RFC 7264
An Extension to the REsource LOcation And Discovery (RELOAD) Protocol to Support Relay Peer Routing
RFC 7264: An Extension to the REsource LOcation And Discovery (RELOAD) Protocol to Support Relay Peer Routing 🎀✨
Okay bestie, this is the RFC that adds an optional extension to RELOAD so peers can use Relay Peer Routing (RPR). Here's the title block:
- Number: RFC 7264
- Stream: Internet Engineering Task Force (IETF) 🌸
- Authors: N. Zong, X. Jiang, R. Even (all from Huawei Technologies), and Y. Zhang (CoolPad / China Mobile) 👑
- Category: Standards Track
- ISSN: 2070-1721
- Date: June 2014
- Obsoletes / Updates: the title block doesn't list anything it obsoletes or updates 🦋
Abstract ✨
So this doc adds an optional extension to RELOAD that supports the relay peer routing mode 💅. RELOAD recommends symmetric recursive routing for messages, and the new extension gives responses a shorter route, which means less overhead on the intermediate peers 🫶. The doc also covers some situations where you'd actually use it.
Status of This Memo 📝
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 info on Internet Standards, check out Section 2 of RFC 5741 🧚.
For the current status, any errata, and how to send feedback, go to http://www.rfc-editor.org/info/rfc7264.
Copyright Notice 💜
Copyright (c) 2014 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 (http://trustee.ietf.org/license-info) as they stand on the publication date. Please read these carefully, because they spell out your rights and restrictions for this document. Any Code Components pulled out of this document must include the Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions, and they come with no warranty, as the Simplified BSD License describes.
Table of Contents 🍓
1. Introduction ....................................................3
2. Terminology .....................................................4
3. Overview ........................................................5
3.1. RPR ........................................................5
3.2. Scenarios Where RPR Can Be Used ............................6
3.2.1. Managed or Closed P2P Systems .......................6
3.2.2. Using Bootstrap Nodes as Relay Peers ................7
3.2.3. Wireless Scenarios ..................................7
4. Relationship between SRR and RPR ................................7
4.1. How RPR Works ..............................................7
4.2. How SRR and RPR Work Together ..............................7
5. RPR Extensions to RELOAD ........................................8
5.1. Basic Requirements .........................................8
5.2. Modification to RELOAD Message Structure ...................8
5.2.1. Extensive Routing Mode ..............................8
5.3. Creating a Request .........................................9
5.3.1. Creating a Request for RPR ..........................9
5.4. Request and Response Processing ............................9
5.4.1. Destination Peer: Receiving a Request and
Sending a Response ..................................9
5.4.2. Sending Peer: Receiving a Response .................10
5.4.3. Relay Peer Processing ..............................10
6. Overlay Configuration Extension ................................10
7. Discovery of Relay Peers .......................................11
8. Security Considerations ........................................11
9. IANA Considerations ............................................11
9.1. A New RELOAD Forwarding Option ............................11
10. Acknowledgments ...............................................11
11. References ....................................................12
11.1. Normative References .....................................12
11.2. Informative References ...................................12
Appendix A. Optional Methods to Investigate Peer Connectivity .....13
Appendix B. Comparison of Cost of SRR and RPR .....................14
B.1. Closed or Managed Networks .................................14
B.2. Open Networks ..............................................151. Introduction ✨
So RELOAD [RFC6940] recommends symmetric recursive routing (SRR) for routing messages, and it describes what extensions you'd need to support extra routing algorithms 🧠. Two other options also get a mention in Appendix A of [RFC6940]: direct response routing (DRR) and relay peer routing (RPR) 💅. Here's the tea (as shown in Section 3): RPR can beat SRR in some scenarios because it can reduce load (CPU and link bandwidth) on intermediate peers 🔥. RPR works best when relay peers are set up ahead of time, so they're publicly reachable in the P2P system. In other scenarios, using RPR and SRR together is more likely to be a win than using SRR alone 🫶.
