draft-ietf-babel-v4viav6-04.txt   draft-ietf-babel-v4viav6-05.txt 
Network Working Group J. Chroboczek Network Working Group J. Chroboczek
Internet-Draft IRIF, University of Paris Internet-Draft IRIF, University of Paris
Updates: 8966 (if approved) 8 June 2021 Updates: 8966 (if approved) 9 June 2021
Intended status: Standards Track Intended status: Standards Track
Expires: 10 December 2021 Expires: 11 December 2021
IPv4 routes with an IPv6 next-hop in the Babel routing protocol IPv4 routes with an IPv6 next hop in the Babel routing protocol
draft-ietf-babel-v4viav6-04 draft-ietf-babel-v4viav6-05
Abstract Abstract
This document defines an extension to the Babel routing protocol that This document defines an extension to the Babel routing protocol that
allows annoncing routes to an IPv4 prefix with an IPv6 next-hop, allows annoncing routes to an IPv4 prefix with an IPv6 next-hop,
which makes it possible for IPv4 traffic to flow through interfaces which makes it possible for IPv4 traffic to flow through interfaces
that have not been assigned an IPv4 address. that have not been assigned an IPv4 address.
Status of This Memo Status of This Memo
skipping to change at page 1, line 34 skipping to change at page 1, line 34
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." 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 Notice
Copyright (c) 2021 IETF Trust and the persons identified as the Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/ Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document. license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
skipping to change at page 2, line 39 skipping to change at page 2, line 39
The role of a routing protocol is to build a routing table, a data 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) structure that maps network prefixes in a given family (IPv4 or IPv6)
to next hops, pairs of an outgoing interface and a neighbour's to next hops, pairs of an outgoing interface and a neighbour's
network address, for example: network address, for example:
destination next hop destination next hop
2001:db8:0:1::/64 eth0, fe80::1234:5678 2001:db8:0:1::/64 eth0, fe80::1234:5678
203.0.113.0/24 eth0, 192.0.2.1 203.0.113.0/24 eth0, 192.0.2.1
When a packet is routed according to a given routing table entry, the When a packet is routed according to a given routing table entry, the
forwarding plane uses a neighbour discovery protocol (the Neighbour forwarding plane typically uses a neighbour discovery protocol (the
Discovery protocol (ND) [RFC4861] in the case of IPv6, the Address Neighbour Discovery protocol (ND) [RFC4861] in the case of IPv6, the
Resolution Protocol (ARP) [RFC0826] in the case of IPv4) to map the Address Resolution Protocol (ARP) [RFC0826] in the case of IPv4) to
next hop address to a link-layer address (a "MAC address"), which is map the next-hop address to a link-layer address (a "MAC address"),
then used to construct the link-layer frames that encapsulate which is then used to construct the link-layer frames that
forwarded packets. encapsulate forwarded packets.
It is apparent from the description above that there is no It is apparent from the description above that there is no
fundamental reason why the destination prefix and the next-hop fundamental reason why the destination prefix and the next-hop
address should be in the same address family: there is nothing address should be in the same address family: there is nothing
preventing an IPv6 packet from being routed through a next hop with 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 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 obtained using ARP), or, conversely, an IPv4 packet from being routed
through a next hop with an IPv6 address. (In fact, it is even 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 of the routing table, which is commonly done in networks using the
OSI protocol suite). OSI protocol suite).
The case of routing IPv4 packets through an IPv6 next hop is The case of routing IPv4 packets through an IPv6 next hop is
particularly interesting, since it makes it possible to build particularly interesting, since it makes it possible to build
networks that have no IPv4 addresses except at the edges and still networks that have no IPv4 addresses except at the edges and still
provide IPv4 connectivity to edge hosts. In addition, since an IPv6 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 configured, the use of such routes enables a mode of operation where
the network core has no statically assigned IP addresses of either the network core has no statically assigned IP addresses of either
family, which significantly reduces the amount of manual family, which significantly reduces the amount of manual
configuration required. configuration required.
