Network Working Group J. Chroboczek Internet-Draft PPS, University of Paris-Diderot Intended status: Experimental November 1, 2015 Expires: May 4, 2016 Homenet profile of the Babel routing protocol draft-chroboczek-homenet-babel-profile-unpublished Abstract This document defines the subset of the Babel routing protocol [RFC6126] and its extensions that a Homenet router must implement. 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 http://datatracker.ietf.org/drafts/current/. 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 May 4, 2016. Copyright Notice Copyright (c) 2015 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) 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. Chroboczek Expires May 4, 2016 [Page 1] Internet-Draft Babel Extension Mechanism November 2015 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Background . . . . . . . . . . . . . . . . . . . . . . . 2 2. The Homenet profile of Babel . . . . . . . . . . . . . . . . 3 2.1. Requirements . . . . . . . . . . . . . . . . . . . . . . 3 2.2. Non-requirements . . . . . . . . . . . . . . . . . . . . 5 3. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5 4. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Normative References . . . . . . . . . . . . . . . . . . 5 4.2. Informative References . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction The core of the Homenet protocol suite consists of HNCP [HNCP], 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 defines the exact subset of the Babel protocol and its extensions that is required by a conformant implementation of the Homenet protocol suite. 1.1. Background The Babel routing protocol and its extensions are defined in a number of documents: o The body of RFC 6126 [RFC6126] defines the core, unextended protocol. It allows Babel's control data to be carried over either link-local IPv6 or IPv4, and in either case allows announcing both IPv4 and IPv6 routes. It leaves link cost estimation, metric computation and route selection to the implementation. Distinct implementations of core RFC 6126 Babel will interoperate and maintain a set of loop-free forwarding paths, but given conflicting metrics or route selection policies may give rise to persistent oscillations. o The informative Appendix A of RFC 6126 suggests a simple and easy to implement algorithm for cost and metric computation that has been found to work satisfactorily in a wide range of topologies. Chroboczek Expires May 4, 2016 [Page 2] Internet-Draft Babel Extension Mechanism November 2015 o While RFC 6126 does not provide an algorithm for route selection, its Section 3.6 suggests selecting the route with smallest metric with some hysteresis. An algorithm that has been found to work well in practice is described in Section III.E of [DELAY-BASED]. o The extension mechanism for Babel is defined in RFC 7557 [RFC7557]. o Four RFCs and Internet-Drafts define optional extensions to Babel: HMAC-based authentication [RFC7298], source-specific routing [BABEL-SS], radio interference aware routing [BABEL-Z], and delay- based routing [BABEL-RTT]. All of these extensions interoperate with the core protocol as well as with each other. 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. Rationale: since Babel allows carrying both IPv4 and IPv6 routes over IPv6, there is no reason to send control traffic encapsulated in IPv4. REQ2: a Homenet implementation of Babel MUST implement the IPv6 subset of the protocol defined in the body of RFC 6126. Rationale: support for IPv6 routing is an essential component of the Homenet architecture. 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 obtaining IPv4 connectivity (such as multiple layers of NAT) is strongly discouraged. Rationale: support for IPv4 will remain necessary for years to come; even in pure IPv6 deployments, including code for supporting IPv4 has very little cost. Since HNCP makes it easy to assign distinct IPv4 prefixes to the links in a network, it is not necessary to resort to multiple layers of NAT, with all of its problems. Note: BS suggest that this should be a MUST. Chroboczek Expires May 4, 2016 [Page 3] Internet-Draft Babel Extension Mechanism November 2015 REQ4: a Homenet implementation of Babel MUST implement the IPv6 subset of source-specific routing, as defined in draft-boutier-babel- source-specific [BABEL-SS]. This implies that it MUST implement the extension mechanism defined in RFC 7557. Rationale: source-specific routing is an essential component of the