--- 1/draft-ietf-babel-v4viav6-07.txt 2022-02-24 10:13:10.842523249 -0800 +++ 2/draft-ietf-babel-v4viav6-08.txt 2022-02-24 10:13:10.858523431 -0800 @@ -1,44 +1,42 @@ Network Working Group J. Chroboczek Internet-Draft IRIF, University of Paris -Updates: 8966 (if approved) 16 January 2022 -Intended status: Standards Track -Expires: 20 July 2022 +Intended status: Experimental 24 February 2022 +Expires: 28 August 2022 IPv4 routes with an IPv6 next hop in the Babel routing protocol - draft-ietf-babel-v4viav6-07 + draft-ietf-babel-v4viav6-08 Abstract This document defines an extension to the Babel routing protocol that - allows annoncing routes to an IPv4 prefix with an IPv6 next-hop, + allows announcing routes to an IPv4 prefix with an IPv6 next-hop, which makes it possible for IPv4 traffic to flow through interfaces - that have not been assigned an IPv4 address. This document updates - RFC 8966. + that have not been assigned an IPv4 address. 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 https://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 20 July 2022. + This Internet-Draft will expire on 28 August 2022. Copyright Notice Copyright (c) 2022 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 (https://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 @@ -47,21 +45,21 @@ described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Specification of Requirements . . . . . . . . . . . . . . 3 2. Protocol operation . . . . . . . . . . . . . . . . . . . . . 3 2.1. Announcing v4-via-v6 routes . . . . . . . . . . . . . . . 4 2.2. Receiving v4-via-v6 routes . . . . . . . . . . . . . . . 4 - 2.3. Prefix and seqno requests . . . . . . . . . . . . . . . . 5 + 2.3. Route and seqno requests . . . . . . . . . . . . . . . . 5 2.4. Other TLVs . . . . . . . . . . . . . . . . . . . . . . . 5 3. ICMPv4 and PMTU discovery . . . . . . . . . . . . . . . . . . 5 4. Protocol encoding . . . . . . . . . . . . . . . . . . . . . . 6 4.1. Prefix encoding . . . . . . . . . . . . . . . . . . . . . 6 4.2. Changes to existing TLVs . . . . . . . . . . . . . . . . 7 5. Backwards compatibility . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 @@ -100,53 +98,53 @@ OSI protocol suite). The case of routing IPv4 packets through an IPv6 next hop is particularly interesting, since it makes it possible to build networks that have no IPv4 addresses except at the edges and still provide IPv4 connectivity to edge hosts. In addition, since an IPv6 next hop can use a link-local address that is autonomously configured, the use of such routes enables a mode of operation where the network core has no statically assigned IP addresses of either family, which significantly reduces the amount of manual - configuration required. + configuration required. (See also [RFC7404] for a discussion of the + issues involved with such an approach.) We call a route towards an IPv4 prefix that uses an IPv6 next hop a "v4-via-v6" route. This document describes an extension that allows the Babel routing protocol [RFC8966] to announce v4-via-v6 routes - across interfaces that have no IPv4 addresses assigned. Section 3 - describes procedures that ensure that all routers can originate - ICMPv4 packets, even if they have not been assigned any IPv4 - addresses. + across interfaces that have no IPv4 addresses assigned but are + capable of forwarding IPv4 traffic. Section 3 describes procedures + that ensure that all routers can originate ICMPv4 packets, even if + they have not been assigned any IPv4 addresses. The extension described in this document is inspired by a previously - defined extension to the BGP protocol [RFC5549]. This document - updates [RFC8966]. + defined extension to the BGP protocol [RFC5549]. 1.1. Specification of Requirements The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 2. Protocol operation The Babel protocol fully supports dual-stack operation: all data that represent a neighbour address or a network prefix are tagged by an Address Encoding (AE), a small integer that identifies the address family (IPv4 or IPv6) of the address of prefix, and describes how it is encoded. This extension defines a new AE, called v4-via-v6, which - has the same format as the existing AE for IPv4 addresses. This new - AE is only allowed in TLVs that carry network prefixes: TLVs that - carry a neighbour address use one of the normal encodings for IPv6 - addresses. + has the same format as the existing AE for IPv4 addresses (AE 1). + This new AE is only allowed in TLVs that carry network prefixes: TLVs + that carry an IPv6 neighbour address use one of the normal encodings + for IPv6 addresses. 2.1. Announcing v4-via-v6 routes A Babel node can use a v4-via-v6 announcement to announce an IPv4 route over an interface that has no assigned IPv4 address. In order to do so, it first establishes an IPv6 next-hop address in the usual manner (either by sending the Babel packet over IPv6, or by including a Next Hop TLV containing an IPv6 address and using AE 2 or 3); it then sends an Update, with AE equal to 4 (v4-via-v6) containing the IPv4 prefix being announced. @@ -166,70 +164,69 @@ not require a next hop, and there is therefore no difference between v4-via-v6 retractions and ordinary retractions. A node MAY send IPv4 retractions only, or it MAY send v4-via-v6 retractions on interfaces that have not been assigned an IPv4 address. 2.2. Receiving v4-via-v6 routes Upon reception of an Update TLV with AE equal to 4 (v4-via-v6) and finite metric, a Babel node computes the IPv6 next hop, as described in Section 4.6.9 of [RFC8966]. If no IPv6 next hop exists, then the - Update MUST be silently ignored. If an IPv6 next hop exists, then - the node MAY acquire the route being announced, as described in - Section 3.5.3 of [RFC8966]; the parameters of the route are as - follows: + Update MUST be ignored. If an IPv6 next hop exists, then the node + MAY acquire the route being announced, as described in Section 3.5.3 + of [RFC8966]; the parameters of the route are as follows: * the prefix, plen, router-id, seqno, metric MUST be computed as for an IPv4 route, as described in Section 4.6.9 of [RFC8966]; * the next hop MUST be computed as for an IPv6 route, as described in Section 4.6.9 of [RFC8966]: it is taken from the last preceding Next Hop TLV with an AE field equal to 2 or 3; if no such entry exists, and if the Update TLV has been sent in a Babel packet carried over IPv6, then the next hop is the network-layer source address of the packet. An Update TLV with a v4-via-v6 AE and metric equal to infinity is a retraction: it announces that a previously available route is being retracted. In that case, no next hop is necessary, and the retraction is treated as described in Section 4.6.9 of [RFC8966]. As usual, a node MAY ignore the update, e.g., due to filtering (Appendix C of [RFC8966]). If a node cannot install v4-via-v6 routes, e.g., due to hardware or software limitations, then routes to - an IPv4 prefix with an IPv6 next hop MUST NOT be selected, as - described in Section 3.5.3 of [RFC8966]. + an IPv4 prefix with an IPv6 next hop MUST NOT be selected. -2.3. Prefix and seqno requests +2.3. Route and seqno requests - Prefix and seqno requests are used to request an update for a given + Route and seqno requests are used to request an update for a given prefix. Since they are not related to a specific next hop, there is no semantic difference between IPv4 and v4-via-v6 requests. Therefore, a node SHOULD NOT send requests of either kind with the AE field being set to 4 (v4-via-v6); instead, it SHOULD request IPv4 updates by sending requests with the AE field being set to 1 (IPv4). When receiving requests, AEs 1 (IPv4) and 4 (v4-via-v6) MUST be treated in the same manner: the receiver processes the request as described in Section 3.8 of [RFC8966]. If an Update is sent, then it - MAY be sent with AE 1 or 4, as described in Section 2.1 above, + MAY be an ordinary IPv4 announcement (AE = 1) or an v4-via-v6 + announcement (AE = 4), as described in Section 2.1 above, irrespective of which AE was used in the request. When receiving a request with AE 0 (wildcard), the receiver SHOULD send a full route dump, as described in Section 3.8.1.1 of [RFC8966]. - Any IPv4 routes contained in the route dump MAY use either AE 1 - (IPv4) or AE 4 (v4-via-v6), as described in Section 2.1 above. + Any IPv4 routes contained in the route dump may use either AE 1 + (IPv4) or AE 4 (v4-via-v6), as described Section 2.1 above. 2.4. Other TLVs The only other TLVs defined by [RFC8966] that carry an AE field are - Next Hop and TLV. Next Hop and IHU TLVs MUST NOT carry the AE 4 (v4- + Next Hop and IHU. Next Hop and IHU TLVs MUST NOT carry the AE 4 (v4- via-v6). 3. ICMPv4 and PMTU discovery The Internet Control Message Protocol (ICMPv4, or simply ICMP) [RFC0792] is a protocol related to IPv4 that is primarily used to carry diagnostic and debugging information. ICMPv4 packets may be originated by end hosts (e.g., the "destination unreachable, port unreachable" ICMPv4 packet), but they may also be originated by intermediate routers (e.g., most other kinds of "destination @@ -247,91 +244,93 @@ Due to this kind of dependency, every Babel router that is able to forward IPv4 traffic MUST be able originate ICMPv4 traffic. Since the extension described in this document enables routers to forward IPv4 traffic received over an interface that has not been assigned an IPv4 address, a router implementing this extension MUST be able to originate ICMPv4 packets even when the outgoing interface has not been assigned an IPv4 address. In such a situation, if a Babel router has an interface that has been - assigned an IPv4 address, or if an IPv4 address has been assigned to - the router itself (to the "loopback interface"), then that IPv4 - address may be used as the source of originated ICMPv4 packets. If - no IPv4 address is available, a Babel router could use the - experimental mechanism described in Section 22 of [RFC7600], which - consists of using the dummy address 192.0.0.8 as the source address - of originated ICMPv4 packets. Note however that using the same - address on multiple routers may hamper debugging and fault isolation, - e.g., when using the "traceroute" utility. + assigned an IPv4 address (other than the loopback address), or if an + IPv4 address has been assigned to the router itself (to the "loopback + interface"), then that IPv4 address may be used as the source of + originated ICMPv4 packets. If no IPv4 address is available, a Babel + router could use the experimental mechanism described in Requirement + R-22 of Section 4.8 [RFC7600], which consists of using the dummy + address 192.0.0.8 as the source address of originated ICMPv4 packets. + Note however that using the same address on multiple routers may + hamper debugging and fault isolation, e.g., when using the + "traceroute" utility. 4. Protocol encoding This extension defines the v4-via-v6 AE, whose value is 4. This AE is solely used to tag network prefixes, and MUST NOT be used to tag neighbour addresses, e.g. in Next Hop or IHU TLVs. This extension defines no new TLVs or sub-TLVs. 4.1. Prefix encoding Network prefixes tagged with AE 4 (v4-via-v6) MUST be encoded and decoded just like prefixes tagged with AE 1 (IPv4), as described in Section 4.3.1 of [RFC8966]. A new compression state for AE 4 (v4-via-v6) distinct from that of AE 1 (IPv4) is introduced, and MUST be used for address compression of - prefixes tagged with AE 4, as described in Section 4.6.9 of [RFC8966] + prefixes tagged with AE 4, as described in Sections 4.5 and 4.6.9 of + [RFC8966] 4.2. Changes to existing TLVs The following TLVs MAY be tagged with AE 4 (v4-via-v6): * Update (Type = 8) * Route Request (Type = 9) * Seqno Request (Type = 10) As AE 4 (v4-via-v6) is suitable only for network prefixes, IHU - (Type = 5) and Next-Hop (Type = 7) TLVs MUST NOT be tagged with AE 4. + (Type = 5) and Next-Hop (Type = 7) TLVs are never sent with AE 4. Such (incorrect) TLVs MUST be ignored upon reception. 4.2.1. Update An Update (Type = 8) TLV with AE 4 is constructed as described in Section 4.6.9 of [RFC8966] for AE 1 (IPv4), with the following specificities: * Prefix. The Prefix field is constructed according to Section 4.1 above. - * Next Hop. The next hop is determined as described in Section 2.2 - above. + * Next Hop. The next hop is built and prased as described in + Section 2.1 and Section 2.2 above. -4.2.2. Other TLVs +4.2.2. Requests When tagged with the AE 4, Route Request and Seqno Request updates MUST be constructed and decoded as described in Section 4.6 of [RFC8966], and the network prefixes contained within them decoded as - described in Section 4.1 above. + described in Section 4.1 above (see also Section 2.3). 5. Backwards compatibility This protocol extension adds no new TLVs or sub-TLVs. This protocol extension uses a new AE. As discussed in Appendix D of [RFC8966] and specified in the same document, implementations that do not understand the present extension will silently ignore the various TLVs that use this new AE. As a result, incompatible versions will ignore v4-via-v6 routes. They will also ignore requests with AE 4, - which, as stated in Section 2.3, are NOT RECOMMENDED. + which, as stated in Section 2.3, are not recommended. Using a new AE introduces a new compression state, used to parse the network prefixes. As this compression state is separate from other AEs' states, it will not interfere with the compression state of unextended nodes. This extension reuses the next-hop state from AEs 2 and 3 (IPv6), but makes no changes to the way in which it is updated, and therefore causes no compatibility issues. @@ -422,20 +421,25 @@ [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI 10.17487/RFC4861, September 2007, . [RFC5549] Le Faucheur, F. and E. Rosen, "Advertising IPv4 Network Layer Reachability Information with an IPv6 Next Hop", RFC 5549, DOI 10.17487/RFC5549, May 2009, . + [RFC7404] Behringer, M. and E. Vyncke, "Using Only Link-Local + Addressing inside an IPv6 Network", RFC 7404, + DOI 10.17487/RFC7404, November 2014, + . + [RFC7600] Despres, R., Jiang, S., Ed., Penno, R., Lee, Y., Chen, G., and M. Chen, "IPv4 Residual Deployment via IPv6 - A Stateless Solution (4rd)", RFC 7600, DOI 10.17487/RFC7600, July 2015, . Author's Address Juliusz Chroboczek IRIF, University of Paris Case 7014