RFC 5177
Network Mobility (NEMO) Extensions for Mobile IPv4
RFC 5177: Network Mobility (NEMO) Extensions for Mobile IPv4 🎀
okay bestie, this is RFC 5177 and it's giving very serious networking 💅 It's from April 2008 and it's on the Standards Track, which means it's a real protocol spec people actually implement 🔥 The authors are K. Leung and G. Dommety from Cisco Systems, V. Narayanan from Qualcomm, Inc., and A. Petrescu from Motorola 🫶 The title block doesn't list anything it obsoletes or updates, so no drama there ✨
Status of This Memo ✨
so this doc is an Internet standards track protocol for the whole Internet community, and it's literally asking for discussion and suggestions 🗣️ For the standardization state and status of this protocol, check the current edition of the "Internet Official Protocol Standards" (STD 1) 📚 Distribution of this memo is unlimited 🌈
Abstract 🦋
this doc is about keeping a Mobile Network connected between a Mobile Router and a Home Agent, by extending Mobile IPv4 🚗 The Mobile Router is responsible for the mobility of one or more network segments or subnets that move together. It hides its mobility from the nodes on the Mobile Network, and those nodes may be fixed in relationship to the Mobile Router and may not have any mobility function at all 🧚
extensions to Mobile IPv4 get introduced here to support Mobile Networks 💖
Table of Contents 🧚
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Examples of Mobile Networks . . . . . . . . . . . . . . . 3
1.2. Overview of Protocol . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Mobile Network Extensions . . . . . . . . . . . . . . . . . . 8
4.1. Mobile Network Request Extension . . . . . . . . . . . . . 8
4.2. Mobile Network Acknowledgement Extension . . . . . . . . . 9
5. Mobile Router Operation . . . . . . . . . . . . . . . . . . . 11
5.1. Error Processing . . . . . . . . . . . . . . . . . . . . . 12
5.2. Mobile Router Management . . . . . . . . . . . . . . . . . 12
6. Home Agent Operation . . . . . . . . . . . . . . . . . . . . . 13
6.1. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.2. Data Structures . . . . . . . . . . . . . . . . . . . . . 14
6.2.1. Registration Table . . . . . . . . . . . . . . . . . . 14
6.2.2. Prefix Table . . . . . . . . . . . . . . . . . . . . . 14
6.3. Mobile Network Prefix Registration . . . . . . . . . . . . 14
6.4. Advertising Mobile Network Reachability . . . . . . . . . 16
6.5. Establishment of Bi-directional Tunnel . . . . . . . . . . 16
6.6. Sending Registration Replies . . . . . . . . . . . . . . . 17
6.7. Mobile Network Prefix Deregistration . . . . . . . . . . . 17
7. Data Forwarding Operation . . . . . . . . . . . . . . . . . . 17
8. Nested Mobile Networks . . . . . . . . . . . . . . . . . . . . 18
9. Routing Protocol between Mobile Router and Home Agent . . . . 18
10. Security Considerations . . . . . . . . . . . . . . . . . . . 19
10.1. Security when Dynamic Routing Protocol Is Used . . . . . . 20
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
13.1. Normative References . . . . . . . . . . . . . . . . . . . 23
13.2. Informative References . . . . . . . . . . . . . . . . . . 241. Introduction 🦋
this doc describes network mobility extensions to Mobile IPv4 💫 The whole goal is to handle mobility scenarios where groups of hosts and routers move together, as one unit 🚌 It's required that all hosts and routers in a Mobile Network be able to run applications connecting to the Internet, and be reachable from the Internet 🌐
if you want the terminology for network mobility (NEMO), a quick read of RFC 4885 [RFC4885] is suggested 📚🤓
1.1. Examples of Mobile Networks 🧸
a Mobile Network links together a set of hosts and routers 🖥️ Connecting it to the Internet happens on two levels, and it's honestly so iconic. First, a Mobile Router is connected on one side to the Mobile Network and on the other side to a wireless access system 📡 Second, a Home Agent placed on the home link manages traffic between the Correspondent Node and a Local Fixed Node (LFN, a node in the Mobile Network) by encapsulating that traffic 🎁
here's the applicability scenario, and it's so cute 🥹 A Mobile Network is formed by a wireless-enabled Personal Digital Assistant (PDA) and a portable photographic camera, linked together by Bluetooth wireless link-layer technology. This is sometimes referred to as a Personal Area Network (PAN) 📷 In the illustration below, the PDA plays the role of a Mobile Router and the camera plays the role of Local Fixed Node 🌸
----
| HA |
---- --------
| / \ ----
-+--------| Internet |---------| CN |
\ / ----
--------
/ \
/ \
/ \
---- ----
| AR | | AR |
---- ----
|cellular |cellular
/ |cellular
| ---- ----
Mobile | | MR | |LFN | ---movement-->
