RFC 8278

Mobile Access Gateway (MAG) Multipath Options

📅 published January 2018, from ietf

RFC 8278: Mobile Access Gateway (MAG) Multipath Options 🎀

okay bestie, the paperwork first 📋✨ This is RFC 8278, titled Mobile Access Gateway (MAG) Multipath Options. It's an Internet Standards Track document from the IETF, so it's an actual standard and not just vibes 👑 It's dated January 2018, with ISSN 2070-1721. The authors are P. Seite (Orange), A. Yegin (Actility), and S. Gundavelli (Cisco). The header doesn't list anything it obsoletes or updates.

Abstract 🌈

okay so the big idea is that this spec extends Proxy Mobile IPv6 (PMIPv6) 💖 It lets a mobile access gateway (MAG) register more than one proxy care-of address (pCoA) with the local mobility anchor (LMA), and it can run multiple IP tunnels with the LMA at the same time. The payoff is that the MAG can use all the access networks it has available to route the mobile node's IP traffic. The document defines two new mobility header options: the MAG Multipath Binding option and the MAG Identifier option 🦋

Status of This Memo ✨

so this is an Internet Standards Track document 💅 It's a product of the Internet Engineering Task Force (IETF) and represents the consensus of the IETF community. It went through public review and got approved for publication by the Internet Engineering Steering Group (IESG). If you want more on Internet Standards, check Section 2 of RFC 7841.

For the current status, any errata, and how to send feedback, go to https://www.rfc-editor.org/info/rfc8278 🔥

Copyright Notice 🫶

Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved 💜

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) as in effect on the date of publication. Please read these carefully, because they spell out your rights and restrictions for this document 🙈 Code Components pulled out of this document must include Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions, and they come without warranty, as the Simplified BSD License describes.

Table of Contents 🍓

1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
2.  Conventions and Terminology . . . . . . . . . . . . . . . . .   4
  2.1.  Conventions . . . . . . . . . . . . . . . . . . . . . . .   4
  2.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   5
3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
  3.1.  Example Call Flow . . . . . . . . . . . . . . . . . . . .   5
  3.2.  Traffic Distribution Schemes  . . . . . . . . . . . . . .   6
4.  Protocol Extensions . . . . . . . . . . . . . . . . . . . . .   7
  4.1.  MAG Multipath Binding Option  . . . . . . . . . . . . . .   7
  4.2.  MAG Identifier Option . . . . . . . . . . . . . . . . . .  10
  4.3.  New Status Code for Proxy Binding Acknowledgement . . . .  11
  4.4.  Signaling Considerations  . . . . . . . . . . . . . . . .  11
5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
6.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
  7.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
  7.2.  Informative References  . . . . . . . . . . . . . . . . .  14
Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  14
Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1. Introduction 🌸

okay so multihoming on IP hosts can seriously level up the user experience 💅 When you use multiple access networks at once, you get better network connectivity, more reliability, and better quality of communication. Some of the goals and perks of multihoming support are:

  • Redundancy/Fault-Recovery
  • Load balancing
  • Load sharing
  • Preference settings

per [RFC4908], people running small-scale networks can benefit from a mobile and fixed multihomed setup that uses mobile IP [RFC6275] and Network Mobility (NEMO) [RFC3963] ✨

The motivation for this work is to extend PMIPv6 with multihoming extensions [RFC4908] so it can do the following:

  • Use GRE as the mobile tunneling, possibly with its key extension [RFC5845].
  • Use UDP encapsulation [RFC5844] to support NAT traversal in an IPv4 networking environment.
  • Use the prefix delegation mechanism [RFC7148].
  • Use the Vendor Specific Mobility Option [RFC5094], for example, so the MAG and LMA can swap info (like WAN interface QoS metrics) and make better traffic-steering decisions 🦋

so PMIPv6 has two mobility entities 🫶 The first is the MAG, which acts as the default gateway for the end node (either a mobile or a fixed node) attached to the MAG's access links. The second is the LMA, which acts as the topological anchor point. An IP tunnel gets created between the MAG and the LMA using any one of the supported encapsulation modes. After that, the MAG and LMA spread the end node's traffic across these tunnels. All PMIPv6 operations happen on behalf of the end node and its correspondent node, which is why PMIPv6 is such a good fit for the multihomed architecture described in [RFC4908] 💖

