Network Mobility P. Thubert
Internet-Draft Cisco Systems
Expires: August 14, 2004 R. Wakikawa
Keio University
V. Devarapalli
Nokia
February 14, 2004
Examples of basic Nemo usage
draft-thubert-nemo-basic-usages-01
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This paper documents some practical scenarios and the associated
issues when deploying Mobile Routers, conforming the Nemo Basic
Support draft [7].
The aim here is specifically to provide some examples of organization
of the Home Network, as they were discussed in the Nemo and Nemo
Design mailing lists.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and concepts . . . . . . . . . . . . . . . . . . . 4
3. General Expectations . . . . . . . . . . . . . . . . . . . . . 6
4. Extended Home Network . . . . . . . . . . . . . . . . . . . . 7
4.1 Returning Home . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Aggregated Home . . . . . . . . . . . . . . . . . . . . . . . 9
5.1 Returning Home . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Virtual Home Network . . . . . . . . . . . . . . . . . . . . . 11
7. Mobile Home . . . . . . . . . . . . . . . . . . . . . . . . . 13
8. Changes from version 00 to 01 . . . . . . . . . . . . . . . . 15
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 17
A. Returning Home emulation in the virtual case . . . . . . . . . 18
Intellectual Property and Copyright Statements . . . . . . . . 19
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1. Introduction
This document assumes that the reader is familiar with Mobile IPv6 as
defined in [6], and with the concept of Mobile Router defined in the
Nemo terminology document [9].
Four different organizations of the Home Network including a
hierachical construction are documented:
Extended Home Network: In this disposition, the Home Network is but
one subnet of a larger aggregation that encompasses the Mobile
Networks, called extended Home Network. When at Home, a Mobile
Router performs normal routing between the Home Link and the
Mobile Networks.
Aggregated Home Network: In this disposition, the Home Network
actually overlaps with the Mobile Networks. When at Home, a Mobile
Router acts as a bridge between the Home Link and the Mobile
Networks.
Virtual Home Network: In this disposition, there is no physical Home
Link at all for the Mobile Routers to come back Home to.
Mobile Home Network: In this disposition, there is a bitwise
hierarchy of Home Networks. A global Home Network is advertised to
the infrastructure by a head Home Agent and further subnetted into
Mobile Networks. Each subnet is owned by a Mobile Router that
registers it in a Nemo fashion while acting as a Home Agent for
that network.
In all cases, the Home Agents collectively advertise only the
aggregation of the Mobile Networks. The dichotomy is kept within the
Home Agents and the Mobile Routers, as opposed to advertised by means
of routing protocols to other parties.
Also, it is valid for a Mobile Router to register using an address
from one of its own Mobile Network Prefixes in all three cases.
The examples provided here aim at illustrating the Nemo Basic Support
draft [7] but are by no mean at limiting its scope of application.
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2. Terminology and concepts
The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this document are to be
interpreted as described in RFC2119 [5].
The following terms used in this document are defined in the IPv6
Addressing Architecture document [4]:
link-local unicast address
link-local scope multicast address
The following terms used in this document are defined in the mobile
IPv6 specification [6]:
home agent (HA)
The following terms used in this document are defined in the mobile
network terminology document [9]:
mobile router (MR)
mobile network
mobile host (MH)
This draft uses the following additional or modified terminology:
Home Link: The link attached to the interface at the Home Agent on
which the Home Prefix is configured. The interface can be a
virtual interface, in which case the Home Link is a virtual Home
Link.
Home Network: The Network formed by the application of the Home
Prefix on the Home Link. With Nemo, the concept of Home Network is
extended as explained below.
Home Address: With Mobile IPv6, a Home Address is derived from the
Home Network prefix. This is generalized in Nemo, with some
limitations: A Home Address can be either derived from the Home
Network or from one of the Mobile Router's Mobile Network
prefixes.
MRHA Tunnel: The bi-directional tunnel between a Mobile Router and
its Home Agent
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Mobile Aggregated Prefix: An aggregation of Mobile Network Prefixes.
Aggregated Home Network: The Home Network associated with a Mobile
Aggregated Prefix. This Aggregation is advertised as a subnet on
the Home Link, and thus used as Home Network for Nemo purposes.