Network < ---- ----
| | |
| -+-----------+-
\ Bluetooththe camera (Local Fixed Node) uploads photo content to a Correspondent Node (CN) server 📸 When the Mobile Network moves away, the Mobile Router serving it changes its point of attachment from one cellular access (Access Router) to another, and gets a new Care-of Address 🚶♀️💨 The Home Agent (HA) encapsulates application traffic for the CN and LFN 🎀
the illustration above is a super simple version of what Mobile IP-based Mobile Networks can do. More complex Mobile Networks are easily accommodated by the Mobile IPv4 extensions in this document (NEMOv4) 💅 For example, laptops used by passengers in a bus, train, ship, or plane should all be considered as forming Mobile Networks, as long as they move together (homogeneously) ✈️🚢
1.2. Overview of Protocol 🌈
like we said before, this doc presents extensions to Mobile IPv4 🫶 The entities sending and receiving these extensions are the Mobile Router and the Home Agent 🤝 The Local Fixed Node doesn't have to run any Mobile IP software. Even though it moves along with the Mobile Network, its IP stack doesn't see any change in addressing 🧘♀️✨
Mobility for the entire Mobile Network is handled by the Mobile Router registering its current point of attachment (Care-of Address) with its Home Agent. The Mobile Router sends an extended Registration Request to the Home Agent, which sends back an extended Registration Reply 💌 This signaling sets up the tunnel between the two entities, as shown in this figure:
LFN MR HA CN
| | | |
| | Extended Registration | |
| |---------------------->| |
| | Request | |
| | | |
| | | |
| | Extended Registration | |
| |<----------------------| |
| | Reply | |
| | | |
|<--------o=======================o-------->|
| | Encapsulated | |
| | Application Traffic | |
| | | |the prefix(es) used within a Mobile Network (either implicitly configured on the Home Agent or explicitly identified by the Mobile Router in the Registration Request) are advertised by the Home Agent for route propagation in the home network 📣 Traffic to and from nodes in the Mobile Network gets tunneled by the Home Agent to the Mobile Router, and vice versa 🚇 Packets from a Local Fixed Node in the Mobile Network can be forwarded by the Mobile Router directly without tunneling (if reverse tunneling were not used), but these packets will be dropped if ingress filtering is turned on at the Access Router 🙈
⚠️ heads up bestie: if ingress filtering is on at the Access Router, those directly forwarded packets from a Local Fixed Node get dropped. Reverse tunneling is what's being talked about here, so keep that in mind 💀
extensively relating to Mobile IPv4 [RFC3344], this spec mainly addresses the co-located Care-of Address mode. Foreign Agent Care-of Address mode (with 'legacy' Foreign Agents [RFC3344]) is supported but without optimization, and with double encapsulation being used 🌷 If you want an optimization for this mode, the gentle reader is directed to an extension document [NEMOv4-FA] 💜
compared to Mobile IPv4, this document specifies an additional tunnel between a Mobile Router's Home Address and the Home Agent. This tunnel sits inside the normal tunnel between the Care-of Address (CoA) and the Home Agent 🪆 In Foreign Agent CoA mode, the tunnel between the Mobile Router and Home Agent is needed so the Foreign Agent can direct the decapsulated packet to the proper visiting Mobile Router 🧚 In co-located CoA mode, the additional tunnel isn't essential and could be eliminated, because the Mobile Router is the recipient of the encapsulated packets for the Mobile Network. A proposal for this feature is in the extending document mentioned above [NEMOv4-FA] 🌟
all traffic between the nodes in the Mobile Network and the Correspondent Nodes goes through the Home Agent. This document doesn't cover route optimization for this traffic 🙃
a similar protocol has been documented in RFC 3963 [RFC3963] for supporting IPv6 Mobile Networks with Mobile IPv6 extensions 🌍
and multihoming for Mobile Routers is outside the scope of this document 🚫
to be continued, stay tuned for part 2 💖🦋
2. Terminology ✨
okay bestie, let's get the vocab down first 💅 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be read as described in RFC 2119 [RFC2119] 🎀
Mobile IPv4 terminology lives in RFC 3344 [RFC3344] 🦋 For network mobility (NEMO) from an IPv6 point of view, check RFC 4885 [RFC4885] 🌸 This doc also defines a few extra terms just for NEMOv4 💜
Mobile Router
RFC 3344 [RFC3344] says a Mobile Router is a mobile node that can be a router, and it's responsible for moving one or more entire networks together 🚆 Think airplane, ship, train, car, bicycle, or even a kayak 🛶 The whole network is riding along, bestie!
Mobile Network Prefix
This is the network prefix of the subnet that gets delegated to a Mobile Router as its Mobile Network 🌈
Prefix Table
A list of Mobile Network Prefixes, indexed by the Home Address of a Mobile Router 🗂️ The Home Agent manages and uses the Prefix Table to figure out which Mobile Network Prefixes belong to which Mobile Router 👑
Local Fixed Node
RFC 4885 [RFC4885] defines a Local Fixed Node (LFN) as a fixed node that belongs to the Mobile Network and can't change its point of attachment 🧚 Quick warning though: don't mix this up with "Long, Fat Network, LFN" from RFC 1323 [RFC1323] 🙈 The vibe is different, and the pronunciation is different too. The RFC 1323 one is "elephan(t)", but a NEMO LFN is "elefen" 🐘 ✨
3. Requirements ✨
so here's the tea 🍵 RFC 3344 says Mobile Networks can be supported by the Mobile Router and Home Agent using static configuration or by running a routing protocol (see Section 4.5 of RFC 3344 [RFC3344]). BUT there's no solution for explicitly registering the Mobile Networks a Mobile Router serves 😭 A solution has to give the Home Agent a way to make sure a Mobile Router claiming a certain Mobile Network Prefix is actually allowed to claim it 🔒 It would also expose the Mobile Network Prefixes (and maybe other subnet-relevant info) in the messages being exchanged, which helps with network debugging 🔍
Here's the wishlist of requirements for Mobile Network support 💖
- A Mobile Router should be able to operate in explicit or implicit mode 🦋 In explicit mode, it may tell the Home Agent which Mobile Network(s) need to be propagated via a routing protocol. A Mobile Router may also run in implicit mode, where the Home Agent learns the Mobile Networks through other means, like from the AAA server, via pre-configuration, or via a dynamic routing protocol 🧭
- The Mobile Network should be supported using Foreign Agents that comply with RFC 3344 [RFC3344] without any changes (these are the 'legacy' Foreign Agents) 🫶
- The Mobile Network should allow Fixed Nodes, Mobile Nodes, or Mobile Routers to be on it 🌸
- The Local Fixed Nodes on a Mobile Network should be able to run their sessions without running Mobile IP stacks 🧚 The Mobile Router that manages the LFNs' Mobile Network is "hiding" mobility events, like changes of the Care-of Address, from the Local Fixed Nodes in that Mobile Network 🙈✨
4. Mobile Network Extensions ✨
4.1. Mobile Network Request Extension
okay so for Explicit Mode, the Mobile Router tells the Home Agent about its Mobile Network Prefixes during registration 📮 The Registration Request can carry zero, one, or several Mobile Network Request extensions, plus any other extensions defined by or in the context of RFC 3344 [RFC3344] 💅 If several Mobile Networks need registering, each one gets its own Mobile Network Request extension, with its own Type, Length, Sub-Type, Prefix Length, and Prefix 🎀 Each extension is encoded in Type-Length-Value (TLV) format, and it follows this layout:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Sub-Type | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Here's the breakdown 🍓
Type:148(Mobile Network Extension)Length: Decimal6Sub-Type:0(Mobile Network Request)Prefix Length: an 8-bit unsigned integer that says how many leftmost bits cover the network part of the address in the Prefix field 🔢Prefix: a 32-bit unsigned integer in network byte-order, holding an IPv4 address whose leftmostPrefix Lengthbits make up the Mobile Network Prefix 🌈
4.2. Mobile Network Acknowledgement Extension
the Registration Reply can carry zero, one, or several Mobile Network Acknowledgement extensions, along with any other extensions defined by or in the context of RFC 3344 [RFC3344] 🦋 For Implicit Mode, the Mobile Network Acknowledgement tells the Mobile Router which prefixes the Home Agent has set up forwarding for 🧭 The Mobile Router can then apply policies, like only tunneling traffic from these Mobile Networks to the Home Agent 🔐 For Explicit Mode, if several Mobile Networks need explicit acknowledgement, each one gets its own Mobile Network Acknowledgement extension, with its own Type, Sub-Type, Length, Prefix, and Prefix Length fields 💖
Big rule here 🚨 At least one Mobile Network Acknowledgement extension MUST be in a successful Registration Reply. That's how the Mobile Router knows its Mobile Network Request extension was processed and not skipped by the Home Agent 👑
A Registration Reply can have any non-zero number of Explicit Mode and Implicit Mode Acknowledgement sub-types, and both sub-types can show up in one Registration Reply 🌸 Each extension is encoded in Type-Length-Value (TLV) format, and it looks like this:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Sub-Type | Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Reserved | Prefix...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+When the registration gets denied with Code HA_MOBNET_ERROR (that's the Code field in the Registration Reply), the Code field in the included Mobile Network Extension tells you why it failed 😭
Type:148(Mobile Network Extension)Length: Decimal8Sub-Type:1(Explicit Mode Acknowledgement) or2(Implicit Mode Acknowledgement) 🧚Code: a value that says success or failure:0: Success ✅1: Invalid prefix (MOBNET_INVALID_PREFIX_LEN) 🙈2: Mobile Router is not authorized for prefix (MOBNET_UNAUTHORIZED) 🚫3: Forwarding setup failed (MOBNET_FWDING_SETUP_FAILED) 💀
Prefix Length: an 8-bit unsigned integer that says how many leftmost bits cover the network part of the address in the Prefix field 🔢Reserved: sent as zero, and ignored on reception 🫧Prefix: a 32-bit unsigned integer in network byte-order, holding an IPv4 address whose leftmostPrefix Lengthbits make up the Mobile Network Prefix 🌈