We call a route towards an IPv4 prefix that uses an IPv6 next hop a 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 "v4-via-v6" route. This document describes an extension that allows
the Babel routing protocol [RFC8966] to announce v4-via-v6 routes the Babel routing protocol [RFC8966] to announce v4-via-v6 routes
across interfaces that have no IPv4 addresses assigned. Section 3 across interfaces that have no IPv4 addresses assigned. Section 3
describes procedures that ensure that all routers can originate describes procedures that ensure that all routers can originate
skipping to change at page 3, line 39 skipping to change at page 3, line 39
1.1. Specification of Requirements 1.1. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2. Protocol operation 2. Protocol operation
The Babel protocol fully supports double-stack operation: all data The Babel protocol fully supports dual-stack operation: all data that
that represent a neighbour address or a network prefix are tagged by represent a neighbour address or a network prefix are tagged by an
an Address Encoding (AE), a small integer that identifies the address Address Encoding (AE), a small integer that identifies the address
family (IPv4 or IPv6) of the address of prefix, and describes how it 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 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 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 AE is only allowed in TLVs that carry network prefixes: TLVs that
carry a neighbour address use one of the normal encodings for IPv6 carry a neighbour address use one of the normal encodings for IPv6
addresses. addresses.
2.1. Announcing v4-via-v6 routes 2.1. Announcing v4-via-v6 routes
A Babel node that needs to announce an IPv4 route over an interface A Babel node that needs to announce an IPv4 route over an interface
skipping to change at page 4, line 19 skipping to change at page 4, line 19
In order to do so, it first establishes an IPv6 next-hop address in 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 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 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) 3); it then sends an Update, with AE equal to 4 (v4-via-v6)
containing the IPv4 prefix being announced. containing the IPv4 prefix being announced.
If the outgoing interface has been assigned an IPv4 address, then, in If the outgoing interface has been assigned an IPv4 address, then, in
the interest of maximising compatibility with existing routers, the the interest of maximising compatibility with existing routers, the
sender SHOULD prefer an ordinary IPv4 announcement; even in that sender SHOULD prefer an ordinary IPv4 announcement; even in that
case, however, it MAY send a v4-via-v6 announcement. A node SHOULD 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 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), address) or to a single neighbour (if sent to a unicast address),
since doing that provides no benefit while doubling the amount of since doing that provides no benefit while doubling the amount of
routing traffic. routing traffic.
Updates with infinite metric are retractions: they indicate that a Updates with infinite metric are retractions: they indicate that a
previously announced route is no longer available. Retractions do previously announced route is no longer available. Retractions do
not require a next hop, and there is therefore no difference between not require a next hop, and there is therefore no difference between
v4-via-v6 retractions and ordinary retractions. A node MAY send IPv4 v4-via-v6 retractions and ordinary retractions. A node MAY send IPv4
retractions only, or it MAY send v4-via-v6 retractions on interfaces retractions only, or it MAY send v4-via-v6 retractions on interfaces
that have not been assigned an IPv4 address. that have not been assigned an IPv4 address.
2.2. Receiving v4-via-v6 routes 2.2. Receiving v4-via-v6 routes
Upon reception of an Update TLV with AE equal to 4 (v4-via-v6) and 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 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 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 Update MUST be silently ignored. If an IPv6 next hop exists, then
the node MAY acquire the route being announced, as described in the node MAY acquire the route being announced, as described in
Section 3.5.3 of [RFC8966]; the parameters of the route are as Section 3.5.3 of [RFC8966]; the parameters of the route are as
follows: follows:
* the prefix, plen, router-id, seqno, metric MUST be computed as for * the prefix, plen, router-id, seqno, metric MUST be computed as for
an IPv4 route, as described in Section 4.6.9 of [RFC8966]; 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 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 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. address of the packet.
An Update TLV with a v4-via-v6 AE and metric equal to infinity is a 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 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]. 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 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 (Appendix C of [RFC8966]). If a node cannot install v4-via-v6
routes, eg., due to hardware or software limitations, then routes to 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 an IPv4 prefix with an IPv6 next hop MUST NOT be selected, as
described in Section 3.5.3 of [RFC8966]. described in Section 3.5.3 of [RFC8966].