Extended Home Network: The network associated with the aggregation of
one or more Home Network(s) and Mobile Network(s). As opposed to
the Mobile IPv6 Home Network that is a subnet, the extended Home
Network is an aggregation and is further subnetted.
Virtual Home Network: The Home Network associated with a Virtual
Network. The Extended Home Network and the Aggregated Home Network
can be configured as Virtual Home Network.
Mobile Home Network: A Mobile Network that is also a Home Network.
The MR that own the Mobile Network Prefix acts as a Home Agent for
it.
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3. General Expectations
With Mobile IPv6, the Home Network is generally a physical network
interconnecting the Home Agents, and the Mobile Nodes that are at
Home. Nemo extends the concept of Home so that it is not only a flat
subnet composed of Home Addresses but an aggregation that is itself
subnetted in mobile and Home Networks. This aggregation is still
referred to as Home.
As an example, say that the aggregation has a global routing prefix
of m = 48 bits (A:B:C::/48), with subnet ID size of n = 16 bits ( n +
m = 64).
Say that a Mobile Router, MR1, owns the Mobile Network Prefix
A:B:C:1::/64: With basic Nemo, and depending on the deployment, MR1
may register using a Home Address from the Home network, A:B:C:0::1,
say, or a Home Address, A:B:C:1::1, say, from one of its Mobile
Network Prefixes.
In a given deployment, one subnet may be reserved for the Home Link
(say A:B:C:0::/64) while the others are attributed to Mobile Routers
as Mobile Networks (as A:B:C:1::/64 for MR1). Another approach could
be to configure the Aggregation of Mobile Networks as the subnet on
the Home Link, and let the Mobile Routers manage the overlapping
networks. Finally, the aggregation could be configured on a virtual
network, with no physical Home Link at all, in which case Home means
topologically and administratively close to the Home Agent that owns
the virtual network.
The following sections provide additional information on these forms
of Home Network:
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4. Extended Home Network
One simple approach can be to reserve one or several subnets from an
aggregation for the Home Link, and to use the other subnets as Mobile
Network Prefixes. In that case, the Home Network and the Mobile
Networks do not overlap. The aggregation is called an extended Home
Network.
|
route v /48 A:B:C::/48
HA
| /64 A:B:C:0::/64
--+-----+--+- . -+- . -+--
| | | |
MR1 MR2 MRi MRN
/64 /64 /64 /64 A:B:C:i::/64 0 < i <= N
extended Home Network
<----------------------------------------------------------->
Home Net Mobile Net Mobile Net ... Mobile Net
<------------><------------><------------> ... <------------>
In that configuration:
o There is one physical Home Network and multiple Mobile Networks
o The Home and the Mobile Network prefixes are tailored to allow for
IPv6 Stateless Address Autoconfiguration with typical interface
identifier length for the type of interface (can be for example /
64).
o The prefix length of the extended Home Network is shorter than
that of the Home Network and the Mobile Network prefixes, since it
is an aggregation (can be for example /48).
o The Mobile Routers are assigned individually a Home Address from
the Home Network and use is to register their Mobile Network
Prefix(es). In that case, the Home Agent performs DAD in the Home
Network as prescribed by Mobile IPv6 for the Home Addresses.
o Alternatively, a Mobile Router could also form a Home Address from
one of its prefixes and use it to register, performing its own DAD
on its ingress network.
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4.1 Returning Home
In the extended Home Network model, the Home Network is configured on
a physical interface of the Home Agent, the Home Link.
A Mobile Router returns Home by connecting directly to the Home Link,
and dropping the MRHA tunnel.
If the Home Address of the Mobile Router is derived from one of its
Mobile Networks, then the MR may connect to the Home Link using an
egress interface and autoconfigure an address on the Home Link. The
MR recognizes the prefix of its Home Agent in order to decide that it
is Home. Note that in that case the Home Address does not match the
Home Prefix.
When at Home, the Mobile Router ensures the connectivity of the
Mobile Network using standard router operations.
In particular, if the HA has the necessary information to continue
routing to the Mobile Network Prefixes in the absence of
registration, for instance if the Home Address of the Mobile Router
is derived from the Home Network, and if the HA uses a static route
to the Mobile Network Prefix(es) via that address, then the
participation of the MR to the Home IGP is not required.
But in the general case, when the MR is at Home, it resumes IGP
operations on the Home Link in order to advertise its Mobile
Networks.
Alternate procedures for ensuring the connectivity of the Mobile
Networks when at Home are described in Section 6. In Particular, it
is
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5. Aggregated Home
One other approach is to consider that the Aggregation of all the
mobile network prefixes is used plainly as the Home Network, refered
to as the Aggregated Home Network. This means that the Mobile
Aggregated Prefix is configured on the Home Link and advertised by
the Home Agent as a subnet.
HA
| /56 Aggreg /56
--+-----+--+- . -+- . -+--
| | | |
MR1 MR2 MRi MRN
------ ------ ------ ------
/64 /64 /64 /64 Aggreg|i /64 0 < i <= N
Aggregated Home
<----------------------------------------------------------->
Mobile Net Mobile Net Mobile Net ... Mobile Net
<------------><------------><------------> ... <------------>
Note: a Mobile Router coming Home sees overlapping prefixes between
the ingress and the egress interface and some specific support may be
needed.
A node on the Home Link will compute that the Aggregated Home Network
is actually a subnet on the Home Link and may use it for
autoconfiguration purposes. Such a node may also install a connected
route to the Aggregated Home Network over the Home Link.
As a result, unless the node has a better (longest match) route to a
given Mobile Network Prefix, it will lookup all MNNs using Neighbor
Discovery over the Home Link.
Thus, the Home Agent MUST intercept all the packets to the MNNs on
the registered prefixes. In order to do so, the Home Agent MAY
perform ND proxying for all addresses in all registered Mobile
Network Prefixes, and protect the Mobile Network Prefix space from
autoconfiguration by uncontrolled visitors on the Home Link.
Alternatives based on a routing protocol or ICMP redirect may apply
in some cases.
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5.1 Returning Home
The Aggregated Home Prefix is configured on a physical interface of
the Home Agent, the Home Link. As a consequence, the Home Agent has a
connected route to the Aggregated Home Network over the Home Link.
A Mobile Router returns Home by connecting directly to the Home Link,
and dropping the MRHA tunnel. The Mobile Router recognizes its Home
Link by a prefix match with its Home Agent. Note that it must expect
a shorter prefix than that of its Mobile Networks, even if its Home
Address is formed out of one of its Mobile Network Prefixes, but that
the Home Address matches the Home Network Prefix.
When a Mobile Router connects to the Home Link using its egress
interface, it MAY set up a bridge between its ingress interface(s)
and the Home Link. Alternatively, the Mobile Router MAY perform ND
proxying for all addresses in its Mobile Network Prefixes, between
the egress and the related ingress interface. Since the prefixes on
the egress and ingress interfaces are overlapping, routing is
disallowed.
HA
| /56 Aggreg /56
--+-----+--+- . -+- . -+--
| | | |
MR1 MR2 MRi MRN
------ ------ ------ ------
/64 /64 /64 /64 Aggreg|i /64 0 < i <= N
Bridging between egress and ingress
Alternatively, if the MR has a single ingress Interface, the Mobile
Router may use the Mobile Link to connect to the Home Link, merging
the two links in a single consistent network.
HA
| /56 Aggreg /56
--+-----+--+- . -+- . -+--
/64 /64 /64 /64 Aggreg|i /64 0 < i <= N
------ ------ ------ ------
MR1 MR2 MRi MRN
| | | |
Merging the Home and the Mobile Networks
This fits the connected route model, since the Aggregated Home is
truly located on that network.
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6. Virtual Home Network
The Home Link can be configured on the Home Agent on a virtual link,
in which case there's no physical Home Link for Mobile Routers to
return Home or for Home Agents to discover each others and perform
the ND level interactions as described in Mobile IPv6. [6]
/48 eg: A:B:C::/48
HA
| /64 A:C:C:E::/64
--+-----+--+- . -+- . -+--
| | | |
MR1 MR2 MRi MRN
/64 /64 /64 /64 A:B:C:i::/64 0 < i <= N
Virtual Home Network
The Extended Home network and the Aggregated Home network models can
be adapted for virtual links. There is no change in the way Home
Addresses are allocated. As in the case of a physical link, the Home
Address of a Mobile router is constructed based on the Home Prefix or
one of the prefixes of its Mobile Network(s).
There are certain advantages to making the Home Link a virtual link:
A virtual link may not experience any disruption related to
physical maintenance or to hardware problems, so it is more
available than a physical link. The high availability of the Home
Link is critical for the mobility service.
