Network Working Group J. Chroboczek
Internet-Draft IRIF, University of Paris-Diderot
Intended status: Experimental July 3, 2017
Expires: January 4, 2018

Homenet profile of the Babel routing protocol


This document defines the subset of the Babel routing protocol [RFC6126] and its extensions that a Homenet router must implement, as well as the interactions between HNCP [RFC7788] and Babel.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on January 4, 2018.

Copyright Notice

Copyright (c) 2017 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 ( in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

1. Introduction

The core of the Homenet protocol suite consists of HNCP [RFC7788], a protocol used for flooding configuration information and assigning prefixes to links, combined with the Babel routing protocol [RFC6126]. Babel is an extensible, flexible and modular protocol: minimal implementations of Babel have been demonstrated that consist of a few hundred of lines of code, while the "large" implementation includes support for a number of extensions and consists of over ten thousand lines of C code.

This document consists of two parts. The first specifies the exact subset of the Babel protocol and its extensions that is required by an implementation of the Homenet protocol suite. The second specifies how HNCP interacts with Babel.

1.1. Background

The Babel routing protocol and its extensions are defined in a number of documents:

2. The Homenet profile of Babel

2.1. Requirements

REQ1: a Homenet implementation of Babel MUST encapsulate Babel control traffic in IPv6 packets sent to the IANA-assigned port 6696 and either the IANA-assigned multicast group ff02::1:6 or to a link-local unicast address.

REQ2: a Homenet implementation of Babel MUST implement the IPv6 subset of the protocol defined in the body of RFC 6126.

REQ3: a Homenet implementation of Babel SHOULD implement the IPv4 subset of the protocol defined in the body of RFC 6126. Use of other techniques for acquiring IPv4 connectivity (such as multiple layers of NAT) is strongly discouraged.

REQ4: a Homenet implementation of Babel MUST implement source-specific routing for IPv6, as defined in draft-boutier-babel-source-specific [BABEL-SS]. This implies that it MUST implement the extension mechanism defined in RFC 7557.

REQ5: a Homenet implementation of Babel MUST use metrics that are of a similar magnitude to the values suggested in Appendix A of RFC 6126. In particular, it SHOULD assign costs that are no less than 256 to wireless links, and SHOULD assign costs between 32 and 196 to lossless wired links.

REQ6: a Homenet implementation of Babel SHOULD distinguish between wired and wireless links; if it is unable to determine whether a link is wired or wireless, it SHOULD make the worst-case hypothesis that the link is wireless. It SHOULD dynamically probe the quality of wireless links and derive a suitable metric from its quality estimation. The algorithm described in Appendix A of RFC 6126 MAY be used.

2.2. Non-requirements

NR1: a Homenet implementation of Babel MAY perform route selection by applying hysteresis to route metrics, as suggested in Section 3.6 of RFC 6126 and described in detail in Section III.E of [BABEL-RTT]. However, it MAY simply pick the route with the smallest metric.

NR2: a Homenet implementation of Babel MAY include support for other extensions to the protocol, as long as they are known to interoperate with both the core protocol and source-specific routing.

3. Interactions between HNCP and Babel

The Homenet architecture cleanly separates between configuration, which is done by HNCP, and routing, which is done by Babel. While the coupling between the two protocols is deliberately kept to a minimum, some interactions are unavoidable.

All the interactions between HNCP and Babel consist of HNCP causing Babel to perform an announcement on its behalf (in particular, under no circumstances does Babel cause HNCP to perform an action). How this is realised is an implementation detail that is outside the scope of this document: while it could conceivably be done using a private communication channel between HNCP and Babel, existing implementations have HNCP install a route in the operating system's kernel which is later picked up by Babel using the existing redistribution mechanisms.

3.1. Requirements

REQ7: if an HNCP node receives a DHCPv6 prefix delegation for prefix P and publishes an External-Connection TLV containing a Delegated-Prefix TLV with prefix P and no Prefix-Policy TLV, then it MUST announce a source-specific default route with source prefix P over Babel.

REQ8: if an HNCP node receives a DHCPv4 lease with an IPv4 address and wins the election for NAT gateway, then it MUST act as a NAT gateway and MUST announce a (non-specific) IPv4 default route over Babel.

REQ9: if an HNCP node assigns a prefix P to an attached link and announces P in an Assigned-Prefix TLV, then it MUST announce a route towards P over Babel.

3.2. Non-requirements

NR3: an HNCP node that receives a DHCPv6 prefix delegation MAY announce a non-specific IPv6 default route over Babel in addition to the source-specific default route mandated by requirement REQ7.

NR4: an HNCP node that receives a DHCPv4 lease with an IPv4 address and wins the election for NAT gateway SHOULD NOT announce a source-specific IPv4 default route.

4. Security Considerations

Both HNCP and Babel carry their control data in IPv6 packets with a link-local source address, and implementations are required to drop packets sent from a global address. Hence, they are only susceptible to attacks from a directly connected link on which the HNCP and Babel implementations are listening.

The security of a Homenet network relies on having a set of trusted "internal" links that are secured at a lower layer (either physically or at the link layer); HNCP and Babel packets are only accepted when they originate on these trusted links (see Section 5 of [RFC7788]). External, leaf and guest links are not trusted, and any HNCP or Babel packets that are received on such links are ignored.

If untrusted links are used for transit, which is NOT RECOMMENDED, and therefore need to carry HNCP and Babel traffic, then HNCP and Babel MUST be secured using an upper-layer security protocol. While both HNCP and Babel support cryptographic authentication, at the time of writing no protocol for autonomous configuration of HNCP and Babel security has been defined.

5. Acknowledgments

A number of people have helped with definining the requirements listed in this document. I am especially indebted to Markus Stenberg for his help.

6. References

6.1. Normative References

[BABEL-SS] Boutier, M. and J. Chroboczek, "Source-Specific Routing in Babel", Internet-Draft draft-boutier-babel-source-specific-01, January 2015.
[RFC6126] Chroboczek, J., "The Babel Routing Protocol", RFC 6126, February 2011.
[RFC7557] Chroboczek, J., "Extension Mechanism for the Babel Routing Protocol", RFC 7557, May 2015.
[RFC7788] Stenberg, M., Barth, S. and P. Pfister, "Home Networking Control Protocol", RFC 7788, DOI 10.17487/RFC7788, April 2016.

6.2. Informative References

[BABEL-RTT] Jonglez, B. and J. Chroboczek, "Delay-based Metric Extension for the Babel Routing Protocol", Internet-Draft draft-jonglez-babel-rtt-extension-01, May 2015.
[BABEL-Z] Chroboczek, J., "Diversity Routing for the Babel Routing Protocol", Internet-Draft draft-chroboczek-babel-diversity-routing-01, February 2016.
[DELAY-BASED] Jonglez, B. and J. Chroboczek, "A delay-based routing metric", March 2014.

Available online from

[RFC7298] Ovsienko, D., "Babel Hashed Message Authentication Code (HMAC) Cryptographic Authentication", RFC 7298, July 2014.

Author's Address

Juliusz Chroboczek IRIF, University of Paris-Diderot Case 7014 75205 Paris Cedex 13, France EMail: