IPv6 Segment Routing Header (SRH)
draft-ietf-6man-segment-routing-header-15
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 8754.
|
|
|---|---|---|---|
| Authors | Clarence Filsfils , Stefano Previdi , John Leddy , Satoru Matsushima , Daniel Voyer | ||
| Last updated | 2018-10-22 (Latest revision 2018-06-29) | ||
| Replaces | draft-previdi-6man-segment-routing-header | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
TSVART Last Call review
(of
-22)
by Joseph Touch
Almost ready
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | In WG Last Call | |
| Document shepherd | Bob Hinden | ||
| IESG | IESG state | Became RFC 8754 (Proposed Standard) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | Robert Hinden <bob.hinden@gmail.com> |
draft-ietf-6man-segment-routing-header-15
Network Working Group C. Filsfils, Ed.
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track S. Previdi
Expires: April 25, 2019 Huawei
J. Leddy
Individual
S. Matsushima
Softbank
D. Voyer, Ed.
Bell Canada
October 22, 2018
IPv6 Segment Routing Header (SRH)
draft-ietf-6man-segment-routing-header-15
Abstract
Segment Routing can be applied to the IPv6 data plane using a new
type of Routing Extension Header. This document describes the
Segment Routing Extension Header and how it is used by Segment
Routing capable nodes.
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 April 25, 2019.
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Copyright Notice
Copyright (c) 2018 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 Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Segment Routing Extension Header . . . . . . . . . . . . . . 4
2.1. SRH TLVs . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1. Padding TLVs . . . . . . . . . . . . . . . . . . . . 6
2.1.2. HMAC TLV . . . . . . . . . . . . . . . . . . . . . . 7
3. SR Nodes . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1. Source SR Node . . . . . . . . . . . . . . . . . . . . . 10
3.2. Transit Node . . . . . . . . . . . . . . . . . . . . . . 11
3.3. SR Segment Endpoint Node . . . . . . . . . . . . . . . . 11
4. Packet Processing . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Source SR Node . . . . . . . . . . . . . . . . . . . . . 11
4.1.1. Reduced SRH . . . . . . . . . . . . . . . . . . . . . 12
4.2. Transit Node . . . . . . . . . . . . . . . . . . . . . . 12
4.3. SR Segment Endpoint Node . . . . . . . . . . . . . . . . 12
4.3.1. FIB Entry Is Locally Instantiated SRv6 END SID . . . 12
4.3.2. FIB Entry is a Local Interface . . . . . . . . . . . 14
4.3.3. FIB Entry Is A Non-Local Route . . . . . . . . . . . 15
4.3.4. FIB Entry Is A No Match . . . . . . . . . . . . . . . 15
4.3.5. Load Balancing and ECMP . . . . . . . . . . . . . . . 15
5. Illustrations . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1. Abstract Representation of an SRH . . . . . . . . . . . . 15
5.2. Example Topology . . . . . . . . . . . . . . . . . . . . 16
5.3. Source SR Node . . . . . . . . . . . . . . . . . . . . . 17
5.3.1. Intra SR Domain Packet . . . . . . . . . . . . . . . 17
5.3.2. Transit Packet Through SR Domain . . . . . . . . . . 17
5.4. Transit Node . . . . . . . . . . . . . . . . . . . . . . 18
5.5. SR Segment Endpoint Node . . . . . . . . . . . . . . . . 18
6. Deployment Models . . . . . . . . . . . . . . . . . . . . . . 18
6.1. Nodes Within the SR domain . . . . . . . . . . . . . . . 18
6.2. Nodes Outside the SR Domain . . . . . . . . . . . . . . . 18
6.2.1. SR Source Nodes Not Directly Connected . . . . . . . 19
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7. Security Considerations . . . . . . . . . . . . . . . . . . . 20
7.1. Source Routing Attacks . . . . . . . . . . . . . . . . . 21
7.2. Service Theft . . . . . . . . . . . . . . . . . . . . . . 21
7.3. Topology Disclosure . . . . . . . . . . . . . . . . . . . 22
7.4. ICMP Generation . . . . . . . . . . . . . . . . . . . . . 22
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
8.1. Segment Routing Header Flags Register . . . . . . . . . . 23
8.2. Segment Routing Header TLVs Register . . . . . . . . . . 23
9. Implementation Status . . . . . . . . . . . . . . . . . . . . 23
9.1. Linux . . . . . . . . . . . . . . . . . . . . . . . . . . 24
9.2. Cisco Systems . . . . . . . . . . . . . . . . . . . . . . 24
9.3. FD.io . . . . . . . . . . . . . . . . . . . . . . . . . . 24
9.4. Barefoot . . . . . . . . . . . . . . . . . . . . . . . . 24
9.5. Juniper . . . . . . . . . . . . . . . . . . . . . . . . . 24
9.6. Huawei . . . . . . . . . . . . . . . . . . . . . . . . . 25
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 25
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
12.1. Normative References . . . . . . . . . . . . . . . . . . 25
12.2. Informative References . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction
Segment Routing can be applied to the IPv6 data plane using a new
type of Routing Extension Header (SRH). This document describes the
Segment Routing Extension Header and how it is used by Segment
Routing capable nodes.
The Segment Routing Architecture [RFC8402] describes Segment Routing
and its instantiation in two data planes MPLS and IPv6.
SR with the MPLS data plane is defined in
[I-D.ietf-spring-segment-routing-mpls].
SR with the IPv6 data plane is defined in
[I-D.filsfils-spring-srv6-network-programming].
The encoding of MPLS labels and label stacking are defined in
[RFC3032].
The encoding of IPv6 segments in the Segment Routing Extension Header
is defined in this document.
Terminology used within this document is defined in detail in
[RFC8402]. Specifically, these terms: Segment Routing, SR Domain,
SRv6, Segment ID (SID), SRv6 SID, Active Segment, and SR Policy.
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2. Segment Routing Extension Header
Routing Headers are defined in [RFC8200]. The Segment Routing Header
has a new Routing Type (suggested value 4) to be assigned by IANA.
The Segment Routing Header (SRH) is defined 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 | Routing Type | Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Entry | Flags | Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[0] (128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
...
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[n] (128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
// Optional Type Length Value objects (variable) //
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Next Header: Defined in [RFC8200]
o Hdr Ext Len: Defined in [RFC8200]
o Routing Type: TBD, to be assigned by IANA (suggested value: 4).
o Segments Left: Defined in [RFC8200]
o Last Entry: contains the index (zero based), in the Segment List,
of the last element of the Segment List.
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o Flags: 8 bits of flags. Following flags are defined:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|U U U U U U U U|
+-+-+-+-+-+-+-+-+
U: Unused and for future use. MUST be 0 on transmission and
ignored on receipt.
o Tag: tag a packet as part of a class or group of packets, e.g.,
packets sharing the same set of properties. When tag is not used
at source it MUST be set to zero on transmission. When tag is not
used during SRH Processing it SHOULD be ignored. The allocation
and use of tag is outside the scope of this document.
o Segment List[n]: 128 bit IPv6 addresses representing the nth
segment in the Segment List. The Segment List is encoded starting
from the last segment of the SR Policy. I.e., the first element
of the segment list (Segment List [0]) contains the last segment
of the SR Policy, the second element contains the penultimate
segment of the SR Policy and so on.
o Type Length Value (TLV) are described in Section 2.1.
2.1. SRH TLVs
This section defines TLVs of the Segment Routing Header.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-----------------------
| Type | Length | Variable length data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-----------------------
Type: An 8 bit value. Unrecognized Types MUST be ignored on receipt.
Length: The length of the Variable length data. It is RECOMMENDED
that the total length of new TLVs be multiple of 8 bytes to avoid the
use of Padding TLVs.
Variable length data: Length bytes of data that is specific to the
Type.
Type Length Value (TLV) contain OPTIONAL information that may be used
by the node identified in the Destination Address (DA) of the packet.
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Each TLV has its own length, format and semantic. The code-point
allocated (by IANA) to each TLV Type defines both the format and the
semantic of the information carried in the TLV. Multiple TLVs may be
encoded in the same SRH.
TLVs may change en route at each segment. To identify when a TLV
type may change en route the most significant bit of the Type has the
following significance:
0: TLV data does not change en route
1: TLV data does change en route
Identifying which TLVs change en route, without having to understand
the Type, is required for Authentication Header Integrity Check Value
(ICV) computation. Any TLV that changes en route is considered
mutable for the purpose of ICV computation, the Type Length and
Variable Length Data is ignored for the purpose of ICV Computation as
defined in [RFC4302].
The "Length" field of the TLV is used to skip the TLV while
inspecting the SRH in case the node doesn't support or recognize the
Type. The "Length" defines the TLV length in octets, not including
the "Type" and "Length" fields.
The following TLVs are defined in this document:
Padding TLV
HMAC TLV
Additional TLVs may be defined in the future.
2.1.1. Padding TLVs
There are two types of padding TLVs, pad0 and padN, the following
applies to both:
Padding TLVs are used to pad the TLVs to a multiple of 8 octets.
More than one Padding TLV MUST NOT appear in the SRH.
The Padding TLVs are used to align the SRH total length on the 8
octet boundary.
When present, a single Pad0 or PadN TLV MUST appear as the last
TLV.
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When present, a PadN TLV MUST have a length from 0 to 5 in order
to align the SRH total length on a 8-octet boundary.
Padding TLVs are ignored by a node processing the SRH TLV, even if
more than one is present.
Padding TLVs are ignored during ICV calculation.
2.1.1.1. PAD0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Type |
+-+-+-+-+-+-+-+-+
Type: to be assigned by IANA (Suggested value 128)
A single Pad0 TLV MUST be used when a single byte of padding is
required. If more than one byte of padding is required a Pad0 TLV
MUST NOT be used, the PadN TLV MUST be used.
2.1.1.2. PADN
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 | Padding (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Padding (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: to be assigned by IANA (suggested value 129).
Length: 0 to 5
Padding: Length octets of padding. Padding bits have no
semantics. They MUST be set to 0 on transmission and ignored on
receipt.
The PadN TLV MUST be used when more than one byte of padding is
required.
2.1.2. HMAC TLV
The keyed Hashed Message Authentication Code (HMAC) TLV is OPTIONAL
and has the following format:
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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 | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HMAC Key ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| //
| HMAC (32 octets) //
| //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: to be assigned by IANA (suggested value 5).
o Length: 38.
o RESERVED: 2 octets. MUST be 0 on transmission and ignored on
receipt.
o HMAC Key ID: A 4 octet opaque number which uniquely identifies the
pre-shared key and algorithm used to generate the HMAC. If 0, the
HMAC is not included.
o HMAC: 32 octets of keyed HMAC, not present if Key ID is 0.
The HMAC TLV is used to verify the source of a packet is permitted to
use the current segment in the destination address of the packet, and
ensure the segment list is not modified in transit.
2.1.2.1. HMAC generation
The HMAC field is the output of the HMAC computation as defined in
[RFC2104], using:
o key: the pre-shared key identified by HMAC Key ID
o HMAC algorithm: identified by the HMAC Key ID
o Text: a concatenation of the following fields from the IPv6 header
and the SRH, as it would be received at the node verifying the
HMAC:
* IPv6 header: source address (16 octets)
* IPv6 header: destination address (16 octets)
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* SRH: Segments Left (1 octet)
* SRH: Last Entry (1 octet)
* SRH: Flags (1 octet)
* SRH: HMAC Key-id (4 octets)
* SRH: all addresses in the Segment List (variable octets)
The HMAC digest is truncated to 32 octets and placed in the HMAC
field of the HMAC TLV.
For HMAC algorithms producing digests less than 32 octets, the digest
is placed in the lowest order octets of the HMAC field. Remaining
octets MUST be set to zero.
2.1.2.2. HMAC Verification
Local policy determines when to check for an HMAC and potentially a
requirement on where the HMAC TLV must appear (e.g. first TLV).
This local policy is outside the scope of this document. It may be
based on the active segment at an SR Segment endpoint node, the
result of an ACL that considers incoming interface, or other packet
fields.
If HMAC verification is successful, the packet is forwarded to the
next segment.
If HMAC verification fails, an ICMP error message (parameter problem,
error code 0, pointing to the HMAC TLV) SHOULD be generated (but rate
limited) and SHOULD be logged.
2.1.2.3. HMAC Pre-Shared Key Algorithm
The HMAC Key ID field allows for the simultaneous existence of
several hash algorithms (SHA-256, SHA3-256 ... or future ones) as
well as pre-shared keys.
The HMAC Key ID field is opaque, i.e., it has neither syntax nor
semantic except as an identifier of the right combination of pre-
shared key and hash algorithm, and except that a value of 0 means
that there is no HMAC field.
At the HMAC TLV verification node the Key ID uniquely identifies the
pre-shared key and HMAC algorithm.
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At the HMAC TLV generating node the Key ID and destination address
uniquely identify the pre-shared key and HMAC algorithm. Utilizing
the destination address with the Key ID allows for overlapping key
IDs amongst different HMAC verification nodes. The Text for the HMAC
computation is set to the IPv6 header fields and SRH fields as they
would appear at the verification node, not necessarily the same as
the source node sending a packet with the HMAC TLV.
Pre-shared key roll-over is supported by having two key IDs in use
while the HMAC TLV generating node and verifying node converge to a
new key.
SRH implementations can support multiple hash functions but MUST
implement SHA-2 [FIPS180-4] in its SHA-256 variant.
The selection of pre-shared key and algorithm, and their distribution
is outside the scope of this document, some options may include:
o in the configuration of the HMAC generating or verifying nodes,
either by static configuration or any SDN oriented approach
o dynamically using a trusted key distribution protocol such as
[RFC6407]
3. SR Nodes
There are different types of nodes that may be involved in segment
routing networks: source SR nodes originate packets with a segment in
the destination address of the IPv6 header, transit nodes that
forward packets destined to a remote segment, and SR segment endpoint
nodes that process a local segment in the destination address of an
IPv6 header.
3.1. Source SR Node
A Source SR Node is any node that originates an IPv6 packet with a
segment (i.e. SRv6 SID) in the destination address of the IPv6
header. The packet leaving the source SR Node may or may not contain
an SRH. This includes either:
A host originating an IPv6 packet.
An SR domain ingress router encapsulating a received packet in an
outer IPv6 header, followed by an optional SRH.
The mechanism through which a segment in the destination address of
the IPv6 header and the Segment List in the SRH, is derived is
outside the scope of this document.
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3.2. Transit Node
A transit node is any node forwarding an IPv6 packet where the
destination address of that packet is not locally configured as a
segment nor a local interface. A transit node is not required to be
capable of processing a segment nor SRH.
3.3. SR Segment Endpoint Node
A SR segment endpoint node is any node receiving an IPv6 packet where
the destination address of that packet is locally configured as a
segment or local interface.
4. Packet Processing
This section describes SRv6 packet processing at the SR source,
Transit and SR segment endpoint nodes.
4.1. Source SR Node
A Source node steers a packet into an SR Policy. If the SR Policy
results in a segment list containing a single segment, and there is
no need to add information to SRH flag or TLV, the DA is set to the
single segment list entry and the SRH MAY be omitted.
When needed, the SRH is created as follows:
Next Header and Hdr Ext Len fields are set as specified in
[RFC8200].
Routing Type field is set as TBD (to be allocated by IANA,
suggested value 4).
The DA of the packet is set with the value of the first segment.
The first element of the SRH Segment List is the ultimate segment.
The second element is the penultimate segment and so on.
The Segments Left field is set to n-1 where n is the number of
elements in the SR Policy.
The Last Entry field is set to n-1 where n is the number of
elements in the SR Policy.
HMAC TLV may be set according to Section 7.
The packet is forwarded toward the packet's Destination Address
(the first segment).
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4.1.1. Reduced SRH
When a source does not require the entire SID list to be preserved in
the SRH, a reduced SRH may be used.
A reduced SRH does not contain the first segment of the related SR
Policy (the first segment is the one already in the DA of the IPv6
header), and the Last Entry field is set to n-2 where n is the number
of elements in the SR Policy.
4.2. Transit Node
As specified in [RFC8200], the only node allowed to inspect the
Routing Extension Header (and therefore the SRH), is the node
corresponding to the DA of the packet. Any other transit node MUST
NOT inspect the underneath routing header and MUST forward the packet
toward the DA according to its IPv6 routing table.
When a SID is in the destination address of an IPv6 header of a
packet, it's routed through an IPv6 network as an IPv6 address.
SIDs, or the prefix(es) covering SIDs, and their reachability may be
distributed by means outside the scope of this document. For
example, [RFC5308] or [RFC5340] may be used to advertise a prefix
covering the SIDs on a node.
4.3. SR Segment Endpoint Node
Without constraining the details of an implementation, the SR segment
endpoint node creates Forwarding Information Base (FIB) entries for
its local SIDs.
When an SRv6-capable node receives an IPv6 packet, it performs a
longest-prefix-match lookup on the packets destination address. This
lookup can return any of the following:
A FIB entry that represents a locally instantiated SRv6 SID
A FIB entry that represents a local interface, not locally
instantiated as an SRv6 SID
A FIB entry that represents a non-local route
No Match
4.3.1. FIB Entry Is Locally Instantiated SRv6 END SID
This document, and section, defines a single SRv6 SID called END.
Future documents may define additional SRv6 SIDs. In which case, the
entire content of this section will be defined in that document.
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If the FIB entry represents a locally instantiated SRv6 SID, process
the next header of the IPv6 header as defined in section 4 of
[RFC8200]
The following sections describe the actions to take while processing
next header fields.
4.3.1.1. SRH Processing
When an SRH is processed {
If Segments Left is equal to zero {
Proceed to process the next header in the packet, whose type
is identified by the Next Header field in the Routing header.
}
Else {
If local policy requires TLV processing {
Perform TLV processing (see TLV Processing)
}
max_last_entry = ( Hdr Ext Len / 2 ) - 1
If ((Last Entry > max_last_entry) or
(Segments Left is greater than (Last Entry+1)) {
Send an ICMP Parameter Problem, Code 0, message to the
Source Address, pointing to the Segments Left field, and
discard the packet.
}
Else {
Decrement Segments Left by 1.
Copy Segment List[Segments Left] from the SRH to the
destination address of the IPv6 header.
If the IPv6 Hop Limit is less than or equal to 1 {
Send an ICMP Time Exceeded -- Hop Limit Exceeded in
Transit message to the Source Address and discard
the packet.
}
Else {
Decrement the Hop Limit by 1
Resubmit the packet to the IPv6 module for transmission
to the new destination.
}
}
}
}
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4.3.1.1.1. TLV Processing
Local policy determines how TLV's are to be processed when the Active
Segment is a local END SID. The definition of local policy is
outside the scope of this document.
For illustration purpose only, two example local policies that may be
associated with an END SID are provided below.
Example 1:
For any packet received from interface I2
Skip TLV processing
Example 2:
For any packet received from interface I1
If first TLV is HMAC {
Process the HMAC TLV
}
Else {
Discard the packet
}
4.3.1.2. Upper-layer Header or No Next Header
Send an ICMP parameter problem message to the Source Address and
discard the packet. Error code (TBD by IANA) "SR Upper-layer Header
Error", pointer set to the offset of the upper-layer header.
A unique error code allows an SR Source node to recognize an error in
SID processing at an endpoint.
4.3.2. FIB Entry is a Local Interface
If the FIB entry represents a local interface, not locally
instantiated as an SRv6 SID, the SRH is processed as follows:
If Segments Left is zero, the node must ignore the Routing header
and proceed to process the next header in the packet, whose type
is identified by the Next Header field in the Routing Header.
If Segments Left is non-zero, the node must discard the packet and
send an ICMP Parameter Problem, Code 0, message to the packet's
Source Address, pointing to the unrecognized Routing Type.
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4.3.3. FIB Entry Is A Non-Local Route
Processing is not changed by this document.
4.3.4. FIB Entry Is A No Match
Processing is not changed by this document.
4.3.5. Load Balancing and ECMP
Within an SR domain, an SR source node encapsulates a packet in an
outer IPv6 header for transport to an endpoint. The SR source node
MUST impose a flow label computed based on the inner packet. The
computation of the flow label is as recommended in [RFC6438] for the
sending Tunnel End Point.
At any transit node within an SR domain, the flow label MUST be used
as defined in [RFC6438] to calculate the ECMP hash toward the
destination address. If flow label is not used, the transit node may
hash all packets between a pair of SR Edge nodes to the same link.
At an SR segment endpoint node, the flow label MUST be used as
defined in [RFC6438] to calculate any ECMP hash used to forward the
processed packet to the next segment.
5. Illustrations
This section provides illustrations of SRv6 packet processing at SR
source, transit and SR segment endpoint nodes.
5.1. Abstract Representation of an SRH
For a node k, its IPv6 address is represented as Ak, its SRv6 SID is
represented as Sk.
IPv6 headers are represented as the tuple of (source, destination).
For example, a packet with source address A1 and destination address
A2 is represented as (A1,A2). The payload of the packet is omitted.
An SR Policy is a list of segments. A list of segments is
represented as <S1,S2,S3> where S1 is the first SID to visit, S2 is
the second SID to visit and S3 is the last SID to visit.
(SA,DA) (S3, S2, S1; SL) represents an IPv6 packet with:
o Source Address is SA, Destination Addresses is DA, and next-header
is SRH.
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o SRH with SID list <S1, S2, S3> with SegmentsLeft = SL.
o Note the difference between the <> and () symbols. <S1, S2, S3>
represents a SID list where the leftmost segment is the first
segment. Whereas, (S3, S2, S1; SL) represents the same SID list
but encoded in the SRH Segment List format where the leftmost
segment is the last segment. When referring to an SR policy in a
high-level use-case, it is simpler to use the <S1, S2, S3>
notation. When referring to an illustration of detailed behavior,
the (S3, S2, S1; SL) notation is more convenient.
At its SR Policy headend, the Segment List <S1,S2,S3> results in SRH
(S3,S2,S1; SL=2) represented fully as:
Segments Left=2
Last Entry=2
Flags=0
Tag=0
Segment List[0]=S3
Segment List[1]=S2
Segment List[2]=S1
5.2. Example Topology
The following topology is used in examples below:
+ * * * * * * * * * * * * * * * * * * * * +
* [8] [9] *
| |
* | | *
[1]----[3]--------[5]----------------[6]---------[4]---[2]
* | | *
| |
* | | *
+--------[7]-------+
* *
+ * * * * * * * SR Domain * * * * * * * +
Figure 3
o 3 and 4 are SR Domain edge routers
o 5, 6, and 7 are all SR Domain routers
o 8 and 9 are hosts within the SR Domain
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o 1 and 2 are hosts outside the SR Domain
5.3. Source SR Node
5.3.1. Intra SR Domain Packet
When host 8 sends a packet to host 9 via an SR Policy <S7,A9> the
packet is
P1: (A8,S7)(A9,S7; SL=1)
5.3.1.1. Reduced Variant
When host 8 sends a packet to host 9 via an SR Policy <S7,A9> and it
wants to use a reduced SRH, the packet is
P2: (A8,S7)(A9; SL=1)
5.3.2. Transit Packet Through SR Domain
When host 1 sends a packet to host 2, the packet is
P3: (A1,A2)
The SR Domain ingress router 3 receives P3 and steers it to SR Domain
egress router 4 via an SR Policy <S7, S4>. Router 3 encapsulates the
received packet P3 in an outer header with an SRH. The packet is
P4: (A3, S7)(S4, S7; SL=1)(A1, A2)
If the SR Policy contains only one segment (the egress router 4), the
ingress Router 3 encapsulates P3 into an outer header (A3, S4). The
packet is
P5: (A3, S4)(A1, A2)
5.3.2.1. Reduced Variant
The SR Domain ingress router 3 receives P3 and steers it to SR Domain
egress router 4 via an SR Policy <S7, S4>. If router 3 wants to use
a reduced SRH, Router 3 encapsulates the received packet P3 in an
outer header with a reduced SRH. The packet is
P6: (A3, S7)(S4; SL=1)(A1, A2)
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5.4. Transit Node
Nodes 5 acts as transit nodes for packet P1, and sends packet
P1: (A8,S7)(A9,S7;SL=1)
on the interface toward node 7.
5.5. SR Segment Endpoint Node
Node 7 receives packet P1 and, using the logic in section 4.3.1,
sends packet
P7: (A8,A9)(A9,S7; SL=0)
on the interface toward router 6.
6. Deployment Models
6.1. Nodes Within the SR domain
SR Source Nodes within an SR Domain are trusted to generate IPv6
packets with SRH. SR segment endpoint nodes receiving packets on
interface that are part of the SR Domain may process any packet
destined to a local segment, containing an SRH.
A SR Source Node connected to the SR Domain via a secure tunnel, e.g.
IPSec tunnel mode [RFC4303] or Ethernet pseudowire [RFC4448], may be
considered trusted and directly connected. Some types of tunnels may
result in additional processing overhead that should be considered in
a deployment.
6.2. Nodes Outside the SR Domain
Nodes outside the SR Domain cannot be trusted. SR Domain Ingress
routers SHOULD discard packets destined to SIDs within the SR Domain
(regardless of the presence of an SRH) to avoid attacks on the SR
Domain as described and referenced in [RFC5095]. As an additional
layer of protection, SR Segment Endpoint nodes SHOULD discard packets
destined to local SIDs from source addresses not part of the SR
Domain.
For example, using the example topology from section 5, all SIDs in
the SR Domain (SIDS S1-S9) are assigned within a single IPv6 prefix,
Prefix-S. All SIDs assigned to a node k are assigned within a single
IPv6 prefix Prefix-Sk, all addresses permitted to source packets
destined to SIDs in the SR Domain are assigned within a single IPv6
prefix Prefix-A.
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An Infrastructure Access List (IACL), applied to the external
interfaces of SR Domain ingress nodes 3 and 4, that discards packets
destined to a SID covered by Prefix-S is used to discard packets
destined to SIDs within the SR Domain.
An IACL, applied to each interface of SR Segment Endpoint Nodes k,
that discards packets destined to a SID covered by Prefix-Sk with a
source address not covered by Prefix-A.
Failure to implement a method of ingress filtering, as defined above,
exposes the SR domain to source routing attacks from nodes outside
the SR Domain, as described and referenced in [RFC5095].
6.2.1. SR Source Nodes Not Directly Connected
Nodes outside the SR Domain may request, by some trusted means
outside the scope of this document, a complete SRH including an HMAC
TLV which is computed correctly for the SRH.
SR Domain ingress routers permit traffic destined to select SIDs with
local policy requiring HMAC TLV processing for those select SIDs,
i.e. those SIDs provide a gateway to the SR Domain for a set of
segment lists.
If HMAC verification is successful, the packet is forwarded to the
next segment. Within the SR Domain no further HMAC check need be
performed.
If HMAC verification fails, an ICMP error message (parameter problem,
error code 0, pointing to the HMAC TLV) SHOULD be generated (but rate
limited) and SHOULD be logged.
For example, extending the topology defined in Figure 3, consider
node 3 offering access to a premium SLA service to node 20. Node 20
is a trusted SR Source not directly connected to the SR Domain.
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+ * * * * * * * * * * * * * * * * * * * * +
* [8] [9] *
| |
* | | *
[20]--[11]--[3]--------[5]----------------[6]---------[4]---[2]
* | | *
| |
* | | *
+--------[7]-------+
* *
+ * * * * * * * SR Domain * * * * * * * +
In order to access the SLA service, node 20 must be able to access
segments within the SR Domain. To provide a secure entry point for
the SLA service, SIDs with local policy requiring HMAC verification
at node k are defined as Hk and assigned from a prefix Prefix-H.
Prefix-H is disjoint with Prefix-S and Prefix-A defined earlier.
Prefix-H is not part of the IACLs applied at the external facing
interfaces of node 3 and 4, allowing external nodes access to it.
SID H3 is a SID covered by Prefix-H at node 3.
Node 20 requests the premium SLA service to node 2 and is provided a
pre-computed SRH and HMAC with destination address H3.
Node 20 sends a packet with destination addresses set to H2, SRH and
HMAC TLV are as provided for the premium SLA service.
Node 3 receives the packet and verifies the HMAC as defined in
section 4.3, forwarding the packet to the next segment in the segment
list or dropping it based on the HMAC result.
This use of an HMAC is particularly valuable within an enterprise
based SR Domain to authenticate a host which is using SRv6 segment
routing as documented in [SRN]. In that example, the HMAC is used to
validate a source node is using a permitted segment list.
7. Security Considerations
This section reviews security considerations related to the SRH,
given the SRH processing and deployment models discussed in this
document.
As describe in Section 6, it is necessary to filter packets ingress
to the SR Domain destined to segments within the SR Domain. This
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ingress filtering is via an IACL at SR Domain ingress border nodes.
Additional protection is applied via an IACL at each SR Segment
Endpoint node, filtering packets not from within the SR Domain,
destined to SIDs in the SR Domain. ACLs are easily supported for
small numbers of prefixes, making summarization important, and when
the prefixes requiring filtering is kept to a seldom changing set.
Additionally, ingress filtering of IPv6 source addresses as
recommended in BCP38 SHOULD be used.
SR Source Nodes not directly connected to the SR Domain may access
specific sets of segments within the SR Domain when secured with the
SRH HMAC TLV. The SRH HMAC TLV provides a means of verifying the
validity of ingress packets SRH, limiting access to the segments in
the SR Domain to only those source nodes with permission.
7.1. Source Routing Attacks
[RFC5095] deprecates the Type 0 Routing header due to a number of
significant attacks that are referenced in that document. Such
attacks include bypassing filtering devices, reaching otherwise
unreachable Internet systems, network topology discovery, bandwidth
exhaustion, and defeating anycast.
Because this document specifies that the SRH is for use within an SR
domain protected by ingress filtering via IACLs, and by
cryptographically authenticated SR source nodes not directly
connected to the SR Domain; such attacks cannot be mounted from
outside an SR Domain. As specified in this document, SR Domain
ingress edge nodes drop packets entering the SR Domain destined to
segments within the SR Domain.
Aditionally, this document specifies the use of IACL on SR Segment
Endpoint nodes within the SR Domain to limit the source addresses
permitted to send packets to a SID in the SR Domain.
Such attacks may, however, be mounted from within the SR Domain, from
nodes permitted to source traffic to SIDs in the domain. As such,
these attacks and other known attacks on an IP network (e.g. DOS/
DDOS, topology discovery, man-in-the-middle, traffic interception/
siphoning), can occur from compromised nodes within an SR Domain.
7.2. Service Theft
Service theft is defined as the use of a service offered by the SR
Domain by a node not authorized to use the service.
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Service theft is not a concern within the SR Domain as all SR Source
nodes and SR segment endpoint nodes within the domain are able to
utilizing the services of the Domain. If a node outside the SR
Domain learns of segments or a topological service within the SR
domain, IACL filtering denies access to those segments.
Nodes outside the SR Domain, capable of intercepting packets from SR
Source nodes not directly connected to the SR Domain utilizing the
SRH HMAC, may steel the outer IP header SRH and HMAC TLV. If such an
attacker is capable of spoofing the source address of the original
sender it may use the IP header and HMAC to access services of the SR
Domain intended for the original SR Source node.
Frequent rekeying of the HMAC TLV helps mitigate against this attack
but cannot prevent it.
However, as described in Section 6.2.1, there exist use cases where
the risk of service threat is of minimum concern and the HMAC TLV is
used primarily to validate that the source is permitted to use the
segment list in the SRH.
7.3. Topology Disclosure
The SRH may contains SIDs of some intermediate SR-nodes in the path
towards the destination, this reveals those addresses to attackers if
they are able to intercept packets containing SRH.
This is applicable within an SR Domain but the disclosure is less
relevant as an attacker has other means of learning topology.
For an SR Source node not directly connected to the SR Domain this
disclosure is applicable. While the segments within the SR domain
disclosed in SRH are protected by ingress filtering, they may be
learned by an attacker external to the SR Domain.
As described in Section 6.2.1, there exist use cases where the risk
of topology disclosure is of minimum concern when the HMAC TLV is
used primarily to validate that the source is permitted to use the
segment list in the SRH.
7.4. ICMP Generation
The generation of ICMPv6 error messages may be used to attempt
denial-of-service attacks by sending an error-causing destination
address or SRH in back-to-back packets. An implementation that
correctly follows Section 2.4 of [RFC4443] would be protected by the
ICMPv6 rate-limiting mechanism.
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8. IANA Considerations
This document makes the following registrations in the Internet
Protocol Version 6 (IPv6) Parameters "Routing Type" registry
maintained by IANA:
Suggested Description Reference
Value
----------------------------------------------------------
4 Segment Routing Header (SRH) This document
This document request IANA to create and maintain a new Registry:
"Segment Routing Header TLVs"
8.1. Segment Routing Header Flags Register
This document requests the creation of a new IANA managed registry to
identify SRH Flags Bits. The registration procedure is "Expert
Review" as defined in [RFC8126]. Suggested registry name is "Segment
Routing Header Flags". Flags is 8 bits, the following bits are
defined in this document:
Suggested Description Reference
Bit
-----------------------------------------------------
4 HMAC This document
8.2. Segment Routing Header TLVs Register
This document requests the creation of a new IANA managed registry to
identify SRH TLVs. The registration procedure is "Expert Review" as
defined in [RFC8126]. Suggested registry name is "Segment Routing
Header TLVs". A TLV is identified through an unsigned 8 bit
codepoint value. The following codepoints are defined in this
document:
Suggested Description Reference
Value
-----------------------------------------------------
5 HMAC TLV This document
128 Pad0 TLV This document
129 PadN TLV This document
9. Implementation Status
This section is to be removed prior to publishing as an RFC.
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9.1. Linux
Name: Linux Kernel v4.14
Status: Production
Implementation: adds SRH, performs END processing, supports HMAC TLV
Details: https://irtf.org/anrw/2017/anrw17-final3.pdf and
[I-D.filsfils-spring-srv6-interop]
9.2. Cisco Systems
Name: IOS XR and IOS XE
Status: Pre-production
Implementation: adds SRH, performs END processing, no TLV processing
Details: [I-D.filsfils-spring-srv6-interop]
9.3. FD.io
Name: VPP/Segment Routing for IPv6
Status: Production
Implementation: adds SRH, performs END processing, no TLV processing
Details: https://wiki.fd.io/view/VPP/Segment_Routing_for_IPv6 and
[I-D.filsfils-spring-srv6-interop]
9.4. Barefoot
Name: Barefoot Networks Tofino NPU
Status: Prototype
Implementation: performs END processing, no TLV processing
Details: [I-D.filsfils-spring-srv6-interop]
9.5. Juniper
Name: Juniper Networks Trio and vTrio NPU's
Status: Prototype & Experimental
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Implementation: SRH insertion mode, Process SID where SID is an
interface address, no TLV processing
9.6. Huawei
Name: Huawei Systems VRP Platform
Status: Production
Implementation: adds SRH, performs END processing, no TLV processing
10. Contributors
Kamran Raza, Darren Dukes, Brian Field, Daniel Bernier, Ida Leung,
Jen Linkova, Ebben Aries, Tomoya Kosugi, Eric Vyncke, David Lebrun,
Dirk Steinberg, Robert Raszuk, Dave Barach, John Brzozowski, Pierre
Francois, Nagendra Kumar, Mark Townsley, Christian Martin, Roberta
Maglione, James Connolly, Aloys Augustin contributed to the content
of this document.
11. Acknowledgements
The authors would like to thank Ole Troan, Bob Hinden, Ron Bonica,
Fred Baker, Brian Carpenter, Alexandru Petrescu, Punit Kumar Jaiswal,
and David Lebrun for their comments to this document.
12. References
12.1. Normative References
[FIPS180-4]
National Institute of Standards and Technology, "FIPS
180-4 Secure Hash Standard (SHS)", March 2012,
<http://csrc.nist.gov/publications/fips/fips180-4/
fips-180-4.pdf>.
[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>.
[RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
of Type 0 Routing Headers in IPv6", RFC 5095,
DOI 10.17487/RFC5095, December 2007,
<https://www.rfc-editor.org/info/rfc5095>.
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[RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain
of Interpretation", RFC 6407, DOI 10.17487/RFC6407,
October 2011, <https://www.rfc-editor.org/info/rfc6407>.
[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>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
12.2. Informative References
[I-D.filsfils-spring-srv6-interop]
Filsfils, C., Clad, F., Camarillo, P., Abdelsalam, A.,
Salsano, S., Bonaventure, O., Horn, J., and J. Liste,
"SRv6 interoperability report", draft-filsfils-spring-
srv6-interop-01 (work in progress), September 2018.
[I-D.filsfils-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J.,
daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
Network Programming", draft-filsfils-spring-srv6-network-
programming-05 (work in progress), July 2018.
[I-D.ietf-spring-segment-routing-mpls]
Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with MPLS
data plane", draft-ietf-spring-segment-routing-mpls-14
(work in progress), June 2018.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997,
<https://www.rfc-editor.org/info/rfc2104>.
[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>.
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[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[RFC4448] Martini, L., Ed., Rosen, E., El-Aawar, N., and G. Heron,
"Encapsulation Methods for Transport of Ethernet over MPLS
Networks", RFC 4448, DOI 10.17487/RFC4448, April 2006,
<https://www.rfc-editor.org/info/rfc4448>.
[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
DOI 10.17487/RFC5308, October 2008,
<https://www.rfc-editor.org/info/rfc5308>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
<https://www.rfc-editor.org/info/rfc6438>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[SRN] and , "Software Resolved Networks: Rethinking Enterprise
Networks with IPv6 Segment Routing", 2018,
<https://inl.info.ucl.ac.be/system/files/
sosr18-final15-embedfonts.pdf>.
Authors' Addresses
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Clarence Filsfils (editor)
Cisco Systems, Inc.
Brussels
BE
Email: cfilsfil@cisco.com
Stefano Previdi
Huawei
Italy
Email: stefano@previdi.net
John Leddy
Individual
US
Email: john@leddy.net
Satoru Matsushima
Softbank
Email: satoru.matsushima@g.softbank.co.jp
Daniel Voyer (editor)
Bell Canada
Email: daniel.voyer@bell.ca
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