Note that there is no Bind Update between the MNN and the CN. The RRH
must be secured based on tokens exchanged in the test phase. For the
sake of security, it may be necessary to add fields to the RRH or to
add a separate option in the Mobility Header.
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A.2 Packet Size Optimization
RRH allows to update the Correspondent BCE on a per packet basis,
which is the highest resolution that we can achieve. While this may
cope with highly mobile and nested configurations, it can also be an
overkill in some situations.
The RRH comes at a cost: it requires processing in all intermediate
Mobile Routers and in the Correspondent Node. Also, a RRH increases
the packet size by more than the size of an IP address per hop in the
Mobile Network.
This is why an additional Routing Header is proposed (type 3). The
semantics of type 3 are very close to type 4 but:
o Type 3 has only one slot, for the Home Address of the source.
o When it can not add the source to the RH type 3 of an outbound
packet, an intermediate MR:
* MR MUST NOT send ICMP (RRH too small)
* MUST NOT put the packet in a reverse tunnel
Rather, it simply overwrites the source and forwards the packet up
the tree as if the RRH had been properly updated.
o Since the path information is not available, the correspondent
MUST NOT update its BCE based on the RH type 3. The CN (or HA)
identifies the source from the entry in slot 0 and may reconstruct
the initial packet using the CareOf in slot 1 as source for AH
purposes.
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/* MR processing on outbound packet with RH type 3 support */
{
if no RH type 3 or 4 in outer header /* First Mobile Router specific */
or RH type 4 present but saturated { /* Need a nested encapsulation */
if RRH is saturated {
do ICMP back (RRH too small)
}
/* put packet in sliding reverse tunnel */
insert new IP header plus RRH
set source address to the MR Home Address
set destination address to the MR Home Agent Address
add an RRH with all slots zeroed out
compute IPsec AH on the resulting packet
}
/* All MRs including first */
if packet size > MTU {
do ICMP back (Packet too Big)
} else if RRH {
select first free slot in RRH bottom up
set it to source address from IP header
overwrite source address in IP header with MR CareOf
transmit packet
} else if RH type 3 {
if slot 0 is still free {
/* this is end-to-end optimization */
set it to source address from IP header
}
overwrite source address in IP header with MR CareOf
transmit packet
}
}
A.2.1 Routing Header Type 3 (Home Address option replacement)
This is an RH-based alternative to the Home Address destination
option. Its usage is described in Appendix A.2.
The decision to send RH type 3 or type 4 is up to the source of the
RRH. Several algorithms may apply, one out of N being the simplest.
IPsec HA processing is done as described in Section 11.1 for Type 4.
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The Type 3 Routing Header has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type=3| Segments Used |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Home Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header
8-bit selector. Identifies the type of header immediately
following the Routing header. Uses the same values as the IPv4
Protocol field [13].
Hdr Ext Len
8-bit unsigned integer. Length of the Routing header in 8-octet
units, not including the first 8 octets. For the Type 3 Routing
header, Hdr Ext Len is always 2.
Routing Type
8-bit unsigned integer. Set to 3.
Segment Used
8-bit unsigned integer. Number of slots used. Either 0 or 1. When
the field is zero, then there is no MR on the path and it is valid
for a CN that does not support RRH to ignore this header.
Reserved
32-bit reserved field. Initialized to zero for transmission;
ignored on reception.
Home Address
128-bit home address of the source of the packet.
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Appendix B. Multi Homing
B.1 Multi-Homed Mobile Network
Consider difference between situation A and B in this diagram:
===?== ==?===
MR1 MR2
| |
==?=====?== ==?====== situation A
MR3 MR4 MR5
| | |
=== === ===
===?== ==?===
MR1 MR2
| |
==?=====?=======?====== situation B
MR3 MR4 MR5
| | |
=== === ===
Going from A to B, MR5 may now choose between MR1 and MR2 for its
Attachment (default) Router. In terms of Tree Information, MR5, as
well as MR3 and MR4, now sees the MR1's tree and MR2's tree. Once MR5
selects its AR, MR2, say, MR5 belongs to the associated tree and
whether MR1 can be reached or not makes no difference.
As long as each MR has a single default router for all its outbound
traffic, 2 different logical trees can be mapped over the physical
configurations in both situations, and once the trees are
established, both cases are equivalent for the processing of RRH.
Note that MR5 MUST use a CareOf based on a prefix owned by its AR as
source of the reverse tunnel, even if other prefixes are present on
the Mobile Network, to ensure that a RH type 2 can be securely routed
back.
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B.2 Multihomed Mobile Router
Consider the difference between situation B and C in this diagram:
===?== ==?===
MR1 MR2
| |
==?=====?=======?====== situation B
MR3 MR4 MR5
| | |
=== === ===
==? ?==
MR1
|
==?=====?=======?====== situation C
MR3 MR4 MR5
| | |
=== === ===
In situation C, MR2's egress interface and its properties are
migrated to MR1. MR1 has now 2 different Home Addresses, 2 Home
Agents, and 2 active interfaces.
If MR1 uses both CareOf addresses at a given point of time, and if
they belong to different prefixes to be used via different attachment
routers, then MR1 actually belongs to 2 trees. It must perform some
routing logic to decide whether to forward packets on either egress
interface. Also, it MUST advertise both tree information sets in its
RA messages.
The difference between situations C and B is that when an attached
router (MR5, say) selects a tree and forwards egress packets via MR1,
it can not be sure that MR1 will actually forward the packets over
that tree. If MR5 has selected a given tree for a specific reason,
then a new source route header is needed to enforce that path on MR1.
The other way around, MR5 may leave the decision up to MR1. If MR1
uses the same attachment router for a given flow or at least a given
destination, then the destination receives consistent RRHs.
Otherwise, the BCE cache will flap, but as both paths are valid, the
traffic still makes it through.
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Appendix C. Changes from Previous Version of the Draft
From -02 to -03
reworded the security part to remove an ambiguity that let the
reader think that RRH is unsafe.
From -01 to -02
Made optional the usage of ICMP warning "RRH too small" (Section
5).
Changed the IPsec processing for Routing Header type 2 (Section
11.1).
From -00 to -01
Added new Tree Information Option fields:
A 8 bits Bandwidth indication that provides an idea of the
egress bandwidth.
A CRC-32 that changes with the egress path out of the tree.
a 32 bits unsigned integer, built by each MR out of a high
order configured preference and 24 bits random constant. This
can help as a tie break in Attachment Router selection.
Reduced the 'negative' part of the lollipop space to 0..255
Fixed acknowledgements (sorry Patrick :)
Changed the type of Tree Information Option from 7 to 10.
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