BIER Z. Zhang
Internet-Draft ZTE Corporation
Intended status: Standards Track B. Wu
Expires: January 13, 2021 Individual
Z. Zhang
Juniper Networks
IJ. Wijnands
Cisco Systems, Inc.
Y. Liu
China Mobile
July 12, 2020
BIER Prefix Redistribute
draft-zwzw-bier-prefix-redistribute-07
Abstract
This document defines a BIER proxy function to interconnect different
underlay routing protocol areas in a network. And a new BIER proxy
range sub-TLV is also defined to convey BIER BFR-id information
across the routing areas.
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 January 13, 2021.
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Copyright Notice
Copyright (c) 2020 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
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Table of Contents
1. Problem statement . . . . . . . . . . . . . . . . . . . . . . 2
2. Proposal . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Advertisement . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. BIER proxy range sub-TLV . . . . . . . . . . . . . . . . 7
3.2. Proxy range sub-TLV usage . . . . . . . . . . . . . . . . 9
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Problem statement
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+-------------------------------------------------------+
| +----+ +----+ PIM |
| +----+ R1 +-------------+ R2 +-----+ |
| | +----+ +----+ | |
| | | |
| | OSPF area 0 / ISIS | |
| | | |
| | +----+ +----+ | |
| +-----+ +------------+ +-----+ |
| +------------+ R3 +---+ +---+ R4 +------------+ |
| | +----+ | | +----+ | |
| | | | | |
| | OSPF area 1 | | OSPF area 2 | |
| | | | | |
| | +----+ +----+ | | +----+ +----+ | |
| +--+ Rm +-----+ Rn +--+ +---+ Rx +----+ Ry +--+ |
| +----+ +----+ +----+ +----+ |
+-------------------------------------------------------+
Figure 1
Figure 1 shows that there are three areas in a traditional network.
In some deployment situations, different routing protocols may also
be used in the network. There are just small amount of routers in
each area. Currently, multicast services are provided in this kind
of network by using protocol independent feature of PIM [RFC7761].
BIER could be a candidate multicast protocol to replace PIM to reduce
multicast states in the network. BIER [RFC8279] is a new
architecture for the forwarding of multicast data packets. It does
not require a protocol for explicitly building multicast distribution
trees, nor does it require intermediate nodes to maintain any per-
flow state. In order to build BIER forwarding plane, BIER key
parameters must be flooded in one BIER domain such as BFR-prefix,
BFR-id, subdomain-id, and so on. The routing protocols which are
used to flood these BIER parameters are called BIER routing underlay.
The associated routing protocol extensions are defined in documents
such as [RFC8401], [RFC8444], [I-D.ietf-bier-idr-extensions],
[I-D.ietf-bier-ospfv3-extensions], and so on.
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+----+ +----+
+----+ R1 +-------------+ R2 +-----+
| +----+ +----+ |
| OSPF / ISIS |
| BIER domain 1 |
| |
| +----+ +----+ |
+-----+ +------------+ +-----+
+------------+ R3 +---+ +---+ R4 +------------+
| +----+ | | +----+ |
| OSPF | | OSPF |
| | | |
| BIER domain 2 | | BIER domain 3 |
| +----+ +----+ | | +----+ +----+ |
+--+ Rm +-----+ Rn +--+ +---+ Rx +----+ Ry +--+
+----+ +----+ +----+ +----+
Figure 2
Based on the BIER design, a BIER domain is limited by the underlay
routing protocols flooding scope. In case we want deploy BIER
instead of PIM, there are several BIER domains because of different
underlay routing areas limitation. Multiple encapsulating/
decapsulation executions are needed to across multiple BIER domains.
These executions slow down the forwarding efficiency. The border
routers also need to maintain overlay state, which is undesired.
For example in figure 2, suppose that R1 and R2 connect with
multicast source. Rm, Rn, Rx and Ry connect with multicast
receivers. According the existed advertisement method defined in
[RFC8401], [RFC8444], and so on, in BIER domain 1, R1, R2, R3 and R4
are BIER edge routers. In BIER domain 2, R3 and Rm, Rn are BIER edge
routers. In BIER domain 3, R4 and Rx, Ry are BIER edge routers.
R1/R2 encapsulates BIER packet when multicast flows come into this
BIER domain, R3/R4 decapsulates the BIER packet, and encapsulates
them again, sends them into BIER domain 2/3. Rm, Rn, Rx and Ry
decapsulates the packets and forwards them to receivers.
Due to the decapsulation and encapsulation execution in R3 and R4,
the forwarding efficiency is slowed down, especially when there are
not large amount of routers in each BIER domain.
Section 2.3 in [RFC8444] defines the duplication function across OSPF
areas. Except the homogenization network, there is the hybrid
network showed in figure 2 that several areas formed by different IGP
protocols, and they are need to be merged into one BIER domain. In
the hybrid network, necessary advertisement transform need to be
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used. And further, necessary optimization method can be used to
reduce the amount of the advertisement items.
2. Proposal
+-------------------------------------------------------+
| +----+ +----+ BIER |
| +----+ R1 +-------------+ R2 +-----+ domain 1 |
| | +----+ +----+ | |
| | OSPF/ISIS | |
| | | |
| | +----+ +----+ | |
| +-----+ +------------+ +-----+ |
| +------------+ R3 +---+ +---+ R4 +------------+ |
| | +----+ | | +----+ | |
| | | | | |
| | OSPF area 1 | | OSPF area 2 | |
| | | | | |
| | +----+ +----+ | | +----+ +----+ | |
| +--+ Rm +-----+ Rn +--+ +---+ Rx +----+ Ry +--+ |
| +----+ +----+ +----+ +----+ |
+-------------------------------------------------------+
Figure 3
It is more efficient to deploy BIER by creating one BIER domain for
the hybrid network to achieve forwarding benefit.
Since the limitation of the BIER routing protocol scope, BFR-id is
confined to only one routing area. A BIER proxy function is
introduced to transport BIER BFR-id information in a BIER domain
across multiple routing protocol areas. So BIER forwarding tables
can be built across multiple underlay routing protocols to replace
encapsulation/ decapsulation processing. In the current deployment,
border router (ABR) has a similar role, ABR summaries unicast routing
information from one routing protocol area and sends it to another
routing area by new routing protocol messages. So ABR can implement
BIER proxy function to summarize BIER BFR-id information from one
routing protocol area and sends it to another routing area.
In figure 3, R3/R4 connects two areas which running same or different
routing protocols, they can be used as BIER proxies to transport BIER
information. For example, after R3 receives BFR-ids information from
OSPF area 1 and sends it to ISIS routing area (the upper area), the
routers in ISIS routing area can generate BIER forwarding items
toward the BFR-ids in OSPF area 1 through R3. Similarly, R3 receives
BFR-ids information from the upper area and sends them into OSPF area
1, the routers in OSPF area 1 can build BIER forwarding items toward
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the BFR-ids in ISIS area. R4 does the same function, the BIER
forwarding plane is constructed accordingly.
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 domain
which includes these three IGP areas, R3 advertises the BFR-ids of
Rm/Rn with associated prefixes (201.1.1.1/32, 201.1.1.2/32) into the
upper area. 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 area
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 area 1 and area 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
area 1. R4 also advertises the prefixes (201.1.1.1/32, 201.1.1.2/32)
with associated BFR-ids into IGP area 2.
After the path calculation, the BIER forwarding plane is built. When
R1/R2 receives multicast packet which should be sent to Rm/Rn/Rx/Ry,
R1/R2 encapsulates the packet with BIER header and send it into the
upper area. When R3/R4 receives the packet, R3/R4 forwards the
packet into IGP area 1 and area 2 according to the BIER forwarding
table without doing the decapsulation and re-encapsulation actions.
Obviously, in order to build the large BIER domain, the BFR-id of
edge router in each IGP area MUST NOT be overlapped.
3. Advertisement
According to [RFC8279], each BFER needs to have a unique (in each
sub-domain) BFR-id, and each BFR and BFER floods itself BIER info
sub-TLV and associated sub-sub-TLVs in the BIER domain. To keep
consistent with the definition in [RFC8444],
[I-D.ietf-bier-ospfv3-extensions], and [RFC8401], BIER info sub-TLV
defined in [RFC8401] and BIER sub-TLV defined in [RFC8444],
[I-D.ietf-bier-ospfv3-extensions] is reused to convey the BFR-id
information. OSPF extended Prefix Opaque LSA [RFC7684] and TLVs 235,
237 defined in [RFC5120], or TLVs 135 [RFC5305], or TLV 236 [RFC5308]
are still used to carry the BFR-id/ BFR-prefix information, etc.
The key parameters got from the original routing protocol should be
adapted to the format of next routing protocol, such as BFR-prefix,
BFR-id, subdomain-id, and so on. Some parameters like BAR, MT-ID has
local significance, So they should be set to same values with BIER
proxy own advertisement when BIER proxy advertise them to the next
routing area.
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And as the two BIER info sub-sub-TLVs (sub-TLVs) including MPLS
encapsulation and BSL conversion also have local significance. The
information carried in these two sub-sub-TLV need not, but MAY, be
advertised to next routing area.
In the same example, when R3 advertises the prefixes of Rm and Rn
into the upper area, R3 may advertise the prefixes one by one, that
is R3 advertises 201.1.1.1/32 with associated BFR-id, and R3
advertises 201.1.1.2/32 with associated BFR-id. If there is dozens
of edge routers in area 1, R3 advertises dozens of prefixes and
associated BFR-ids into the upper area. When R3 advertises the
prefixes from the upper area into area 1, R3 advertises the prefixes
of R1 and R2 with associated BFR-ids separately, and R3 advertises
the prefixes of Rx and Ry which come from R4 into area 1 one by one.
R4 does it as well.
3.1. BIER proxy range sub-TLV
In some cases unicast default route and aggregated/ summarized routes
are used in some routing areas and routers in next area can not see
the specific BFR-prefix routes from original area. Like in figure 3,
in case R3/R4 does not advertise specific ISIS unicast routes to OSPF
area and only advertises unicast default route or aggregated/
summarized route to OSPF area 1/2, when R3/R4 advertises BIER info
sub-TLV to OSPF area 1/2, R3 MUST advertise the prefix with default
route or aggregated/ summarized route. In that case, multiple BFR-
ids will be mapped to one prefix. In order to advertise BFR-ids
optimally, we define a new BIER proxy range sub-TLV to advertise the
information of BFR-ids.
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 4
o Type: 8-bit unsigned integer. TBD to indicate the BIER proxy
range sub-TLV.
o Length: 8-bit unsigned integer. Length of the BIER proxy range
sub-TLV in 4-octet units, not including the first 4 octets.
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o Subdomain-id: 8-bit unsigned integer. The subdomain-id from
original advertisement.
o resv: 8-bit unsigned integer. The reserved field.
o BFR-id: 16-bit unsigned integer. The first BFR-id from original
advertisement.
o BFR-id range: 16-bit unsigned integer. The range of BFR-ids with
one subdomain-id.
The BIER proxy range sub-TLV is attached to the aggregated/
summarized route prefix or default route prefix. The summarized/
aggregated/ default prefix may need multiple BIER proxy range sub-
TLVs when the BFR-ids covered by the prefix are allocated from
different ranges (even if they're from a single range but some BFR-
ids in the range map to the BIER prefixes that are covered by a
different summarized/ aggregated prefix, then that single large range
needs to be broken into smaller ranges).
When a BFR receives a default/summary route with a BIER proxy range
sub-TLV, it builds a BIRT route with that default/summary prefix. It
also builds multiple BIFT entries for each BFR-IDs covered in the
proxy range sub-TLV, using the same forwarding information as in the
BIRT route. It is possible that a BFR-ID is covered in the proxy
range sub-TLV of multiple default/summary routes. In that case, ECMP
can 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 only follows
the P2 route in BIRT.
The proxy range sub-TLV can also be attached to a host BIER prefix
itself. Consider the situation where BGP-LU [RFC8277] is used for a
seamless MPLS [I-D.ietf-mpls-seamless-mpls] environment. An ABR/ASBR
advertises BIER prefixes via BGP over an area/AS to other ABR/ASBRs
but the BIER prefixes are not advertised into the IGP for the area/
AS. The ABR/ASBR does advertise the BIER prefix for itself into the
IGP for the area/AS, with a BIER proxy range sub-TLV to cover the
BFR-IDs for BFRs that the ABR/ASBR has learned (either through IGP or
through BGP signaling). When an internal BFR receives it, it treats
as if a default summary route had been received with the proxy range
sub-TLV. Note that this imaginary default summary route is only for
the purpose of building BIRT/BIFT entries and not used for unicast
forwarding.
With this scheme, even though the BIER prefixes are not advertised
into the IGP for the area/AS and unicast traffic for those BIER
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prefixes are tunneled through, corresponding BIFT entries are
maintained inside the area/AS for the purpose of efficient BIER
forwarding. Otherwise, BIER forwarding through the area/AS would be
tunneled just like unicast case.
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, it 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.
3.2. Proxy range sub-TLV usage
In the same example of figure 3, in case there are 40 edge routers in
area 1, the BFR-ids of area 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
prefixes are not overlapped with the prefixes in any other area.
When R3 advertises these prefixes into the upper area, the proxy
range sub-TLV can be used to optimize the advertisement. That is R3
can advertise only one prefix 201.1.1.0/24, with the BFR-id set to
51, the BFR-id range set to 40, into the upper area. Then the BIER
overlay is built among R1, R2, Rm, Rn, Rx and Ry. R3 and R4 need not
maintain the multicast overlay states.
When R3 advertises the prefixes from the upper area and area 2 into
area 1, R3 may advertise only one default route (0.0.0.0/0) into area
1 if one or more continuous BFR-id range can be attached. Suppose
that the BFR-id in the upper area starts from 1001 to 1050, the BFR-
id in area 2 starts from 201 to 250, and these ranges are not
overlapped with the ranges in any other area. 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 5
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The optimized summary/ aggregated or default prefix can be generated
by the operation policy which is configured by the network
administrator.
In case the range of BFR-ids in one area is overlapped with the BFR-
ids in any other area, the proxy range sub-TLV can not be used. In
the same example above, if the BFR-ids in area 1 are 21, 31, 41,
etc., the BFR-ids in area 2 are 22, 32, 42, etc., even if the
summarized prefixes are not overlapped with the prefixes in any other
area, when R3 advertises the summarized prefixes in area 1 into the
upper area, the proxy range sub-TLV may not optimize the
advertisement.
After the forwarding plane is built, 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. When R3/R4 receives the packet, R3/R4 need not
decapsulate and re-encapsulate the packet. R3/R4 just forwards the
packet according to the BIER forwarding table. When the packet
reaches Rm and Rx, Rm and Rx remove the BIER header and forward it to
receivers.
4. 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.
5. Security Considerations
Implementations must assure that malformed TLV and Sub-TLV
permutations do not result in errors which cause hard protocol
failures.
6. Acknowledgements
The authors would like to thank Stig Venaas for his valuable comments
and suggestions.
7. References
7.1. Normative References
[I-D.ietf-bier-idr-extensions]
Xu, X., Chen, M., Patel, K., Wijnands, I., and T.
Przygienda, "BGP Extensions for BIER", draft-ietf-bier-
idr-extensions-07 (work in progress), September 2019.
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[I-D.ietf-bier-ospfv3-extensions]
Psenak, P., Nainar, N., and I. Wijnands, "OSPFv3
Extensions for BIER", draft-ietf-bier-ospfv3-extensions-02
(work in progress), May 2020.
[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>.
[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>.
7.2. Informative References
[I-D.ietf-mpls-seamless-mpls]
Leymann, N., Decraene, B., Filsfils, C., Konstantynowicz,
M., and D. Steinberg, "Seamless MPLS Architecture", draft-
ietf-mpls-seamless-mpls-07 (work in progress), June 2014.
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[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>.
Authors' Addresses
Zheng(Sandy) Zhang
ZTE Corporation
EMail: zzhang_ietf@hotmail.com
Bo Wu
Individual
EMail: w1973941761@163.com
Zhaohui Zhang
Juniper Networks
EMail: zzhang@juniper.net
IJsbrand Wijnands
Cisco Systems, Inc.
EMail: ice@cisco.com
Yisong Liu
China Mobile
EMail: liuyisong.ietf@gmail.com
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