The Home Agent does not have to defend the Mobile Router's Home
Address through Proxy Neighbor Discovery. The Home Agent does not
also have to perform Duplicate Address Detection (DAD) for the
Mobile Router's Home Address when it receives a Binding Update
from the Mobile Router.
The Mobile Router does not have to implement the Returning Home
procedure (section 11.5.4 of Mobile IPv6. [6]).
In order for a Mobile Router to emulate returning Home, it can
connect to one or more access link(s) configured for that purpose on
the Home Agent. The Mobile Router, after connecting to the access
link, SHOULD not send any routing protocol updates on the egress
interface because the routing information from the Mobile Router
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might adversely affect IPv6 route aggregation on the Home Network.
However, the Mobile Router must register its binding as if it was
accessing a foreign link.
There are also some drawbacks to the virtual Home Link approach:
There can be only one Home Agent since Mobile IPv6 relies on
Neighbor Discovery on the Home Link for other HA discovery and for
Duplicate Address Detection.
The Home Agent must maintain a Binding Cache entry for a Mobile
Router and forwarding state for its Mobile Network even when the
Mobile Router is directly connected to it. All traffic to and from
the Mobile Network is sent through the bi-directional tunnel
regardless of the Mobile Router location. This results in a
tunneling overhead even though the Mobile Router is connected to
the Home Network.
Some solutions can be proposed in order to perform an equivalent of
returning Home on a virtual Home Network. One such approach is
sketched in appendix as an illustration.
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7. Mobile Home
In this disposition, there is a bitwise hierarchy of Home Networks. A
global Home Network is advertised to the infrastructure by a head
Home Agent(s) and further subnetted into Mobile Networks. As a
result, only the Home Agent(s) responsible for the most global
(shortest prefix) aggregation receive all the packets for all the
Mobile Network prefixes, which are leaves in the hierarchy tree.
Each subnet is owned by a Mobile Router that registers it in a Nemo
fashion while acting as a Home Agent for that network. This Mobile
Router is at Home at the upper level of hierarchy. This configuration
is referred to as Mobile Home.
An example of that is the Cab Co configuration. Say a Taxi Company
owns a /32 prefix. This prefix is advertised at a fixed point, the
Headquarters say. Regional offices are deployed around the world.
Even though these regional offices are relatively stable in terms of
location and prefix requirement -say this changes every few years-
making them mobile allows a simpler management when a move has to
take place, or should the ISP service change. Finally, each regional
office owns a number of taxis, each one equipped with a mobile router
and an associated /64 prefix.
To illustrate this, here is a possible addressing scheme:
global Home Network CAB:C0::/32 owned by HQ
<------------------------------------------------------------------->
HQ extended Home Net Mobile Home for SFO office
(casa)
CAB:C0:CA5A::/48 CAB:C0:5F0::/48
<----------------------------> ... <-------------------------------->
|
Home for offices HQ |
CAB:C0:CA5A:CA5A::/64 MN |
<----------------------><----> |
CAB:C0:CA5A:CA5A::CA5A |
CAB:C0:CA5A:CA5A::CA5B |
are HAs on link with for each office a route like |
|
CAB:C0:CA5A:CA5A::5F0 <---------------------- via
is the Home addr
of SFO office
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and recursively for each Office, say San Francisco (SFO) as example:
Mobile Home Network CAB:C0:5f0::/48 owned by SFO office
<------------------------------------------------------------------>
HQ Home Network Mobile Networks for taxis
for offices
CAB:C0:5F0:5F0::/64 CAB:C0:5F0:CAB1::/64 CAB:C0:5F0:....::/6
<-------------------><-------------------> ... <------------------->
CAB:C0:5F0:5F0::5F0 |
is HA on link with for |
each taxi a route like |
|
CAB:C0:5F0:5F0::CAB1 <------ via
is the Home addrSsync
of CAB 1
Note that the hierarchy occurs at a configuration level and may not
be reflected in the actual connection between nodes. For instance in
the Cab Co case, cabs are roaming within the city, each one attaching
to a different hot spot, while the regional office is connected to
the infrastructure using some ISP connection.
But it is also possible to reflect the organizational hierarchy in a
moving cloud of Mobile Router. If a Mobile Home Agent acts as root-MR
for a nested configuration of its own MRs, then the communication
between MRs is confined within the nested structure.