Taking the LTE and WLAN networking environments as examples, the PMIPv6-based multihomed architecture looks like Figure 1 🌈 In this example, IP flows Flow-1 and Flow-3 are routed over Tunnel-1, and Flow-2 is routed over Tunnel-2. Flow-4, though, is distributed across both Tunnel-1 and Tunnel-2 paths. iconic 🔥

     Flow-1
      |
      |Flow-2              _----_
      | |         CoA-1  _(      )_   Tunnel-1  Flow-1
      | |    .---=======(   LTE    )========\   Flow-3
      | |    |           (_      _)          \  Flow-4
      | |    |             '----'             \
      | | +=====+                              \  +=====+    _----_
      | '-|     |                               \ |     |  _(      )_
      '---| MAG |                                 | LMA |-( Internet )--
      .---|     |                                 |     |  (_      _)
      | .-|     |                               / |     |    '----'
      | | +=====+                              /  +=====+
      | |    |             _----_             /
      | |    |    CoA-2  _(      )_ Tunnel-2 /
      | |    .---=======(   WLAN  )========/    Flow-2
      | |                (_     _)              Flow-4
      | |                  '----'
      |Flow-3
      |
     Flow0-4

Figure 1: Multihomed MAG Using Proxy Mobile IPv6

okay but here's the catch 🙈 The current version of PMIPv6 does not let a MAG register more than one pCoA with the LMA. Put another way, only one MAG/LMA link (an IP-in-IP tunnel) can be used at a time. This document fixes that limitation by defining the multiple pCoAs extension for PMIPv6 💅✨

2. Conventions and Terminology 🎀

2.1. Conventions 💜

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

2.2. Terminology 🧚

All mobility-related terms used in this document are to be interpreted as defined in [RFC5213], [RFC5844], and [RFC7148]. This document also uses the following term:

IP-in-IP

IP-within-IP encapsulation [RFC2473] [RFC4213] 🦋

3. Overview ✨

3.1. Example Call Flow 📞

Okay bestie, Figure 2 is the call flow showing multi-access support with PMIPv6 💅 The MAG in this scenario has both WLAN and LTE interfaces and is also set up with multihoming 🌈 Here's how it goes:

Steps (1) and (2): The MAG attaches to both the WLAN and LTE networks. Then it gets two different pCoAs, one for each access 🦋

Step (3): The MAG sends a Proxy Binding Update (PBU) over LTE, carrying the new MAG Multipath Binding (MMB) and MAG Network Access Identifier (MAG-NAI) options, to the LMA ✨ This can be for a physical mobile node attached to the MAG, or for a logical mobile node configured on the mobile access gateway. A logical mobile node is basically a logical representation of a mobile node, set up as a configuration that's always enabled on the MAG 🧚 The mobility session created on the LMA (so, a Binding Cache Entry (BCE) gets made) is marked with multipath support 💜

Step (4): The LMA replies with a Proxy Binding Acknowledgement (PBA) that includes the Home Network Prefix (HNP) and other session parameters allocated for that mobility session 🎀

Step (5): An IP tunnel gets created between the MAG and the LMA over LTE access, using any one of the supported encapsulation modes 🌸

Steps (6) to (8): The MAG repeats steps (3) to (5) over WLAN access 📶 This time it includes the HNP it got in step (4) in the PBU. The LMA updates its binding cache by creating a new mobility session for this MAG. Iconic 👑

Steps (9) and (10): The IP hosts MN_1 and MN_2 get IP addresses from the mobile network prefix that the LMA delegated to the MAG 🫶