2.3. Prefix and seqno requests 2.3. Prefix and seqno requests
Prefix and seqno requests are used to request an update for a given 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. no semantic difference between IPv4 and v4-via-v6 requests.
Therefore, a node SHOULD NOT send requests of either kind with the AE 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 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). 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 When receiving requests, AEs 1 (IPv4) and 4 (v4-via-v6) MUST be
treated in the same manner: the receiver processes the request as 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 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 sent with AE 1 or 4, as described in Section 2.1 above,
irrespective of which AE was used in the request. irrespective of which AE was used in the request.
When receiving a request with AE 0 (wildcard), the receiver SHOULD 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]. 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 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. (IPv4) or AE 4 (v4-via-v6), as described in Section 2.1 above.
2.4. Other TLVs 2.4. Other TLVs
The only other TLVs defined by [RFC8966] that carry an AE field are 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). via-v6).
3. ICMPv4 and PMTU discovery 3. ICMPv4 and PMTU discovery
The Internet Control Message Protocol (ICMPv4, or simply ICMP) The Internet Control Message Protocol (ICMPv4, or simply ICMP)
[RFC792] is a protocol related to IPv4 that is primarily used to [RFC792] is a protocol related to IPv4 that is primarily used to
carry diagnostic and debugging information. ICMPv4 packets may be carry diagnostic and debugging information. ICMPv4 packets may be
originated by end hosts (e.g., the "destination unreachable, port originated by end hosts (e.g., the "destination unreachable, port
unreachable" ICMPv4 packet), but they may also be originated by unreachable" ICMPv4 packet), but they may also be originated by
intermediate routers (e.g., most other kinds of "destination intermediate routers (e.g., most other kinds of "destination
skipping to change at page 6, line 41 skipping to change at page 6, line 41
range [RFC1918]. If no more suitable address is available, then a 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 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 of the IMCPv4 packets that it sends. Note however that using the
same address on multiple routers may hamper debugging and fault same address on multiple routers may hamper debugging and fault
isolation, e.g., when using the "traceroute" utility. isolation, e.g., when using the "traceroute" utility.
4. Protocol encoding 4. Protocol encoding
This extension defines the v4-via-v6 AE, whose value is 4. This AE 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 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. This extension defines no new TLVs or sub-TLVs.
4.1. Prefix encoding 4.1. Prefix encoding
Network prefixes tagged with AE 4 (v4-via-v6) MUST be encoded and 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 decoded just like prefixes tagged with AE 1 (IPv4), as described in
Section 4.3.1 of [RFC8966]. Section 4.3.1 of [RFC8966].
A new compression state for AE 4 (v4-via-v6) distinct from that of AE A new compression state for AE 4 (v4-via-v6) distinct from that of AE
skipping to change at page 7, line 32 skipping to change at page 7, line 32
4.2.1. Update 4.2.1. Update
An Update (Type = 8) TLV with AE 4 is constructed as described in 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 Section 4.6.9 of [RFC8966] for AE 1 (IPv4), with the following
specificities: specificities:
* Prefix. The Prefix field is constructed according to Section 4.1 * Prefix. The Prefix field is constructed according to Section 4.1
above. 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. above.
4.2.2. Other TLVs 4.2.2. Other TLVs
When tagged with the AE 4, Route Request and Seqno Request updates When tagged with the AE 4, Route Request and Seqno Request updates
MUST be constructed and decoded as described in Section 4.6 of MUST be constructed and decoded as described in Section 4.6 of
[RFC8966], and the network prefixes contained within them decoded as [RFC8966], and the network prefixes contained within them decoded as
described in Section 4.1 above. described in Section 4.1 above.
5. Backwards compatibility 5. Backwards compatibility
 End of changes. 19 change blocks. 
30 lines changed or deleted 30 lines changed or added

This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/