Network Working Group A. Bashandy, Ed.
Internet Draft C. Filsfils
Intended status: Standard Track L. Ginsberg
Expires: September 2017 Cisco Systems
Bruno Decraene
Orange
March 10, 2017
IS-IS Extensions to Support Segment Routing over IPv6 Dataplane
draft-bashandy-isis-srv6-extensions-00
Abstract
Segment Routing (SR) allows for a flexible definition of end-to-end
paths by encoding paths as sequences of topological sub-paths, called
"segments". Segment routing architecture can be implemented over an
MPLS data plane as well as an IPv6 data plane. This draft describes
the IS-IS extensions required to support Segment Routing over an IPv6
data plane.
Status of this Memo
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Table of Contents
1. Introduction...................................................3
1.1. Conventions used in this document.........................3
2. SRv6-Capabilities sub-TLV......................................4
3. SRv6-function Descriptor.......................................6
4. SRv6-SID TLV...................................................7
5. Function Code points...........................................8
6. Advertising SRv6 SIDs associated with a Neighbor...............8
6.1. P2P SRv6 X-SID sub-TLV....................................9
6.2. LAN SRv6 X-SID sub-TLV...................................10
7. IANA Considerations...........................................11
7.1. SRv6 SID TLV and sub-TLVs................................11
7.2. IS-IS SRv6-functions Codepoints Registry.................12
7.3. SRv6 Capabilities sub-TLV................................12
7.4. P2P SRv6 X-SID and LAN SRv6 X-SID sub-TLVs...............12
7.5. IS-IS SRv6 X-SID sub-sub-TLV Codepoints Registry.........13
8. Security Considerations.......................................13
9. Contributors..................................................13
10. References...................................................14
10.1. Normative References....................................14
10.2. Informative References..................................15
11. Acknowledgments..............................................16
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1. Introduction
With Segment Routing (SR)[9], a node steers a packet through an
ordered list of instructions, called segments.
Segments are identified through Segment Identifiers (SIDs).
Segment Routing can be directly instantiated on the IPv6 data plane
through the use of the Segment Routing Header defined in [10]. SRv6
refers to this SR instantiation on the IPv6 dataplane.
The network programming paradigm [11] is central to SRv6.
It describes how any function can be bound to a SID and how any
network program can be expressed as a combination of SID's.
It defines several well-known functions such as End, End.X,
T.Insert, T.Encaps, etc.
This document specifies IS-IS extensions that allow IS-IS protocol
to encode some of these functions.
Familiarity with the network programming paradigm [11] is necessary
to understand the extensions specified in this document.
This document defines one new top level IS-IS_TLV and three new IS-
IS sub-TLVs.
The SRv6 Capabilities sub-TLV announces the ability to support SRv6
and some functions defined in [11] as well as advertising
limitations when applying such functions.
The SRv6 SID top level TLV, the P2P SRv6 X-SID sub-TLV, and the LAN
SRv6 X-SID sub-TLV are used to advertise which SIDs are instantiated
at a node and what function is bound to each instantiated SID.
Only ISIS-related functions such as End and its variants D and X
[11] are defined in this document.
1.1. Conventions used in this document
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 RFC-2119
[8].
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In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to
be interpreted as carrying RFC-2119 [8] significance.
2. SRv6-Capabilities sub-TLV
As described in [10] and [11], the list of Segments is stored in the
segment routing header referred hereafter as "SRH".
A router that supports SRv6 MUST be able to process the segment
routing header as described in [10] and [11] up to the limitations
set by the advertised SRv6-capabilities sub-TLV.
To announce this ability, a router uses the newly defined SRv6-
capabilities sub-TLV of the router capabilities TLV [1]. The SRv6-
capabilities sub-TLV may contain optional sub-sub-TLVs in the
future.
The SRv6 Capabilities sub-TLV has the following format:
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 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| max-SL |Max-End-Pop-SRH| Max-T-Ins-SRH |Max-T-Encap-SRH|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| max-End-D-SRH |
+-+-+-+-+-+-+-+-+
Type: Suggested value 22, to be assigned by IANA
Length: 7 + length of sub-sub-TLVs
Flags: 2 octets The following flags are defined:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
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E-flag: If set, then router is able to apply "T.Encap"
operation
Max-SL: 1 octet.
This field specifies the maximum value of the "SL" field [10] in
the SRH of a received packet before applying the function
associated with a SID.
Max-End-Pop-SRH: 1 Octet
This field specifies the maximum number of SIDs in the top SRH in
an SRH stack that the router can apply "PSP" or USP" [11] flavors
to. If the value of this field is zero, then the router cannot
apply PSP or USP flavors.
Max-T-Ins-SRH: 1 octet
This field specifies the maximum number of SIDs that can be
inserted as part of the "T.insert" behavior [11]. If the value of
this field is zero, then the router cannot apply any variation of
the "T.insert" behavior.
Max-T-Encap-SRH: 1 octet
This field specifies the maximum number of SIDs that can be
included as part of the "T.Encap" behavior [11]. If this field is
zero and the "E" flag is set, then the router can apply T.Encap
by encapsulating the incoming packet in another IPv6 header
without SRH the same way IPinIP encapsulation is performed. If
the "E" flag is clear, then this field SHOULD be transmitted as
zero and MUST be ignored on receipt.
max-End-D-SRH: 1 octet
This field specifies the maximum number of SIDs in an SRH when
applying "End.DX6" and "End.DT6" functions. If this field is
zero, then the router cannot apply "End.DX6" or "End.DT6"
functions if the extension header right underneath the outer IPv6
header is an SRH.
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3. SRv6-function Descriptor
The SRv6 SID TLV defined in Section 4, P2P SRv6 X-SID sub-TLV
specified in Section 6.1, and LAN SRv6 X-SID sub-TLV specified in
section 6.2 MUST include one SRv6 function Descriptor.
When included in the SRv6 SID TLV, the descriptor is encoded as a
sub-TLV. When included in a P2P/LAN SRv6 X-SID sub-TLV, the
descriptor is encoded as a sub-sub-TLV.
The SRv6-function Descriptor encodes the function (and its flavors)
bound to the SRv6 SID advertised in the SRv6 SID TLV [11].
The SRv6 SID function Descriptor has the following format:
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 | Behavior (variable) ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: See IANA considerations in Section 7.
Length: 3 * (number of functions)
Behavior: One function (with its associated flavors) encoded in 3
octets as shown in the following diagram
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P|U| Reserved | Function |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The first octet encodes flags. This document defines two flags to
specify the flavor(s) [11] associated with the SRv6 function
specified in the "Function" field:
P bit: If set, then the PSP flavor [11] is associated with the
function encoded in the "function" field
U bit: If set, then the USP flavor [11] is associated with the
function encoded in the "function" field
Reserved Bits SHOULD be transmitted as 0 and MUST be ignored on
receipt.
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The second two octets encode the function. Function code points
are defined in Section 5.
For a given SRv6 SID function encoded in the "Function" field,
the "P" and "U" bits are set/cleared according to the rules of
enabling/disabling the PSP and USP flavors, respectively, for
that function as specified in [11].
4. SRv6-SID TLV
A new top level TLV is introduced to advertise SRv6 Segment
Identifiers (SID) and their attributes.
The new TLV is used to advertise SRv6 SIDs with any of the functions
defined in [11] whose code point is defined in this document except
those SIDs which must be associated with a particular neighbor in
order to be correctly applied [11]. SRv6 SIDs associated with a
neighbor are advertised in the sub-TLVs defined in Section 6.
This new TLV shares the sub-TLV space defined for TLVs 135, 235, 236
and 237.
The SRv6 SID TLV has the following format
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 | flags | SID-size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (variable) . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-tlv-len | Sub-TLVs (variable) . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 27 (Suggested value to be assigned by IANA)
Length: variable.
One or more SID entries, each of which has the following format:
Flags: 1 octet. The following flags are defined
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|D| Reserved |
+-+-+-+-+-+-+-+-+
where:
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D bit: When the SID is leaked from level-2 to level-1, the D
bit MUST be set. Otherwise, this bit MUST be clear. SIDs with
the D bit set MUST NOT be leaked from level-1 to level-2. This
is to prevent looping.
The remaining bits are reserved for future use. They SHOULD be
set to zero on transmission and MUST be ignored on receipt.
SID-Size: 1 octet. Number of bits in the SID field.
SID: 1-16 octets. This field encodes the advertised SRv6 SID. The
"SID-size" field can have the values 1-128 and indicates the
number of bits in the SID. The SRv6 SID is encoded in the
minimal number of octets for the given number of bits. The owning
router may associate one or more functions as specified in [11],
in other documents, or as locally configured.
Sub-TLV-length: 1 octet. Number of octets used by sub-TLVs
The function associated with the advertised SID is specified by
the SRv6-Function Descriptor sub-TLV specified in Section 3.
5. Function Code points.
This section defines the code points for supported functions
associated with SRv6 SIDs. Functions are defined in [11].
o 0: Reserved
o 1: End Function.
o 2: End.DX6 Function.
o 3: End.DT6 Function.
o 4: End.X Function.
6. Advertising SRv6 SIDs associated with a Neighbor.
Certain SRv6 functions [11] must be associated with a particular
neighbor, and in case of multiple layer 3 links to the same
neighbor, with a particular link in order to be correctly applied.
This document specifies how to advertise two such functions in IS-
IS, namely End.X and End.DX6 [11].
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SIDs associated with End.X and End.DX6 functions are advertised
within neighbor reachability TLVs.
This document defines two new sub-TLVs of TLV 22 [4], 23 [6], 222
[5], 223[6], and 141 [7] namely "P2P SRv6 X-SID" and "LAN SRv6 X-
SID".
6.1. P2P SRv6 X-SID sub-TLV
This sub-TLV is used to advertise one or more SRv6 SIDs associated
with End.X and End.DX6 [11] functions over a point to point
adjacency.
The "P2P SRv6 X-SID" sub-TLV has the following format
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 | Flags | SID-size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (variable) . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|sub-sub-tlv-len| Sub-sub-TLVs (variable) . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 40 (Suggested value to be assigned by IANA)
Length: variable.
One or more SIDs each of which has the following format:
Flags: 1 octet. No flags defined in this document
SID-Size: 1 octet. Number of bits in the SID field.
SID: 1-16 octets. This field encodes the advertised SRv6 SID. The
"SID-size" field can have the values 1-128 and indicates the
number of bits in the SID. The SRv6 SID is encoded in the
minimal number of octets for the given number of bits. The owning
router may associate one or more functions as specified in [11],
in other documents, or as locally configured.
Sub-sub-TLV-length: 1 octet. Number of octets used by sub-sub-
TLVs
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The function associated with the advertised SID is specified by the
SRv6-Function Descriptor sub-sub-TLV specified in Section 3. If the
SRv6-Function Descriptor is encoded in the P2P SRv6 X-SID sub-TLV,
then the encoded SRv6 SID function MUST include only the code points
of SRv6 SID functions that require the specification of a neighbor
to be correctly applied. This document specifies the code points of
two such functions, namely End.X and End.DX6 [11].
6.2. LAN SRv6 X-SID sub-TLV
This sub-TLV is used to advertise one or more SRv6 SIDs associated
with End.X and End.DX6 [11] functions over a LAN adjacency. The "LAN
SRv6 X-SID" sub-TLV has the following format
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 | System ID (6 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | SID-size | SID (variable) . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|sub-sub-tlv-len| sub-sub-TLVs (variable) . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 41 (Suggested value to be assigned by IANA)
Length: variable.
System-ID: 6 octets of IS-IS System-ID of length "ID Length" as
defined in [2].
One or more SIDs each of which has the following format:
Flags 1 Octet. No flags are defined in this document
SID-Size: 1 octet. Number of bits in the SID field.
SID: 1-16 octets. This field encodes the advertised SRv6 SID. The
"SID-size" field can have the values 1-128 and indicates the
number of bits in the SID. The SRv6 SID is encoded in the
minimal number of octets for the given number of bits. The owning
router may associate one or more functions as specified in [11],
in other documents, or as locally configured.
Sub-sub-TLV-length: 1 octet. Number of octets used by sub-sub-
TLVs
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The function associated with the advertised SID is specified by the
SRv6-Function Descriptor sub-sub-TLV specified in Section 3. If the
SRv6-Function Descriptor is encoded in the P2P SRv6 X-SID sub-TLV,
then the encoded SRv6 SID function MUST include only the code points
of SRv6 SID functions that require the specification of a neighbor
to be correctly applied. This document specifies the code points of
two such functions, namely End.X and End.DX6 [11].
7. IANA Considerations
This documents request allocation for the following TLVs, sub-
TLVs, and sub-sub-TLVs as well updating the ISIS TLV registry and
defining a new registry.
7.1. SRv6 SID TLV and sub-TLVs
This document adds the following new TLV to the IS-IS TLV Codepoints
registry.
Value: 27 (suggested - to be assigned by IANA)
Name: SRv6 SID
The name of the "Sub-TLVs for TLVs 135, 235, 236 and 237 registry"
needs to be changed to "Sub-TLVs for TLVs 27, 135, 235, 236 and 237
registry".
This document adds a new sub-TLV to the (renamed) "Sub-TLVs for TLVs
27, 135, 235, 236 and 237 registry".
Value: 5 (Suggested - to be assigned by IANA)
Name: SRv6-function Descriptor
The revised table of sub-TLVs in the registry should be:
Type 27 135 235 236 237
1 n y y y y
2 n y y y y
3 y y y y y
4 y y y y y
5(new)y n n n n
11 y y y y y
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12 y y y y y
7.2. IS-IS SRv6-functions Codepoints Registry
This document requests the creation of a new IANA managed registry
to identify SRv6 SID functions. The registration procedure is
"Expert Review" as defined in [3]. Suggested registry name is "SRv6
SID Function Types". A function identifier is an unsigned 8 bits
value. The following values are defined by this document:
0 Reserved
1 End function.
2 End.DX6 function.
3 End.DT6 function.
4 End.X function.
7.3. SRv6 Capabilities sub-TLV
This document adds the definition of a new sub-TLV in the "Sub-
TLVs for TLV 242 registry".
Type: 22 (Suggested - to be assigned by IANA)
Description: SRv6 Capabilities
7.4. P2P SRv6 X-SID and LAN SRv6 X-SID sub-TLVs
This document adds the definition of two new sub-TLVs in the "sub-
TLVs for TLV 22, 23, 141, 222 and 223 registry".
Type: 40 (suggested - to be assigned by IANA)
Description: Point-to-Point SRv6 X-SID
Type: 41 (suggested - to be assigned by IANA)
Description: LAN SRv6 X-SID
Type 22 23 141 222 223
40 y y y y y
41 y y y y y
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7.5. IS-IS SRv6 X-SID sub-sub-TLV Codepoints Registry
This document requests the creation of a new IANA managed registry
to identify SRv6 SID functions encoded in P2P/LAN X-SID sub-TLVs.
The registration procedure is "Expert Review" as defined in [3].
Suggested registry name is "SRv6 X-SID sub-sub-TLV Codepoints
Registry". The following values are defined by this document:
Value: 5 (Suggested - to be assigned by IANA)
Name: SRv6-function Descriptor
This sub-sub-TLV MAY appear in either the Point-to-Point SRv6 X-SID
or the LAN SRv6 X-SID sub-TLVs described in Section 7.4.
8. Security Considerations
TBD
9. Contributors
The following people gave a substantial contribution to the content
of this document and should be considered as co-authors:
Stefano Previdi (editor)
Cisco Systems, Inc.
Via Del Serafico, 200
Rome 00142
Italy
Email: sprevidi@cisco.com
Peter Psenak
Cisco Systems
Apollo Business Center Mlynske nivy 43
Bratislava 821 09
Slovakia
Email: ppsenak@cisco.com
Paul Wells
Cisco Systems
Saint Paul,
Minisota,
United States
Email: pauwells@cisco.com
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Daniel Voyer
Email: daniel.voyer@bell.ca
Satoru Matsushima
Email: satoru.matsushima@g.softbank.co.jp
Bart Peirens
Email: bart.peirens@proximus.com
Hani Elmalky
Email: hani.elmalky@ericsson.com
Prem Jonnalagadda
Email: prem@barefootnetworks.com
Milad Sharif
Email: msharif@barefootnetworks.com>
Robert Hanzl
Cisco Systems
Millenium Plaza Building, V Celnici 10, Prague 1,
Prague, Czech Republic
Email rhanzl@cisco.com
10. References
10.1. Normative References
[1] Previdi, S., Ginsberg, L., Chen, M., IS-IS Extensions for
Advertising Router Information", RFC7981, October 2016
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[2] International Organization for Standardization, "Intermediate
system to Intermediate system intra-domain routeing information
exchange protocol for use inconjunction with the protocol for
providing theconnectionless-mode Network Service (ISO 8473)",
ISO/IEC 10589:2002, Second Edition, Nov 2002.
[3] T Narten and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", RFC5226, May 2008
[4] T. Li, "IS-IS Extensions for Traffic Engineering", RFC5305,
October 2008
[5] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: MultiTopology
(MT) Routing in Intermediate System to Intermediate Systems
(IS-ISs)", RFC 5120, DOI 10.17487/RFC5120, February 2008,
<http://www.rfc-editor.org/info/rfc5120>.
[6] McPherson, D., Ed., Ginsberg, L., Previdi, S., and M. Shand,
"Simplified Extension of Link State PDU (LSP) Space for IS-IS",
RFC 5311, DOI 10.17487/RFC5311, February 2009, <http://www.rfc-
editor.org/info/rfc5311>.
[7] M. Chen, R. Zhang, X. Duan, "ISIS Extensions in Support of
Inter-Autonomous System (AS) MPLS and GMPLS Traffic
Engineering", RFC 5316, December 2008
[8] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119,
March 1997, <http://www.rfc-editor.org/info/rfc2119>.
10.2. Informative References
[9] Filsfils, C., Previdi, S., Decraene, B., Litkowski, S., and R.
Shakir, "Segment Routing Architecture", draft-ietf-spring-
segment-routing-11 (work in progress), Feb 2017.
[10] Previdi, S., Filsfils, C., Field, B., Leung, I., Linkova, J.,
Aries, E., Kosugi, T., Vyncke, E., and D. Lebrun, "IPv6 Segment
Routing Header (SRH)", draft-ietf-6man-segment-routing-header-
05 (work in progress), Feb 2017.
[11] C. Fisfils, D. Voyer, D. Bernier, Bell Canada, D. Steinberg, R.
Raszuk, S. Matsushima, D. Lebrun, B. Decraene, B. Peirens, S.
Salsano, G. Naik, H. Elmalky, P. Jonnalagadda, M. Sharif, A.
Ayyangar, Force10 Networks, A. Bashandy, K. Raza, D. Dukes, F.
Clad, P. Camarillo, "SRv6 Network Programming", draft-filsfils-
spring-srv6-network-programming-00 (work in progress), May 2017
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11. Acknowledgments
This document was prepared using 2-Word-v2.0.template.dot.
Authors' Addresses
Ahmed Bashandy
Cisco Systems
170 West Tasman Dr, San Jose, CA 95134, USA
Email: bashandy@cisco.com
Clarence Filsfils
Cisco Systems
Brussels, Belgium
Email: cfilsfil@cisco.com
Les Ginsberg
Cisco Systems, Inc.
US
Email: ginsberg@cisco.com
Bruno Decraene
Orange
Issy-les-Moulineaux
FR
Email: bruno.decraene@orange.com
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