Quick note: this doc focuses on RPR mode and its RELOAD extensions as a standalone solution. For DRR, check out [RFC7263] 🦋.
Here's the roadmap. The problem statement is in Section 3. How to combine RPR and SRR is in Section 4. The RELOAD extension for RPR is defined in Section 5. Discovery of relay peers is in Section 7. Some optional ways to check peer connectivity are in Appendix A. And Appendix B compares the cost of SRR and RPR in both managed and open networks 🗺️.
2. Terminology 📚
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].
We use terms from the base RELOAD spec [RFC6940] a lot in this doc. We also use terms from the NAT behavior discovery doc [RFC5780]. Any other terms are defined inline when they show up, and they're also listed below so you can look them up 🔍.
Publicly Reachable: A peer is publicly reachable if it can receive unsolicited messages from any other peer in the same overlay. Note: "Publicly" does not mean that the peers must be on the public Internet, because the RELOAD protocol may be used in a closed network. 🙈
Relay Peer: A relay peer is a type of publicly reachable peer that can receive unsolicited messages from all other peers in the overlay and forward the responses from destination peers towards the sender of the request. 🧚
Relay Peer Routing (RPR): "RPR" refers to a routing mode in which responses to Peer-to-Peer SIP (P2PSIP) requests are sent by the destination peer to a relay peer transport address that will forward the responses towards the sending peer. For simplicity, the abbreviation "RPR" is used in the rest of this document. 💖
Symmetric Recursive Routing (SRR): "SRR" refers to a routing mode in which responses follow the reverse path of the request to get to the sending peer. For simplicity, the abbreviation "SRR" is used in the rest of this document. 🌈
Direct Response Routing (DRR): "DRR" refers to a routing mode in which responses to P2PSIP requests are returned to the sending peer directly from the destination peer based on the sending peer's own local transport address(es). For simplicity, the abbreviation "DRR" is used in the rest of this document. 🦋
3. Overview 🌸
RELOAD is expected to work in a huge range of application scenarios, and the situations where it gets deployed are wildly different 🌍. Some deployments are global, like a Skype-style system built to provide public service. Others run in small closed networks. SRR works in any situation, but RPR may work better in some specific scenarios 💅.
3.1. RPR 🦋
RELOAD is a simple request-response protocol. After a peer sends a request, it waits for a response from a destination peer. There are several ways the destination peer can send a response back to the source peer. This section gives you the details on RPR. The same kinds of illustrative setups also show up in Appendix B.1 of [RFC7263] 🧁.
Here's the RPR story. If peer A knows it's behind a NAT (or NATs) and knows one or more relay peers it has had prior connections with, peer A can try RPR 🫶. Say peer A is associated with relay peer R. When it sends the request, peer A includes information describing peer R's transport address in the request. When peer X gets the request, peer X sends the response to peer R, and peer R forwards it directly to peer A over the existing connection ✨. Figure 1 shows the whole thing. RPR also gives responses a shorter route than SRR does, which means less overhead on intermediate peers 🙌. Setting up a connection to the relay with Transport Layer Security (TLS) takes multiple round trips ⏳. For a cost comparison between SRR and RPR, see Appendix B.
A B C D X R
| Request | | | | |
|----------->| | | | |
| | Request | | | |
| |----------->| | | |
| | | Request | | |
| | |----------->| | |
| | | | Request | |
| | | |----------->| |
| | | | | Response |
| | | | |---------->|
| | | | Response | |
|<-----------+------------+------------+------------+-----------|
| | | | | |
Figure 1: RPR ModeThis technique depends on how many peers like peer A need relay peers, and how many peers like peer R can actually act as relay peers 👑. It also needs a mechanism so peers can figure out which peers they can use as relays 🔎. That mechanism may be based on configuration. For example, an initial list of relay peers can be supplied as part of the overlay configuration. Another option is a response message in which the responding peer announces that it can serve as a relay peer 📣.
3.2. Scenarios Where RPR Can Be Used 🌈
In this section, we'll list several scenarios where using RPR would improve performance 💖.
3.2.1. Managed or Closed P2P Systems 🏫
Okay so, as described in Section 3.2.1 of [RFC7263], lots of P2P systems run in a closed or managed environment 🔒, which means network admins can manage the whole system way better 💅. For example, the admin can deploy several relay peers that are publicly reachable in the system and list them in the configuration file 📝. Once peers learn where those relay peers are, peers behind NATs can use RPR with help from them 🦋. Peers MUST also support SRR in case RPR fails. Backup plan, bestie 🫶.
Another use case is to install relay peers on the managed network boundary 🧱, so external peers can send responses to peers inside the managed network 🌸.
3.2.2. Using Bootstrap Nodes as Relay Peers 🥾
Bootstrap nodes are typically publicly reachable in a RELOAD architecture ✨. So one possible scenario is using the bootstrap nodes as relay peers for RPR 🧚. A relay peer SHOULD be publicly accessible and maintain a direct connection with its client. Which is why bootstrap nodes are giving perfect relay peer energy 👑.
3.2.3. Wireless Scenarios 📶
In some mobile deployments, using RPR may help reduce radio battery usage and bandwidth used by the intermediate peers 🔋. The service provider may recommend using RPR based on their knowledge of the topology 🗺️.
4. Relationship between SRR and RPR 🤝
4.1. How RPR Works ⚙️
Peers using RPR MUST maintain a connection with their relay peer(s). This can be done the same way as establishing a neighbor connection between peers using the Attach method [RFC6940] 🔗.
A requirement for RPR is that the source peer conveys its relay peer's (or peers') transport address(es) in the request 📬. That way the destination peer knows where the relay peers are and sends the response to a relay peer first. The request MUST also include the requesting peer's Node-ID or IP address, which lets the relay peer route the response back to the right peer 🎯.
Being a relay peer doesn't require more functionality than an ordinary peer 💁. Relay peers follow the same procedure as an ordinary peer to forward messages. The only difference is that relay peers may carry a larger traffic burden 🏋️. Relay peers can decide whether to accept a new connection based on their current burden 🙈.
4.2. How SRR and RPR Work Together 💞
RPR is not intended to replace SRR 🙅. It's better to use these two modes together so they adapt to each peer's specific situation 🌈. The informative suggestions for transitioning between SRR and RPR are the same as the ones for DRR, so check Section 4.2 of [RFC7263] for more details 📖. If a relay peer is provided by the service provider, peers SHOULD prefer RPR over SRR. However, RPR SHOULD NOT be used in the open Internet, or if the administrator does not feel they have enough information about the overlay network topology 🚫. A new overlay configuration element specifying the usage of RPR is defined in Section 6 ✨.
5. RPR Extensions to RELOAD 🧩
Adding support for RPR requires extensions to the current RELOAD protocol 🛠️. In this section we define the required extensions, including extensions to the message structure and message processing 💖.
5.1. Basic Requirements 📋
All peers MUST be able to process requests for routing in SRR and MAY support RPR routing requests.
5.2. Modification to RELOAD Message Structure 🪄
RELOAD provides an extensible framework to accommodate future extensions 🌱. In this section we define an RPR routing option for the extensive routing mode specified in [RFC7263]. The state-keeping flag [RFC7263] is needed to support the RPR mode 🎀.
5.2.1. Extensive Routing Mode 🛣️
The new RouteMode value for RPR is defined below for the ExtensiveRoutingModeOption structure 👀:
enum {(0),DRR(1),RPR(2),(255)} RouteMode;
struct {
RouteMode routemode;
OverlayLinkType transport;
IpAddressPort ipaddressport;
Destination destinations<1..2^8-1>;
} ExtensiveRoutingModeOption;Note that the DRR value in RouteMode is defined in [RFC7263] 📝.
Here's what each field does, bestie 💅:
RouteMode: refers to which type of routing mode is indicated to the destination peer 🧭.OverlayLinkType: refers to the transport type that is used to deliver responses from the destination peer to the relay peer 🚚.IpAddressPort: refers to the transport address that the destination peer should use for sending responses. This will be a relay peer address for RPR 📍.Destination: refers to the relay peer itself. If the routing mode is RPR, then the destination contains two items: the relay peer's Node-ID and the sending peer's Node-ID 🫧.
5.3. Creating a Request 📨
5.3.1. Creating a Request for RPR ✍️
When using RPR for a transaction, the sending peer MUST set the IGNORE-STATE-KEEPING flag in the ForwardingHeader. Additionally, the peer MUST construct and include a ForwardingOption structure in the ForwardingHeader. When constructing the ForwardingOption structure, the fields MUST be set as follows:
- The type MUST be set to
extensive_routing_mode. - The
ExtensiveRoutingModeOptionstructure MUST be used for the option field within theForwardingOptionstructure. The fields MUST be defined as follows:- 2.1)
routemodeset to0x02(RPR). - 2.2)
transportset as appropriate for the relay peer. - 2.3)
ipaddressportset to the transport address of the relay peer through which the sender wishes the message relayed. - 2.4) The destination structure MUST contain two values. The first MUST be defined as type "node" and set with the values for the relay peer. The second MUST be defined as type "node" and set with the sending peer's own values.
- 2.1)
5.4. Request and Response Processing 🔁
This section gives normative text for message processing after RPR is introduced 📜. Here we only describe the additional procedures for supporting RPR. Please refer to [RFC6940] for the RELOAD base procedures 📚.
5.4.1. Destination Peer: Receiving a Request and Sending a Response 📬
When the destination peer receives a request, it checks the options in the forwarding header 👂. If the destination peer cannot understand the extensive_routing_mode option in the request, it MUST attempt to use SRR to return an "Error_Unknown_Extension" response (defined in Sections 6.3.3.1 and 14.9 of [RFC6940]) to the sending peer 🙅♀️.
If the routing mode is RPR, the destination peer MUST construct a destination_list for the response with two entries as defined in [RFC6940]. The first entry MUST be set to the relay peer's Node-ID from the option in the request, and the second entry MUST be the sending peer's Node-ID from the option in the request 🧾.
In the event that the routing mode is set to RPR and there are not exactly two destinations, the destination peer MUST try to send an "Error_Unknown_Extension" response (defined in Sections 6.3.3.1 and 14.9 of [RFC6940]) to the sending peer using SRR 🚨.
After the peer constructs the destination_list for the response, it sends the response to the transport address indicated in the ipaddressport field in the option, using the specific transport mode in the ForwardingOption 🚀. If the destination peer receives a retransmit with SRR preference on the message it is trying to respond to now, the responding peer SHOULD abort the RPR response and use SRR. Switching back to SRR, no drama 💖.
5.4.2. Sending Peer: Receiving a Response 📥
When a response comes in, the peer follows the rules in [RFC6940] 🙌. If the sender used RPR and did not get a response until the timeout, it MAY resend the message using either RPR (but with a different relay peer, if available) or SRR.
5.4.3. Relay Peer Processing 🦸♀️
Relay peers are designed to forward responses to peers who are not publicly reachable 🏠. For the routing of the response, this document still uses the destination_list. The only difference from SRR is that the destination_list is not the reverse of the via_list. Instead, it's constructed from the forwarding option as described below 🔄.
When a relay peer receives a response, it MUST follow the rules in [RFC6940]. It receives the response, validates the message, readjusts the destination_list, and forwards the response to the next hop in the destination_list based on the connection table. There is no added requirement for the relay peer 🫶.
6. Overlay Configuration Extension ⚡
This document uses the new RELOAD overlay configuration element, "route-mode", inside each "configuration" element, as defined in Section 6 of [RFC7263] 🧁. The route mode MUST be "RPR".