   +=====+ +=====+     +=====+      +=====+      +=====+         +=====+
   | MN_1| | MN_2|     | MAG |      | WLAN|      | LTE |         | LMA |
   +=====+ +=====+     +=====+      +=====+      +=====+         +=====+
      |       |           |            |            |               |
      |       |           |            |            |               |
      |       |           | (1) ATTACH |            |               |
      |       |           | <--------> |            |               |
      |       |           | (2) ATTACH              |               |
      |       |           | <---------------------->|               |
      |       |           | (3) PBU (MAG-NAI, MMB, ...)             |
      |       |           | ------------------------*-------------->|
      |       |           |                                         |
      |       |           |                                   Accept PBU
      |       |           |                               (allocate HNP,
      |       |           |                                  create BCE)
      |       |           | (4) PBA (MMB, ...)                      |
      |       |           | <-----------------------*---------------|
      |       |           | (5) TUNNEL INTERFACE CREATION over LTE  |
      |       |           |-============== TUNNEL ==*==============-|
      |       |           |                                         |
      |       |           | (6) PBU (MAG-NAI, MMB, ...)             |
      |       |           | -----------*--------------------------->|
      |       |           |                                         |
      |       |           |                                   Accept PBU
      |       |           |                                 (update BCE)
      |       |           | (7) PBA (MMB, ...)                      |
      |       |           | <----------*--------------------------- |
      |       |           | (8) TUNNEL INTERFACE CREATION over WLAN |
      |       |           |-===========*== TUNNEL =================-|
      |   (9) ATTACH      |                                         |
      | <---------------> |                                         |
      |       |(10) ATTACH|                                         |
      |       |<--------> |                                         |

Figure 2: Functional Separation of the Control and User Planes

3.2. Traffic Distribution Schemes 🚦

So once the MAG has registered a multipath binding with the LMA, there are going to be multiple established overlay tunnels between them 🦋 The MAG and the LMA can use any one, or more, of the available tunnel paths to route the mobile node's IP traffic. This specification does not recommend or define any specific traffic distribution scheme. BUT it does call out two well-known approaches that implementations can potentially use: per-flow and per-packet traffic distribution 💅

Per-Flow Traffic Distribution 🌊

  • In this approach, the MAG and the LMA associate each of the IP flows (upstream and downstream) with a specific tunnel path. The packets in a given IP flow are always routed on the same overlay tunnel path. They are never split and routed concurrently on more than one tunnel path. A given flow can be moved from one tunnel path to another, but the flow is never split 🫶 The decision to bind a given IP flow to a specific tunnel path is based on the traffic distribution policy. That policy is either statically configured on both the MAG and the LMA, or dynamically negotiated over PMIPv6 signaling. The Flow Binding extension [RFC6089] and Traffic Selectors for Flow Bindings [RFC6088] define the mechanism and the semantics for exchanging the traffic policy between two tunnel peers. The same mechanism and the mobility options are used here 🎀

Per-Packet Traffic Distribution 🎆

  • In this approach, packets belonging to a given IP flow will be split and routed across more than one tunnel path. The exact approach for traffic distribution, or the distribution weights, is outside the scope of this specification 🙈 In a very simplistic approach, assuming the established tunnel paths have symmetric characteristics, the packets can be equally distributed on all the available tunnel paths. In a different scenario, when the links have different speeds, the chosen approach can be based on weighted distribution (e.g., n:m ratio). BUT in any of these approaches, implementations have to be sensitive to asymmetric link characteristics and the resulting issues, like reordering, buffering, and the impact on application performance. Care must be taken to make sure there's no negative impact on application performance from using this approach 💀

4. Protocol Extensions 🔧

4.1. MAG Multipath Binding Option 🎀

The MAG Multipath Binding option is a new mobility header option, defined for use with PBU and PBA messages exchanged between the LMA and the MAG ✨

This mobility header option is used for requesting multipath support. It indicates that the MAG is asking the LMA to register the current CoA associated with the request as one of the many CoAs through which the MAG can be reached. It's also used for carrying the information related to the access network associated with that CoA 🌈

The MAG Multipath Binding option does not have any alignment requirement. Its format is shown in Figure 3:

   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      |    If-ATT     |    If-Label   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Binding ID   |B|O|             Reserved                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: MAG Multipath Binding Option

Type 🏷️

Type: MAG Multipath Binding (63)

Length 📏

8-bit unsigned integer indicating the length of the option in octets, excluding the Type and Length fields.

Interface Access-Technology Type (If-ATT) 📡

This 8-bit field identifies the Access-Technology type of the interface through which the mobile node is connected. The permitted values for this are from the Access Technology Type registry <https://www.iana.org/assignments/mobility-parameters/> defined in [RFC5213].

Interface Label (If-Label) 🏷️

This 8-bit unsigned integer represents the interface label 💖

The interface label is an identifier configured on the WAN interface of the MAG. All the WAN interfaces of the MAG that are used for sending PBU messages are configured with a label. The labels merely identify the type of WAN interface and are mainly used in application-routing policies. For example, a Wi-Fi interface can be configured with a label "9" and an LTE interface with a label "11". The same label can also be configured on two WAN interfaces with similar characteristics (e.g., two Ethernet interfaces with the same label) 🌸

Interface labels are signaled from the MAG to the LMA in the PBU messages, and both the LMA and the MAG can mark each of the dynamically created Binding/Tunnel with the associated label. These labels are used to generate consistent application-routing rules on both the LMA and the MAG. For example, there can be a policy requiring HTTP packets to be routed over an interface with the interface label "9". If none of the interfaces with interface label "9" are available, the traffic needs to be routed over the interface with the interface label "11". The MAG and the LMA can apply this routing rule by exchanging interface labels in PBU messages and associating the application flows with tunnels that have the matching interface labels 🧠

Binding Identifier (BID) 🆔

This 8-bit unsigned integer is used for identifying the binding. The permitted values are 1 through 254. The values 0 and 255 are reserved 🔢

The MAG identifies each of the mobile node's bindings with a unique identifier. The MAG includes that identifier in the PBU message. When the PBU request is accepted by the LMA, the resulting binding is associated with this BID in the mobile node's Binding Cache entry 🦋

Bulk Re-registration Flag (B) 🔁

If set to a value of (1), this flag tells the LMA to consider this as a request to update the binding lifetime of all the mobile node's bindings upon accepting this specific request. The (B) flag MUST NOT be set to a value of (1) if the value of the Registration Overwrite (O) flag is set to a value of (1). 🚫

Registration Overwrite (O) 🗂️

If set to a value of (1), this flag tells the LMA that, upon accepting this request, it should replace all of the mobile node's existing bindings with this binding. This flag MUST NOT be set to a value of (1) if the value of the Bulk Re-registration Flag (B) is set to a value of (1). This flag MUST be set to a value of (0) in De-Registration requests 🙅‍♀️

Reserved 🫧

This field is unused in this specification. The value MUST be set to zero (0) by the sender and MUST be ignored by the receiver 🤍

4.2. MAG Identifier Option ✨

okay so this one is the MAG Identifier option 🎀. It's a brand new mobility header option made for PBU and PBA messages going between the LMA and the MAG, and its whole job is carrying the MAG's identity 🫶. It has no alignment requirements, so no padding drama 💅.

   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      |  Subtype      |  Reserved     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Identifier ...                      ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: MAG Identifier Option 🌸

Type

The type is MAG Identifier (64) 🍓.

Length

This is an 8-bit unsigned integer that tells you the length of the option in octets, and it doesn't count the Type and Length fields themselves 🧮.

Subtype

This is a one-byte unsigned integer used to figure out what kind of thing the Identifier field holds. The accepted values are the registered type values from the "Mobile Node Identifier Option Subtypes" registry at https://www.iana.org/assignments/mobility-parameters/ 📋.

Reserved

This field is unused in this specification. The value MUST be set to zero (0) by the sender and MUST be ignored by the receiver 🙈.

Identifier

This is a variable-length identifier, and its type is whatever the Subtype field says it is 🦋.

4.3. New Status Code for Proxy Binding Acknowledgement 💜

this document defines one new Status Code value to use in PBA messages 🎀.

The LMA SHOULD use this error code when it rejects a PBU message from a MAG that's asking for a multipath binding 🙅‍♀️. The potential reason for rejecting the request is:

  • The LMA does not support multipath binding.
CANNOT_SUPPORT_MULTIPATH_BINDING (Cannot Support Multipath Binding):
180

4.4. Signaling Considerations 🧠

okay this section is basically the rulebook for how the MAG and LMA talk about multipath, so let's go through it 🔥.

  • The MAG, when requesting multipath support, MUST include the MAG Multipath Binding option (Section 4.1) in each of the PBU messages that it sends through the different WAN interfaces. Including this option is a hint that the MAG is asking for multipath support. On top of that, the MAG Identifier option MUST also be present in the PBU message 🫶.
  • If the MAG knows the LMA supports the multipath binding option defined in this specification, and it chooses to use multiple paths, then it can send the PBU packets for each of the paths, either one after another or all at once ⚡. But if the MAG isn't aware of the LMA's capability, then it SHOULD first discover that capability by sending PBU packets with multipath on only one path first. This makes sure the LMA won't be overwriting the binding of one path with the other path 👀.
  • If the LMA supports multipath capability as defined in this specification, and it enables that for a mobile node's session because the MAG asked, then the LMA MUST include the Multipath Binding option (Section 4.1) without the MAG-NAI option (Section 4.2) in the corresponding PBA reply 💖.
  • If the LMA is a legacy LMA that doesn't support this specification, the LMA will skip the MAG Multipath Binding option (and MAG-NAI option) and process the rest of the message as specified in the base PMIPv6 specification ([RFC5213]). It also won't include the MAG Multipath Binding option (or the MAG-NAI option) in the PBA message. When the MAG gets a PBA message without the MAG Multipath Binding option, it SHOULD disable multipath support for the mobile node 😭.
  • If the mobile node isn't authorized for multipath support, then the LMA will reject the request by sending a PBA message with the Status field value set to CANNOT_SUPPORT_MULTIPATH_BINDING (Section 4.3) 🚫. The LMA MUST echo the MAG Multipath Binding option (without the MAG-NAI option) in the PBA message. When the MAG gets this message, it SHOULD disable multipath support for the mobile node 💅.

5. IANA Considerations 📚

this specification defines a brand new mobility option: the MAG Multipath Binding option 🦋. The format of this option is described in Section 4.1. The type value 63 has been allocated for this mobility option from the "Mobility Options" registry at http://www.iana.org/assignments/mobility-parameters 🎀.

This specification also defines another new mobility option: the MAG Identifier option. Its format is described in Section 4.2. The type value 64 has been allocated for this mobility option from the "Mobility Options" registry at http://www.iana.org/assignments/mobility-parameters ✨.

This document defines a new status value, CANNOT_SUPPORT_MULTIPATH_BINDING (180), for use in PBA messages, as described in Section 4.3. This value has been assigned from the "Status Codes" registry at http://www.iana.org/assignments/mobility-parameters 🌈.

6. Security Considerations 💀

okay this is the serious part, bestie, so pay attention 🙈🔥. This specification lets a MAG set up multiple PMIPv6 tunnels with an LMA by registering a care-of address for each of its connected access networks. Basically, the mobile node's IP traffic can get routed through any of the tunnel paths, based on the negotiated flow policy 🛤️. This new capability has no impact on the protocol security.

On top of that, this specification defines two new mobility header options: the MAG Multipath Binding option and the MAG Identifier option. They're carried like any other mobility header option, as specified in [RFC5213]. So they inherit the security guidelines from [RFC5213] 🔒.

Bottom line: this specification does not weaken the security of the PMIPv6 Protocol and does not introduce any new security vulnerabilities. Phew 😮‍💨💖

7. References 📖

7.1. Normative References

7.2. Informative References

Acknowledgements 🫶

the authors want to give a big shoutout to everyone in the Distributed Mobility Management Working Group for their discussions and feedback on this topic 🌸. They also want to thank Jouni Korhonen, Jong Hyouk Lee, Dirk Von-Hugo, Seil Jeon, Carlos Bernardos, Robert Sparks, Adam Roach, Kathleen Moriarty, Hilarie Orman, Ben Campbell, Warren Kumari, and Dhananjay Patki for their review feedback 👑. Extra special thanks to Mirja Kuehlewind for a very thorough review and for suggesting many text improvements 💜✨.

Authors' Addresses 🦋

Pierrick Seite
Orange
4, rue du Clos Courtel, BP 91226
Cesson-Sevigne  35512
France

Email: pierrick.seite@orange.com


Alper Yegin
Actility
Turkey

Email: alper.yegin@actility.com


Sri Gundavelli
Cisco
170 West Tasman Drive
San Jose, CA  95134
United States of America

Email: sgundave@cisco.com

That's the whole spec, bestie. You made it through! 🌈💅🎀

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