This can be illustrated in the case of a fleet at sea. Say that now
SFO is a communication ship of a fleet, using a satellite link to
join the infrastructure, and that the cabs are Mobile Routers
installed on smaller ships, equipped with low range radios.
If SFO is also the root-MR of a nested structure of cabs, the
communication between cabs is relayed by SFO and does not require the
satellite link. SFO recursively terminates the nested tunnels to the
cabs and reencapsulates all the packets between the nested cloud and
correspondents in the infrastructure in a single tunnel to CA5A, this
providing for nested Nemo Route Optimization.
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8. Changes from version 00 to 01
Added Mobile Home Section
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9. Acknowledgements
The authors wish to thank:
Erik Nordmark, Kent Leung, Thierry Ernst, TJ Kniveton, Patrick
Wetterwald and Alexandru Petrescu for their contributions.
References
[1] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
[2] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998.
[3] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[4] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6)
Addressing Architecture", RFC 3513, April 2003.
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[6] Johnson, D., Perkins, C. and J. Arkko, "Mobility Support in
IPv6", draft-ietf-mobileip-ipv6-24 (work in progress), July
2003.
[7] Devarapalli, V., "Nemo Basic Support Protocol",
draft-ietf-nemo-basic-support-02 (work in progress), December
2003.
[8] Ernst, T., "Network Mobility Support Goals and Requirements",
draft-ietf-nemo-requirements-01 (work in progress), May 2003.
[9] Ernst, T. and H. Lach, "Network Mobility Support Terminology",
draft-ietf-nemo-terminology-00 (work in progress), May 2003.
[10] Wakikawa, R., Devarapalli, V. and P. Thubert, "Inter Home
Agents Protocol (HAHA)", draft-wakikawa-mip6-nemo-haha-00 (work
in progress), October 2003.
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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
Ryuji Wakikawa
Keio University and WIDE
5322 Endo Fujisawa Kanagawa
252-8520
JAPAN
EMail: ryuji@sfc.wide.ad.jp
Vijay Devarapalli
Nokia Research Center
313 Fairchild Drive
Mountain View, CA 94043
USA
EMail: vijay.devarapalli@nokia.com
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Appendix A. Returning Home emulation in the virtual case
When a Home Link is virtual, all traffic to and from the Mobile
Network is sent through the bi-directional tunnel even at the Home
Link. This section describes one possible mechanism that extends
basic Nemo to eliminate this tunneling overhead.
Although the Home Link is virtual, the Home Agent has at least one
physical link to communicate with the external world. One or several
of such links, called the virtual Home Access Links, are conceptually
associated with the virtual Home Link and considered as part of Home.
When accessing one of its virtual Home Access Links, a Mobile Router
autoconfigures a Care-of Address from a Router Advertisement as it
would do on any visited link, in order to perform the next binding
flow.
If the Mobile Router is configured to recognize the virtual Home
Access Links as part of Home, it deregisters by sending a Binding
update with null lifetime sourced at the CareOf. Alternatively, the
Home Agent may indicate that the MR has moved to the virtual Home
Access Links as a status code in the binding acknowledgement. The
status code implies that Home Agent successsful de-register the
binding at the virtual Home Access Link. Detection of the virtual
Home Access Links is achieved by a prefix comparison(s) between the
care-of address and the prefix(es) on the virtual Home Access
Link(s).
With both approaches, the result of the binding flow is a
deregistration. Consequently, both the Mobile Router and the Home
Agent disable the bi-directional tunnel. At that point, the Home
Agent configures its forwarding in order to reach the Mobile Router
and its mobile networks at Home. For instance, this may take the form
of a route to the Mobile Network prefixes via the MR Home Address,
and a connected host route to the MR Home Address via the virtual
Home Access link.
After successful binding de-registration, the Mobile Router MUST
receive packets meant to the Mobile Router's Home Address at the
Virtual Home Link. How to intercept packets addressed to the Home
Address depends on implementations of the Mobile Router. If the Home
Address is not configured at the egress interface, the Mobile Router
MUST use proxy Neighbor Discovery to intercept all packets addressed
to the Home Address on the virtual Home Link. Otherwise, the Mobile
Router does not have to perform any special operation at the virtual
Home Link.
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