RFC 6654
Gateway-Initiated IPv6 Rapid Deployment on IPv4 Infrastructures (GI 6rd)
Gateway-Initiated IPv6 Rapid Deployment on IPv4 Infrastructures (GI 6rd) 🦋
okay bestie, let's get into it 💖 here's the title block, the important facts first:
- RFC number: 6654
- Stream: Independent Submission
- Category: Informational
- Date: July 2012
- ISSN: 2070-1721
- Authors: T. Tsou (Huawei Technologies (USA)), C. Zhou (Huawei Technologies), T. Taylor (Huawei Technologies), and Q. Chen (China Telecom) 🫶
- Obsoletes / Updates: none listed in this title block
Abstract ✨
ok so this doc proposes a different way to do the IPv6 Rapid Deployment on IPv4 Infrastructures (6rd) model from RFC 5969 🌈 basic 6rd lets IPv6 hosts reach IPv6 networks across an IPv4 access network by using 6-in-4 tunnels. the catch is that 6rd needs a device on the customer site (the 6rd customer edge, or 6rd-CE) to do it, and that device also needs an IPv4 address 😬
the alternative here starts the 6-in-4 tunnels from an operator-owned Gateway that sits where the operator's IPv4 network edge is, instead of from the customer's gear. that's why it's called "Gateway-initiated 6rd" (GI 6rd) 🎀 the perks are that customer equipment doesn't need any changes, and no IPv4 addresses have to be handed out to customer equipment. that second part is a big deal in a high-growth environment, since it means way less pressure on IPv4 addresses 🔥
Status of This Memo ✨
this doc is NOT an Internet Standards Track spec. it's just published for info 💅
it's a contribution to the RFC Series, independent of any other RFC stream. the RFC Editor picked to publish it at their discretion, and they make no statement about whether it's valuable for implementation or deployment 🧚 documents approved for publication by the RFC Editor aren't candidates for any level of Internet Standard, see Section 2 of RFC 5741.
for info about the current status of this doc, any errata, and how to give feedback, check http://www.rfc-editor.org/info/rfc6654 💜
Copyright Notice 🌸
Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved.
this doc is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) as they stood on the publication date. please read those carefully, bestie, because they spell out your rights and restrictions for this doc 🙈
Table of Contents 🍓
1. Introduction ....................................................2
2. Problem Statement ...............................................3
3. Proposed Solution ...............................................4
3.1. Prefix Delegation ..........................................5
3.2. Relevant Differences from Basic 6rd ........................6
4. Security Considerations .........................................7
5. Acknowledgements ................................................7
6. References ......................................................7
6.1. Normative References .......................................7
6.2. Informative References .....................................71. Introduction 🧚
okay so 6rd [RFC5969] is a transition tool that connects IPv6 devices across an IPv4 network to an IPv6 network. once they get there, the packets can be routed natively 💫 here's the topology in Figure 1.
+--------------+ +-----------------+ +---------+
| | | | | |
+-----+ +-----+ | Provider +--------+ | |
|IPv6 | | 6rd |__| IPv4 | Border |__| IPv6 |
|Host | | CE | | Network | Router | | Network |
+-----+ +-----+ | +--------+ | |
| Customer LAN | | | | |
+--------------+ +-----------------+ +---------+
Figure 1: 6rd Deployment Topologyin Figure 1, the CE is the customer edge router. it gets a delegated IPv6 prefix, but it also gets an IPv4 address so it can be reached through the IPv4 network 😭 if every customer gets a public IPv4 address, it makes the IPv4 shortage worse for operators dealing with a high rate of growth in broadband subscribers. private addresses with 6rd dodge that problem, but they bring their own complications 💀
2. Problem Statement 🎀
picture an operator with a high subscriber growth rate. that growth puts pressure on their stock of available public IPv4 addresses, so the operator is motivated to offer IPv6 access as fast as possible 🏃♀️ Figure 2 shows the kind of network situation this doc has in mind.
+----+ +-------------------+ +----------------+
|Host|\ | | | |
+----+ \_+---+ +----+ Metro +----+ | Backbone |
_|CPE|----| GW | Network | BR |--| Network |
+----+ / +---+ +----+ (IPv4) +----+ | (IPv6) |
|Host|/ | | | |
+----+ +-------------------+ +----------------+
Host = IPv6 customer host device
CPE = customer edge device (customer-provided)
GW = provider edge device (Gateway)
BR = border router (dual stack)Specialized GW and BR functions are described in the next section.
