Internet DRAFT - draft-ietf-bier-php
draft-ietf-bier-php
BIER Z. Zhang
Internet-Draft Juniper Networks
Intended status: Standards Track 6 February 2024
Expires: 9 August 2024
BIER Penultimate Hop Popping
draft-ietf-bier-php-11
Abstract
Bit Index Explicit Replication (BIER) can be used as provider tunnel
for Multicast Virtual Private Network (MVPN), Global Table Multicast
or Ethernet Virtual Private Network (EVPN). It is possible that not
all routers in the provider network support BIER and there are
various methods to handle BIER-incapable transit routers. However
those methods assume the MVPN/EVPN Provider Edges (PEs) are BIER-
capable. This document specifies a method to allow BIER-incapable
routers to act as MVPN/EVPN PEs with BIER as the transport, by having
the upstream BIER Forwarding Router (BFR) that is connected directly
or indirectly via a tunnel to a BIER-incapable PE remove the BIER
header and send the payload to the PE.
Requirements Language
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.
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 9 August 2024.
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Copyright Notice
Copyright (c) 2024 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
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
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
2. Specifications . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Signaling . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. BIRT/BIFT Calculation . . . . . . . . . . . . . . . . . . 5
3. Security Considerations . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
The BIER architecture includes three layers: the "routing underlay",
the "BIER layer", and the "multicast flow overlay". The multicast
flow overlay is responsible for the BIER Forwarding Egress Routers
(BFERs) to signal to BIER Forwarding Ingress Routers (BFIRs) that
they are interested in receiving certain multicast flows so that
BFIRs can encode the correct bitstring for BIER forwarding by the
BIER layer.
MVPN [RFC6513] [RFC6514] and EVPN [RFC7432] are two similar overlays
where BGP Auto-Discovery routes for MVPN/EVPN are exchanged among all
PEs to signal which PEs need to receive multicast traffic for all or
certain flows. Typically the same provider tunnel type is used for
traffic to reach all receiving PEs.
Consider an MVPN/EVPN deployment where enough provider routers are
BIER-capable for BIER to become the preferred choice of provider
tunnel [RFC8556] [I-D.ietf-bier-evpn]. However, some PEs cannot be
upgraded to support BIER forwarding. While there are ways to allow
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an ingress PE to send traffic to some PEs with one type of tunnel and
send traffic to some other PEs with a different type of tunnel, the
procedure becomes complicated and forwarding is not optimized.
One way to solve this problem is to use Penultimate Hop Popping (PHP)
so that the upstream BFR can pop the BIER header [RFC8296] and send
the payload "natively" (note that the upstream BFR can be connected
directly or indirectly via any type of tunnel to the PE). This is
similar to Multi-Protocol Label Switching (MPLS) PHP though it is the
BIER header that is popped.
The transition of an existing MVPN/EVPN deployment with traditional
provider tunnels to using BIER with some PEs not capable of receiving
BIER packets can be incremental. All PEs are first upgraded to
support BIER at least in the control plane, with those not capable of
BIER forwarding requesting PHP. Then BIER-capable ingress PEs
independently and incrementally switch to BIER transport.
While the above text uses MVPN/EVPN as example, BIER PHP is
applicable to any scenario where the multicast flow overlay edge
router does not support BIER, as long as the edge router does not
need to know the transmitting BFIR or participate in BIER OAM
procedures.
This works well if a BIER-incapable PE only needs to receive
multicast traffic. If it needs to send multicast traffic as well,
then it must Ingress Replicate to a BIER-capable helper PE, who will
in turn relay the packet to other PEs. The helper PE is either a
Virtual Hub as specified in [RFC7024] for MVPN and
[I-D.ietf-bess-evpn-virtual-hub] for EVPN, or an AR-Replicator as
specified in [I-D.ietf-bess-evpn-optimized-ir] for EVPN.
2. Specifications
The BIER Penultimate Hop Popping is intended only for the scenario
where a multicast flow overlay router for a BIER domain does not
support BIER forwarding, either entirely or just for some particular
BitStringLengths (BSL). In the latter case, PHP is only for BIER
packets with those BSL. The flow overlay router would be a BFER if
it did support BIER forwarding, and PHP would not be done by its
penultimate hop.
The procedures in this section apply only if, by means outside the
scope of this document, it is known that all potential penultimate
hop BFRs support PHP (i.e., able to pop the BIER header when sending
to a requesting flow overlay router) , and that the payload after
BIER header is one of the following:
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* MPLS packets with downstream-assigned label at top of stack (i.e.,
the Proto field in the BIER header is 1). For example, a label
from a Domain-wide Common Block (DCB) is used as specified in
[I-D.ietf-bess-mvpn-evpn-aggregation-label].
* IPv4/IPv6 multicast packets for which Reverse Path Forwarding
check is disabled.
2.1. Signaling
With IS-IS signaling, a sub-TLV in another sub-TLV is called sub-sub-
TLV (and more sub-levels are possible like sub-sub-sub-TLV). With
other signaling protocols, a sub-TLV in another sub-TLV is still
called sub-TLV. For convenience, in this document we use sub-TLV
even when it is sub-sub-TLV in IS-IS, as there is no ambiguity with
the name itself (e.g. MPLS Encapsulation).
A BIER-incapable router, if acting as a multicast flow overlay router
for BIER, MUST signal its BIER information as specified in [RFC8401],
[RFC8444], [I-D.ietf-bier-ospfv3-extensions], or
[I-D.ietf-bier-idr-extensions] with a PHP sub-TLV included in the
BIER sub-TLV (or TLV in case of BGP) attached to the BIER-incapable
router's BFR-prefix to request BIER PHP from other BFRs. The type of
the sub-TLV or sub-TLV is TBD, and the length is 0.
With MPLS encapsulation, the BIER-incapable multicast flow overlay
router MAY omit the BIER MPLS Encapsulation sub-LV, or MUST set the
Label field in BIER MPLS Encapsulation sub-TLV to Implicit Null Label
[RFC3032].
With MPLS encapsulation, if a BFER (that does support BIER but) does
not support a certain BSL, it MAY advertise a corresponding BIER MPLS
Encapsulation sub-TLV with the Label field to Implicit Null Label to
request PHP for that BSL. It MUST NOT include the PHP sub-TLV in
this case.
With non-MPLS encapsulation [I-D.ietf-bier-lsr-non-mpls-extensions],
the BIER-incapable multicast flow overlay router MAY omit the BIER
non-MPLS Encapsulation sub-TLV, or MUST set the BIFT-id field in the
BIER non-MPLS Encapsulation sub-TLV to 0.
With non-MPLS encapsulation, if a BFER (that does support BIER but)
does not support certain BSL, it MAY advertise a corresponding BIER
non-MPLS Encapsulation sub-TLV but set the BIFT-id field to 0 to
request PHP for that BSL. It MUST NOT include the PHP sub-TLV in
this case.
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2.2. BIRT/BIFT Calculation
If a BFR follows section 6.9 of [RFC8279] to handle BIER-incapable
routers, it MUST treat a router as BIER-incapable for a BSL if the
label in the corresponding MPLS Encapsulation sub-TLV advertised by
the router is Implicit Null, or if the BIFT-id in the corresponding
non-MPLS Encapsulation sub-TLV is 0. It MUST treat the router as
BIER-incapable for all BSLs if the router advertises a PHP sub-TLV.
That way, the router will not used as a transit BFR for certain or
for all BSLs.
If the downstream neighbor (either resulting in IGP calculation or
carried in the BIER Nexthop sub-TLV in case of BGP) for a BFR-prefix
is the one advertising the prefix with a PHP sub-TLV or with an
Implicit Null Label in its BIER MPLS Encapsulation sub-TLV, or with
BIFT-id 0 in its BIER non-MPLS Encapsulation sub-TLV, then when the
corresponding BIRT or BIFT entry is created/updated, the forwarding
behavior MUST be that the BIER header is removed and the payload be
sent to the downstream router without the BIER header, either
directly or over any type of tunnel.
3. Security Considerations
This specification does not introduce additional security concerns
beyond those already discussed in BIER architecture and OSPF/IS-IS/
BGP extensions for BIER signaling.
4. IANA Considerations
This document requests a new sub-sub-TLV type value from the "Sub-
sub-TLVs for BIER Info Sub-TLV" registry within the "IS-IS TLV
Codepoints" registry:
Type Name
---- ----
TBD BIER PHP Request
This document requests a new sub-TLV type value from the OSPFv2
Extended Prefix TLV Sub-TLV registry:
Type Name
---- ----
TBD BIER PHP Request
This document requests a new sub-TLV type value from the OSPFv3
Extended LSA Sub-TLVs registry:
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Type Name
---- ----
TBD BIER PHP Request
This document requests a new sub-TLV type value from the BGP BIER TLV
sub-TLV Types registry requested in [I-D.ietf-bier-idr-extensions]:
Type Name
---- ----
TBD BIER PHP Request
5. Acknowledgements
The author wants to thank Eric Rosen and Antonie Przygienda for their
review, comments and suggestions. The author also wants to thank
Senthil Dhanaraj for his suggestion of requesting PHP if a BFER does
not support certain BSL.
6. References
6.1. Normative References
[I-D.ietf-bess-mvpn-evpn-aggregation-label]
Zhang, Z. J., Rosen, E. C., Lin, W., Li, Z., and I.
Wijnands, "MVPN/EVPN Tunnel Aggregation with Common
Labels", Work in Progress, Internet-Draft, draft-ietf-
bess-mvpn-evpn-aggregation-label-14, 4 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
mvpn-evpn-aggregation-label-14>.
[I-D.ietf-bier-evpn]
Zhang, Z. J., Przygienda, T., Sajassi, A., and J. Rabadan,
"EVPN BUM Using BIER", Work in Progress, Internet-Draft,
draft-ietf-bier-evpn-14, 2 January 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-bier-
evpn-14>.
[I-D.ietf-bier-idr-extensions]
Xu, X., Chen, M., Patel, K., Wijnands, I., Przygienda, T.,
and Z. J. Zhang, "BGP Extensions for BIER", Work in
Progress, Internet-Draft, draft-ietf-bier-idr-extensions-
10, 13 June 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-bier-idr-extensions-10>.
[I-D.ietf-bier-lsr-non-mpls-extensions]
Dhanaraj, S., Yan, G., Wijnands, I., Psenak, P., Zhang, Z.
J., and J. Xie, "LSR Extensions for BIER non-MPLS
Encapsulation", Work in Progress, Internet-Draft, draft-
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ietf-bier-lsr-non-mpls-extensions-02, 27 January 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-bier-
lsr-non-mpls-extensions-02>.
[I-D.ietf-bier-ospfv3-extensions]
Psenak, P., Nainar, N. K., and I. Wijnands, "OSPFv3
Extensions for BIER", Work in Progress, Internet-Draft,
draft-ietf-bier-ospfv3-extensions-07, 1 December 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-bier-
ospfv3-extensions-07>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., 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, <https://www.rfc-editor.org/info/rfc8296>.
[RFC8401] Ginsberg, L., Ed., Przygienda, T., Aldrin, S., and Z.
Zhang, "Bit Index Explicit Replication (BIER) Support via
IS-IS", RFC 8401, DOI 10.17487/RFC8401, June 2018,
<https://www.rfc-editor.org/info/rfc8401>.
[RFC8444] Psenak, P., Ed., Kumar, N., Wijnands, IJ., Dolganow, A.,
Przygienda, T., Zhang, J., and S. Aldrin, "OSPFv2
Extensions for Bit Index Explicit Replication (BIER)",
RFC 8444, DOI 10.17487/RFC8444, November 2018,
<https://www.rfc-editor.org/info/rfc8444>.
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[RFC8556] Rosen, E., Ed., Sivakumar, M., Przygienda, T., Aldrin, S.,
and A. Dolganow, "Multicast VPN Using Bit Index Explicit
Replication (BIER)", RFC 8556, DOI 10.17487/RFC8556, April
2019, <https://www.rfc-editor.org/info/rfc8556>.
6.2. Informative References
[I-D.ietf-bess-evpn-optimized-ir]
Rabadan, J., Sathappan, S., Lin, W., Katiyar, M., and A.
Sajassi, "Optimized Ingress Replication Solution for
Ethernet VPN (EVPN)", Work in Progress, Internet-Draft,
draft-ietf-bess-evpn-optimized-ir-12, 25 January 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
evpn-optimized-ir-12>.
[I-D.ietf-bess-evpn-virtual-hub]
Patel, K., Sajassi, A., Drake, J., Zhang, Z. J., and W.
Henderickx, "Virtual Hub-and-Spoke in BGP EVPNs", Work in
Progress, Internet-Draft, draft-ietf-bess-evpn-virtual-
hub-00, 26 January 2020,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
evpn-virtual-hub-00>.
[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
2012, <https://www.rfc-editor.org/info/rfc6513>.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
<https://www.rfc-editor.org/info/rfc6514>.
[RFC7024] Jeng, H., Uttaro, J., Jalil, L., Decraene, B., Rekhter,
Y., and R. Aggarwal, "Virtual Hub-and-Spoke in BGP/MPLS
VPNs", RFC 7024, DOI 10.17487/RFC7024, October 2013,
<https://www.rfc-editor.org/info/rfc7024>.
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, <https://www.rfc-editor.org/info/rfc7432>.
Author's Address
Zhaohui Zhang
Juniper Networks
Email: zzhang@juniper.net
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