draft-ietf-6man-segment-routing-header-00.txt   draft-ietf-6man-segment-routing-header-01.txt 
Network Working Group S. Previdi, Ed. Network Working Group S. Previdi, Ed.
Internet-Draft C. Filsfils Internet-Draft C. Filsfils
Intended status: Standards Track Cisco Systems, Inc. Intended status: Standards Track Cisco Systems, Inc.
Expires: June 16, 2016 B. Field Expires: September 19, 2016 B. Field
Comcast Comcast
I. Leung I. Leung
Rogers Communications Rogers Communications
J. Linkova J. Linkova
Google Google
E. Aries E. Aries
Facebook Facebook
T. Kosugi T. Kosugi
NTT NTT
E. Vyncke E. Vyncke
Cisco Systems, Inc. Cisco Systems, Inc.
D. Lebrun D. Lebrun
Universite Catholique de Louvain Universite Catholique de Louvain
December 14, 2015 March 18, 2016
IPv6 Segment Routing Header (SRH) IPv6 Segment Routing Header (SRH)
draft-ietf-6man-segment-routing-header-00 draft-ietf-6man-segment-routing-header-01
Abstract Abstract
Segment Routing (SR) allows a node to steer a packet through a Segment Routing (SR) allows a node to steer a packet through a
controlled set of instructions, called segments, by prepending a SR controlled set of instructions, called segments, by prepending an SR
header to the packet. A segment can represent any instruction, header to the packet. A segment can represent any instruction,
topological or service-based. SR allows to enforce a flow through topological or service-based. SR allows to enforce a flow through
any path (topological, or application/service based) while any path (topological, or application/service based) while
maintaining per-flow state only at the ingress node to the SR domain. maintaining per-flow state only at the ingress node to the SR domain.
Segment Routing can be applied to the IPv6 data plane with the Segment Routing can be applied to the IPv6 data plane with the
addition of a new type of Routing Extension Header. This draft addition of a new type of Routing Extension Header. This draft
describes the Segment Routing Extension Header Type and how it is describes the Segment Routing Extension Header Type and how it is
used by SR capable nodes. used by SR capable nodes.
skipping to change at page 2, line 15 skipping to change at page 2, line 15
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 16, 2016. This Internet-Draft will expire on September 19, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Segment Routing Documents . . . . . . . . . . . . . . . . . . 3 1. Segment Routing Documents . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Data Planes supporting Segment Routing . . . . . . . . . 4 2.1. Data Planes supporting Segment Routing . . . . . . . . . 4
2.2. Segment Routing (SR) Domain . . . . . . . . . . . . . . . 4 2.2. Segment Routing (SR) Domain . . . . . . . . . . . . . . . 4
2.2.1. SR Domain in a Service Provider Network . . . . . . . 5 2.2.1. SR Domain in a Service Provider Network . . . . . . . 5
2.2.2. SR Domain in a Overlay Network . . . . . . . . . . . 6 2.2.2. SR Domain in a Overlay Network . . . . . . . . . . . 6
3. Segment Routing Extension Header (SRH) . . . . . . . . . . . 7 3. Segment Routing Extension Header (SRH) . . . . . . . . . . . 8
3.1. SRH and RFC2460 behavior . . . . . . . . . . . . . . . . 11 3.1. SRH TLVs . . . . . . . . . . . . . . . . . . . . . . . . 10
4. SRH Procedures . . . . . . . . . . . . . . . . . . . . . . . 11 3.1.1. Ingress Node TLV . . . . . . . . . . . . . . . . . . 10
4.1. Segment Routing Node Functions . . . . . . . . . . . . . 11 3.1.2. Egress Node TLV . . . . . . . . . . . . . . . . . . . 11
4.1.1. Source SR Node . . . . . . . . . . . . . . . . . . . 12 3.1.3. Opaque Container TLV . . . . . . . . . . . . . . . . 12