Figure 2: Typical Network Scenario for IPv6 Transitionthe backbone is going to be the first part of the operator's network to support IPv6 👑 the metro network is not so easy to upgrade, since lots of devices need changes and existing services might get affected. so any way of providing IPv6 access has to minimize the changes needed on devices in the metro network 🫠
compared to the situation for basic 6rd [RFC5569], the operator is assumed to have no control over the capabilities of the IP devices on the customer premises. so the operator can't assume any of those devices can support 6rd ✨
if the customer equipment is in bridged mode and IPv6 is deployed to sites through a Service Provider's (SP's) IPv4 network, the IPv6-only host needs an IPv6 address to reach the IPv6 service. in this case, 6to4 [RFC3056] or 6rd can be used. BUT each IPv6-only host may need one matching IPv4 address when using a public IPv4 address in 6to4 or 6rd, and that puts great address pressure on the operators 😩
if the CPE in the figure above is acting in bridging mode, each host behind it needs to be directly assigned an IPv6 prefix so it can access IPv6 services. if the CPE is acting in routing mode, only the CPE needs an IPv6 prefix, and it delegates prefixes to the hosts behind it 🧚
if the Gateway only supports IPv4, then an IPv4 address must also be assigned to each host (bridging mode) or to the CPE (routing mode). both of these cases put pressure on the provider's stock of IPv4 addresses, and bridging mode especially 🔥
if the Gateway is dual stack, there may be a way for all communication between the Gateway and the customer site to use IPv6, so you don't need to assign IPv4 addresses to customer devices at all. the next section presents a possible solution 🌈
3. Proposed Solution 💅
for basic 6rd [RFC5969], the 6rd CE starts the 6-in-4 tunnel to the dual-stack border router (the 6rd Border Relay in 6rd terminology) to carry its IPv6 traffic. to stop the customer premises equipment from having to do this job, the tunneling function has to move to a network device 🙌 this doc names a functional element, the 6rd Gateway, to handle that task. from here on, the 6rd Gateway and 6rd Border Relay are just called the Gateway and Border Relay, respectively.
the Gateway's functions are:
- to generate and allocate Gateway-initiated 6rd delegated prefixes for IPv6-capable customer devices, as described in Section 3.1;
- to forward outgoing IPv6 packets through a tunnel to a Border Relay, which extracts them and forwards them to an IPv6 network, same as for 6rd;
- to extract incoming IPv6 packets tunneled from the Border Relay and forward them to the correct user device.
in the proposed solution there's only one tunnel from each Gateway to the Border Relay, which hugely cuts down how many tunnels the Border Relay has to handle 🦋 the deployment scenario that matches the problem statement in Section 2 puts the Gateway together with the IP edge of the access network. that's shown in Figure 2, and it's the usual spot for the Broadband Network Gateway (BNG) in a fixed broadband network. by assumption, the metro network beyond the BNG is IPv4. transport between the customer site and the Gateway is over Layer 2 🎀
the elements of the proposed solution are:
- the IPv6 prefix assigned to the customer site contains the compressed IPv4 address of the network-facing side of the Gateway, plus a manually provisioned or Gateway-generated customer site identifier. Figure 3 illustrates this 💖
- the Border Relay can route incoming IPv6 packets to the correct Gateway. it does this by extracting the compressed Gateway address from the IPv6 destination address, expanding it to a full 32-bit IPv4 address, and setting that as the destination address of the encapsulated packet 🧚♀️
- the Gateway can route incoming packets to the correct link after decapsulation, using a mapping from either the full IPv6 prefix or the customer site identifier extracted from that prefix to the appropriate link 👑
3.1. Prefix Delegation
okay bestie, looking back at Figure 2 🦋 the customer equipment gets its prefix the normal way through the Gateway/IP edge, using either DHCPv6 or SLAAC ✨ Figure 3 shows what the assigned prefix looks like and how every piece gets derived, all inside one complete address 💅
+--------------------+-----------+
| 32-bit Gateway IPv4 address |
+--------------------+-----------+