5. Mobile Router Operation ✨
a Mobile Router basically operates like a Mobile Node does, as set out in RFC 3344 [RFC3344] 🎀 On top of keeping mobility bindings for its Home Address, the Mobile Router and the Home Agent together keep forwarding info for the Mobile Network Prefix(es) assigned to the Mobile Router 🗺️
A Mobile Router SHOULD set the 'T' bit to 1 in every Registration Request it sends, to say it needs reverse tunnels for all traffic 🚇 Without reverse tunnels, all the traffic from the Mobile Network gets hit by ingress filtering in the visited networks 🛑 When a successful Registration Reply comes in, the Mobile Router processes the registration according to RFC 3344 [RFC3344], and then these steps happen too 💖
- Check the Mobile Network Acknowledgement extension(s) in the Registration Reply 🔍
- Create a tunnel to the Home Agent if the Mobile Router is registered in reverse tunneling mode 🦋
- Set up a default route via this tunnel or the egress interface when the Mobile Router is registered with or without reverse tunneling, respectively 🧭
Per this spec, a Mobile Router can operate in one of two modes: explicit or implicit 🌈 In explicit mode, the Mobile Router includes Mobile Network Prefix info in every Registration Request (as Mobile Network Request extensions) 📮 In implicit mode, it leaves that info out of every Registration Request 🫥 In that case, the Home Agent gets the Mobile Network Prefixes some other way, not through Mobile IP, and one example is static configuration on the Home Agent 🧚
A Mobile Router can get a co-located Care-of Address or a Foreign Agent Care-of Address, whether it's running in explicit or implicit mode 🌸
For deregistration, the Mobile Router sends a registration request with lifetime set to zero and without any Mobile Network Request extensions 👋
5.1. Error Processing 🚨
Okay so, in a Mobile IP Registration Reply message there can be two Code fields 👀: one that belongs to the Registration Reply header (the 'proper' Code), and one tucked inside the Mobile Network Acknowledgement Extension (just called the 'Code'). A Mobile Router reads the values of the Code field in the Mobile Network Acknowledgement Extension of the Registration Reply to spot any error about managing the Mobile Network Prefixes by the Home Agent. It also reads the values of the Code field in the Registration Reply header (the proper Code). Two fields, two jobs, no drama 💅
If the Code field in the Registration Reply (the proper) is set to HA_MOBNET_DISALLOWED, then the Mobile Router MUST stop sending Registration Requests with any Mobile Network Prefix extensions to that Home Agent. Bye-bye, extensions 🫠
If the Code field in the Registration Reply (the proper) is set to HA_MOBNET_ERROR, then the Mobile Router MUST stop sending Registration Requests that contain any of the Mobile Network Prefixes defined by the values of the fields Prefix and Prefix Length in the Mobile Network Acknowledgement extension. Note that the registration is denied in this case, and no forwarding for any Mobile Network Prefixes would be set up by the Home Agent for the Mobile Router. So it's a full no, bestie 🙅♀️
It's possible that the Mobile Router gets a Registration Reply with no Mobile Network extensions at all. That happens if the registration was handled by a Mobile IPv4 Home Agent that doesn't support this specification whatsoever. In that case, the absence of Mobile Network extensions must be interpreted by the Mobile Router as the case where the Home Agent does not support Mobile Networks. Silence is an answer too, iykyk 🤫
All the error code values have been assigned by IANA; see Section 11. 🧚
5.2. Mobile Router Management
Running a Mobile Router in a Mobile IPv4 environment comes with some requirements for managing the initial configuration and keeping an eye on the ongoing status info 👀. Mobile Router maintenance indicators may need to be exposed in a manner consistent with other Mobile IPv4 indicators, so everything matches. Very organised, very cute 🎀
The objects for the Management Information Base (MIB) for Mobile IPv4 are defined in RFC 2006 [RFC2006]. The basic Mobile IP model describes three entities: Mobile Node, Home Agent, and Foreign Agent. On top of those, this document proposes a functional entity called the Mobile Router 🦋
The necessary initial configuration at a NEMOv4-enabled Home Agent includes, but is not limited to, the contents of the Prefix Table. The Mobile Router MAY need to store the Mobile Network Prefixes as the initial configuration. It's giving "prep before the party" 🎉
The definition of MIB objects related to the Mobile Router and to a NEMOv4-enabled Home Agent is outside the scope of this document. That's a different story, bestie 📚
6. Home Agent Operation ✨
6.1. Summary
A Home Agent MUST support all the operations specified in RFC 3344 [RFC3344] for Mobile Node support. The Home Agent MUST support both implicit and explicit modes of operation for a Mobile Router. Non-negotiable, the Home Agent has to be able to do both 👑
The Home Agent processes the registration in accordance with RFC 3344 [RFC3344], which includes route setup to the Mobile Router's Home Address via the tunnel to the Care-of Address. On top of that, for a Mobile Router registering in explicit mode, the following steps are taken:
- Check that the Mobile Network Prefix information is valid.
- Ensure the Mobile Network Prefix(es) is/are authorized to be on the Mobile Router.
- Create a tunnel to the Mobile Router if it does not already exist.
- Set up route for the Mobile Network Prefix via this tunnel.
- Propagate Mobile Network Prefix routes via routing protocol if necessary.
- Send the Registration Reply with the Mobile Network Acknowledgement extension(s).
If there are any subnet routes via the tunnel to the Mobile Router that are not specified in the Mobile Network extensions, these routes are removed. Clean up that closet 🧹
In the case where the Mobile Node is not permitted to act as a Mobile Router, the Home Agent sends a Registration Reply message whose Code field is HA_MOBNET_DISALLOWED (the proper Code field of the Registration Reply). Access denied, sweetie 🚫
For a Mobile Router registering in implicit mode, the Home Agent performs steps 3-6 above, once the registration request is processed successfully. Skipping the prefix checks since there are no extensions to check 🙈
For deregistration, the Home Agent removes the tunnel to the Mobile Router and all routes using this tunnel. The Mobile Network extensions are ignored. Goodbye tunnel, goodbye routes 🫶
6.2. Data Structures
6.2.1. Registration Table
The Registration Table in the Home Agent, in accordance with RFC 3344 [RFC3344], contains binding information for every Mobile Node registered with it. RFC 3344 [RFC3344] defines the format of a Registration Table. In addition to all the parameters specified by RFC 3344 [RFC3344], the Home Agent MUST store the Mobile Network Prefixes associated with the Mobile Router in the corresponding registration entry, when the corresponding registration was performed in explicit mode. When the Home Agent is advertising reachability to Mobile Network Prefixes served by a Mobile Router, the information stored in the Registration Table can be used. The receipts are all in there 🧾
6.2.2. Prefix Table
The Home Agent must be able to authorize a Mobile Router for use of Mobile Network Prefixes when the Mobile Router is operating in explicit mode. Also, when the Mobile Router operates in implicit mode, the Home Agent must be able to locate the Mobile Network Prefixes associated with that Mobile Router. The Home Agent may store the Home Address of the Mobile Router along with the Mobile Network prefixes associated with that Mobile Router. If the Mobile Router does not have a Home Address assigned, this table may store the Network Access Identifier (NAI) [RFC2794] of the Mobile Router that will be used in dynamic Home Address assignment. A little address book for the Mobile Router, lowkey iconic 📒
6.3. Mobile Network Prefix Registration
The Home Agent must process Registration Requests coming from Mobile Routers in accordance with this section. RFC 3344 [RFC3344] specifies that the Home Address of a mobile node registering with a Home Agent must belong to a prefix advertised on the home network. In accordance with this specification, however, the Home Address must be configured from a prefix that is served by the Home Agent, not necessarily the one on the home network. Plot twist 🌸
If the Registration Request is valid, the Home Agent checks to see if there are any Mobile Network Prefix extensions included in the Registration Request.
If so, the Mobile Network Prefix information is obtained from the included extensions, and the Home Address from the Home Address field of the Registration Request. For every Mobile Network Prefix extension included in the registration request, the Home Agent MUST perform a check against the Prefix Table. If the Prefix Table does not contain at least one entry pairing that Home Address to that Mobile Network Prefix, then the check fails; otherwise, it succeeds. Pairing check, very serious 🔍
Following this check against the Prefix Table, the Home Agent MUST construct a Registration Reply containing Mobile Network Acknowledgement extensions. For a Mobile Network Prefix for which the check was unsuccessful, the Code field in the corresponding Mobile Network Acknowledgement extension should be set to MOBNET_UNAUTHORIZED.
For a Mobile Network Prefix for which the check was successful, the Code field in the respective Mobile Network Acknowledgement extensions should be set to 0. ✅
The Home Agent MUST attempt to set up forwarding for each Mobile Network Prefix extension for which the Prefix Table check was successful. If the forwarding setup fails for a particular Mobile Network Prefix (for reasons such as not enough memory available or not enough devices available), the Code field in the respective Mobile Network Acknowledgement extension should be set to MOBNET_FWDING_SETUP_FAILED. Rough day, but the info still gets sent back 😭
If forwarding and setup was successful for at least one Mobile Network Prefix, then the Code field (the proper) of the Registration Reply message should be set to 0. Otherwise, when forwarding and setup was unsuccessful for each and every Mobile Network Prefix, that Code (the proper) should be HA_MOBNET_ERROR. One win is enough to get a 0 🎀
If the Registration Request is sent in implicit mode, i.e., without any Mobile Network Request extension, the Home Agent may use pre-configured Mobile Network prefix information for the Mobile Router to set up forwarding. Pre-loaded info, no extension needed 🧚
If the Home Agent is updating an existing binding entry for the Mobile Router, it MUST check all the prefixes in the Registration Table against the prefixes included in the Registration Request. If one or more Mobile Network prefixes are missing from the included information in the registration request, the Home Agent MUST delete those prefixes from the registration table. Also, the Home Agent MUST disable forwarding for those prefixes. Missing prefixes get the boot, no exceptions 🥾
If all checks are successful, the Home Agent either creates a new entry for the Mobile Router or updates an existing binding entry for it, and returns a successful registration reply back to the Mobile Router or the Foreign Agent (if the Registration Request was received from a Foreign Agent). Everybody's happy, the vibes are immaculate ✨
In accordance with RFC 3344 [RFC3344], the Home Agent does proxy Address Resolution Protocol (ARP) for the Mobile Router Home Address when the Mobile Router Home Address is derived from the home network. Proxy ARP, doing the most 👀
If the 'T' bit is set, the Home Agent creates a bi-directional tunnel for the corresponding Mobile Network prefixes or updates the existing bi-directional tunnel. This tunnel is maintained independent of the reverse tunnel for the Mobile Router home address itself. Two tunnels, zero drama, periodt 💅
6.4. Advertising Mobile Network Reachability
If the Mobile Network prefixes served by the Home Agent are aggregated with the home network prefix, and the Home Agent is the default router on the home network, the Home Agent does not have to advertise the Mobile Network Prefixes. The routes for the Mobile Network Prefix are automatically aggregated into the home network prefix (it is assumed that the Mobile Network Prefixes are automatically aggregated into the home network prefix). If the Mobile Router updates the Mobile Network prefix routes via a dynamic routing protocol, the Home Agent SHOULD propagate the routes on the appropriate networks. Less work, more vibes 🌈
6.5. Establishment of Bi-directional Tunnel
The Home Agent creates and maintains a bi-directional tunnel for the Mobile Network prefixes of a Mobile Router registered with it. A Home Agent supporting IPv4 Mobile Router operation MUST be able to forward packets destined to the Mobile Network prefixes served by the Mobile Router to its Care-of Address. Also, the Home Agent MUST be able to accept packets tunneled by the Mobile Router with the source address of the outer header set to the Care-of Address of the Mobile Router, and that of the inner header set to the Mobile Router's Home Address or an address from one of the registered Mobile Network prefixes. The tunnel is the main character here 🦋💖
6.6. Sending Registration Replies 💌
Okay bestie, so the Home Agent MUST set the status code in the registration reply to 0 ✨ to show the Registration Request was processed fine and forwarding got set up for at least one Mobile Network prefix served by the Mobile Router. The Registration Reply MUST also contain at least one Mobile Network Acknowledgement extension 🎀.
If the Home Agent can't set up forwarding for one or more Mobile Network prefixes served by the Mobile Router, it MUST put the status Code MOBNET_FWDING_SETUP_FAILED in the Mobile Network Acknowledgement Extension of the Registration Reply 😭. When the prefix length is zero or greater than decimal 32, the status Code MUST be set to MOBNET_INVALID_PREFIX_LEN 🙈.
If the Mobile Router isn't authorized to forward packets to a Mobile Network prefix included in the request, the Home Agent MUST set the Code to MOBNET_UNAUTHORIZED 💀.
6.7. Mobile Network Prefix Deregistration 🦋
If the Registration Request is for deregistering the Care-of Address, the Home Agent, once it's processed successfully, MUST delete the entry (or entries) from its Registration Table 🧹. Then the Home Agent tears down the bi-directional tunnel and stops forwarding any packets to or from the Mobile Router, bye bye tunnel 👋. The Home Agent MUST ignore any included Mobile Network Request extension in a deregistration request 💅.
7. Data Forwarding Operation 🚀
Okay so for traffic going to the nodes in the Mobile Network, the Home Agent MUST do double tunneling 🪆 if the Mobile Router registered with a Foreign Agent Care-of Address. In that case, the Home Agent MUST wrap the packet in the tunnel header (source IP address set to Home Agent, and destination IP address set to Mobile Router's Home Address), and then wrap it one more time with the tunnel header (source IP address set to Home Agent, and destination IP address set to CoA) 🎀✨.
For optimization, the Home Agent SHOULD only encapsulate the packet with the tunnel header (source IP address set to Home Agent, and destination IP address set to CoA) for co-located CoA mode 🌸.
When a Home Agent gets a packet from the Mobile Network prefix through the bi-directional tunnel, it MUST de-encapsulate the packet and route it as a normal IP packet 📦. It MUST also verify that the incoming packet has the source IP address set to the Care-of Address of the Mobile Router 🔍. If the source address isn't set to the Care-of Address of the Mobile Router, the packet MUST be dropped 🚫. Not today, sus packet 😤.
For traffic from the nodes in the Mobile Network, the Mobile Router encapsulates the packet with a tunnel header (source IP address set to Mobile Router's Home Address, and destination IP address set to Home Agent) if reverse tunnel is enabled 🔁. Otherwise, the packet is routed directly to the Foreign Agent or access router 🛣️.
In co-located CoA mode, the Mobile Router MAY encapsulate one more time with a tunnel header (source IP address set to the CoA and destination IP address set to Home Agent) 🧁.
8. Nested Mobile Networks 🪆💕
Nested Network Mobility is a scenario where a Mobile Router lets another Mobile Router attach to its Mobile Network 🤯. There could be arbitrary levels of nested mobility, honestly so many layers 😭. Each Mobile Router works the same way whether it attaches to another Mobile Router or to a fixed Access Router on the Internet 👑. The solution described here doesn't put any restriction on the number of levels for nested mobility 🌈. Two issues should be noted though 👀.
First, whenever physical loops happen in a nested aggregation of Mobile Networks, this protocol neither detects nor solves them 🌀, so datagram forwarding may get blocked 🚧. Second, Mobile Routers in a deep nested aggregation of Mobile Networks might add a lot of overhead to the data packets, since each level of nesting adds another tunnel header encapsulation 🐌. Applications that don't support MTU discovery get hurt by the extra header encapsulations, because the usable MTU shrinks with each level of nesting 💔.
9. Routing Protocol between Mobile Router and Home Agent 🛰️
There are lots of perks to running a dynamic routing protocol between the Mobile Router and the Home Agent 🤩. If the Mobile Network is pretty big, with several wireless subnets, then the topology changes inside the moving network can be shared from the Mobile Router to the Home Agent using a dynamic routing protocol 🗺️. The NEMOv4 protocol extensions to Mobile IPv4, as defined in the previous sections, aren't there to tell the Home Agent about these topology changes 🙅♀️. Their job is to manage the mobility of the Mobile Router 💜.
Similarly, topology changes in the home network can be shared with the Mobile Router using a dynamic routing protocol 🏡. This might be needed when new fixed networks get added to the home network 🧩.
Again, the NEMOv4 extensions aren't meant to tell the Mobile Router about topology changes at home 💁♀️.
Examples of dynamic routing protocols include, but aren't limited to, OSPF Version 2 [RFC2328], BGP [RFC4271], and RIP [RFC2453] 📚.
The recommendations are about how the routing protocol and the Mobile IPv4 implementation work together on the Mobile Router and on the Home Agent 🤝. The goal is to do that (1) without creating incoherent states in the forwarding information bases at home and on the Mobile Router, (2) without introducing topologically incorrect addressing information in the visited domain, and (3) without duplicating sent data or over-provisioning security 🔐.
The information exchanged between the Mobile Router and the Home Agent goes over the bi-directional tunnel set up by the Mobile IPv4 exchange Registration Request - Registration Reply (see Section 6.5) 🚇. If a network address and prefix of a subnet in the moving network is sent by the Mobile Router within a routing protocol message, then they SHOULD NOT be sent in the Mobile IPv4 Registration Request too 🙅. This avoids incoherencies in the forwarding information bases 💅. The Mobile Router SHOULD use NEMOv4 implicit mode in this case (see Section 3) ✨.
The Mobile Router SHOULD NOT send routing protocol information updates in the foreign network 🙈. The subnet addresses and prefixes valid in the moving network are topologically incorrect in the visited network 🌍.
If the Mobile Router and the Home Agent use a dynamic routing protocol over the tunnel interface, and that protocol has security mechanisms to protect its messages, then the security recommendations in Section 10.1 apply 🔒.
10. Security Considerations 🛡️💖
Okay, this part is super serious, so pay attention bestie 🥹. The Mobile Network extension is protected by the same rules as the Mobile IP extensions in registration messages 🔐. See the Security Considerations section in RFC 3344 [RFC3344] 📖.
The Home Agent MUST be able to verify that the Mobile Router is authorized to provide mobility service for the Mobile Networks in the Registration Request, before it anchors these Mobile Network Prefixes on behalf of the Mobile Router 🕵️♀️. Forwarding for prefixes MUST NOT be set up without successful authorization of the Mobile Router for those prefixes 🚫. The Mobile Router MUST be notified when a registration fails because it couldn't be successfully authorized for the prefixes it requested 📣.
All Registration Requests and replies MUST be authenticated by the MN-HA Authentication Extension as specified in RFC 3344 [RFC3344] 🔑. When the registration request is sent in explicit mode, i.e., with one or more Mobile Network Prefix extensions, all the Mobile Network Prefix extensions MUST be included before the MN-HA Authentication extension 📋. These extensions MUST also be included in the calculation of the MN-HA authenticator value 🧮.
The Mobile Router should perform ingress filtering on all the packets received on the Mobile Network before reverse tunneling them to the Home Agent 🧹. The Mobile Router MUST drop any packets that don't have a source address belonging to the Mobile Network 🗑️.
The Mobile Router MUST also make sure that the source address of packets arriving on the Mobile Network isn't the same as the Mobile Router's IP address on any interface 👀. These checks protect against nodes trying to launch IP spoofing attacks through the bi-directional tunnel 🥷.
The Home Agent, when it receives packets through the bi-directional tunnel, MUST verify that the source addresses of the outer IP header of the packets are set to the Mobile Router's Care-of Address 🕵️. It also MUST ensure that the source address of the inner IP header is a topologically correct address on the Mobile Network 🧭. This stops nodes from using the Home Agent to launch attacks inside the protected network 🚨.
10.1. Security when Dynamic Routing Protocol Is Used 🔐🦋
If a dynamic routing protocol is used between the Mobile Router and the Home Agent to pass the Mobile Network information into the home network, the routing updates SHOULD be protected with IPsec ESP confidentiality between the Mobile Router and Home Agent 🫶. That keeps information about the home network topology from being visible to eavesdroppers 👁️💅.
11. IANA Considerations ✨
okay bestie, IANA is the org that keeps track of all the protocol numbers, so this section is basically the group chat where new numbers get handed out 🎀
IANA has already set up rules for the existing registry "Mobile IPv4 numbers - per RFC 3344" 📋. The numbering space for Extensions that can show up in Mobile IP control messages (the ones sent to and from UDP port number 434) should be modified 🔧. Note that "should" here is the RFC 2119 word, so it's a SHOULD kind of change 💅.
The new Values and Names for the Type for Extensions in Mobile IP control messages are:
+-------+--------------------------+
| Value | Name |
+-------+--------------------------+
| 148 | Mobile Network Extension |
+-------+--------------------------+
Table 1: New Values and Names for Extensions in Mobile IP Control
MessagesA brand new number space was created for the Values and Names for the Sub-Type for Mobile Network Extensions 🌈. It's initially defined to hold these entries, allocated by this document:
+-------+-----------------------------------------+
| Value | Name |
+-------+-----------------------------------------+
| 0 | Mobile Network Request Extension |
| 1 | Explicit Mode Acknowledgement Extension |
| 2 | Implicit Mode Acknowledgement Extension |
+-------+-----------------------------------------+
Table 2: New Values and Names for the Sub-Type for Mobile Network
ExtensionsThe policy for future assignments to this number space is Standards Action or IESG Approval (see [RFC2434]) 🦋. So new numbers here need that approval, no shortcuts 🙅♀️.
The new Code Values for Mobile IP Registration Reply messages are the following (for a registration denied by the Home Agent) 💀:
+-------+-----------------------------------------------------------+
| Value | Name |
+-------+-----------------------------------------------------------+
| 147 | Mobile Network Prefix operation error (HA_MOBNET_ERROR) |
| 148 | Mobile Router operation is not permitted |
| | (HA_MOBNET_DISALLOWED) |
+-------+-----------------------------------------------------------+
Table 3: New Code Values for Mobile IP Registration ReplyA new number space was also created for the Code Values for the Mobile Network Acknowledgement Extension 🍓. It's initially defined to hold these entries, allocated by this document (result of registration, as sent by the Home Agent):
+---+---------------------------------------------------------------+
| 0 | Success |
| 1 | Invalid prefix length (MOBNET_INVALID_PREFIX_LEN) |
| 2 | Mobile Router is not authorized for prefix |
| | (MOBNET_UNAUTHORIZED) |
| 3 | Forwarding setup failed (MOBNET_FWDING_SETUP_FAILED) |
+---+---------------------------------------------------------------+
Table 4: New Code Values for Mobile Network Acknowledgement ExtensionThe policy for future assignments to this number space is, again, Standards Action or IESG Approval (see [RFC2434]) 🫶.
12. Acknowledgements 🌸
The authors want to thank Christophe Janneteau, George Popovich, Ty Bekiares, Ganesh Srinivasan, Alpesh Patel, Ryuji Wakikawa, George Tsirtsis, and Henrik Levkowetz for their helpful discussions, reviews, and comments 💖. Vijay Devarapalli extensively reviewed one of the later versions of the document 👑. Hans Sjostrand identified the last clarifications about Foreign Agent mode treatment ✨. Pete McCann contributed necessary refinements of many statements 💅.
Mobile IPv4 versions as early as 1996 (RFC 2002 by Charles Perkins) described Mobile Networks and Mobile Routers support 🧚.
Fred Templin pointed out the potential confusion around the term "LFN" 🙈.
Amanda Baber of IANA agreed on the principles for allocating numbers in this specification and suggested improvements to the IANA section 🎀.
Tim Polk of the IESG spotted a deeply entrenched error in managing the Code fields 😭.
Lars Eggert of the IESG suggested allowing the otherwise legal non-contiguous netmask fields, instead of only prefix lengths 🦋.
Dan Romascanu of the IESG pointed out how important it is that Mobile Routers and NEMOv4-enabled Home Agents are manageable, and deployable in MIP4 environments 🔥.
David Borman of TSV-DIR reviewed this document as part of the transport area directorate's ongoing effort to review key IETF documents 🌈. He also raised how the growing usable MTU could negatively affect applications deep inside a Mobile Network ⭐.
Gonzalo Camarillo gave a generalist review, bringing an extra set of eyes to documents being considered for publication (General Area Review Team) 💜.
Jari Arkko of the IESG reviewed the document, suggested necessary improvements, and diligently shepherded it through the IESG 👑🫶.
13. References 📚
13.1. Normative References
[RFC1323] Jacobson, V., Braden, B., and D. Borman, "TCP Extensions for High Performance", RFC 1323, May 1992.
[RFC2006] Cong, D., Hamlen, M., and C. Perkins, "The Definitions of Managed Objects for IP Mobility Support using SMIv2", RFC 2006, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
[RFC2453] Malkin, G., "RIP Version 2", STD 56, RFC 2453, November 1998.
[RFC2794] Calhoun, P. and C. Perkins, "Mobile IP Network Access Identifier Extension for IPv4", RFC 2794, March 2000.
[RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344, August 2002.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006.
13.2. Informative References
[NEMOv4-FA] Tsirtsis, G., Park, V., Narayanan, V., and K. Leung, "FA extensions to NEMOv4 Base", Work in Progress, February 2008.
[RFC3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert, "Network Mobility (NEMO) Basic Support Protocol", RFC 3963, January 2005.
[RFC4885] Ernst, T. and H-Y. Lach, "Network Mobility Support Terminology", RFC 4885, July 2007.
Authors' Addresses 💌
Kent Leung Cisco Systems 170 W. Tasman Drive San Jose, CA 95134 USA
Phone: +1 408-526-5030 EMail: kleung@cisco.com
Gopal Dommety Cisco Systems 170 W. Tasman Drive San Jose, CA 95134 USA
Phone: +1 408-525-1404 EMail: gdommety@cisco.com
Vidya Narayanan QUALCOMM, Inc. 5775 Morehouse Dr San Diego, CA USA
Phone: +1 858-845-2483 EMail: vidyan@qualcomm.com
Alexandru Petrescu Motorola Parc les Algorithmes Saint Aubin Gif-sur-Yvette, Essonne 91140 France
Phone: +33 169354827 EMail: alexandru.petrescu@motorola.com
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