--- 1/draft-ietf-babel-v4viav6-04.txt 2021-06-09 06:13:10.683820606 -0700 +++ 2/draft-ietf-babel-v4viav6-05.txt 2021-06-09 06:13:10.707821202 -0700 @@ -1,19 +1,19 @@ Network Working Group J. Chroboczek Internet-Draft IRIF, University of Paris -Updates: 8966 (if approved) 8 June 2021 +Updates: 8966 (if approved) 9 June 2021 Intended status: Standards Track -Expires: 10 December 2021 +Expires: 11 December 2021 - IPv4 routes with an IPv6 next-hop in the Babel routing protocol - draft-ietf-babel-v4viav6-04 + IPv4 routes with an IPv6 next hop in the Babel routing protocol + draft-ietf-babel-v4viav6-05 Abstract This document defines an extension to the Babel routing protocol that allows annoncing 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. Status of This Memo @@ -23,21 +23,21 @@ 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 10 December 2021. + This Internet-Draft will expire on 11 December 2021. Copyright Notice Copyright (c) 2021 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 @@ -73,43 +73,43 @@ The role of a routing protocol is to build a routing table, a data structure that maps network prefixes in a given family (IPv4 or IPv6) to next hops, pairs of an outgoing interface and a neighbour's network address, for example: destination next hop 2001:db8:0:1::/64 eth0, fe80::1234:5678 203.0.113.0/24 eth0, 192.0.2.1 When a packet is routed according to a given routing table entry, the - forwarding plane uses a neighbour discovery protocol (the Neighbour - Discovery protocol (ND) [RFC4861] in the case of IPv6, the Address - Resolution Protocol (ARP) [RFC0826] in the case of IPv4) to map the - next hop address to a link-layer address (a "MAC address"), which is - then used to construct the link-layer frames that encapsulate - forwarded packets. + forwarding plane typically uses a neighbour discovery protocol (the + Neighbour Discovery protocol (ND) [RFC4861] in the case of IPv6, the + Address Resolution Protocol (ARP) [RFC0826] in the case of IPv4) to + map the next-hop address to a link-layer address (a "MAC address"), + which is then used to construct the link-layer frames that + encapsulate forwarded packets. It is apparent from the description above that there is no fundamental reason why the destination prefix and the next-hop address should be in the same address family: there is nothing preventing an IPv6 packet from being routed through a next hop with an IPv4 address (in which case the next hop's MAC address will be obtained using ARP), or, conversely, an IPv4 packet from being routed through a next hop with an IPv6 address. (In fact, it is even - possible to store link-layer addresses directly in the next hop entry + possible to store link-layer addresses directly in the next-hop entry of the routing table, which is commonly done in networks using the 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 + 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. 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 @@ -122,23 +122,23 @@ 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 double-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 + 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. 2.1. Announcing v4-via-v6 routes A Babel node that needs to announce an IPv4 route over an interface @@ -146,88 +146,88 @@ 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. If the outgoing interface has been assigned an IPv4 address, then, in the interest of maximising compatibility with existing routers, the sender SHOULD prefer an ordinary IPv4 announcement; even in that case, however, it MAY send a v4-via-v6 announcement. A node SHOULD - NOT send both ordinary IPv4 and v4-via-v6 annoucements for the same + NOT send both ordinary IPv4 and v4-via-v6 announcements for the same prefix over a single interface (if the update is sent to a multicast address) or to a single neighbour (if sent to a unicast address), since doing that provides no benefit while doubling the amount of routing traffic. Updates with infinite metric are retractions: they indicate that a previously announced route is no longer available. Retractions do 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 + 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: * 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 + * 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 + 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 + 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 + 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, eg., due to hardware or software limitations, then routes to - an IPv4 prefix with an IPv6 next-hop MUST NOT be selected, as + 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]. 2.3. Prefix and seqno requests Prefix 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 + 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, 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. 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 TLV. 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) [RFC792] 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 @@ -262,21 +262,21 @@ range [RFC1918]. If no more suitable address is available, then a router MAY use the IPv4 dummy address 192.0.0.8 as the source address of the IMCPv4 packets that it sends. 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, eg. in Next-Hop or IHU TLVs. + 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 @@ -299,21 +299,21 @@ 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 + * Next Hop. The next hop is determined as described in Section 2.2 above. 4.2.2. Other TLVs 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. 5. Backwards compatibility