Homenet architecture. The extension mechanism is required by source-specific routing. Source-specific routing for IPv4 is not required, since home networks tend to implement NAT at the border router, making source-specific routing for IPv4 redundant. REQ5: a Homenet implementation of Babel MUST implement HMAC-based authentication, as defined in RFC 7298, MUST implement the two mandatory-to-implement algorithms defined in RFC 7298, and MUST enable and require authentication when instructed to do so by HNCP. Rationale: some home networks include "guest" links that can be used by third parties that are not necessarily fully trusted. In such networks, it is essential that the routing protocol be secured. Since Babel makes extensive use of multicast packets, lower-layer mechanisms such as DTLS or dynamically keyed IPsec are not useful. (Statically keyed IPsec, perhaps with keys rotated by HNCP, is vulnerable to replay attacks and would therefore require the addition of a nonce mechanism to Babel.) Note: there is no consensus about this requirement. A simpler solution is to disable Babel on guest interfaces. MS suggests we might want to weaken this to SHOULD. Note: this needs expanding with an explanation of how HNCP is supposed to signal the use of authentication. REQ6: a Homenet implementation of Babel SHOULD distinguish between wired and wireless links, and SHOULD dynamically probe the quality of wireless links and derive a suitable metric from its quality estimation. We suggest the simple algorithm described in Appendix A of RFC 6126. Rationale: support for wireless transit links is a "killer feature" of Homenet, something that is requested by our users and easy to explain to our bosses. In the absence of dynamically computed metrics, the routing protocol tends to minimise the number of links crossed by a route, and therefore prefers long, lossy links to shorter, lossless ones. In wireless networks, "hop-count routing is worst-path routing". REQ7: a Homenet implementation of Babel MUST use metrics that are of a similar magnitude to the values suggested in Appendix A of Chroboczek Expires May 4, 2016 [Page 4] Internet-Draft Babel Extension Mechanism November 2015 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. Rationale: if two implementations of Babel choose very different values for link costs, combining routers from different vendors will lead to sub-optimal routing. 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. Rationale: hysteresis is only useful in congested and highly dynamic networks. In a typical home network, stable and uncongested, the feedback loop that hysteresis compensates for does not occur. 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. Rationale: delay-based routing is useful in redundant meshes of tunnels, which do not occur in typical home networks (which typically use at most one VPN link). Interference-aware routing, on the other hand, is likely to be useful in home networks, but the extension requires further evaluation before it can be recommended for widespread deployment. 3. Acknowledgments 4. References 4.1. Normative References [BABEL-SS] Boutier, M. and J. Chroboczek, "Source-Specific Routing in Babel", draft-boutier-babel-source-specific-01 (work in progress), January 2015. [RFC6126] Chroboczek, J., "The Babel Routing Protocol", RFC 6126, February 2011. [RFC7298] Ovsienko, D., "Babel Hashed Message Authentication Code (HMAC) Cryptographic Authentication", RFC 7298, July 2014. Chroboczek Expires May 4, 2016 [Page 5] Internet-Draft Babel Extension Mechanism November 2015 [RFC7557] Chroboczek, J., "Extension Mechanism for the Babel Routing Protocol", RFC 7557, May 2015. 4.2. Informative References [BABEL-RTT] Jonglez, B. and J. Chroboczek, "Delay-based Metric Extension for the Babel Routing Protocol", draft-jonglez- babel-rtt-extension-01 (work in progress), May 2015. [BABEL-Z] Chroboczek, J., "Diversity Routing for the Babel Routing Protocol", draft-chroboczek-babel-diversity-routing-00 (work in progress), July 2014. [DELAY-BASED] Jonglez, B. and J. Chroboczek, "A delay-based routing metric", March 2014. Available online from http://arxiv.org/abs/1403.3488 [HNCP] Stenberg, M., Barth, S., and P. Pfister, "Home Networking Control Protocol", draft-ietf-homenet-hncp-09 (work in progress), August 2015. Author's Address Juliusz Chroboczek PPS, University of Paris-Diderot Case 7014 75205 Paris Cedex 13 France Email: jch@pps.univ-paris-diderot.fr Chroboczek Expires May 4, 2016 [Page 6]