[Docs] [txt|pdf] [Tracker] [Email] [Diff1] [Diff2] [Nits]
Versions: 00 01 02 03 04 05 06 07
Network Working Group P. Thubert
Internet-Draft M. Molteni
Expires: August 18, 2007 Cisco Systems
February 14, 2007
IPv6 Reverse Routing Header and its application to Mobile Networks
draft-thubert-nemo-reverse-routing-header-07
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 18, 2007.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Thubert & Molteni Expires August 18, 2007 [Page 1]
Internet-Draft The Reverse Routing Header February 2007
Abstract
NEMO basic support enables Mobile Networks by extending Mobile IP to
Mobile Routers. In the case of nested Mobile Networks, this involves
the overhead of nested tunnels between the Mobile Routers and their
Home Agents, and causes a number of security issues.
This proposal alleviates those problems as well as other minor ones,
by using a source routing within the mobile nested structure,
introducing a new routing header, called the reverse routing header.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Recursive complexity . . . . . . . . . . . . . . . . . . . 4
2. Terminology and Assumptions . . . . . . . . . . . . . . . . . 6
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 7
3. An Example . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. New Routing Headers . . . . . . . . . . . . . . . . . . . . . 12
4.1. Routing Header Type 2 (MIPv6 RH with extended
semantics) . . . . . . . . . . . . . . . . . . . . . . . . 12
4.2. Routing Header Type 4 (The Reverse Routing Header) . . . . 14
4.3. Extension Header order . . . . . . . . . . . . . . . . . . 17
5. Optimum number of slots in RRH . . . . . . . . . . . . . . . . 19
6. Reverse Routability test . . . . . . . . . . . . . . . . . . . 21
7. Modifications to IPv6 Neighbor Discovery . . . . . . . . . . . 22
7.1. Modified Router Advertisement Message Format . . . . . . . 22
8. MIPv6 flows . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.1. DHAAD . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.2. Binding Updates . . . . . . . . . . . . . . . . . . . . . 23
9. Home Agent Operation . . . . . . . . . . . . . . . . . . . . . 24
10. Mobile Router Operation . . . . . . . . . . . . . . . . . . . 26
10.1. Processing of ICMP "RRH too small" . . . . . . . . . . . . 26
10.2. Processing of ICMP error . . . . . . . . . . . . . . . . . 27
10.3. Processing of RHH for Outbound Packets . . . . . . . . . . 27
10.4. Processing of the extended Routing Header Type 2 . . . . . 28
10.5. Decapsulation . . . . . . . . . . . . . . . . . . . . . . 30
Thubert & Molteni Expires August 18, 2007 [Page 2]
Internet-Draft The Reverse Routing Header February 2007
11. Mobile Host Operation . . . . . . . . . . . . . . . . . . . . 31
12. Security Considerations . . . . . . . . . . . . . . . . . . . 32
12.1. IPsec Processing . . . . . . . . . . . . . . . . . . . . . 32
12.1.1. Routing Header type 2 . . . . . . . . . . . . . . . . 32
12.1.2. Routing Header type 4 . . . . . . . . . . . . . . . . 32
12.2. New Threats . . . . . . . . . . . . . . . . . . . . . . . 34
13. IANA considerations . . . . . . . . . . . . . . . . . . . . . 36
14. Protocol Constants . . . . . . . . . . . . . . . . . . . . . . 37
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 38
16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39
16.1. informative reference . . . . . . . . . . . . . . . . . . 39
16.2. normative reference . . . . . . . . . . . . . . . . . . . 39
Appendix A. Optimizations . . . . . . . . . . . . . . . . . . . . 41
A.1. Path Optimization with RRH . . . . . . . . . . . . . . . . 41
A.2. Packet Size Optimization . . . . . . . . . . . . . . . . . 42
A.2.1. Routing Header Type 3 (Home Address option
replacement) . . . . . . . . . . . . . . . . . . . . 43
Appendix B. Multi Homing . . . . . . . . . . . . . . . . . . . . 46
B.1. Multi-Homed Mobile Network . . . . . . . . . . . . . . . . 46
B.2. Multihomed Mobile Router . . . . . . . . . . . . . . . . . 47
Appendix C. Changes from Previous Version of the Draft . . . . . 48
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 50
Intellectual Property and Copyright Statements . . . . . . . . . . 51
Thubert & Molteni Expires August 18, 2007 [Page 3]
Internet-Draft The Reverse Routing Header February 2007
1. Introduction
This document assumes that the reader is familiar with the Mobile
Networks terminology defined in [9] and [1], with Mobile IPv6 defined
in [10], and with the NEMO basic support defined in [11].
Generally a Mobile Network may be either solid (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, telescopic 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 introduces a new Routing Header (RH), called the Reverse
Routing Header (RRH), to perform source routing within the mobile
structure. RRH is a variant of IPv4 Loose Source and Record Route
(LSRR) [12] 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 from Mobile IPv6 [10]. 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.
Thubert & Molteni Expires August 18, 2007 [Page 4]
Internet-Draft The Reverse Routing Header February 2007
If this was done, then each CN, by receiving all the binding messages
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
Thubert & Molteni Expires August 18, 2007 [Page 5]
Internet-Draft The Reverse Routing Header February 2007
2. Terminology and Assumptions
2.1. Terminology
This document assumes that the reader is familiar with Mobile IPv6 as
defined in [10] and with the concept of Mobile Router defined in the
NEMO terminology document [1]. In particular, the "Nested Mobility
Terms" introduced in the NEMO terminology are repeatedly used in this
document.
Solid 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 Solid Mobile Network can
be either singly or multi-homed. A Solid Mobile Network may be
composed of more then one link and may interconnect several
routers, but all routers in the Solid Mobile Network are fixed
with respect to each other.
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
|
===============
IPv6 Mobile Host:
A IPv6 Host, with support for MIPv6 MN, and the additional NEMO
capability described in this draft.
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.
Thubert & Molteni Expires August 18, 2007 [Page 6]
Internet-Draft The Reverse Routing Header February 2007
Inbound direction:
direction from outside the Mobile Network to inside
Outbound direction:
direction from inside the Mobile Network to outside
RRH:
Reverse Routing Header, defined in this specification
NULL RRH:
A NULL RRH is an RRH with a null "Segments Used" field
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 Solid 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.
Thubert & Molteni Expires August 18, 2007 [Page 7]
Internet-Draft The Reverse Routing Header February 2007
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 Solid 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 [11], we would have three
bi-directional nested tunnels:
-----------.
--------/ /-----------.
-------/ | | /--------
CN ------( - - | - - - | - - - | - - - | - - (----- LFN
MR3_HA -------\ | | \-------- MR3
MR2_HA --------\ \----------- MR2
MR1_HA ----------- MR1
Thubert & Molteni Expires August 18, 2007 [Page 8]
Internet-Draft The Reverse Routing Header February 2007
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 5. 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 | | | | |
+-------+-------++ -- ++----+-------+-------+---------+ +-------
Thubert & Molteni Expires August 18, 2007 [Page 9]
Internet-Draft The Reverse Routing Header February 2007
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 9, 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 | | | | |
+-------+-------++ -- ++----+-------+-------+---------+ +-------
Thubert & Molteni Expires August 18, 2007 [Page 10]
Internet-Draft The Reverse Routing Header February 2007
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 [10], 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 12.2.
MR1, which is the initial destination in the IP header, looks at the
RH and processes it according to Section 10, 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 10 and sends it to LFN. The packet that reaches
LFN is the plain IPv6 packet that was sent by CN.
Thubert & Molteni Expires August 18, 2007 [Page 11]
Internet-Draft The Reverse Routing Header February 2007
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 [10],
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 [13]. 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 9; the processing by the MRs is described in Section 10.4;
and the security aspects are treated in Section 12.2.
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 10.4, otherwise it will operate as
prescribed by IPv6 [13] when the routing type is unrecognized.
Thubert & Molteni Expires August 18, 2007 [Page 12]
Internet-Draft The Reverse Routing Header February 2007
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 [14].
Thubert & Molteni Expires August 18, 2007 [Page 13]
Internet-Draft The Reverse Routing Header February 2007
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 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) [12] 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
Thubert & Molteni Expires August 18, 2007 [Page 14]
Internet-Draft The Reverse Routing Header February 2007
the Tree Information Option described in Section 5.
Thubert & Molteni Expires August 18, 2007 [Page 15]
Internet-Draft The Reverse Routing Header February 2007
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 [14].
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
Thubert & Molteni Expires August 18, 2007 [Page 16]
Internet-Draft The Reverse Routing Header February 2007
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 [13] 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.
Thubert & Molteni Expires August 18, 2007 [Page 17]
Internet-Draft The Reverse Routing Header February 2007
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
Thubert & Molteni Expires August 18, 2007 [Page 18]
Internet-Draft The Reverse Routing Header February 2007
5. Optimum number of slots in RRH
If its current Attachment Router conforms to Tree Discovery as
specified in [2], a MR knows its current tree depth from the Tree
Information Option (RA-TIO). The maximum number of slots needed in
the RRH is the same value as the MR's own tree depth (that is the
TreeDepth as received from the AR incremented by one).
When sending a Binding Update, a MR always reinitializes the number
of slots in the RRH to the maximum of DEF_RRH_SLOTS and its tree
depth, if the latter is known from a reliable hint such as RA-TIO.
The message may have a number of unused (NULL) slots, when it is
received by the Home Agent. The HA crops out the extra entries in
order to send a RH of type 2 back with its response. The RH type 2
in the resulting Binding Ack contains the number of required slots
that the MR now uses until it gets a hint that the topology changes
or until the next Binding update.
In the case of a NULL RRH, the HA does not include a RH 2 at all.
This may happen in the process of a DHAAD message (see Section 8.1)
The number of slots in the RRH MUST NOT be larger than MAX_RRH_SLOTS.
If a MR is deeper in a tree then MAX_RRH_SLOTS, the packets will be
reencapsulated by a MR up high in the tree, or dropped, depending on
that MR security policy.
In runtime, it may happen that the RRH has fewer slots than required
for 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 had a wrong representation of the topology.
To solve this problem a new ICMP message is introduced, "RRH
Warning", type 64. A MR on the tree egress path that gets a packet
without a free slot in the RRH MAY send that ICMP "RRH warning" back
to the MR that inserted the RRH in the first place.
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 NOT be
larger than MAX_RRH_SLOTS. 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.
Thubert & Molteni Expires August 18, 2007 [Page 19]
Internet-Draft The Reverse Routing Header February 2007
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 10.3).
Checksum
The ICMP checksum [15].
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.
Thubert & Molteni Expires August 18, 2007 [Page 20]
Internet-Draft The Reverse Routing Header February 2007
6. Reverse Routability test
Compared to [10], the RRH models presents an opening for an attack
against the CoA or any address in the RRH. This risk is discussed in
Section 12.2.
For deployments where this risk is acceptable, MR and HA can proceed
as described further in the draft, and in particular, enable any
packet with proper authentication to update the RRH in the Binding
Cache Entry.
For other deployments, this risk might be unacceptable. This section
presents a mechanism that SHOULD be present in all implementations,
and configurable as an option in the Home Agent. The mechanism
expects that all binding messages are subject to proper
authentication
The mechanism, when configured, works like this:
When a HA receives a BU with a change in either the CoA or any entry
in the RRH, it will reject the binding with a status code 135
"Sequence number out of window". The HA stores the RRH and the CoA
in a transit zone inside the binding cache entry. The HA also forges
a new Sequence Counter that it places in the BA as a challenge.
Upon the BA with status code 135 "Sequence number out of window", the
MR builds a new BU with the resynchronized Sequence Number, and a
Routing Header of type 4.
Upon receiving a BU that matches the information in the transit zone
(same CoA, same RRH, valid sequence), the HA accepts the BU and
updates its binding cache entry information as described further in
this document.
When the mechanism is triggered, the HA does not accept to update its
binding cache when a packet indicates a change in the CoA or the RRH,
but drops the packet instead.
Thubert & Molteni Expires August 18, 2007 [Page 21]
Internet-Draft The Reverse Routing Header February 2007
7. Modifications to IPv6 Neighbor Discovery
7.1. Modified Router Advertisement Message Format
Mobile IPv6 [10] modifies the format of the Router Advertisement
message [16] 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 [16]:
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.
Thubert & Molteni Expires August 18, 2007 [Page 22]
Internet-Draft The Reverse Routing Header February 2007
8. MIPv6 flows
8.1. DHAAD
Conforming MIPv6 [10], a MR normally does not identify itself in its
DHAAD messages, using a Home Address option. For the same reason, a
RRH with a Home address in slot 0 is not required here, either. Yet,
this specification allows a MR to send its DHAAD messages with a NULL
RRH, as opposed to no RRH at all.
This is generally useful if the attachment router is not bound yet,
for whatever reason, and more specifically in the case of the Mobile
Home Network as described in [3]. In the latter case, an HA is
mobile and may happen to be located under one of its MRs (within its
subtree), which is a dead lock for the NEMO basic support..
Since MRs may forward packets with an RRH even if themselves are not
bound yet, the packets from nested MRs can be forwarded and the
responses are source routed back, allowing the nested MRs to bind.
In particular, if a nested MR is also a mobile Home Agent, it becomes
reachable from its own MRs, which breaks the deadlock.
Also, this alleviates the need for the attachment router to forward
DHAAD messages across its own MRHA tunnel.
HAs MUST respond by reversing the RRH into a RH2 if a RRH is present
and not NULL. A NULL RRH is ignored.
8.2. Binding Updates
A MIPv6 or NEMO Binding Update provides more information than just
the path in the nested cloud so they are still used as described in
MIPv6 [10] for Home Registration and de-registration. The only
difference when using a RRH is that the Home Address Destination
Option and the alternate CareOf MIP option MUST be omitted.
The Binding Update flow is also used to update the optimum size of
the RRH, as described in Section 5.
The HA MUST save the RRH in its binding cache, either in the original
form or in the form of an RH type 2, ready to be added to the tunnel
header of the MRHA packets. The RRH format is very close to that of
the RH type 2, designed to minimize the process of the transmutation.
Thubert & Molteni Expires August 18, 2007 [Page 23]
Internet-Draft The Reverse Routing Header February 2007
9. Home Agent Operation
This section inherits from chapter 10 of MIPv6 [10], 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 [10] 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/ESP
authentication.
As further explained in Section 8.2, 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 12.2, 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.
Thubert & Molteni Expires August 18, 2007 [Page 24]
Internet-Draft The Reverse Routing Header February 2007
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
reverse Routability test transit zone: a candidate RRH and a
challenge sequence counter.
This draft extends [10] 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 [11], 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).
Thubert & Molteni Expires August 18, 2007 [Page 25]
Internet-Draft The Reverse Routing Header February 2007
10. Mobile Router Operation
This section inherits from chapter 11 of [10], 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 [10] 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 [11]. But, as opposed to the
NEMO Basic Support, nested tunnels are generally avoided.
10.1. 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.
Thubert & Molteni Expires August 18, 2007 [Page 26]
Internet-Draft The Reverse Routing Header February 2007
10.2. 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.
10.3. Processing of RHH for Outbound Packets
The forwarding of a packet with a non saturated RRH consists in fact
in passing the hot potato to the attachment router, which does not
require the MRHA tunnel to be up.
So, it happens as soon as a MR has selected its attachment router and
before the binding flow has actually taken place. Also, this process
is much safer since the packet is not forwarded home.
Thubert & Molteni Expires August 18, 2007 [Page 27]
Internet-Draft The Reverse Routing Header February 2007
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 if bound */
if reverse tunnel is established {
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
} else return
}
/* All MRs including first, even if not bound home */
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)
}
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 12.1.
10.4. Processing of the extended Routing Header Type 2
if Segments Left = 0 {
Thubert & Molteni Expires August 18, 2007 [Page 28]
Internet-Draft The Reverse Routing Header February 2007
/* 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
}
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 MNP {
discard the packet
return
}
/* new check: keep MIPv6 behavior prevent packets from being
* forwarded outside the node.
*/
if Segments Left is 0 and Address[i] isn't the node's own
home address {
discard the packet
return
}
swap the IPv6 Destination Address and Address[i]
Thubert & Molteni Expires August 18, 2007 [Page 29]
Internet-Draft The Reverse Routing Header February 2007
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;
}
}
}
}
10.5. 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.
Thubert & Molteni Expires August 18, 2007 [Page 30]
Internet-Draft The Reverse Routing Header February 2007
11. 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.
Thubert & Molteni Expires August 18, 2007 [Page 31]
Internet-Draft The Reverse Routing Header February 2007
12. Security Considerations
This section is not complete; further work is needed to analyze 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.
12.1. IPsec Processing
The IPsec [17] AH [18] and ESP [19] 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.
12.1.1. Routing Header type 2
Due to the possible usage of Doors [4] 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 intirety 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 validation.
12.1.2. 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.
Thubert & Molteni Expires August 18, 2007 [Page 32]
Internet-Draft The Reverse Routing Header February 2007
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.
Thubert & Molteni Expires August 18, 2007 [Page 33]
Internet-Draft The Reverse Routing Header February 2007
12.2. 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 [13] 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 [18].
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 pollute 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
Thubert & Molteni Expires August 18, 2007 [Page 34]
Internet-Draft The Reverse Routing Header February 2007
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?
Yet, the CoA and the RRH are not protected on the way and might be
modified by a rogue router in the middle. Also, if proper SeND [20]
is not in place in the visited network, the MR might be fooled into
autoconfiguring a CoA from a prefix that does not exist or is not
actually there. This draft proposes in Section 6 an optional Reverse
Routability test to confirm that the MR is reachable at the CoA via
the RRH.
Thubert & Molteni Expires August 18, 2007 [Page 35]
Internet-Draft The Reverse Routing Header February 2007
13. IANA considerations
This document requires IANA to define 2 new IPv6 Routing Header
types.
Thubert & Molteni Expires August 18, 2007 [Page 36]
Internet-Draft The Reverse Routing Header February 2007
14. Protocol Constants
DEF_RRH_SLOTS: 7
MAX_RRH_SLOTS: 10
Thubert & Molteni Expires August 18, 2007 [Page 37]
Internet-Draft The Reverse Routing Header February 2007
15. 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 :)-.
Thubert & Molteni Expires August 18, 2007 [Page 38]
Internet-Draft The Reverse Routing Header February 2007
16. References
16.1. informative reference
[1] Ernst, T. and H. Lach, "Network Mobility Support Terminology",
draft-ietf-nemo-terminology-06 (work in progress),
November 2006.
[2] Thubert, P., "Nested Nemo Tree Discovery",
draft-thubert-tree-discovery-04 (work in progress),
November 2006.
[3] Thubert, P., "NEMO Home Network models",
draft-ietf-nemo-home-network-models-06 (work in progress),
February 2006.
[4] 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.
[5] Devarapalli, V., "Local HA to HA protocol",
draft-devarapalli-mip6-nemo-local-haha-01 (work in progress),
March 2006.
[6] Giaretta, G. and A. Patel, "Problem Statement for bootstrapping
Mobile IPv6", draft-ietf-mip6-bootstrap-ps-05 (work in
progress), May 2006.
[7] Ernst, T., "Network Mobility Support Goals and Requirements",
draft-ietf-nemo-requirements-06 (work in progress),
November 2006.
[8] Ng, C., "Analysis of Multihoming in Network Mobility Support",
draft-ietf-nemo-multihoming-issues-06 (work in progress),
June 2006.
16.2. normative reference
[9] Manner, J. and M. Kojo, "Mobility Related Terminology",
RFC 3753, June 2004.
[10] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
[11] Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert,
"Network Mobility (NEMO) Basic Support Protocol", RFC 3963,
January 2005.
Thubert & Molteni Expires August 18, 2007 [Page 39]
Internet-Draft The Reverse Routing Header February 2007
[12] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[13] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
[14] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by an On-
line Database", RFC 3232, January 2002.
[15] Conta, A. and S. Deering, "Internet Control Message Protocol
(ICMPv6) for the Internet Protocol Version 6 (IPv6)
Specification", RFC 2463, December 1998.
[16] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998.
[17] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[18] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
November 1998.
[19] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
(ESP)", RFC 2406, November 1998.
[20] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
Thubert & Molteni Expires August 18, 2007 [Page 40]
Internet-Draft The Reverse Routing Header February 2007
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 11.
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 10. 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.
Thubert & Molteni Expires August 18, 2007 [Page 41]
Internet-Draft The Reverse Routing Header February 2007
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.
Thubert & Molteni Expires August 18, 2007 [Page 42]
Internet-Draft The Reverse Routing Header February 2007
/* MR processing on outbound packet with RH type 3 support */
{
if no RH type 3 or 4 in outer header /* Case of first MR */
or RH type 4 present but saturated { /* Causing nested encap */
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 12.1 for Type 4.
Thubert & Molteni Expires August 18, 2007 [Page 43]
Internet-Draft The Reverse Routing Header February 2007
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 [14].
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.
Thubert & Molteni Expires August 18, 2007 [Page 44]
Internet-Draft The Reverse Routing Header February 2007
Home Address
128-bit home address of the source of the packet.
Thubert & Molteni Expires August 18, 2007 [Page 45]
Internet-Draft The Reverse Routing Header February 2007
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.
Thubert & Molteni Expires August 18, 2007 [Page 46]
Internet-Draft The Reverse Routing Header February 2007
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.
Thubert & Molteni Expires August 18, 2007 [Page 47]
Internet-Draft The Reverse Routing Header February 2007
Appendix C. Changes from Previous Version of the Draft
From -06 to -07
Added a reverse Routability test.
From -04 to -05
Tree Information option: now a reference to a separate draft.
Removed RRH heartbeat.
Added a DHAAD section
Clarified how RRH solves the mobile home deadlock.
new section "Optimum number of slots in RRH" from ICMP section
From -03 to -04
TI option: renamed the F (fixed) flag bit to G (grounded).
Binding Update: Made clear that the BU flow conforms MIPv6 and
NEMO but that RRH replaces both Home address Option and Alternate
CareOf option.
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 12.1).
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.
Thubert & Molteni Expires August 18, 2007 [Page 48]
Internet-Draft The Reverse Routing Header February 2007
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.
Thubert & Molteni Expires August 18, 2007 [Page 49]
Internet-Draft The Reverse Routing Header February 2007
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
Thubert & Molteni Expires August 18, 2007 [Page 50]
Internet-Draft The Reverse Routing Header February 2007
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Thubert & Molteni Expires August 18, 2007 [Page 51]
Html markup produced by rfcmarkup 1.129d, available from
https://tools.ietf.org/tools/rfcmarkup/