Network mobility support is concerned with managing the mobility of
an entire network. This arises when a router connecting a network to
the Internet dynamically changes its point of attachment to the fixed
infrastructure, thereby causing the reachability of the entire
network to be changed in relation to the fixed Internet topology.
Such a network is referred to as a mobile network. Without
appropriate mechanisms to support network mobility, sessions
established between nodes in the mobile network and the global
Internet cannot be maintained after the mobile router changes its
point of attachment. As a result, existing sessions would break and
connectivity to the global Internet would be lost.
This document defines the specific terminology needed to describe the
problem space, the design goals , and the solutions for network
mobility support. This terminology aims to be consistent with the
usual IPv6 terminology  and the generic mobility-related terms
already defined in the Mobility Related Terminology  and in the
Mobile IPv6 specification . Some terms introduced in this
document may only be useful for defining the problem scope and
functional requirements of network mobility support.
Note that the abbreviation NEMO stands for either "a NEtwork that is
MObile" or "NEtwork MObility". The former (see Section 2.1) is used
as a noun, e.g., "a NEMO" meaning "a mobile network". The latter
(see Section 7) refers to the concept of "network mobility", as in
"NEMO Basic Support", and is also the working group's name.
Section 2 introduces terms to define the architecture, while terms
needed to emphasize the distinct functionalities of those
architectural components are described in Section 3. Section 4,
Section 5, and Section 6 describe terms pertaining to nested
mobility, multihoming, and different configurations of mobile
networks at home, respectively. The different types of mobility are
defined in Section 7. The last section lists miscellaneous terms
that do not fit into any other section.
2. Architectural Components
A mobile network is composed of one or more mobile IP-subnets and is
viewed as a single unit. This network unit is connected to the
Internet by means of one or more mobile routers (MRs). Nodes behind
the MR (referred to as MNNs) primarily comprise fixed nodes (nodes
unable to change their point of attachment while maintaining ongoing
sessions), and possibly mobile nodes (nodes able to change their
point of attachment while maintaining ongoing sessions). In most
cases, the internal structure of the mobile network will be stable
(no dynamic change of the topology), but this is not always true.
Figure 1 illustrates the architectural components involved in network
mobility and are defined in the following paragraphs: Mobile Router
(MR), Mobile Network (NEMO), Mobile Network Node (MNN), "ingress
interface", "egress interface", and Correspondent Node (CN). The
other terms, "access router" (AR), "Fixed Node (FN)", "Mobile Node
(MN)", "home agent" (HA), "home link", and "foreign link", are not
terms specific to network mobility and thus are defined in .
CN ->|_|-| Internet
|-| | |<- home link
_ | |-| _ | _
|-|_|-|_____| |-|_|-|-|_|<- HA (Home Agent)
| \ | _
foreign link ->| ^ |-|_|<- MR (Mobile Router)
.. AR (access ___|___
router) _| |_
Figure 1: Mobile Network on the Home LinkFigure 2 shows a single mobile subnet. Figure 3 illustrates a larger
mobile network comprising several subnets, attached to a foreign
_ | |-| | |<- home link
|_|-| _ | _ | |-| _ | _
2 MNNs -> _ |-|_|-|-|_|-|_____| |-|_|-|-|_|<- HA
|_|-| . | \ \ |
| . |<- foreign ^AR
mobile subnet -> . link
Figure 2: Single Mobile Subnet on a Foreign Link
mobile subnet->| | _____
_ | |-| | |<- home link
MNN1->|_|-|'i'_'e'| _ | |-| _ | _
|--|_|--|-|_|-|_____| |-|_|-|-|_|<- HA
'i'| | \ |
mobile subnet-^ _| . |<- foreign
|_| . link
MNN2 -^ .
'i': MR's ingress interface
'e': MR's egress interface
Figure 3: Larger Mobile Network Made up of 2 Mobile Subnets
At the network layer, MRs get access to the global Internet from an
Access Router (AR) on a visited link. An MR maintains the Internet
connectivity for the entire mobile network. A given MR has one or
more egress interfaces and one or more ingress interfaces. When
forwarding a packet to the Internet, the packet is transmitted
upstream through one of the MR's egress interfaces to the AR; when
forwarding a packet from the AR down to the mobile network, the
packet is transmitted downstream through one of the MR's ingress
2.1. Mobile Network (NEMO)
As defined in :
An entire network, moving as a unit, which dynamically changes its
point of attachment to the Internet and thus its reachability in the
topology. The mobile network is composed of one or more IP-subnets
and is connected to the global Internet via one or more Mobile
Routers (MR). The internal configuration of the mobile network is
assumed to be relatively stable with respect to the MR.
Rearrangement of the mobile network and changing the attachment point
of the egress interface to the foreign link are orthogonal processes
and do no affect each other.
2.2. Mobile Subnet
A link (subnet) that comprises, or is located within, the mobile
2.3. Mobile Router (MR)
As defined in :
A router capable of changing its point of attachment to the Internet,
moving from one link to another link. The MR is capable of
forwarding packets between two or more interfaces, and possibly
running a dynamic routing protocol modifying the state by which it
does packet forwarding.
An MR acts as a gateway between an entire mobile network and the rest
of the Internet, and has one or more egress interfaces and one or
more ingress interfaces. Packets forwarded upstream to the rest of
the Internet are transmitted through one of the MR's egress
interfaces; packets forwarded downstream to the mobile network are
transmitted through one of the MR's ingress interfaces.
2.4. Egress Interface
As defined in :
The network interface of an MR attached to the home link if the MR is
at home, or attached to a foreign link, if the MR is in a foreign
2.5. Ingress Interface
As defined in :
The interface of an MR attached to a link inside the mobile network.
2.6. Mobile Network Prefix (MNP)
As defined in :
A bit string that consists of some number of initial bits of an IP
address which identifies the entire mobile network within the
Internet topology. All nodes in a mobile network necessarily have an
address containing this prefix.
2.7. Mobile Network Node (MNN)
As defined in :
Any node (host or router) located within a mobile network, either
permanently or temporarily. A Mobile Network Node may be either a
fixed node (LFN) or a mobile node (either VMN or LMN).
2.8. Correspondent Node (CN)
Any node that is communicating with one or more MNNs. A CN could be
either located within a fixed network or within a mobile network, and
could be either fixed or mobile.
2.9. Correspondent Router (CR)
Refers to the entity that is capable of terminating a Route
Optimization session on behalf of a Correspondent Node (see also NEMO
Route Optimization in Section 7.5).
2.10. Correspondent Entity (CE)
Refers to the entity with which a Mobile Router or Mobile Network
Node attempts to establish a Route Optimization session. Depending
on the Route Optimization approach, the Correspondent Entity may be a
Correspondent Node or Correspondent Router (see also NEMO Route
Optimization in Section 7.5).
3. Functional Terms
Within the term Mobile Network Node (MNN), we can distinguish between
Local Fixed Nodes (LFN), Visiting Mobile Nodes (VMN), and Local
Mobile Nodes (LMN). The distinction is a property of how different
types of nodes can move in the topology and is necessary to discuss
issues related to mobility management and access control; however, it
does not imply that network mobility or host mobility should be
handled differently. Nodes are classified according to their
function and capabilities with the rationale that nodes with
different properties may have different requirements.
Figure 4 illustrates a VMN changing its point of attachment from its
home link located outside the mobile network to within a mobile
network. The figure also illustrates an LMN changing its point of
attachment within the mobile network.
mobile subnet 1 | _ +++++++<<<+++++++++++
|-|_|-| + +
++<<<LMN-| \ | + |-MR
+ | + _____ | _ HA_MR
+ | _ | + | |-|-|_|
+ LMN _ |-|_|-| _ | _ | | _
++++>|_|-| \ |--|_|--|-|_|-|_____|-|-|_|
| | ^ | \ | HA_VMN
VMN _ | MR |
^ mobile subnet 2 +
+++>>>+++ = changing point of attachment
Figure 4: LFN vs LMM vs VMN
In a typical-use case of NEMO Basic Support , only the MR and the
HA are NEMO-enabled. LFNs are not MIPv6-enabled nor NEMO-enabled.
On the other hand, a VMN or an LMN acting as a mobile router may be
NEMO-enabled, whereas a VMN or an LMN acting as a mobile node may be
For NEMO Extended Support, details of the capabilities are not yet
known at the time of this writing, but NEMO-enabled nodes may be
expected to implement some sort of Route Optimization.