7. Discovery of Relay Peers 🔍
There are several ways to distribute information about relay peers throughout the overlay 🌐. P2P network providers can deploy some relay peers and advertise them in the configuration file 📣. With the configuration file at hand, peers can get relay peers to try RPR 🙌.
Another way is to treat the relay peer as a service. A service advertisement and discovery mechanism can then be used to discover relay peers too, for example using the same mechanism as the one used in Traversal Using Relays around NAT (TURN) server discovery, as discussed in [RFC6940] 🕵️♀️. Another option is to let a peer advertise its capability to be a relay in the response to an Attach or Join [RFC6940] 💌.
8. Security Considerations 🚨
This is the serious part, so let's be real 😤. The normative security recommendations of Section 13 of [RFC6940] are applicable to this document. As a routing alternative, the security part of RPR conforms to Section 13.6 of [RFC6940], which describes routing security 🔐. RPR behaves like a DRR requesting node towards the destination node 🎭.
The RPR relay peer is not necessarily an arbitrary node. For example, it could be a managed network, a bootstrap node, or a configured relay peer. It should be a trusted node, because a trusted node will be less of a risk, as outlined in Section 13 of [RFC6940] 🛡️.
To address possible DoS attacks, the relay peer SHOULD also limit the number of maximum connections. This is required in order to also reduce load on the relay peer, as explained in Section 4.1 💀.
9. IANA Considerations 🗂️
9.1. A New RELOAD Forwarding Option 🆕
A new RELOAD Forwarding Option type has been added to the "RELOAD Forwarding Option Registry" defined in [RFC6940] 🎉.
Code: 2
Forwarding Option: extensive_routing_mode10. Acknowledgments 💜
David Bryan helped extensively with this document and provided some of the text, analysis, and ideas contained here 🫶. The authors would like to thank Ted Hardie, Narayanan Vidya, Dondeti Lakshminath, Bruce Lowekamp, Stephane Bryant, Marc Petit-Huguenin, and Carlos Jesus Bernardos Cano for their constructive comments 🌷.
11. References 📚
11.1. Normative References 📖
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6940] Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and
H. Schulzrinne, "REsource LOcation And Discovery (RELOAD)
Base Protocol", RFC 6940, January 2014.
[RFC7263] Zong, N., Jiang, X., Even, R., and Y. Zhang, "An Extension
to the REsource LOcation And Discovery (RELOAD) Protocol
to Support Direct Response Routing", RFC 7263, June 2014.11.2. Informative References 📚
- [RFC3424] Daigle, L. and IAB, "IAB Considerations for UNilateral Self-Address Fixing (UNSAF) Across Network Address Translation", RFC 3424, November 2002.
- [RFC5780] MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery Using Session Traversal Utilities for NAT (STUN)", RFC 5780, May 2010.
