BIER Prefix Redistribute
draft-ietf-bier-prefix-redistribute-01
| Document | Type | Active Internet-Draft (bier WG) | |
|---|---|---|---|
| Authors | Zheng Zhang , Bo Wu , Zhaohui (Jeffrey) Zhang , IJsbrand Wijnands , Yisong Liu , Hooman Bidgoli | ||
| Last updated | 2021-12-23 | ||
| Replaces | draft-zwzw-bier-prefix-redistribute | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | plain text html xml htmlized pdfized bibtex | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
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| Send notices to | (None) |
draft-ietf-bier-prefix-redistribute-01
BIER Z. Zhang
Internet-Draft ZTE Corporation
Intended status: Standards Track B. Wu
Expires: 26 June 2022 Individual
Z. Zhang, Ed.
Juniper Networks
IJ. Wijnands
Cisco Systems, Inc.
Y. Liu
China Mobile
H. Bidgoli
Nokia
23 December 2021
BIER Prefix Redistribute
draft-ietf-bier-prefix-redistribute-01
Abstract
This document defines a BIER proxy function to support a single BIER
sub-domain over multiple underlay routing protocol regions
(Autonomous Systems or IGP areas). A new BIER proxy range sub-TLV is
defined to redistribute BIER BFR-id information across the routing
regions.
Requirements Language
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.
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 26 June 2022.
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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
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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Problem statement . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Multipe IGP domains . . . . . . . . . . . . . . . . . . . 3
2.2. Seamless MPLS Network . . . . . . . . . . . . . . . . . . 4
3. Proposed Solution . . . . . . . . . . . . . . . . . . . . . . 4
4. Specifications . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Redistribution of BIER Information . . . . . . . . . . . 5
4.2. BIER proxy range sub-TLV . . . . . . . . . . . . . . . . 6
4.3. BIRT/BIFT Calculation . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Proxy range sub-TLV usage . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Terminology
It is assumed that readers of this document are familiar with BIER
architecture [RFC8279] and OSPF/ISIS/BGP signaling for BIER
[RFC8401], [RFC8444], [I-D.ietf-bier-idr-extensions],
[I-D.ietf-bier-ospfv3-extensions]. The following terminologies are
listed for convenience. (to be added)...
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2. Problem statement
BIER [RFC8279] is a new multicast architecture that does not need
per-tree state inside a network for multicast forwarding. BIER
forwarding state (which is not per-tree) is built according to a
routing underlay, which is defaulted to an IGP domain though not
limited to that. In this routin underlay, BIER information like
BIER-prefix, BFR-id, subdomain-id, and encapsulation is propagated
using IGP or BGP as specified in documents such as [RFC8401],
[RFC8444], [I-D.ietf-bier-idr-extensions],
[I-D.ietf-bier-ospfv3-extensions],
[I-D.ietf-bier-lsr-ethernet-extensions].
In some deployment situations, different routing protocols may be
used in differet parts of a network yet there are just small number
of BFERs in each protocol domain, so a single BIER sub-domain is
desired. This requires BIER information redistribution among
different protocols, as described in the following two sections.
2.1. Multipe IGP domains
+----+ +----+
+----+ R1 +-------------+ R2 +-----+
| +----+ +----+ |
| OSPF / ISIS |
| domain 1 |
| |
| +----+ +----+ |
+-----+ +------------+ +-----+
+------------+ R3 +---+ +---+ R4 +------------+
| +----+ | | +----+ |
| OSPF | | OSPF |
| | | |
| domain 2 | | domain 3 |
| +----+ +----+ | | +----+ +----+ |
+--+ Rm +-----+ Rn +--+ +---+ Rx +----+ Ry +--+
+----+ +----+ +----+ +----+
Figure 1
While one could treat each IGP domain in the above network as a
separate BIER sub-domain, the border routers R3/R4 would need
decapsulate incoming BIER header in one BIER sub-domain, forward
based on flow overlay per-tree state, and re-ecapsulate with a BIER
header for forwarding in the next BIER sub-domain. This not only is
inefficient in forwarding, but also require per-tree state on the
border routers, which is undesired.
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A better solution is to treat the entire network of multiple IGP
domains as single BIER sub-domain with a single routing underlay.
2.2. Seamless MPLS Network
Figure 1 could also depict a Seamless MPLS
[I-D.ietf-mpls-seamless-mpls] network, where BGP-LU [RFC8277] is used
to distribute routes for edge routers (e.g. R1/R2/Rm/Rn/Rx/Ry) among
the edge routers and border routers (e.g. R3/R4), but those routes
are not redistributed into other IGP areas/domains. With that,
internal routers in an area/domain will only have routes to local
nodes, yet they still need to build BIER forwarding state for BFERs
in other areas/domains.
3. Proposed Solution
For the multiple IGP domains scenario in Section 2.1, BIER
information from one domain needs to be redistributed into another
domain, like that BIER information is redistributed from one IGP area
to another as specified in [RFC8401], [RFC8444], and
[I-D.ietf-bier-ospfv3-extensions].
Specifically, when an ASBR redistributes BIER prefixes for BFERs from
one protocol domain to another, BIER information is also
redistributed except the encapsulation information (because BFRs in
one domain will not directly send BIER packets to BFRs in the other
domain so only the BFR-IDs of the BFERs matters). When BIER prefixes
for non-BFIR/BFER (i.e. whose BFR-ID is 0) are redistributed, BIER
information is not redistributed.
If route summarization is used, because a summarized prefix may cover
many BFERs, the BFR-IDs of those covered BFERs needs to be explicitly
listed in proxy range sub-TLV (see Section 4.2). In case of Seamless
MPLS (Section 2.2), when a border router advertise BIER information
for itself in one area/domain, it also explicitly lists the BFIRs/
BFERs in other areas/domains that are reachable via itself in the
proxy range sub-TLV.
In figure 1, R3/R4 connects two routing domains. After R3 receives
BIER information for Rm/Rn from domain 2 and redistribute to domain
1, BFRs in domain 1 can build BIER forwarding state for BFERs in
domain 2 through R3. Similarly, R3 receives BIER information for R1/
R2 from domain 1 and redistribute into domain 2. BFRs in domain 2
can build BIER forwarding state for BFERs in domain 1 through R3.
For example, in this network, suppose that Rm and Rn have the prefix
of 201.1.1.1/32, 201.1.1.2/32. In order to build one BIER sub-domain
which includes these three IGP domains, R3 advertises the BFR-ids of
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Rm/Rn with associated prefixes (201.1.1.1/32, 201.1.1.2/32) into the
upper domain. Similarly, R4 advertises the BFR-ids of Rx/Ry with
associated prefixes (202.1.1.1/32, 202.1.1.2/32) into the upper
domain too.
And R3/R4 advertises the prefixes of R1 and R2 (suppose that the
prefixes are 200.1.1.1/32 and 200.1.1.2/32) with associated BFR-ids
into IGP domain 1 and domain 2. Also, R3 advertises the prefixes
learned from R4 (202.1.1.1/32, 202.1.1.2/32) with associated BFR-ids
into IGP domain 1. R4 also advertises the prefixes (201.1.1.1/32,
201.1.1.2/32) with associated BFR-ids into IGP domain 2.
Obviously, in order to build the large BIER sub-domain, the BFR-id of
edge router in each IGP domain MUST NOT overlap.
4. Specifications
4.1. Redistribution of BIER Information
Consider a BIER sub-domain that spans multiple routing domains. The
procedures in this section apply if a border router, which is also a
BFR, redistribute routing information from one routing domain into
another.
If a redistributed route is for a host route for a BFIR/BFER (i.e.
the BFR-ID is not zero) in the same sub-domain, BIER information for
the BFIR/BFERs MUST be advertised in the target routing domain as
following:
* If the target routing domain is OSPFv2, a BIER Sub-TLV [RFC8444]
is attached to the OSPFv2 Extended Prefix TLV in the OSPFv2
Extended Prefix Opaque LSA [RFC7684] corresponding to the
redistributed host route.
* If the target routing domain is OSPFv3, a BIER Sub-TLV
[I-D.ietf-bier-ospfv3-extensions] is attached to the OSPFv3
Extended LSA TLVs in the Intra-Area-Prefix TLV [RFC8362].
corresponding to the redistributed host route.
* If the target routing domain is ISIS, a BIER Info Sub-TLV
[RFC8401] is attached to the TLVs of 235, 237, [RFC5120], 135
[RFC5305], or 236 [RFC5308].
* If the target routing domain is BGP, a BIER TLV
[I-D.ietf-bier-idr-extensions] is attached to BGP Path Attribute.
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The BIER Sub-TLV (in case of OSPF2 and OSPFv3), BIER Info Sub-TLV (in
case of IS-IS) and BIER TLV (in case of BGP) are encoded as specified
in [RFC8444], [I-D.ietf-bier-ospfv3-extensions], and [RFC8401], and
[I-D.ietf-bier-idr-extensions]. The encapsulation sub-TLV SHOULD NOT
be included because it would not be used.
If a redistributed route is for a host route for a transit BFR (i.e.
the BFR-ID is zero), BIER information for the BFR SHOULD NOT be
redistributed, because it would not be used.
If the redistributed route is a summary or default route, and it
covers some BFIR/BFERs, a BIER Sub-TLV (for OSPFv2 and OSPFv3), or a
BIER Info Sub-TLV (in case of IS-IS), or a BIER TLV (in case of BGP)
MUST be used to advertise the covered BFIRs/BFERs via the BIER proxy
range sub-TLV as specified in the following section.
4.2. BIER proxy range sub-TLV
The BIER Sub-TLV can include a proxy range sub-TLV, which lists
BFIRs/BFERs covered by a summary/default route or reachable via a
BFR.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | subdomain-id | resv |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFR-id | BFR-id range |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFR-id | BFR-id range |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
figure 2
* Type: 8-bit unsigned integer. TBD to indicate the BIER proxy
range sub-TLV.
* Length: 8-bit unsigned integer. Length of the BIER proxy range
sub-TLV in 4-octet units, not including the first 4 octets.
* Subdomain-id: 8-bit unsigned integer.
* resv: 16-bit unsigned integer. The reserved field.
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* BFR-id: 16-bit unsigned integer. The first BFR-id from original
advertisement.
* BFR-id range: 16-bit unsigned integer. The range of BFR-ids with
one subdomain-id.
The BIER proxy range sub-TLV is included in the BIER Sub-TLV for an
aggregated/summary route prefix or default route prefix, or in the
BIER Sub-TLV for a BIER prefix (for a border router in a Seamless
MPLS network). Multiple BIER proxy range sub-TLVs MAY be included in
the BIER Sub-TLV.
The range in the BIER proxy range sub-TLV can be as granular as to
advertise individual BFR-ids. Though a larger range can increase
advertisement efficiency, that requires careful planning for BFR-id
assignment.
When the proxy range sub-TLV is used, the mapping between a BIER
prefix and its BFR-id is no longer conveyed in the routing underlay.
As a result, the mapping must be provided by other means, e.g. in the
multicast overlay.
4.3. BIRT/BIFT Calculation
If a BFR receives a BIER prefix whose BIER Sub-TLV includes a proxy
range sub-TLV (i.e., the Seamless MPLS scenario), it treats as if
that the originator advertised a default route with the proxy range
sub-TLV. Note that this imaginary default route is only for the
purpose of building BIRT/BIFT entries and not used for unicast
forwarding.
With the BIER prefixes originated in the local routing area/domain,
the BIER prefixes and summary/default routes redistributed into the
local routing area/domain, and the imaginary default route mentioned
above, a BFR builds BIRTs as specified in [RFC8279] with entries
including host/summary/default prefixes.
BIFT entries are then derived from a corresponding BIRT. For a BFER
covered by the proxy range sub-TLVs associated with the summary/
default prefixes (whether or not the deafult prefix is the imaginary
one as mentioned above), its BIFT entry is derived from the summary/
default prefix entry in the BIRT. It is possible that a BFER is
covered in the proxy range sub-TLV of multiple default/summary
routes. In that case, ECMP MAY be used and longest match SHOULD be
used. For example, if ABR1 advertises default/summary route P1 while
ABR2 advertises a more specific summary route P2 and both have a
proxy range sub-TLV that covers BFR-ID 100, then the BIFT entry for
BFR-ID 100 should follow the P2 route in BIRT.
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With this scheme, even though the BIER prefixes are not advertised
into the IGP for an area/domain in a Seamless MPLS network and
unicast traffic for those BIER prefixes are tunneled through,
corresponding BIFT entries are maintained inside the area/domain for
the purpose of efficient BIER forwarding. Otherwise, BIER forwarding
through the area/domain would be tunneled just like unicast case.
5. IANA Considerations
IANA is requested to set up a new types of sub-TLV (TLV) registry
value for BIER proxy range advertisement in OSPF, ISIS, BGP, etc.
6. Security Considerations
Implementations must assure that malformed TLV and Sub-TLV
permutations do not result in errors which cause hard protocol
failures.
7. Acknowledgements
The authors would like to thank Stig Venaas for his valuable comments
and suggestions.
8. References
8.1. Normative References
[I-D.ietf-bier-idr-extensions]
Xu, X., Chen, M., Patel, K., Wijnands, I., and A.
Przygienda, "BGP Extensions for BIER", Work in Progress,
Internet-Draft, draft-ietf-bier-idr-extensions-07, 6
September 2019, <https://www.ietf.org/archive/id/draft-
ietf-bier-idr-extensions-07.txt>.
[I-D.ietf-bier-lsr-ethernet-extensions]
Dhanaraj, S., Yan, G., Wijnands, I., Psenak, P., Zhang,
Z., and J. Xie, "LSR Extensions for BIER over Ethernet",
Work in Progress, Internet-Draft, draft-ietf-bier-lsr-
ethernet-extensions-02, 2 December 2020,
<https://www.ietf.org/archive/id/draft-ietf-bier-lsr-
ethernet-extensions-02.txt>.
[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-05, 19 November 2021,
<https://www.ietf.org/archive/id/draft-ietf-bier-ospfv3-
extensions-05.txt>.
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[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008,
<https://www.rfc-editor.org/info/rfc5120>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
DOI 10.17487/RFC5308, October 2008,
<https://www.rfc-editor.org/info/rfc5308>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
[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>.
[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>.
[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>.
8.2. Informative References
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[I-D.ietf-mpls-seamless-mpls]
Leymann, N., Decraene, B., Filsfils, C., Konstantynowicz,
M., and D. Steinberg, "Seamless MPLS Architecture", Work
in Progress, Internet-Draft, draft-ietf-mpls-seamless-
mpls-07, 28 June 2014, <https://www.ietf.org/archive/id/
draft-ietf-mpls-seamless-mpls-07.txt>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[RFC8277] Rosen, E., "Using BGP to Bind MPLS Labels to Address
Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017,
<https://www.rfc-editor.org/info/rfc8277>.
Appendix A. Proxy range sub-TLV usage
This appendix is to make the function understood more easily. Except
for inter-area case, the function is also suitable for inter-as case.
In the same example of figure 1, in case there are 40 edge routers in
domain 1, the BFR-ids of domain 1 start from 51 to 90, and the
prefixes of these routers start from 201.1.1.1/32 to 201.1.1.40/32.
These assigned BFR-IDs are not overlapped with the BFR-IDs in any
other domain.
In order to build a BIER sub-domain across these areas, the two
advertisement methods defined in Section 4.2 can be used:
* As a transit node, R3 advertises the BIER sub-TLV with BFR-ID set
to 0. When R3 is not allowed to advertise the summary or specific
prefixes into the upper domain, R3 can advertise the proxy range
sub-TLV with the host prefix directly. So there are two sub-TLVs
advertisement associated with the host prefix of R3.
* As a transit node, R3 advertises the BIER sub-TLV with BFR-ID set
to 0. When R3 is allowed to advertise the summary prefix into the
upper domain, R3 can advertise the proxy range sub-TLV with the
summarized prefix, 201.1.1.0/24, with the BFR-id set to 51, the
BFR-id range set to 40, into the upper domain. In this case,
there are two prefixes advertised by R3. But the summary prefix
can not be used to encapsulate BIER packet directly in case of
tunneling case. The summary prefix is only used to generate the
BIFT.
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Then the router in the uppler domain can build the BIER forwarding
table, the nexthops of BFR-IDs in the proxy range sub-TLV are set to
R3.
The same function is also applied to R4 when it advertises the BFR-
IDs to the upper domain. This method is also applied to R3/R4 when
it advertises the BFR-IDs to the lower domain. When R3 advertises
the prefixes from the upper domain and domain 2 into domain 1, except
the host prefix of R3 with BFR-ID set to 0, R3 may advertise only one
default route (0.0.0.0/0) into domain 1 if one or more continuous
BFR-id range can be attached. Suppose that the BFR-id in the upper
domain starts from 1001 to 1050, the BFR-id in domain 2 starts from
201 to 250, and these ranges are not overlapped with the ranges in
any other domain. Suppose that the sub-domain ID is 1, the BIER
proxy range sub-TLV may be advertised like this:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBD | 2 | 1 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1001 | 50 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 201 | 50 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
figure 3
Then the BIER overlay is built among R1, R2, Rm, Rn, Rx and Ry. R3
and R4 need not maintain the multicast overlay states. The optimized
summary/ aggregated or default prefix can be generated by the
operation policy which is configured by the network administrator.
If two or more ABRs in one domain are used to reistribute the prefix,
for example in figure 4 below:
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+-------------------------------------------------------+
| +----+ +----+ BIER |
| +-----------+ R1 +-------------+ R2 +-----+ domain 1 |
| | +----+ +----+ | |
| | OSPF/ISIS | |
| | | |
| | +----+ +----+ +----+ | |
| +--+ +----+ +------------+ +-----+ |
| +--+ R5 +----+ R3 +---+ +---+ R4 +------------+ |
| | +----+ +----+ | | +----+ | |
| | | | | |
| | OSPF domain 1 | | OSPF domain 2 | |
| | | | | |
| | +----+ +----+ | | +----+ +----+ | |
| +--+ Rm +-----+ Rn +--+ +---+ Rx +----+ Ry +--+ |
| +----+ +----+ +----+ +----+ |
+-------------------------------------------------------+
Figure 4
As the ABRs, except the host prefixes of R3 and R5 advertisement, R3
and R5 can both advertise the proxy range sub-TLV with their host
prefix, the routers can select one of them as the nexthop, or select
both of them for ECMP.
If R3 and R5 are allowed to advertise the summary prefix received
from the upper domain. They can advertise the same summary prefixes
or the different prefixes according to the operation policy. When
they advertise the same summary prefixes, the R3 and R5 can also be
used for ECMP. When they advertise the different summary prefixes,
the more specific prefixes are used to generate the BIER forwarding
table. Whatever the same or different prefixes are advertised, the
nexthop is set to R3/R5.
In case the range of BFR-ids in one domain is overlapped with the
BFR-ids in any other domain, the proxy range sub-TLV may not be used.
In the same example above, if the BFR-ids in domain 1 are 21, 31, 41,
etc., the BFR-ids in domain 2 are 22, 32, 42, etc., even if the
summarized prefixes are not overlapped with the prefixes in any other
domain, when R3 advertises the summarized prefixes in domain 1 into
the upper domain, the proxy range sub-TLV may not optimize the
advertisement.
After the forwarding plane is built, the nexthop of the range BFR-IDs
is set to the ABR router. For example, when R1 receives multicast
packet, and the receivers of this flow are connected by Rm and Rx, R1
encapsulates BIER header in front of the flow packet with BFR-ids set
to Rm and Rx. The routers in the upper domain forward the packet to
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Internet-Draft BIER Prefix Redistribute December 2021
the ABR routers: R3, R4 and R5. When R3/R4/R5 receives the packet,
R3/R4/R5 needs not decapsulate and re-encapsulate the packet. R3/R4/
R5 just forwards the packet according to the BIER forwarding table.
Similar with the upper domain, the routers in lower domain forward
the packet to the edge routers: Rm and Rx. When the packet reaches
Rm and Rx, Rm and Rx remove the BIER header and forward it to
receivers.
Authors' Addresses
Zheng(Sandy) Zhang
ZTE Corporation
Email: zhang.zheng@zte.com.cn
Bo Wu
Individual
Email: w1973941761@163.com
Zhaohui Zhang (editor)
Juniper Networks
Email: zzhang@juniper.net
IJsbrand Wijnands
Cisco Systems, Inc.
Email: ice@cisco.com
Yisong Liu
China Mobile
Email: liuyisong.ietf@gmail.com
Hooman Bidgoli
Nokia
Email: hooman.bidgoli@nokia.com
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