3.1. Local Fixed Node (LFN)
A fixed node (FN), either a host or a router, that belongs to the
mobile network and is unable to change its point of attachment while
maintaining ongoing sessions. Its address is taken from an MNP.
3.2. Visiting Mobile Node (VMN)
Either a mobile node (MN) or a mobile router (MR), assigned to a home
link that doesn't belong to the mobile network and that is able to
change its point of attachment while maintaining ongoing sessions. A
VMN that is temporarily attached to a mobile subnet (used as a
foreign link) obtains an address on that subnet (i.e., the address is
taken from an MNP).
3.3. Local Mobile Node (LMN)
Either a mobile node (MN) or a mobile router (MR), assigned to a home
link belonging to the mobile network and which is able to change its
point of attachment while maintaining ongoing sessions. Its address
is taken from an MNP.
3.4. NEMO-Enabled Node (NEMO-Node)
A node that has been extended with network mobility support
capabilities as described in NEMO specifications.
3.5. MIPv6-Enabled Node (MIPv6-Node)
A node that has been extended with host mobility support capabilities
as defined in the Mobile IPv6 specification .
4. Nested Mobility Terms
Nested mobility occurs when there is more than one level of mobility,
i.e., when a mobile network acts as an access network and allows
visiting nodes to attach to it. There are two cases of nested
o The attaching node is a single VMN (see Figure 4). For instance,
when a passenger carrying a mobile phone gets Internet access from
the public access network deployed on a bus.
o The attaching node is an MR with nodes behind it, i.e., a mobile
network (see Figure 5). For instance, when a passenger carrying a
PAN gets Internet access from the public access network deployed
on a bus.
For the second case, we introduce the following terms:
4.1. Nested Mobile Network (nested-NEMO)
A mobile network is said to be nested when a mobile network (sub-
NEMO) is attached to a larger mobile network (parent-NEMO). The
aggregated hierarchy of mobile networks becomes a single nested
mobile network (see Figure 5).
The mobile network at the top of the hierarchy connecting the
aggregated nested mobile networks to the Internet (see Figure 5).
The upstream mobile network providing Internet access to another
mobile network further down the hierarchy (see Figure 5).
The downstream mobile network attached to another mobile network up
in the hierarchy. It becomes subservient of the parent-NEMO. The
sub-NEMO is getting Internet access through the parent-NEMO and does
not provide Internet access to the parent-NEMO (see Figure 5).
The MR(s) of the root-NEMO used to connect the nested mobile network
to the fixed Internet (see Figure 5).
The MR(s) of the parent-NEMO.
The MR(s) of the sub-NEMO, which is connected to a parent-NEMO
In a nested NEMO, indicates the number of sub-MRs a packet has to
cross between a MNN and the root-MR.
A MNN in the root-NEMO is at depth 1. If there are multiple root-
NEMOs, a different depth is computed from each root-MR.
_ | _ | |
_ |-|_|-| _ |-|_|-|-| |-| _
_ |-|_|-| \ |-|_|-| \ | |_____| | _ |-|_|
_ |-|_|-| | | | |-|_|-|
|_|-| \ | \ |
MNN AR sub-MR AR root-MR AR AR HA
sub-NEMO root-NEMO fl Internet Home Network
Figure 5: Nested Mobility: a sub-NEMO attached to a larger mobile
5. Multihoming Terms
Multihoming, as currently defined by the IETF, covers site-
multihoming  and host multihoming. We enlarge this terminology to
include "multihomed mobile router" and "multihomed mobile network".
The specific configurations and issues pertaining to multihomed
mobile networks are covered in .
5.1. Multihomed Host or MNN
A host (e.g., an MNN) is multihomed when it has several addresses to
choose between, i.e., in the following cases when it is:
o Multi-prefixed: multiple prefixes are advertised on the link(s) to
which the host is attached, or
o Multi-interfaced: the host has multiple interfaces to choose from,
on or not on the same link.
5.2. Multihomed Mobile Router
From the definition of a multihomed host, it follows that a mobile
router is multihomed when it has several addresses to choose between,
i.e., in the following cases when the MR is:
o Multi-prefixed: multiple prefixes are advertised on the link(s) to
which an MR's egress interface is attached, or
o Multi-interfaced: the MR has multiple egress interfaces to choose
between, on or not on the same link (see Figure 6).
_ _ | |
|_|-| _ |-|_|-| |-| _
_ |-|_|=| \ |_____| | _ |-|_|
|_|-| | |-|_|-|
MNNs MR AR Internet AR HA
Figure 6: Multihoming: MR with multiple E-faces
5.3. Multihomed Mobile Network (multihomed-NEMO)
A mobile network is multihomed when a MR is multihomed or there are
multiple MRs to choose between (see the corresponding analysis in
_ |-|_|-| _____
|_|-| |-| |
MNNs _ | | |-| _
|_|-| _ |-|_____| | _ |-|_|
Figure 7: Multihoming: NEMO with Multiple MRs5.4. Nested Multihomed Mobile Network
A nested mobile network is multihomed when either a root-MR is
multihomed or there are multiple root-MRs to choose between.
Split-NEMO refers to the case where a mobile network becomes two or
more independent mobile networks due to the separation of Mobile
Routers that are handling the same MNP (or MNPs) in the original
mobile network before the separation.
Figure 6 and Figure 7 show two examples of multihomed mobile
networks. Figure 8 shows two independent mobile networks. NEMO-1 is
single-homed to the Internet through MR1. NEMO-2 is multihomed to
the Internet through MR2a and MR2b. Both mobile networks offer
access to visiting nodes and networks through an AR.
Let's consider the two following nested scenarios in Figure 8:
Scenario 1: What happens when MR2a's egress interface is attached to
* NEMO-2 becomes subservient to NEMO-1
* NEMO-1 becomes the parent-NEMO to NEMO-2 and the root-NEMO for
the aggregated nested mobile network
* NEMO-2 becomes the sub-NEMO
* MR1 is the root-MR for the aggregated nested mobile network
* MR2a is a sub-MR in the aggregated nested mobile network
* NEMO-2 is still multihomed to the Internet through AR1 and ARz
* The aggregated nested mobile network is not multihomed, since
NEMO-2 cannot be used as a transit network for NEMO-1
Scenario 2: What happens when MR1's egress interface is attached to
* NEMO-1 becomes subservient to NEMO-2
* NEMO-1 becomes the sub-NEMO
* NEMO-2 becomes the parent_NEMO to NEMO-1 and also the root-NEMO
for the aggregated nested mobile network
* MR2a and MR2b are both root-MRs for the aggregated nested
* MR1 is a sub-MR in the aggregated nested mobile network
* NEMO-1 is not multihomed
* The aggregated nested mobile network is multihomed
_ | _ |
|_|-|-|_|-| _ _____
NEMO-1 MNNs _ | MR1 |-|_|-| |
|_|-| ARx | |-| _
AR1 \ | | _ | | | _ |-|_|
_ |-|_|-| | |-|_|-|
_ |-|_|-| ARy | | |
|_|-| MR2a _ | |
NEMO-2 MNNs _ | |-|_|-| |
|_|-| _ | ARz |_____|
Figure 8: Nested Multihomed NEMO
6. Home Network Model Terms
The terms in this section are useful to describe the possible
configurations of mobile networks at the home. For a better
understanding of the definitions, the reader is recommended to read
, where such configurations are detailed.
6.1. 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.
6.2. Home Network
The Network formed by the application of the Home Prefix to the Home
Link. With NEMO, the concept of Home Network is extended as
6.3. 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 derived either from the Home Network or from one of
the Mobile Router's MNPs.
6.4. Mobile Home Network
A Mobile Network (NEMO) that is also a Home Network. The MR, or one
of the MR(s), that owns the MNP may act as the Home Agent for the
mobile nodes in the Mobile Home Network.
6.5. Distributed Home Network
A Distributed Home Network is a Home Network that is distributed
geographically between sites. The aggregated Home Prefix is
partitioned between the sites and advertised by all sites.
This aggregated Home Prefix can be further aggregated within a
service provider network or between service providers, to form a
prefix that is announced into the Internet by the service provider(s)
from multiple points.
The sites may be connected using a mesh of private links and tunnels.
A routing protocol is used within and between sites to exchange
routes to the subnets associated to the sites and, eventually, to
Mobile Routers registered off-site.
6.6. Mobile Aggregated Prefix
An aggregation of Mobile Network Prefixes.
6.7. 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 the Home Network for NEMO purposes.
6.8. 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.
6.9. Virtual Home Network
An aggregation of Mobile Network Prefixes that is in turn advertised
as the Home Link Prefix. The Extended Home Network and the
Aggregated Home Network can be configured as Virtual Home Network.
7. Mobility Support Terms
7.1. Host Mobility Support
Host Mobility Support is a mechanism that maintains session
continuity between mobile nodes and their correspondents upon the
mobile host's change of point of attachment. It can be achieved
using Mobile IPv6 or other mobility support mechanisms.
7.2. Network Mobility Support (NEMO Support)
Network Mobility Support is a mechanism that maintains session
continuity between mobile network nodes and their correspondents upon
a mobile router's change of point of attachment. Solutions for this
problem are classified into NEMO Basic Support, and NEMO Extended
7.3. NEMO Basic Support
NEMO Basic Support is a solution to preserve session continuity by
means of bidirectional tunneling between MRs and their HAs, much like
what is done with Mobile IPv6  for mobile nodes when Routing
Optimization is not used. Only the HA and the MR are NEMO-enabled.
RFC 3963  is the solution specified by the NEMO Working Group for
NEMO Basic Support.
7.4. NEMO Extended Support
NEMO Extended support is to provide performance optimizations,
including routing optimization between arbitrary MNNs and CNs.
7.5. NEMO Routing Optimization (NEMO RO)
The term "Route Optimization" is accepted in a broader sense than
already defined for IPv6 Host Mobility in  to loosely refer to any
approach that optimizes the transmission of packets between a Mobile
Network Node and a Correspondent Node.
For more information about NEMO Route Optimization in the NEMO
context, see the problem statement  and the solution space
7.6. MRHA Tunnel
The bidirectional tunnel between a Mobile Router and its Home Agent.
7.7. Pinball Route
A pinball route refers to the non-direct path taken by packets, which
are routed via one or more Home Agents, as they transit between a
Mobile Network Node and a Correspondent Node.
A packet following a pinball route would appear like a ball bouncing
off one or more Home Agents before reaching its final destination.
8. Security Considerations
As this document only provides terminology and describes neither a
protocol, procedure, or an implementation, there are no security
considerations associated with it.
The material presented in this document takes most of the text from
documents initially submitted to the former MobileIP WG and MONET BOF
and was published as part of a PhD dissertation . The authors
would therefore like to thank both Motorola Labs Paris and INRIA
(PLANETE team, Grenoble, France), where this terminology originated,
for the opportunity to bring it to the IETF, and particularly Claude
Castelluccia for his advice, suggestions, and direction, Alexandru
Petrescu and Christophe Janneteau. We also acknowledge input from
Erik Nordmark, Hesham Soliman, Mattias Petterson, Marcelo Bagnulo,
T.J. Kniveton, Masafumi Watari, Chan-Wah Ng, JinHyeock Choi, and
numerous other people from the NEMO Working Group. The Home Network
Model section is contributed by Pascal Thubert, Ryuji Wakikawa, and
10.1. Normative References
 Ernst, T., "Network Mobility (NEMO) Support Goals and
Requirements", RFC 4886, July 2007.
 Deering, S. and R. Hinden, "Internet Protocol Version 6
(IPv6)", RFC 2460, December 1998.
 Manner, J. and M. Kojo, "Mobility Related Terminology",
RFC 3753, June 2004.
 Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
 Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert,
"Network Mobility (NEMO) Basic Support Protocol", RFC 3963,
 Thubert, P., Wakikawa, R., and V. Devarapalli, "Network
Mobility (NEMO) Home Network Models", RFC 4887, July 2007.
 Ng, C-W., Thubert, P., Watari, M., and F. Zhao, "Network
Mobility Route Optimization Problem Statement", RFC 4888,
 Ng, C-W., Zhao, F., Watari, M., and P. Thubert, "Network
Mobility Route Optimization Solution Space Analysis", RFC 4889,
10.2. Informative References
 Abley, J., Black, B., and V. Gill, "Goals for IPv6 Site-
Multihoming Architectures", RFC 3582, August 2003.
 Ng, C-W., Paik, E-K., Ernst, T., and M. Bagnulo, "Analysis of
Multihoming in Network Mobility Support", Work in Progress,
 Ernst, T., "Network Mobility Support in IPv6", PhD's Thesis.,
Universite Joseph Fourier, Grenoble, France , October 2001.
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