Appendix A. Optional Methods to Investigate Peer Connectivity 🕵️
Okay bestie, this section is for informational purposes only ✨ It's a little toolkit of mechanisms you can reach for when the configuration info doesn't say whether RPR can be used. It's basically a roundup of methods a peer can use to figure out its own network location compared with NAT 🦋 These methods may help a peer decide which routing mode it may wish to try. ngl, there is no foolproof way to determine whether a peer is publicly reachable, other than via out-of-band mechanisms 💀
This document addresses UNilateral Self-Address Fixing (UNSAF) [RFC3424] considerations by specifying a fallback plan to SRR [RFC6940]. SRR is not an UNSAF mechanism. This document does not define any new UNSAF mechanisms. Main character energy, no new UNSAF stuff here 💅
For RPR to function correctly, a peer may attempt to determine whether it is publicly reachable. If it is not, RPR may be chosen to route the response with help from relay peers, or the peers should fall back to SRR. NATs and firewalls are two major contributors to preventing RPR from functioning properly 🙈 There are a number of techniques by which a peer can get its reflexive address on the public side of the NAT. After obtaining the reflexive address, a peer can perform further tests to learn whether the reflexive address is publicly reachable. If the address appears to be publicly reachable, the peer to which the address belongs can be a candidate to serve as a relay peer. Peers that are not publicly reachable may still use RPR to shorten the response path, with help from relay peers 🫶
Some conditions that are unique in P2PSIP architecture could be leveraged to facilitate the tests. In a P2P overlay network, each peer has only a partial view of the whole network and knows of a few peers in the overlay. P2P routing algorithms can easily deliver a request from a sending peer to a peer with whom the sending peer has no direct connection. This makes it easy for a peer to ask other peers to send unsolicited messages back to the requester 🧚
The approaches for a peer to get the addresses needed for further tests, as well as the test for learning whether a peer may be publicly reachable, are the same as those for DRR. Please refer to Appendix A of [RFC7263] for more details 🌸
Appendix B. Comparison of Cost of SRR and RPR 🍓
The major advantage of using RPR is that it reduces the number of intermediate peers traversed by the response. This reduces the load, such as processing and communication bandwidth, on those peers' resources. Less traffic through the middle, less stress on everyone 🌈
B.1. Closed or Managed Networks
As described in Section 3, many P2P systems run in a closed or managed environment (e.g., carrier networks), so network administrators would know that they could safely use RPR 👑
The number of hops for a response in SRR and in RPR are listed in the following table. Note that the same types of illustrative settings can be found in Appendix B.1 of [RFC7263].
Mode | Success | No. of Hops | No. of Msgs
------------------------------------------------
SRR | Yes | log(N) | log(N)
RPR | Yes | 2 | 2
RPR (DTLS) | Yes | 2 | 7+2Table 1: Comparison of SRR and RPR in Closed Networks
From the above comparison, it is clear that:
- In most cases when the number of peers (N) > 4 (2^2), RPR uses fewer hops than SRR. Using a shorter route means less overhead and resource usage on intermediate peers, which is an important consideration for adopting RPR in the cases where such resources as CPU and bandwidth are limited, e.g., the case of mobile, wireless networks 📱
- In the cases when N > 512 (2^9), RPR also uses fewer messages than SRR.
- In the cases when N < 512, RPR uses more messages than SRR (but still uses fewer hops than SRR), so the consideration of whether to use RPR or SRR depends on other factors such as using less resources (bandwidth and processing) from the intermediate peers. Section 4 provides use cases where RPR has a better chance of working or where the considerations of intermediary resources are important 💜
B.2. Open Networks
In open networks (e.g., the Internet) where RPR is not guaranteed to work, RPR can fall back to SRR if it fails after trial, as described in Section 4.2. Based on the same settings as those listed in Appendix B.1, the number of hops, as well as the number of messages for a response in SRR and RPR, are listed in the following table:
Mode | Success | No. of Hops | No. of Msgs
----------------------------------------------------------------
SRR | Yes | log(N) | log(N)
RPR | Yes | 2 | 2
| Fail & fall back to SRR | 2+log(N) | 2+log(N)
RPR (DTLS) | Yes | 2 | 7+2
| Fail & fall back to SRR | 2+log(N) | 9+log(N)Table 2: Comparison of SRR and RPR in Open Networks
From the above comparison, it can be observed that trying to first use RPR could still provide an overall number of hops lower than directly using SRR. The detailed analysis is the same as that for DRR and can be found in [RFC7263] 🦋
Authors' Addresses
Ning Zong Huawei Technologies
EMail: zongning@huawei.com
Xingfeng Jiang Huawei Technologies
EMail: jiang.x.f@huawei.com
Roni Even Huawei Technologies
EMail: roni.even@mail01.huawei.com
Yunfei Zhang CoolPad / China Mobile
EMail: hishigh@gmail.com
📦 where this page comes from
- ietf: rfc7264 2014-06
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms