RFC 4798

Connecting IPv6 Islands over IPv4 MPLS Using IPv6 Provider Edge Routers (6PE)

📅 published February 2007, from ietf

RFC 4798: Connecting IPv6 Islands over IPv4 MPLS Using IPv6 Provider Edge Routers (6PE) 🎀

okay bestie, this one is a Standards Track doc from the Network Working Group 🧚 It's dated February 2007 and the authors are J. De Clercq (Alcatel-Lucent), D. Ooms (OneSparrow), S. Prevost (BT), and F. Le Faucheur (Cisco) 💜 The title block doesn't list anything it obsoletes or updates, so no old RFCs are getting replaced here ✨

Status of This Memo ✨

this doc specifies an Internet standards track protocol for the Internet community, and it's asking everyone for discussion and suggestions for improvements 🫶 for the current 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 🌈

Copyright Notice 🦋

Abstract 🌸

this doc explains how to connect IPv6 islands over a Multiprotocol Label Switching (MPLS)-enabled IPv4 cloud 💖 the trick is using IPv6 Provider Edge routers (6PE). these are Dual Stack, so they can talk to the IPv6 islands on one side and the MPLS core on the other. the core itself only needs to run IPv4 MPLS 🙈 the 6PE routers swap IPv6 reachability info right through the core, using Multiprotocol BGP (MP-BGP) over IPv4. the BGP Next Hop field carries the IPv4 address of the 6PE router, so dynamically set up IPv4-signaled MPLS Label Switched Paths (LSPs) can be used with no explicit tunnel configuration needed ✨

Table of Contents 💅

   1. Introduction ....................................................2
      1.1. Requirements Language ......................................4
   2. Protocol Overview ...............................................4
   3. Transport over IPv4-signaled LSPs and IPv6 Label Binding ........5
   4. Crossing Multiple IPv4 Autonomous Systems .......................7
   5. Security Considerations ........................................10
   6. Acknowledgements ...............................................10
   7. References .....................................................11
      7.1. Normative References ......................................11
      7.2. Informative References ....................................11

1. Introduction ✨

okay so there are a few ways to give IPv6 connectivity over an MPLS core network [RFC4029] 🎀 (i) you require MPLS networks to set up IPv6-signaled Label Switched Paths (LSPs) and then use those LSPs for IPv6 connectivity, (ii) you use configured tunneling over IPv4-signaled LSPs, or (iii) you use the IPv6 Provider Edge (6PE) approach defined in this doc 💖

the 6PE approach is kinda required as an alternative to standard tunnels 😭 it's built for an MPLS environment where all tunnels are set up dynamically. that way it's perfect for places where configuring and maintaining explicit tunnels is just not an option 🙅‍♀️

this doc describes how the 6PE approach works for connecting IPv6 islands over an IPv4 MPLS cloud. the edge routers that connect to the IPv6 islands have to be Dual Stack Multiprotocol-BGP-speaking routers [RFC4760], while the core routers only need to run IPv4 MPLS 🧚 the approach uses MP-BGP over IPv4, identifies the 6PE routers by their IPv4 address, and rides on IPv4-signaled MPLS LSPs that don't need any explicit tunnel configuration 🦋

the terminology of [RFC2460] and [RFC4364] is used all throughout 👑

in this doc, an 'IPv6 island' is a network running native IPv6 as per [RFC2460] 🌈 a classic example is a customer's IPv6 site, connected through its IPv6 Customer Edge (CE) router to one (or more) Dual Stack Provider Edge router(s) of a Service Provider. those IPv6 Provider Edge routers (6PE) hook up to an IPv4 MPLS core network ✨

          +--------+
          |site A  CE---+  +-----------------+
          +--------+    |  |                 |       +--------+
                       6PE-+  IPv4 MPLS core +-6PE--CE site C |
          +--------+    |  |                 |       +--------+
          |site B  CE---+  +-----------------+
          +--------+

           IPv6 islands          IPv4 cloud       IPv6 island
          <-------------><---------------------><-------------->

                                Figure 1

this interconnection method is mainly for an Internet Service Provider (ISP) that already has an IPv4 MPLS network 💅 that ISP knows BGP (maybe it already sells BGP/MPLS VPN services) and wants to offer IPv6 to some of its customers 🎀 but the ISP may not (yet) want to upgrade its network core to IPv6, or use only IPv6-over-IPv4 tunneling. with 6PE, the provider only has to upgrade some Provider Edge (PE) routers to Dual Stack operation so they act as 6PE routers (and as route reflectors, if those are used to exchange IPv6 reachability among 6PE routers). the IPv4 MPLS core routers stay totally untouched 🙈 those 6PE routers give connectivity to IPv6 islands, and they can also run other services at the same time (IPv4 connectivity, IPv4 L3VPN services, L2VPN services, etc.) 🍓 plus, with 6PE, no tunnels need to be explicitly configured, and no IPv4 headers have to be stuck in front of the IPv6 packets between the customer and the provider edge 😭

the ISP gets IPv6 connectivity to its peers and upstreams through means outside the scope of this doc, and its 6PE routers readvertise that over the IPv4 MPLS core with MP-BGP 💜

the interface between the edge router of the IPv6 island (the Customer Edge (CE) router) and the 6PE router is a native IPv6 interface, which can be physical or logical ✨ a routing protocol (IGP or EGP) may run between the CE router and the 6PE router to distribute IPv6 reachability info. or you can use static routes and/or a default route on the 6PE router and the CE router to control reachability instead 🧚 an IPv6 island may also connect to the provider network over more than one interface 🌸

the 6PE approach in this doc works for customers who already have an IPv4 service from the network provider and also need IPv6 🫶 it works for customers who only need IPv6 connectivity too 💖

the scenario is also described in [RFC4029] 🦋

heads up: the 6PE approach in this doc gives global IPv6 reachability. IPv6 VPNs aren't in scope here, and they're covered in [RFC4659] 👑

deploying 6PE over an existing IPv4 MPLS cloud doesn't need any new mechanisms in the core (other than possibly the stuff described at the end of Section 3 for dealing with dynamic MTU discovery) 🌈 setting up and running 6PE has a lot in common with an IPv4 VPN service ([RFC4364]) or an IPv6 VPN service ([RFC4659]) over an IPv4 MPLS core, because they all use MP-BGP to distribute non-IPv4 reachability information for transport over an IPv4 MPLS core ✨ but 6PE is somewhat simpler, since it doesn't involve all the VPN concepts, like Virtual Routing and Forwarding (VRFs) tables 💅

1.1. Requirements Language 🎀

the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this doc are to be interpreted as described in RFC 2119 [RFC2119] 🫶

2. Protocol Overview 🦋

each IPv6 site is connected to at least one Provider Edge router that sits on the border of the IPv4 MPLS cloud 🧚 we call that router a 6PE router. the 6PE router MUST be dual stack IPv4 and IPv6 💖 it MUST be configured with at least one IPv4 address on the IPv4 side and at least one IPv6 address on the IPv6 side 🌈 the configured IPv4 address needs to be routable in the IPv4 cloud, and there needs to be a label bound via an IPv4 label distribution protocol to that IPv4 route 🔥

because of this, every 6PE router knows which MPLS label to use to send packets to any other 6PE router ✨ an MPLS network already offering BGP/MPLS IP VPN services already meets these requirements, so it's basically giving 💅

no extra routes need to be injected into the IPv4 cloud 🙈

we call a 6PE router that receives IPv6 packets from an IPv6 site an ingress 6PE router (relative to those IPv6 packets) 👑 and a 6PE router that forwards IPv6 packets to an IPv6 site an egress 6PE router (relative to those IPv6 packets) 🌸

interconnecting IPv6 islands over an IPv4 MPLS cloud happens in these steps:

Exchange IPv6 reachability information among 6PE routers with MP-BGP [RFC2545]:

the 6PE routers MUST exchange the IPv6 prefixes over MP-BGP sessions as per [RFC2545] running over IPv4 🫶 the MP-BGP Address Family Identifier (AFI) used MUST be IPv6 (value 2). in doing so, the 6PE routers convey their IPv4 address as the BGP Next Hop for the advertised IPv6 prefixes ✨ the IPv4 address of the egress 6PE router MUST be encoded as an IPv4-mapped IPv6 address in the BGP Next Hop field 💖 this encoding is consistent with the definition of an IPv4-mapped IPv6 address in [RFC4291] as an "address type used to represent the address of IPv4 nodes as IPv6 addresses" 🦋 on top of that, the 6PE MUST bind a label to the IPv6 prefix as per [RFC3107]. the Subsequence Address Family Identifier (SAFI) used in MP-BGP MUST be the "label" SAFI (value 4) as defined in [RFC3107] 🧚 the rationale for this and the label allocation policies are discussed in Section 3 🎀

Transport IPv6 packets from the ingress 6PE router to the egress 6PE router over IPv4-signaled LSPs:

the ingress 6PE router MUST forward IPv6 data over the IPv4-signaled LSP toward the egress 6PE router. that egress router is identified by the IPv4 address advertised in the IPv4-mapped IPv6 address of the BGP Next Hop for the corresponding IPv6 prefix 👑

as required by the BGP specification [RFC4271], PE routers form a full peering mesh unless Route Reflectors are used 🌈

3. Transport over IPv4-signaled LSPs and IPv6 Label Binding ✨

okay so this is where the IPv4-mapped IPv6 addresses get to be iconic 🦋 A 6PE router that needs to forward an IPv6 packet can automatically figure out which IPv4-signaled LSP to use for a given IPv6 destination, just by looking at the MP-BGP routing information. no manual lookup, no drama 💅

The IPv4-signaled LSPs can be set up with any existing label setup technique [RFC3031] (LDP, RSVP-TE, etc.) 🌸

bestie, this part is a must-do 😭 To make sure systems that implement the 6PE approach in this document can actually talk to each other, all of them MUST support tunneling over IPv4-signaled MPLS LSPs established by LDP [RFC3036]. that's the baseline, no exceptions 🫶

When tunneling IPv6 packets across the IPv4 MPLS backbone, the ingress 6PE Router does NOT go the "prepend an IPv4 header, then impose a label based on that header" route. instead, the ingress 6PE Router MUST directly perform label imposition on the IPv6 header, without prepending any IPv4 header at all 🧚 The (outer) label that gets imposed MUST correspond to the IPv4-signaled LSP that starts on the ingress 6PE Router and ends on the egress 6PE Router 💜

in theory, this could work with a single level of labels 🤔 but a second level of labels is a total glow-up. those labels are bound to IPv6 prefixes through MP-BGP advertisements, as described in [RFC3107] ✨

here's why the second label is so worth it 💖 With a second level label, Penultimate Hop Popping (PHP) can happen on the IPv4 Label Switch Router (LSR) right before the egress 6PE router, and that penultimate router doesn't need any IPv6 capabilities or upgrades. why? because it still only transmits MPLS packets after the PHP, instead of having to send IPv6 packets and encapsulate them properly 🍓

there's also a plot twist 🙈 An existing IPv4-signaled LSP that uses the "IPv4 Explicit NULL label" on the last hop can't carry IPv6 with just a single label, because that label can't carry native IPv6 traffic (see [RFC3032]). this might happen because the LSP is already carrying IPv4 traffic under the Pipe Diff-Serv Tunneling Model defined in [RFC3270]. it could carry labeled IPv6 traffic though (see [RFC4182]) 🎀

so yeah, a second label MUST be used with the 6PE approach. no skipping it 👑

The label that MP-BGP binds to the IPv6 prefix tells the egress 6PE Router that the packet is an IPv6 packet 🌈 The label the egress 6PE Router advertises through MP-BGP MAY be an arbitrary label value, which identifies an IPv6 routing context or an outgoing interface to send the packet to. it MAY also be the IPv6 Explicit Null Label. and an ingress 6PE Router MUST be able to accept any label advertised this way 🦋

Now the MTU stuff, which is a lot but it matters 😭 [RFC2460] requires that every link in the IPv6 Internet have an MTU of 1280 octets or larger. so on MPLS links used to carry IPv6 under the 6PE approach that do not support link-specific fragmentation and reassembly, the MTU must be configured to at least 1280 octets plus the encapsulation overhead ✨

some IPv6 hosts might send packets bigger than the MTU available in the IPv4 MPLS core, and they rely on Path MTU discovery to learn about those limits 🌸 To make MTU discovery simpler, one option is for the network administrator to engineer the MTU on the core facing interfaces of the ingress 6PE so it matches the core MTU 💅 Then the ingress 6PE can send ICMP 'Packet Too Big' messages back without those packets ever entering the MPLS core 🫶 Otherwise, routers in the IPv4 MPLS network have the option to generate an ICMP "Packet Too Big" message using the mechanisms in Section 2.3.2, "Tunneling Private Addresses through a Public Backbone" of [RFC3032] 🧚

⚠️ bestie, this is the scary part 😭 If a core router has an outgoing link with an MTU smaller than 1280 and receives an encapsulated IPv6 packet larger than 1280, the mechanisms in [RFC3032] may mean the "Packet Too Big" message never makes it back to the sender. why? According to [RFC4443], the core router builds an ICMP "Packet Too Big" message filled with the invoking packet up to 1280 bytes. then, when it's forwarded downstream toward the egress PE as per [RFC3032], the MTU of the outgoing link makes the packet get dropped 💀 This can cause real operational problems, because the originator notices their data isn't getting through without knowing why or where it's being discarded 🙈 This issue only shows up if the MTU recommendation above (at least 1280 octets plus encapsulation overhead on MPLS links) isn't followed, maybe because of a misconfiguration 🍓

4. Crossing Multiple IPv4 Autonomous Systems 🌍

okay this section is about the case where two IPv6 islands are connected to different Autonomous Systems (ASes) 💜

Just like the multi-AS backbone operations for IPv4 VPNs described in Section 10 of [RFC4364], three main approaches can be distinguished 👑

a. eBGP redistribution of IPv6 routes from AS to neighboring AS 🦋

This approach is the equivalent, for exchanging IPv6 routes, of procedure (a) in Section 10 of [RFC4364] for exchanging VPN-IPv4 routes 🌸

In this approach, the 6PE routers use IBGP (according to [RFC2545] and [RFC3107], and as described in this document for the single-AS situation) to redistribute labeled IPv6 routes either to an Autonomous System Border Router (ASBR) 6PE router, or to a route reflector that has an ASBR 6PE router as a client ✨ The ASBR then uses eBGP to redistribute the (non-labeled) IPv6 routes to an ASBR in another AS. that ASBR passes them to the 6PE routers in its AS, as described earlier in this specification, or maybe to yet another ASBR, which keeps passing them along etc. 🧚

There may be one, or multiple, ASBR interconnections across any two ASes 💖 IPv6 needs to be activated on the inter-ASBR links, and each ASBR 6PE router has at least one IPv6 address on the interface to that link 🫶

No inter-AS LSPs are used here. Effectively, each AS has its own separate mesh of LSPs across its 6PE routers 🎀

In this approach, the ASBR exchanging IPv6 routes may peer over IPv6 or IPv4. The exchange of IPv6 routes MUST be carried out as per [RFC2545] 💅

Note that the peering ASBR in the neighboring AS, which the IPv6 routes were distributed to over eBGP, should in turn redistribute those routes to the 6PEs in its AS using IBGP, encoding its own IPv4 address as the IPv4-mapped IPv6 BGP Next Hop 🌈

b. eBGP redistribution of labeled IPv6 routes from AS to neighboring AS 🌟

This approach is the equivalent, for exchanging IPv6 routes, of procedure (b) in Section 10 of [RFC4364] for exchanging VPN-IPv4 routes 💜

In this approach, the 6PE routers use IBGP (as described earlier in this document for the single-AS situation) to redistribute labeled IPv6 routes either to an Autonomous System Border Router (ASBR) 6PE router, or to a route reflector that has an ASBR 6PE router as a client. The ASBR then uses eBGP to redistribute the labeled IPv6 routes to an ASBR in another AS. That ASBR passes them to the 6PE routers in its AS, as described earlier in this specification, or maybe to another ASBR, which keeps passing them along, etc. 🦋

There may be one, or multiple, ASBR interconnections across any two ASes 🌸 IPv6 may or may not be activated on the inter-ASBR links 🙈

This approach requires that label switched paths be established across ASes 🍓 So the corresponding considerations for procedure (b) in Section 10 of [RFC4364] apply equally to this approach for IPv6 🫶

In this approach, the ASBR exchanging IPv6 routes may peer over IPv4 or IPv6 (and if it's IPv6, obviously IPv6 needs to be activated on the inter-ASBR link). When peering over IPv6, the exchange of labeled IPv6 routes MUST be carried out as per [RFC2545] and [RFC3107]. When peering over IPv4, the exchange of labeled IPv6 routes MUST be carried out as per [RFC2545] and [RFC3107], with the IPv4 address of the ASBR encoded as an IPv4-mapped IPv6 address in the BGP Next Hop field 👑

c. Multi-hop eBGP redistribution of labeled IPv6 routes between source and destination ASes, with eBGP redistribution of labeled IPv4 routes from AS to neighboring AS. 🌈

This approach is the equivalent, for exchanging IPv6 routes, of procedure (c) in Section 10 of [RFC4364] for exchanging VPN-IPv4 routes ✨

In this approach, IPv6 routes are neither maintained nor distributed by the ASBR routers 💖 The ASBR routers don't need to be dual stack. They may be IPv4/MPLS-only routers 🧚 An ASBR needs to maintain labeled IPv4 /32 routes to the 6PE routers within its AS, and it uses eBGP to distribute these routes to other ASes 🎀 ASBRs in any transit ASes also have to use eBGP to pass along the labeled IPv4 /32 routes 💅 This results in an IPv4 label switched path from the ingress 6PE router to the egress 6PE router 🌸 Now 6PE routers in different ASes can establish multi-hop eBGP connections to each other over IPv4, and they can exchange labeled IPv6 routes (with an IPv4-mapped IPv6 BGP Next Hop) over those connections 🫶

IPv6 need not be activated on the inter-ASBR links 🦋

The considerations for procedure (c) in Section 10 of [RFC4364] apply equally to this approach for IPv6. That includes the possible use of multi-hop eBGP connections via route reflectors in different ASes, and the use of a third label in case the IPv4 /32 routes for the PE routers are NOT made known to the P routers 🙈

This approach requires that IPv4 label switched paths be established across the ASes, leading from a packet's ingress 6PE router to its egress 6PE router 🍓 So the considerations for procedure (c) in Section 10 of [RFC4364], about LSPs spanning multiple ASes, apply equally to this approach for IPv6 💜

Note also that the exchange of IPv6 routes can only start after BGP has created IPv4 connectivity between the ASes 🌟

5. Security Considerations 🔒

okay so this section is about the security stuff, and it's giving very "careful, we're in charge of trust here" energy 🫶 The extensions in this document let BGP share reachability info about IPv6 routes across an MPLS IPv4 core network. No brand-new security issues pop up beyond what already exists in BGP-4 and MP-BGP for IPv6. ✨

The security features of BGP, plus whatever security policy the ISP domain has, still apply 💅

For inter-AS distribution of IPv6 routes under case (a) of Section 4 of this document, there are no new security issues beyond the ones already in eBGP for IPv6 [RFC2545]. Easy 🍓

Now cases (b) and (c) of Section 4 are where it gets spicy 🌶️ Those procedures need label switched paths to be set up across the AS boundaries, so the right trust relationships have to exist between all the ASes along the path. You have to watch out for "label spoofing" 👀 So an ASBR 6PE SHOULD only accept labeled packets from its peer ASBR 6PE when the topmost label is one it has explicitly signaled to that peer ASBR 6PE. 💖

Case (c) of Section 4 is even trickier, ngl 😭 The MPLS label that comes with the IPv6 routes over multi-hop eBGP is sent straight from the egress 6PE to ingress 6PEs in another AS (or through route reflectors). That label gets advertised right through the AS boundaries, transparently. So when the egress 6PE that sent the labeled IPv6 routes gets a data packet with that label on top of its stack, it might not be able to tell whether the ingress 6PE that pushed the label was actually allowed to do that. Which means one AS could be open to label spoofing from a different AS. 🙈 The same issue applies to option (c) of Section 10 of [RFC4364]. Just like with [RFC4364], fixing this particular issue is still for further study 🔍

6. Acknowledgements 🎀

big thank-yous to Gerard Gastaud and Eric Levy-Abegnoli, who helped with this doc 🫶 We also want to thank Tri T. Nguyen, who started this document but sadly passed away much too soon 🕯️🌸 And a shoutout to Pekka Savola for the super valuable comments and suggestions ✨

7. References 📚

7.1. Normative References

[RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
           Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
           (IPv6) Specification", RFC 2460, December 1998.

[RFC2545]  Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol
           Extensions for IPv6 Inter-Domain Routing", RFC 2545, March
           1999.

[RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
           Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
           Encoding", RFC 3032, January 2001.

[RFC3036]  Andersson, L., Doolan, P., Feldman, N., Fredette, A., and
           B. Thomas, "LDP Specification", RFC 3036, January 2001.

[RFC3107]  Rekhter, Y. and E. Rosen, "Carrying Label Information in
           BGP-4", RFC 3107, May 2001.

[RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
           Architecture", RFC 4291, February 2006.

[RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
           "Multiprotocol Extensions for BGP-4", RFC 4760, January
           2007.

7.2. Informative References

[RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
           Label Switching Architecture", RFC 3031, January 2001.

[RFC3270]  Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen,
           P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi-
           Protocol Label Switching (MPLS) Support of Differentiated
           Services", RFC 3270, May 2002.

[RFC4029]  Lind, M., Ksinant, V., Park, S., Baudot, A., and P.
           Savola, "Scenarios and Analysis for Introducing IPv6 into
           ISP Networks", RFC 4029, March 2005.

[RFC4182]  Rosen, E., "Removing a Restriction on the use of MPLS
           Explicit NULL", RFC 4182, September 2005.

[RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
           Protocol 4 (BGP-4)", RFC 4271, January 2006.

[RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
           Networks (VPNs)", RFC 4364, February 2006.

[RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
           Message Protocol (ICMPv6) for the Internet Protocol
           Version 6 (IPv6) Specification", RFC 4443, March 2006.

[RFC4659]  De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur,
           "BGP-MPLS IP Virtual Private Network (VPN) Extension for
           IPv6 VPN", RFC 4659, September 2006.

Authors' Addresses 💌

Jeremy De Clercq
Alcatel-Lucent
Copernicuslaan 50
Antwerpen  2018
Belgium

EMail: jeremy.de_clercq@alcatel-lucent.be


Dirk Ooms
OneSparrow
Belegstraat 13
Antwerpen  2018
Belgium

EMail: dirk@onesparrow.com


Stuart Prevost
BT
Room 136 Polaris House, Adastral Park, Martlesham Heath
Ipswich Suffolk IP5 3RE
England
EMail: stuart.prevost@bt.com


Francois Le Faucheur
Cisco
Domaine Green Side, 400 Avenue de Roumanille
Biot, Sophia Antipolis  06410
France

EMail: flefauch@cisco.com

This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights.

This document and the information in it are provided on an "AS IS" basis, and the contributor, the organization they represent or are sponsored by (if any), the Internet Society, the IETF Trust, and the Internet Engineering Task Force all disclaim ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property 🦋

The IETF doesn't take a position on whether any Intellectual Property Rights or other rights claimed to cover the technology in this document are valid or in scope, or on whether licenses for them are available. It also doesn't claim to have checked for any such rights. You can find the rules about rights in RFC documents in BCP 78 and BCP 79 📖

Copies of IPR disclosures made to the IETF Secretariat, any assurances of licenses to be made available, or the results of attempts to get a general license or permission for implementers or users to use these proprietary rights can be found in the IETF on-line IPR repository at:

http://www.ietf.org/ipr

The IETF invites anyone interested to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that might cover technology needed to implement this standard. Send that info to the IETF at:

ietf-ipr@ietf.org

Acknowledgement 💜

Funding for the RFC Editor function is currently provided by the Internet Society. ✨

📦 where this page comes from

ietf: rfc4798 2007-02
💖 girlified by claude-haiku-5-5 on 2026-10-17: a language model's rewrite of the original, under its terms