| Network Working Group | J. Xie |
| Internet-Draft | Huawei Technologies |
| Intended status: Standards Track | L. Geng |
| Expires: January 2, 2020 | China Mobile |
| M. McBride | |
| Futurewei | |
| R. Asati | |
| Cisco | |
| S. Dhanaraj | |
| G. Yan | |
| Y. Xia | |
| Huawei | |
| July 1, 2019 |
Encapsulation for BIER in Non-MPLS IPv6 Networks
draft-xie-bier-ipv6-encapsulation-02
This document proposes a BIER IPv6 (BIERv6) encapsulation for Non-MPLS IPv6 Networks using the IPv6 Destination Option extension header.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] and [RFC8174].
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 January 2, 2020.
Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved.
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Bit Index Explicit Replication (BIER) [RFC8279] is an architecture that provides optimal multicast forwarding without requiring intermediate routers to maintain any per-flow state by using a multicast-specific BIER header.
[RFC8296] defines a common BIER Header format for MPLS and Non-MPLS networks. It has defined two types of encapsulation methods using the common BIER Header, (1) BIER encapsulation in MPLS networks, here-in after referred as MPLS BIER Header in this document and (2) BIER encapsulation in Non-MPLS networks, here-in after referred as Non-MPLS BIER Header in this document. [RFC8296] also assigned Ethertype=0xAB37 for Non-MPLS BIER Header packets to be directly carried over the Ethernet links.
This document proposes a BIER IPv6 encapsulation for Non-MPLS IPv6 Networks, defining a method to carry the standard Non-MPLS BIER header (as defined in [RFC8296]) in the native IPv6 header. A new IPv6 Option type - BIER Option is defined to encode the standard Non-MPLS BIER header and this newly defined BIER Option is carried under the Destination Options header of the native IPv6 Header [RFC8200].
This document details one of the proposed solutions for transporting BIER packets in an IPv6 network. To better understand the overall BIER IPv6 problem space, use cases and proposed solutions, refer to [I-D.ietf-bier-ipv6-requirements].
Readers of this document are assumed to be familiar with the terminology and concepts of the documents listed as Normative References.
The following new terms are used throughout this document:
Destination Options Header and the Options that can be carried under this extension header is defined in [RFC8200]. This document defines a new Option type - BIER Option, to encode the Non-MPLS BIER header. As specified in Section 4.2 [RFC8200], the BIER Option follows type-length-value (TLV) encoding format and the standard Non-MPLS BIER header [RFC8296] is encoded in the value portion of the BIER Option TLV.
This BIER Option MUST be carried only inside the IPv6 Destination Options header and MUST NOT be carried under the Hop-by-Hop Options header.
Co-existence of Destination Options Header with BIER option TLV and other IPv6 extension headers MUST confirm to the general requirements defined in [RFC8200]. In addition to the requirements defined in [RFC8200], this document requires that the Destination Options Header with a BIER Option TLV MUST appear only after the Routing Header if the Routing Header is present in the IPv6 Header.
The BIER Option is encoded in type-length-value (TLV) format as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Non-MPLS BIER Header (defined in RFC8296) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
BIER is generally a hop-by-hop and one-to-many architecture, and thus the IPv6 Destination Address (DA) being a Multicast Address is a proper approach for both the two paradigms in BIERv6 encapsulation.
This document proposes to use multicast address FF0X::AB37 (to be allocated and reserved by IANA - See Section 6.2) as the IPv6 destination address for the BIERv6 packets to be forwarded in the BIER domain.
All the interfaces of the BFRs supporting the BIERv6 encapsulation defined in this document MUST subscribe and listen to BIER multicast address FF0X::AB37 belong to scopes [1, 2, 3, 4, 5, E] defined in [RFC7346]. However it is RECOMMENDED to use Realm-Local scope (scope value 3), that is FF03:AB37 as a destination address while forwarding the BIERv6 packet, as this scope zone is exactly the BIERv6 Domain. The use of other scopes is outside the scope of this document.
Use of a Unicast Address as a IPv6 Destination Address is permissible and useful in certain cases.
The unicast address used in BIERv6 packet targeting a BFR SHOULD be the IPv6 BFR-Prefix advertised from this BFR. When a BFR advertises the BIER information with BIERv6 encapsulation capability, the IPv6 BFR-prefix of this BFR MUST be selected specifically for BIERv6 packet forwarding. Locally this "BIER Specific" IPv6 address is initialized in FIB with a flag of "BIER specific handling", represented as End.BIER function. For convenience, the indication in FIB share the same space as SRv6 Endpoints Behaviors defined in [I-D.ietf-spring-srv6-network-programming]. Apart from this sharing of code space, there is nothing dependent on SRv6. The co-existance of BIERv6 and SRv6 is outside the scope of this document.
BFR Prefix is used only in control plane in BIER MPLS encapsulation but not used in data plane. While in BIERv6, BFR prefix is used in both control plane and data plane. The "BIER Specific" IPv6 address can be used for BIER MPLS in control plane too. So it is RECOMMENDED to use a "BIER specific" IPv6 address as BFR prefix when deploying BIER in IPv6 network from the scratch. One should be careful not use the IPv6 address selected as BFR prefix for other purpose like BGP session until the "BIER specific handling" can do more general process.
The following is an example of configuring a BIER specific IPv6 address and using this address as BFR prefix:
# Config a BIER specific IPv6 address with 128-bit mask on loopback0.
interface loopback0
ipv6 address 2019::AB37 128 End.BIER
# Config the BIER-specific IPv6 address on loopback0 as BFR Prefix.
bier sub-domain 6 ipv6-underlay
bfr-prefix interface loopback0
The address used as "BIER specific" IPv6 address can be from inside the scope of an SRv6 Locator or outside the scope of the SRv6 Locator(s) since it is a host prefix (128-bit prefix-length prefix).
Each "BIER specific" address can be used in one or many sub-domains as BFR-prefix, such that it can be associated with one or many Multi-Topologies (MTs) or algorithms.
More than one "BIER specific" address are also allowed as different BFR-prefix of more than one sub-domain, as described in section 2 of [RFC8279].
The following is an example pseudo-code of the End.BIER function:
1. IF NH = 60 AND HopLimit > 0 ;;Ref1
2. IF (OptType1 = BIER) and (OptLength1 = HdrExtLen*8 + 4) ;;Ref2
3. Lookup the BIER Header inside the BIER option TLV.
4. Forward via the matched entry.
5. ELSE
6. Drop the packet.
7. ELSE IF Last_NH = ICMPv6 ;;Ref3
8. Send to CPU.
9. ELSE
10. Drop the packet.
Ref2: The first TLV is BIER type and is the only one in Destination options header.
Ref3: An ICMPv6 packet using End.BIER as destination address.
As a multicast packet enters the BIER domain in a Non-MPLS IPv6 network, the multicast packet will be encapsulated with BIERv6 Header.
Typically a BIERv6 header would contain the Destination Options Header as the only Extensions Header besides IPv6 Header. However, it is allowed and possible for other extension headers to appear along with the Destination Options Header as long as the requirements listed in section 3.1 of this document is met.
Format of the multicast packet with BIERv6 encapsulation carrying only the Destination Options header is depicted in the below figure.
+---------------+--------------+------------
| IPv6 header | Dest Options | X type of
| | Header with | multicast
| | BIER Option | packet
| | |
| Next Hdr = 60 | Nxt Hdr = X |
+---------------+--------------+------------
Format of the multicast packet with BIERv6 encapsulation carrying other extension headers along with Destination Options extension header is required to follow general recommendations of [RFC8200] and examples in other RFCs. [RFC6275] introduces how the order should be when other extension headers carries along with Home address option in a destination options header. Similar to this example, this document requires the Destination Options Header carrying the BIER option MUST be placed as follows:
Source Address field in the IPv6 header MUST be a routable IPv6 unicast address of the BFIR in any case.
BFIR encodes the Non-MPLS BIER header in the above mentioned encapsulation format and forwards the BIERv6 packet to the nexthop BFR following the local BIFT table.
BFRs in the IPv6 network, processes and replicates the packets towards the BFERs using the local BIFT table. The bit-string field in the Non-MPLS BIER header may be changed by the BFRs as they replicate the packet. BFRs MUST follow the procedures defined in section 3.1 as they modify the other fields in the Non-MPLS BIER header. The source address in the IPv6 header MUST NOT be modified by the BFRs.
There is no BIER-specific processing, and all the 8 steps in section 6.5 of RFC8279 apply to BIERv6 packet processing. However, there are some IPv6-specific processing procedures due to the base and general procedures of IPv6.
On the overlay layer, when a multicast packet enters the BIER domain in a Non-MPLS IPv6 network, the Ingress BFR (BFIR) encapsulates the multicast packet with a BIERv6 Header, transforming it to a BIERv6 packet. The BIERv6 header includes an IPv6 header and IPv6 Destination Options Header within a standard Non-MPLS BIER header. Source Address field in the IPv6 header MUST be set to a routable IPv6 unicast address of the BFIR. Destination Address field in the IPv6 header is set to a BIER multicast address, FF0X::AB37, if the next-hop BFR is directly connected, or MAY be set to a unicast address in case of the scenarios discussed in section 3.2.
On the BIER layer, upon receiving an BIERv6 packet, the BFR processes the IPv6 header first. This is the general procedure of IPv6.
If the IPv6 Destination address is the BIER multicast address, a 'BIER Specific Handling' indication will be obtained by the preceding Multicast DA lookup (MFIB lookup). The BIER option, if exists, will be checked to decide which neighbor(s) to replicate the BIERv6 packet to.
If the IPv6 Destination address is an IPv6 BFR-Prefix unicast address of this BFR, a 'BIER Specific Handling' indication will be obtained by the preceding Unicast DA lookup (FIB lookup). The BIER option, if exists, will be checked to decide which neighbor(s) to replicate the BIERv6 packet to.
It is a local behavior to handle the combination of extension headers, options and the BIER option(s) in destination options header when a 'BIER Specific Handling' indication is got by the preceding MFIB or FIB lookup. Early deployment of BIERv6 may require there is only one BIER option TLV in the destination options header followed the IPv6 header. How other extension headers or more BIER option TLVs in a BIERv6 packet is handled is outside the scope of this document.
A packet having a 'BIER Specific Handling' indication but not having a BIER option MAY be processed normally as normal multicast or unicast forwarding procedures do, or MAY be dropped.
A packet not having a 'BIER Specific Handling' indication but having a BIER option SHOULD be processed normally as normal multicast or unicast forwarding procedures, which may be a behavior of drop, or send to CPU, or other behaviors in existing implementations.
The Destination Address field in the IPv6 Header MUST change to the nexthop BFR's BFR Prefix if Unicast address is used in BIERv6.
The Hop Limit field of IPv6 header MUST decrease by 1 when sending packets to a BFR neighbor, while the TTL in the BIER header MUST be unchanged.
The BitString in the BIER header in the Destination Options Header may change when sending packets to a neighbor. Such change of BitString MUST be aligned with the procedure defined in RFC8279. Because of the requirement to change the content of the option when forwarding BIERv6 packet, the BIER option type should have chg flag 1 per section 4.2 of RFC8200.
The procedures applies normally if a bit corresponding to the self bfr-id is set in the bit-string field of the Non-MPLS BIER header of the BIERv6 packet. The node is considered to be an Egress BFR (BFER) in this case. The BFER removes the BIERv6 header, including the IPv6 header and the Destination Options header, and copies the packet to the multicast flow overlay. The egress VRF of a packet may be determined by a single MFIB lookup on the BFER using both the IPv6 SA and IPv6 DA.
A BIERv6 packet with a special IPv6 Destination Address, either multicast or unicast, would be processed by BIER forwarding procedure only when the 'BIER valid' flag has been obtained ahead of time in the normal MFIB or FIB lookup of the IPv6 header. Otherwise the packet with an IPv6 BIER Option will be dropped, as if the Option is not recognize by the node.
An IPv6 packet with BIER multicast address FF0X::AB37 as destination address, but does not carry IPv6 BIER Option will be dropped.
Allocation is expected from IANA for a BIER Option Type codepoint from the "Destination Options and Hop-by-Hop Options" sub-registry of the "Internet Protocol Version 6 (IPv6) Parameters" registry. The value 0x70 is suggested.
+-----------+-----+-----+-------+-------------+------------+
| Hex Value | act | chg | rest | Description | Reference |
+-----------+-----+-----+-------+-------------+------------+
| 0x70 | 01 | 1 | 10000 | BIER Option | This draft |
+-----------+-----+-----+-------+-------------+------------+
Figure 1: IPv6 Option Type Suggested
Allocation is expected from IANA for a BIER Multicast Address from the "Variable Scope Multicast Addresses" sub-registry of the "IPv6 Multicast Address Space Registry" registry. The address 'FF0X::AB37' is suggested.
+-----------------------+---------------------+------------+
| Address(es) | Description | Reference |
| | | |
+-----------------------+---------------------+------------+
| FF0X:0:0:0:0:0:0:AB37 | ALL_BIER_FORWARDERS | This draft |
+-----------------------+---------------------+------------+
Figure 2: Multicast Address Suggested
Allocation is expected from IANA for an End.BIER function codepoint from the "SRv6 Endpoint Behaviors" sub-registry. The value 60 is suggested.
+-------+--------+--------------------------+------------+
| Value | Hex | Endpoint function | Reference |
+-------+--------+--------------------------+------------+
| TBD | TBD | End.BIER | This draft |
+-------+--------+--------------------------+------------+
Figure 3: End.BIER Function
The authors would like to thank Stig Venaas for his valuable comments. Thanks IJsbrand Wijnands, Greg Shepherd, Tony Przygienda, Toerless Eckert, Jeffrey Zhang for the helpful comments to improve this document.
| [RFC6275] | Perkins, C., Johnson, D. and J. Arkko, "Mobility Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 2011. |
| [RFC7346] | Droms, R., "IPv6 Multicast Address Scopes", RFC 7346, DOI 10.17487/RFC7346, August 2014. |
| [RFC8200] | Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 2017. |
| [RFC8279] | Wijnands, IJ., Rosen, E., Dolganow, A., Przygienda, T. and S. Aldrin, "Multicast Using Bit Index Explicit Replication (BIER)", RFC 8279, DOI 10.17487/RFC8279, November 2017. |
| [RFC8296] | Wijnands, IJ., Rosen, E., Dolganow, A., Tantsura, J., Aldrin, S. and I. Meilik, "Encapsulation for Bit Index Explicit Replication (BIER) in MPLS and Non-MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January 2018. |
| [I-D.ietf-bier-ipv6-requirements] | McBride, M., Xie, J., Dhanaraj, S. and R. Asati, "BIER IPv6 Requirements", Internet-Draft draft-ietf-bier-ipv6-requirements-00, May 2019. |
| [I-D.ietf-spring-srv6-network-programming] | Filsfils, C., Camarillo, P., Leddy, J., daniel.voyer@bell.ca, d., Matsushima, S. and Z. Li, "SRv6 Network Programming", Internet-Draft draft-ietf-spring-srv6-network-programming-00, April 2019. |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC8174] | Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017. |