|<---IPv4MaskLen --->| o bits | Gateway or manually
/ / generated value, unique
Configured / / / for the Gateway
| / / |
| / / V
| V p bits | o bits | n bits |m bits | 64 bits |
+----------------+------------+---------+-------+----------------+
| | Gateway |Customer | | |
| Common prefix | Identifier | Site |subnet | interface ID |
| | | Index | ID | |
+----------------+------------+---------+-------+----------------+
|<------ GI 6rd delegated prefix ------>|
Figure 3: Gateway-Initiated 6rd Address Format for a Customer Siteso the common prefix is the first p bits of the GI 6rd delegated prefix, and it's configured in the Gateway 🌸 this chunk is shared across multiple customers AND multiple Gateways, which is so cute. You can use multiple common prefix values in one network, either for service separation or for scalability ✨
The Gateway Identifier is equal to the o low-order bits of the Gateway IPv4 address on the virtual link to the Border Relay 🧚 the number of bits o is equal to (32 - IPv4MaskLen), where IPv4MaskLen is the length of the IPv4 prefix the Gateway IPv4 addresses come from. IPv4MaskLen gets configured in both the Gateways and the Border Relays, so everybody's on the same page 🫶
The Customer Site Index is basically a sequence number given to each individual customer site that a Gateway serves 🍓 the index for a given customer site must be unique across the Gateway, no exceptions. The length n of the Customer Site Index is provisioned in the Gateway, and it must be big enough to fit however many customer sites that Gateway is expected to serve 😭
okay, let's do the math together 🎀 imagine a 6rd domain with ten million IPv6-capable customer devices (a rather high number, given that 6rd is meant for the early stages of IPv6 deployment 💀). The estimated number of 6rd Gateways needed to serve this domain is on the order of 3,300, each one serving 30,000 customer devices. With best-case compression for the Gateway addresses, the Gateway Identifier field has length o = 12 bits. If 6-in-4 tunneling is being used, that best case is more likely to be achievable than it would be if the IPv4 addresses belonged to the customer devices 👑 and the customer device index, which is the more controllable parameter, has length n = 15 bits ✨
so overall, these figures suggest the length p of the common prefix can be 29 bits for a /56 delegated prefix, or 21 bits if /48 delegated prefixes need to be handed out 🌈 the numbers really do slay.
3.2. Relevant Differences from Basic 6rd
a bunch of the points in [RFC5969] still apply, with one simple swap: the Gateway takes the place of the 6rd CE 💖 when it comes to configuration, the definition of IPv4MaskLen changes, and there are other differences like the ones in the previous section. Since special configuration of customer equipment is not required, the 6rd DHCPv6 option is inapplicable 🙈
also, the link for the customer site to the network now only stretches as far as the Gateway, so Neighbor Unreachability Detection on the customer devices is limited in scope the same way 🦋
4. Security Considerations
no new security considerations are raised in this document beyond the ones already covered in the Security Considerations section of [RFC5969] 🔐 so go read that one, bestie, it's the whole story 😭💅
5. Acknowledgements
big thanks to Ole Troan for his technical comments on an early version of this document 🫶💜
6. References
6.1. Normative References
- [RFC5969] Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4 Infrastructures (6rd) -- Protocol Specification", RFC 5969, August 2010.
6.2. Informative References
- [RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via IPv4 Clouds", RFC 3056, February 2001.
- [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 Infrastructures (6rd)", RFC 5569, January 2010.
Authors' Addresses ✨
Tina Tsou
Huawei Technologies (USA)
2330 Central Expressway
Santa Clara, CA 95050
USA
EMail: Tina.Tsou.Zouting@huawei.com
Cathy Zhou
Huawei Technologies
Bantian, Longgang District
Shenzhen 518129
P.R. China
EMail: cathy.zhou@huawei.com
Tom Taylor
Huawei Technologies
Ottawa, Ontario
Canada
EMail: tom.taylor.stds@gmail.com
Qi Chen
China Telecom
109 Zhongshan Ave. West
Tianhe District, Guangzhou 510630
P.R. China
EMail: chenqi.0819@gmail.com📦 where this page comes from
- ietf: rfc6654 2012-07
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms