Network Working Group P. Thubert

Network Working Group P. Thubert
Request for Comments: 4887 Cisco Systems
Category: Informational R. Wakikawa
Keio University and WIDE
V. Devarapalli
Azaire Networks
July 2007

Network Mobility Home Network Models

Status of This Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Copyright Notice

Copyright (C) The IETF Trust (2007).

Abstract

This paper documents some of the usage patterns and the associated
issues when deploying a Home Network for Network Mobility (NEMO)-
enabled Mobile Routers, conforming to the NEMO Basic Support. The
aim here is specifically to provide some examples of organization of
the Home Network, as they were discussed in NEMO-related mailing
lists.

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RFC 4887 Home Network Models with NEMO Basic July 2007

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Concepts . . . . . . . . . . . . . . . . . . . 4
3. General Expectations . . . . . . . . . . . . . . . . . . . . . 4
4. MIP Home Network . . . . . . . . . . . . . . . . . . . . . . . 5
5. NEMO Extended Home Network . . . . . . . . . . . . . . . . . . 5
5.1. Configuration . . . . . . . . . . . . . . . . . . . . . . 5
5.2. Returning Home . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Home Address from MNP . . . . . . . . . . . . . . . . . . 7
5.4. Deployment Caveats . . . . . . . . . . . . . . . . . . . . 8
5.4.1. Mobile Router Side . . . . . . . . . . . . . . . . . . 8
5.5. Applicability . . . . . . . . . . . . . . . . . . . . . . 8
6. NEMO Aggregated Home Network . . . . . . . . . . . . . . . . . 8
6.1. Configuration . . . . . . . . . . . . . . . . . . . . . . 8
6.2. Returning Home . . . . . . . . . . . . . . . . . . . . . . 9
6.2.1. Returning Home with the Egress Interface . . . . . . . 10
6.2.2. Returning Home with the Ingress Interface . . . . . . 10
6.3. Applicability . . . . . . . . . . . . . . . . . . . . . . 11
6.4. Deployment Caveats . . . . . . . . . . . . . . . . . . . . 11
6.4.1. Home Agent Side . . . . . . . . . . . . . . . . . . . 11
6.4.2. Mobile Router Side . . . . . . . . . . . . . . . . . . 11
7. NEMO Virtual Home Network . . . . . . . . . . . . . . . . . . 12
7.1. Configuration . . . . . . . . . . . . . . . . . . . . . . 12
7.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 14
8. NEMO Mobile Home Network . . . . . . . . . . . . . . . . . . . 14
8.1. Configuration . . . . . . . . . . . . . . . . . . . . . . 14
8.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 17
9. Security Considerations . . . . . . . . . . . . . . . . . . . 17
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
11.1. Normative References . . . . . . . . . . . . . . . . . . . 17
11.2. Informative References . . . . . . . . . . . . . . . . . . 18

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1. Introduction

This document assumes that the reader is familiar with IPv6 Mobility
as defined by Mobile IPv6 and the Network Mobility (NEMO) Basic
Support. In order to read this document properly, it is important to
realize that in NEMO, the Home Network can encompass much more than
the Home Link, as it spans the Home Link and all the Links that the
Mobile Routers (MRs) carry with them. Exactly how the two concepts
relate in a given deployment depends on the organization of the Home
Network, as described below.

Five different organizations of the Home Network including a
hierarchical construction are documented:

MIPv6 Home Network: A short reminder of what the Home Network is
with Mobile IP, in order to help the reader figure out the
evolution toward NEMO.

NEMO Extended Home Network: In this arrangement, the Home Network is
only 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. More in Section 5.

NEMO Aggregated Home Network: In this arrangement, 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. More in Section 6.

Virtual Home Network: In this arrangement, there is no physical Home
Link at all for the Mobile Routers to come back home to. More in
Section 7.

NEMO Mobile Home Network: In this arrangement, there is a bitwise
hierarchy of Home Networks. A global Home Network is advertised
to the infrastructure by a head Home Agent (HA) 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. More in Section 8.

In all cases, the Home Agents collectively advertise only the
aggregation of the Mobile Networks. The subnetting is kept within
the Home Agents and the Mobile Routers, as opposed to advertised by
means of routing protocols to other parties.

The examples provided here aim at illustrating the NEMO Basic Support
[5] but do not aim at limiting its scope of application; additional
cases may be added in the future.

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RFC 4887 Home Network Models with NEMO Basic July 2007

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 RFC 2119 [2].

Most of the mobility-related terms used in this document are defined
in the Mobility Related Terminology document [3] and in the Mobile
IPv6 (MIP6) specification [4].

In addition, some terms were created or extended for NEMO. These
specific terms are defined in the Mobile Network Terminology document
[6]:

Home Link

Home Network

Home Address

MRHA Tunnel

Mobile Aggregated Prefix

Aggregated Home Network

Extended Home Network

Virtual Home Network

Mobile Home Network

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, consider the case where the aggregation has a global
routing prefix of m = 48 bits (A:B:C::/48), with a subnet ID size of
n = 16 bits (n + m = 64):

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When a Mobile Router, MR1, uses the Mobile Network Prefix (MNP) A:B:
C:1::/64 with the NEMO Basic Support, MR1 may register using a Home
Address from the Home network (i.e., A:B:C:0::1) or a Home Address
from one of its MNPs (i.e., A:B:C:1::1) depending on the deployment.

In a given deployment, one subnet may be reserved for the Home Link
(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
advertises the virtual network.

The following sections provide additional information on these forms
of Home Network.

4. MIP Home Network

In the Mobile IPv6 (MIP6) specification [4], Mobile Nodes are at home
when they are connected to their Home Link, where they recognize
their Home Prefix in Router Advertisement messages. Also, a binding
is checked using Duplicate Address Detection (DAD) on the Home Link,
and Home Agents discover each other by means of Neighbor Discovery
(ND) extensions over that link.

The Home Prefix that is advertized on the Home Link is a final
prefix, as opposed to an aggregation, and it may be used by hosts on
the Home Link for autoconfiguration purposes.

As we see, the concept of a Home Network for Mobile IPv6 is really a
prefix on a link, served by one or more Home Agents as opposed to a
routed mesh. We will see in the next sections that NEMO needs
additional prefixes for use by the Mobile Networks. For that reason,
NEMO extends the concept of Home Network into a more complex,
aggregated structure.

5. NEMO Extended Home Network

5.1. Configuration

One simple way of extending the MIP Home Network is to use additional
prefixes, contiguous to the Home Link Prefix inherited from MIPv6, as
Mobile Network Prefixes. As this model trivially extends the MIP
Home Network, the resulting aggregation is called a NEMO Extended
Home Network. It is depicted in Figure 1.

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|
route v /48 A:B:C::/48

HA
| /64 Home Link: A:B:C:0::/64
--+-----+--+- . -+- . -+--
| | | |
MR1 MR2 MRi MRN
| | | |
------ ------ ------ ------
/64 /64 /64 /64 MNP: A:B:C:i::/64

Extended Home Network
<----------------------------------------------------------->

Home Net Mobile Net Mobile Net ... Mobile Net
<------------><------------><------------> ... <------------>

Figure 1: Extended Home Network

In that arrangement:

o There is one physical Home Network and multiple Mobile Networks

o The Home Prefix and the MNPs are tailored to allow for IPv6
Stateless Address Autoconfiguration with typical interface
identifier length for the type of interface (for example, can be
/64).

o The prefix length of the Extended Home Network is shorter than
that of the Home Network and the MNPs, since it is an aggregation
(for example, can be /48).

o Since the Extended Home Network operations inherit trivially from
MIPv6, it can be seen as natural that the Mobile Routers be
assigned their Home Addresses from the prefix on the Home Link.
In that case, a Home Agent can perform DAD on the Home Link as
prescribed by Mobile IPv6 for the Mobile Router Home Addresses
(MRHAs).

5.2. 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.

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When at home, the Mobile Router ensures the connectivity of the
Mobile Network using standard router operations.

In implicit mode, the Home Agent has the necessary information to
continue routing to the MNPs in the absence of registration, assuming
that the Mobile Router is at home, and the participation of the
Mobile Router to the home Interior Gateway Protocol (IGP) is not
required.

But in explicit mode, or if the Mobile Router uses an IGP over the
MRHA tunnel, then it needs to resume its IGP operations on the Home
Link in order to advertise its Mobile Networks to the HA, unless some
other means such as static routes are deployed to cover the case.

Alternative procedures for ensuring the connectivity of the Mobile
Networks when at home are described in Section 7.

5.3. Home Address from MNP

We saw that a natural extension of the MIP procedure is to derive the
Home Address of a Mobile Router from the prefix on the Home Link.
Alternatively, NEMO basic support allows that a Mobile Router forms
its Home Address from one of its Mobile Network Prefixes.

In that case, the Home Address does not match the Home Link Prefix,
and there is a need to configure the Home Agent in a specific mode
with the support for the Extended Home Network and the range of the
Mobile Network Prefixes. Based on that new configuration, the Home
Agent can accept a Home Address that is not from the Home Link, and
it will know that it should not perform any DAD.

Also, if the Mobile Router uses a Home Address that is derived from
its MNP, some specific support is required on the Mobile Router as
well. In order to determine that it is at home, the Mobile Router
recognizes the well-known prefix of its Home Agent as opposed to
matching the prefix on the Home Link with that of its Home Address.

When connecting to the Home Link, the Mobile Router also need to
autoconfigure an address on the Egress interface as opposed to
assigning its home Address to the interface.

For all these reasons, this submode of Extended Home Network is not a
trivial extension of the MIPv6 Home Model, and it might not be
compatible with all implementations.

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5.4. Deployment Caveats

5.4.1. Mobile Router Side

In explicit mode, the routing to the MNP via the Mobile Router must
be restored when the Mobile Router is at home. This is normally
performed by the Mobile Router by means of the existing IGP. In that
case, a specific support is required on the Mobile Router to control
the routing protocol operation, enabling the participation in the IGP
if and only if the Mobile Router is at home.

The NEMO Basic Support does not mandate a specific routing protocol
though the support for some well-known routing protocols can be
expected from many implementations. An implementation might provide
an automatic toggle to start/stop routing on an egress interface when
the mobile router comes back/leaves home. When such a toggle is
unavailable, then a specific interface should be reserved to attach
to home with the appropriate settings for security and routing.

5.5. Applicability

The Extended Home Network keeps the MIP6 concept of a Home Network
for both Mobile Nodes and Mobile Routers to take their Home Address
from. Since there is no overlap between the prefixes that are
assigned to MNPs and prefix(es) that are dedicated to the Home Link,
it is possible for MNs and Mobile Routers to coexist with that model.

Also, when the Home Address is derived from the prefix on the Home
Link, the Home Agent behavior on the link trivially extends that of
MIP and the support for that configuration should be available with
all implementations.

There are a number of issues with returning home when a Mobile Router
configures its Home Address from the MNP as described in Section 5.3.
Therefore, we do not recommend this mechanism if the Mobile Routers
attach to the Home Network.

6. NEMO Aggregated Home Network

6.1. Configuration

One other approach is to consider that the aggregation of all the
MNPs is used plainly as the Home Link Prefix. In this model, the
Home Network is referred to as a NEMO 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, as depicted in
Figure 2.

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HA
| /56 Aggreg /56
--+-----+--+- . -+- . -+--
| | | |
MR1 MR2 MRi MRN
| | | |
------ ------ ------ ------
/64 /64 /64 /64 Aggreg|i /64 0 < i <= N

Aggregated Home Network == Home Network
<----------------------------------------------------------->

Mobile Net Mobile Net Mobile Net ... Mobile Net
<------------><------------><------------> ... <------------>

Figure 2: Aggregated Home Network

In that model, it seems natural to subnet the whole range of
addresses into Mobile Network prefixes, as opposed to reserving one
prefix for the Home Link, which would boil down to the Extended Home
Network model. If the prefix on the Home Link is really an
aggregation and not a final prefix, it should not be allowed for
autoconfiguration or Home Address allocation.

Note that in that case, it makes sense for a Mobile Router to
register using a Home Address from one of its own MNPs. Taking the
Home Address from its own range guarantees the uniqueness of the
suffix. That uniqueness can be checked by the Mobile Router on its
Ingress network (see [3]) using DAD.

6.2. 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.

When the Mobile Router forms its Home Address out of one of its MNPs,
since the Home Network prefix is an aggregation that encompasses all
the MNPs, the Home Address actually matches both prefixes. To
properly identify the Home Network as it returns home, the MR must
expect a shorter prefix length than that of the MNP from which the
Home Address was formed.

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6.2.1. Returning Home with the Egress Interface

A Mobile Router coming home via its Egress interface sees overlapping
prefixes between the Ingress and the Egress interfaces and some
specific support may be needed:

When a Mobile Router connects to the Home Link using its Egress
Interface, it might set up a bridge between its Ingress interface(s)
and the Home Link, if the interfaces are compatible.

Alternatively, the Mobile Router might perform ND proxying for all
addresses in its MNPs, between the Egress interface and the related
Ingress interface, as described in [8]. Since the prefixes on the
Egress and Ingress interfaces are overlapping, routing is disallowed.

The Mobile Router does not need to join the local IGP when returning
home, even if it is using the explicit Prefix Mode. When the Mobile
Router is not registered, the Home Agent simply expects that all
Mobile Network Nodes (MNNs) will be reachable over the Home Link.

HA
|
-------+--+--- /56
|
Egress |
MR at home
|
--+--- /64

Figure 3: Bridging between Egress and Ingress

6.2.2. Returning Home with the Ingress Interface

Alternatively, if the Mobile Router has a single Ingress interface,
the Mobile Router may use the NEMO-Link to connect to the Home Link,
merging the two links in a single consistent network.

HA
|
-------+-+---- /56
|
---+-- /64
|
MR at home
Egress |

Figure 4: Merging the Home and the Mobile Networks

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This fits the connected route model, since the Aggregated Home
Network is truly located on that network. Note that in that case, it
makes sense for a Mobile Router to register using a Home Address from
one of its own MNPs.

6.3. Applicability

With this model, there is no specific space for independent nodes, as
any address in the aggregation belongs to a MNP, and thus to a Mobile
Router. This configuration excludes the cohabitation with MIP6 MNs
on the Home Link.

6.4. Deployment Caveats

6.4.1. Home Agent Side

A node on the Home Link receiving a Router Advertisement that
includes the Aggregated Home Network prefix might use that prefix for
Address Autoconfiguration. Such a node would 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 would look up all MNNs on that MNP
using Neighbor Discovery over its interface to the Home Link, and
fail.

Thus, on the Home Link, the Home Agent must intercept all the packets
for ALL the Mobile Network Nodes on the registered prefixes; that is,
for ALL nodes attached to Mobile Routers that are away from home.
This should be a layer 2 operation, rather than layer 3. The Home
Agent might, for example, perform some form of ND proxying for all
addresses in all registered Mobile Network Prefixes.

The Home Agent must also protect the MNP space from autoconfiguration
by uncontrolled visitors at Neighbor Discovery level.

There is a need to provide a specific configuration on the Home Agent
to specify that it operates in Aggregated Mode. If a Home Agent
implementation is simply derived from that of MIP, then the
capability to perform the required proxying might not exist, and the
Aggregated Mode will not operate properly for nodes on the Home Link.

6.4.2. Mobile Router Side

If the Mobile Router returns home by Egress, a specific support is
required to control the bridging operation depending on whether or
not a Mobile Router is at home. This support might not be present in
all implementations.

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The NEMO Basic Support does not mention a specific behavior for
bridging though bridging capabilities can be expected from many
implementations. An implementation might provide an automatic toggle
to start/stop bridging on an Egress interface when the Mobile Router
comes back/leaves home. When such a toggle is unavailable, then a
specific interface should be reserved to attach to home with the
appropriate settings for security and bridging.

Also, note that NEMO authorizes multiple registrations for a same MNP
by different Mobile Routers. This is a case of multihoming, and it
normally means that the Mobile Routers are interconnected by the
Ingress network that bears the common MNP. But there is no provision
in NEMO Basic Support to test that this condition is met at binding
time and maintained over time.

It is thus possible for 2 different Mobile Routers to register the
same prefix with different Home Addresses, and this will cause an
undetected problem if the corresponding Ingress interfaces are not
connected.

When the Home Address of a Mobile Router is derived from its MNP,
there is thus an additional risk of an undetected misconfiguration if
the Home Address is autoconfigured from the Ingress interface as
opposed to statically assigning an address and MNP.

A Mobile Router that is at home must own an address from the
aggregation on its Egress interface and an address from its MNP -- a
subnet of that aggregation -- on its Ingress interface. A pure
router will reject that configuration, and the Mobile Router needs to
act as a bridge to use it. In order to deploy the Aggregated Home
Network model, one must check whether that support is available in
the Mobile Routers if returning home is required.

7. NEMO Virtual Home Network

7.1. Configuration

The Home Link can be configured on the Home Agent on a virtual link,
in which case there is no physical Home Link for Mobile Routers to
return home to, or for Home Agents to discover each other and perform
the ND-level interactions on, as described in Mobile IPv6 [4].

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/48 e.g.: A:B:C::/48
HA
| /64 A:B:C::/64
--+-----+--+- . -+- . -+--
| | | |
MR1 MR2 MRi MRN
/64 /64 /64 /64 A:B:C:i::/64 0 < i <= N

Figure 5: Virtual Home Network

The Extended Home Network and the Aggregated Home Network models can
be adapted for virtual links.

As in the case of a physical link, the Home Address of a Mobile
Router can be constructed based on a dedicated subnet of the Home
Prefix or one of the Mobile Router MNPs.

Note that since the Home Address is never checked for DAD, it makes
the configuration easier to take it from the MNP as opposed to a
specific subnet.

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 [4]).

There are also some drawbacks to the Virtual Home Link approach:

RFC 3775 [4] and RFC 3963 [5] do not provide the specific support
for a Mobile Node to emulate returning home on a Virtual Home
Network. In particular, in the case of NEMO, the routing
information from the Mobile Router being injected on the IGP might
adversely affect IPv6 route aggregation on the Home Network.

There can be only one Home Agent since Mobile IPv6 relies on
Neighbor Discovery on the Home Link for other Home Agent discovery
and for Duplicate Address Detection.

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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.

Suggestions on how to perform an equivalent of returning home on a
Virtual Home Network have been proposed, but this topic is outside of
the scope of this document.

7.2. Applicability

NEMO operations rely on ND extensions over the Home Link for the Home
Agent to Home Agent communication.

Making the Home Link virtual bars the deployment of multiple Home
Agents, which may be desirable for reasons of load balancing. Please
refer to the NEMO multihoming issues [9] for more on this.

Yet, for a deployment where a single Home Agent is enough, making the
Home Link virtual reduces the vulnerability to some attacks and to
some hardware failures, while making the Home Agent operation faster.

Note that NEMO basic does not mandate the support of Virtual Home
Networks.

8. NEMO Mobile Home Network

8.1. Configuration

In this arrangement, 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
MNPs, 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 this is the Cab Co configuration. Cab Co is a taxi
company that uses a /32 prefix for its Home Network, this prefix
being advertised by the company headquarters (HQ). Regional offices
are deployed around the country. Even though these regional offices

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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.

To illustrate this configuration, we make up the prefixes to reflect
their role, like CAB:C0::/32 for the Home Network:

global Home Network CAB:C0::/32 advertised 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

Figure 6: CAB Company HQ Configuration

Finally, each regional office owns a number of taxis, each one
equipped with a mobile router and an associated /64 prefix.

For each Office, say San Francisco (SFO) as an example:

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Mobile Home Network CAB:C0:5F0::/48 owned by SFO office
<------------------------------------------------------------------>

SFO Home Network Mobile Networks for taxis
for taxis <---------------------...--------------------->
CAB:C0:5F0:5F0::/64 CAB:C0:5F0:CAB1::/64 CAB:C0:5F0:....::/64
<-------------------><-------------------> ... <------------------->
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 Address
of CAB 1

Figure 7: CAB Company regional configuration

Note that this is a hierarchy in terms of MR-HA relationship, which
may not be reflected in the physical arrangement of nodes at a given
point of time. For instance, in the Cab Co case, some SFO cabs might
attach to any hot spot or Cab Co office in a different city, and the
SFO office might be at home if it is co-located with the
headquarters. But note that SFO should never attach to one of its
own cabs. This would create a stalemate situation, as documented in
the NEMO Route Optimization (RO) problem statement [7].

But it is also possible to reflect the organizational hierarchy in a
moving cloud of Mobile Routers. If a Mobile Home Agent acts as
root-MR for a nested configuration of its own Mobile Routers, then
the communication between Mobile Routers is confined within the
nested structure.

This can be illustrated in the case of a fleet at sea. Assume that
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 its own cabs, the
communication between cabs is relayed by SFO and does not require the
satellite link. As for traffic to the outside of the nested NEMO,
SFO recursively terminates the nested tunnels from its cabs and
reencapsulates all the packets between the nested cloud and
correspondents in the infrastructure in a single tunnel to CA5A. As
a result, the unwanted effect of nesting of tunnels is avoided over
the Internet part of the packet path.

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RFC 4887 Home Network Models with NEMO Basic July 2007

8.2. Applicability

This complex topology applies to a large distributed fleet, mostly if
there is a single interchange point with the Internet (e.g., a
Network Address Transition (NAT) or a SOCKS [1] server farm) where
the super Home Agent could be located.

One specific benefit is that when 2 Mobile Routers travel together
with a common Home Agent, the traffic between the 2 is not
necessarily routed via the infrastructure, but can stay confined
within the mobile cloud, the Mobile Home Agent acting as a rendezvous
point between the Mobile Routers. This applies particularly well for
a fleet at sea when the long-haul access may be as expensive as a
satellite link.

9. Security Considerations

This document only explains how a Home Network can be deployed to
support Mobile Routers and does not introduce any additional security
concerns. Please see RFC 3963 [5] for security considerations for
the NEMO Basic Support protocol.

10. Acknowledgements

The authors wish to thank Erik Nordmark, Jari Arkko, Henrik
Levkowetz, Scott Hollenbeck, Ted Hardie, David Kessens, Pekka Savola,
Kent Leung, Thierry Ernst, TJ Kniveton, Patrick Wetterwald, Alexandru
Petrescu, and David Binet for their contributions.

11. References

11.1. Normative References

[1] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and L.
Jones, "SOCKS Protocol Version 5", RFC 1928, March 1996.

[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.

[3] Manner, J. and M. Kojo, "Mobility Related Terminology",
RFC 3753, June 2004.

[4] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.

[5] Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert,
"Network Mobility (NEMO) Basic Support Protocol", RFC 3963,
January 2005.

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RFC 4887 Home Network Models with NEMO Basic July 2007

[6] Ernst, T. and H. Lach, "Network Mobility Support Terminology",
July 2007.

11.2. Informative References

[7] Ng, C., Thubert, P., Watari, M., and F. Zhao, "Network Mobility
Route Optimization Problem Statement", RFC 4888, July 2007.

[8] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, April 2006.

[9] Ng, C., "Analysis of Multihoming in Network Mobility Support",
Work in Progress, February 2007.

Authors' Addresses

Pascal Thubert
Cisco Systems
Village d'Entreprises Green Side
400, Avenue de Roumanille
Batiment T3, Biot - Sophia Antipolis 06410
FRANCE

Phone: +33 4 97 23 26 34
EMail: [email protected]

Ryuji Wakikawa
Keio University and WIDE
5322 Endo Fujisawa Kanagawa
252-8520
JAPAN

EMail: [email protected]

Vijay Devarapalli
Azaire Networks
3121 Jay Street
Santa Clara, CA 94054
USA

EMail: [email protected]

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RFC 4887 Home Network Models with NEMO Basic July 2007

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