4.1.2. SR Domain Ingress Node . . . . . . . . . . . . . . . 13 3.1.4. Padding TLV . . . . . . . . . . . . . . . . . . . . . 12
4.1.3. Transit Node . . . . . . . . . . . . . . . . . . . . 13 3.1.5. HMAC TLV . . . . . . . . . . . . . . . . . . . . . . 13
4.1.4. SR Segment Endpoint Node . . . . . . . . . . . . . . 13 3.2. SRH and RFC2460 behavior . . . . . . . . . . . . . . . . 14
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14 4. SRH Procedures . . . . . . . . . . . . . . . . . . . . . . . 15
5.1. Threat model . . . . . . . . . . . . . . . . . . . . . . 14 4.1. Source SR Node . . . . . . . . . . . . . . . . . . . . . 15
5.1.1. Source routing threats . . . . . . . . . . . . . . . 15 4.2. Transit Node . . . . . . . . . . . . . . . . . . . . . . 16
5.1.2. Applicability of RFC 5095 to SRH . . . . . . . . . . 15 4.3. SR Segment Endpoint Node . . . . . . . . . . . . . . . . 16
5.1.3. Service stealing threat . . . . . . . . . . . . . . . 16 5. Security Considerations . . . . . . . . . . . . . . . . . . . 17
5.1.4. Topology disclosure . . . . . . . . . . . . . . . . . 16 5.1. Threat model . . . . . . . . . . . . . . . . . . . . . . 17
5.1.5. ICMP Generation . . . . . . . . . . . . . . . . . . . 16 5.1.1. Source routing threats . . . . . . . . . . . . . . . 18
5.2. Security fields in SRH . . . . . . . . . . . . . . . . . 17 5.1.2. Applicability of RFC 5095 to SRH . . . . . . . . . . 18
5.2.1. Selecting a hash algorithm . . . . . . . . . . . . . 18 5.1.3. Service stealing threat . . . . . . . . . . . . . . . 19
5.2.2. Performance impact of HMAC . . . . . . . . . . . . . 18 5.1.4. Topology disclosure . . . . . . . . . . . . . . . . . 19
5.2.3. Pre-shared key management . . . . . . . . . . . . . . 19 5.1.5. ICMP Generation . . . . . . . . . . . . . . . . . . . 19
5.3. Deployment Models . . . . . . . . . . . . . . . . . . . . 20 5.2. Security fields in SRH . . . . . . . . . . . . . . . . . 20
5.3.1. Nodes within the SR domain . . . . . . . . . . . . . 20 5.2.1. Selecting a hash algorithm . . . . . . . . . . . . . 21
5.3.2. Nodes outside of the SR domain . . . . . . . . . . . 20 5.2.2. Performance impact of HMAC . . . . . . . . . . . . . 21
5.3.3. SR path exposure . . . . . . . . . . . . . . . . . . 21 5.2.3. Pre-shared key management . . . . . . . . . . . . . . 22
5.3.4. Impact of BCP-38 . . . . . . . . . . . . . . . . . . 21 5.3. Deployment Models . . . . . . . . . . . . . . . . . . . . 23
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 5.3.1. Nodes within the SR domain . . . . . . . . . . . . . 23
7. Manageability Considerations . . . . . . . . . . . . . . . . 22 5.3.2. Nodes outside of the SR domain . . . . . . . . . . . 23
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 22 5.3.3. SR path exposure . . . . . . . . . . . . . . . . . . 24
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22 5.3.4. Impact of BCP-38 . . . . . . . . . . . . . . . . . . 24
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
10.1. Normative References . . . . . . . . . . . . . . . . . . 22 7. Manageability Considerations . . . . . . . . . . . . . . . . 25
10.2. Informative References . . . . . . . . . . . . . . . . . 23 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
10.1. Normative References . . . . . . . . . . . . . . . . . . 25
10.2. Informative References . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
1. Segment Routing Documents 1. Segment Routing Documents
Segment Routing terminology is defined in Segment Routing terminology is defined in
[I-D.ietf-spring-segment-routing]. [I-D.ietf-spring-segment-routing].
Segment Routing use cases are described in Segment Routing use cases are described in
[I-D.ietf-spring-problem-statement] and [I-D.ietf-spring-problem-statement] and
[I-D.ietf-spring-ipv6-use-cases]. [I-D.ietf-spring-ipv6-use-cases].
Segment Routing protocol extensions are defined in Segment Routing protocol extensions are defined in
[I-D.ietf-isis-segment-routing-extensions], and [I-D.ietf-isis-segment-routing-extensions], and
[I-D.ietf-ospf-ospfv3-segment-routing-extensions]. [I-D.ietf-ospf-ospfv3-segment-routing-extensions].
2. Introduction 2. Introduction
Segment Routing (SR), defined in [I-D.ietf-spring-segment-routing], Segment Routing (SR), defined in [I-D.ietf-spring-segment-routing],
allows a node to steer a packet through a controlled set of allows a node to steer a packet through a controlled set of
instructions, called segments, by prepending a SR header to the instructions, called segments, by prepending an SR header to the
packet. A segment can represent any instruction, topological or packet. A segment can represent any instruction, topological or
service-based. SR allows to enforce a flow through any path service-based. SR allows to enforce a flow through any path
(topological or service/application based) while maintaining per-flow (topological or service/application based) while maintaining per-flow
state only at the ingress node to the SR domain. Segments can be state only at the ingress node to the SR domain. Segments can be
derived from different components: IGP, BGP, Services, Contexts, derived from different components: IGP, BGP, Services, Contexts,
Locators, etc. The list of segment forming the path is called the Locators, etc. The list of segment forming the path is called the
Segment List and is encoded in the packet header. Segment List and is encoded in the packet header.
SR allows the use of strict and loose source based routing paradigms SR allows the use of strict and loose source based routing paradigms
without requiring any additional signaling protocols in the without requiring any additional signaling protocols in the
skipping to change at page 5, line 22 skipping to change at page 5, line 25
Segment Routing Header (SRH) defined in this document equally applies Segment Routing Header (SRH) defined in this document equally applies
to all the above examples. to all the above examples.
While the source routing model defined in [RFC2460] doesn't mandate While the source routing model defined in [RFC2460] doesn't mandate
which node is allowed to insert (or modify) the SRH, it is assumed in which node is allowed to insert (or modify) the SRH, it is assumed in
this document that the SRH is inserted in the packet by its source. this document that the SRH is inserted in the packet by its source.
For example: For example:
o At the node originating the packet (host, server). o At the node originating the packet (host, server).
o At the ingress node of a SR domain where the ingress node receives o At the ingress node of an SR domain where the ingress node
an IPv6 packet and encapsulates it into an outer IPv6 header receives an IPv6 packet and encapsulates it into an outer IPv6
followed by a Segment Routing header. header followed by a Segment Routing header.
2.2.1. SR Domain in a Service Provider Network 2.2.1. SR Domain in a Service Provider Network
The following figure illustrates an SR domain consisting of an The following figure illustrates an SR domain consisting of an
operator's network infrastructure. operator's network infrastructure.
(-------------------------- Operator 1 -----------------------) (-------------------------- Operator 1 -----------------------)
( ) ( )
( (-----AS 1-----) (-------AS 2-------) (----AS 3-------) ) ( (-----AS 1-----) (-------AS 2-------) (----AS 3-------) )
( ( ) ( ) ( ) ) ( ( ) ( ) ( ) )
skipping to change at page 7, line 24 skipping to change at page 7, line 39
segment list of the SRH or in the DA, segments identifying other segment list of the SRH or in the DA, segments identifying other
overlay nodes. This implies that packets with an SRH may traverse overlay nodes. This implies that packets with an SRH may traverse
operator's networks but, obviously, these SRHs cannot contain an operator's networks but, obviously, these SRHs cannot contain an
address/segment of the transit operators 1, 2 and 3. The SRH address/segment of the transit operators 1, 2 and 3. The SRH
originated by the overlay can only contain address/segment under the originated by the overlay can only contain address/segment under the
administration of the overlay (e.g. address/segments supported by A1, administration of the overlay (e.g. address/segments supported by A1,
A2, A3, B1, B2, B3, C1,C2 or C3). A2, A3, B1, B2, B3, C1,C2 or C3).
In this model, the operator network nodes are transit nodes and, In this model, the operator network nodes are transit nodes and,
according to [RFC2460], MUST NOT inspect the routing extension header according to [RFC2460], MUST NOT inspect the routing extension header
since there are not the DA of the packet. since they are not the DA of the packet.
It is a common practice in operators networks to filter out, at It is a common practice in operators networks to filter out, at
ingress, any packet whose DA is the address of an internal node and ingress, any packet whose DA is the address of an internal node and
it is also possible that an operator would filter out any packet it is also possible that an operator would filter out any packet
destined to an internal address and having an extension header in it. destined to an internal address and having an extension header in it.
This common practice does not impact the SR-enabled traffic between This common practice does not impact the SR-enabled traffic between
the overlay nodes as the intermediate transit networks do never see a the overlay nodes as the intermediate transit networks do never see a
destination address belonging to their infrastructure. These SR- destination address belonging to their infrastructure. These SR-
enabled overlay packets will thus never be filtered by the transit enabled overlay packets will thus never be filtered by the transit
skipping to change at page 8, line 4 skipping to change at page 8, line 20
3. Segment Routing Extension Header (SRH) 3. Segment Routing Extension Header (SRH)
A new type of the Routing Header (originally defined in [RFC2460]) is A new type of the Routing Header (originally defined in [RFC2460]) is
defined: the Segment Routing Header (SRH) which has a new Routing defined: the Segment Routing Header (SRH) which has a new Routing
Type, (suggested value 4) to be assigned by IANA. Type, (suggested value 4) to be assigned by IANA.
The Segment Routing Header (SRH) is defined as follows: The Segment Routing Header (SRH) is defined as follows:
0 1 2 3 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 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 | | Next Header | Hdr Ext Len | Routing Type | Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| First Segment | Flags | HMAC Key ID | | First Segment | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Segment List[0] (128 bits IPv6 address) | | Segment List[0] (128 bits IPv6 address) |
| | | |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| | | |
... ...
| | | |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Segment List[n] (128 bits IPv6 address) | | Segment List[n] (128 bits IPv6 address) |
| | | |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | // //
| Policy List[0] (optional) | // Optional Type Length Value objects (variable) //
| | // //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Policy List[1] (optional) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Policy List[2] (optional) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Policy List[3] (optional) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| |
| HMAC (256 bits) |
| (optional) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where: where:
o Next Header: 8-bit selector. Identifies the type of header o Next Header: 8-bit selector. Identifies the type of header
immediately following the SRH. immediately following the SRH.
o Hdr Ext Len: 8-bit unsigned integer, is the length of the SRH o Hdr Ext Len: 8-bit unsigned integer, is the length of the SRH
header in 8-octet units, not including the first 8 octets. header in 8-octet units, not including the first 8 octets.
skipping to change at page 9, line 30 skipping to change at page 9, line 23
o First Segment: contains the index, in the Segment List, of the o First Segment: contains the index, in the Segment List, of the
first segment of the path which is in fact the last element of the first segment of the path which is in fact the last element of the
Segment List. Segment List.
o Flags: 16 bits of flags. Following flags are defined: o Flags: 16 bits of flags. Following flags are defined:
1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C|P|R|R| Policy Flags | |C|P|O|A|H| Unused |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
C-flag: Clean-up flag. Set when the SRH has to be removed from C-flag: Clean-up flag. Set when the SRH has to be removed from
the packet when packet reaches the last segment. the packet when the packet reaches the last segment.
P-flag: Protected flag. Set when the packet has been rerouted P-flag: Protected flag. Set when the packet has been rerouted
through FRR mechanism by a SR endpoint node. through FRR mechanism by an SR endpoint node.
R-flags. Reserved and for future use. O-flag: OAM flag. When set, it indicates that this packet is
an operations and management (OAM) packet.
Policy Flags. Define the type of the IPv6 addresses encoded A-flag: Alert flag. If present, it means important Type Length
into the Policy List (see below). The following have been Value (TLV) objects are present. See Section 3.1 for details
defined: on TLVs objects.
Bits 4-6: determine the type of the first element after the H-flag: HMAC flag. If set, the HMAC TLV is present and is
segment list. encoded as the last TLV of the SRH. In other words, the last
36 octets of the SRH represent the HMAC information. See
Section 3.1.5 for details on the HMAC TLV.
Bits 7-9: determine the type of the second element. Unused: Reserved and for future use. SHOULD be unset on
transmission and MUST be ignored on receipt.
Bits 10-12: determine the type of the third element. o RESERVED: SHOULD be unset on transmission and MUST be ignored on
receipt.
Bits 13-15: determine the type of the fourth element. 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 path. I.e., the first element of the
segment list (Segment List [0]) contains the last segment of the
path while the last segment of the Segment List (Segment List[n])
contains the first segment of the path. The index contained in
"Segments Left" identifies the current active segment.
The following values are used for the type: o Type Length Value (TLV) are described in Section 3.1.
0x0: Not present. If value is set to 0x0, it means the 3.1. SRH TLVs
element represented by these bits is not present.
0x1: SR Ingress. This section defines TLVs of the Segment Routing Header.
0x2: SR Egress. Type Length Value (TLV) contain optional information that may be used
by the node identified in the DA of the packet. It has to be noted
that the information carried in the TLVs is not intended to be used
by the routing layer. Typically, TLVs carry information that is
consumed by other components (e.g.: OAM) than the routing function.
0x3: Original Source Address. Each TLV has its own length, format and semantic. The code-point
allocated (by IANA) to each TLV defines both the format and the
semantic of the information carried in the TLV. Multiple TLVs may be
encoded in the same SRH.
0x4 to 0x7: currently unused and SHOULD be ignored on The "Length" field of the TLV is primarily used to skip the TLV while
reception. inspecting the SRH in case the node doesn't support or recognize the
TLV codepoint. The "Length" defines the TLV length in octets and not
including the "Type" and "Length" fields.
o HMAC Key ID and HMAC field, and their use are defined in The primary scope of TLVs is to give the receiver of the packet
Section 5. information related to the source routed path (e.g.: where the packet
entered in the SR domain and where it is expected to exit).
o Segment List[n]: 128 bit IPv6 addresses representing the nth Additional TLVs may be defined in the future.
segment in the Segment List. The Segment List is encoded starting
from the last segment of the path. I.e., the first element of the
segment list (Segment List [0]) contains the last segment of the
path while the last segment of the Segment List (Segment List[n])
contains the first segment of the path. The index contained in
"Segments Left" identifies the current active segment.
o Policy List. Optional addresses representing specific nodes in 3.1.1. Ingress Node TLV
the SR path such as:
SR Ingress: a 128 bit generic identifier representing the The Ingress Node TLV is optional and identifies the node this packet
ingress in the SR domain (i.e.: it needs not to be a valid IPv6 traversed when entered the SR domain. The Ingress Node TLV has
address). following format:
SR Egress: a 128 bit generic identifier representing the egress 0 1 2 3
in the SR domain (i.e.: it needs not to be a valid IPv6 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
address). +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | RESERVED | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Ingress Node (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Original Source Address: IPv6 address originally present in the where:
SA field of the packet.
The segments in the Policy List are encoded after the segment list o Type: to be assigned by IANA (suggested value 1).
and they are optional. If none are in the SRH, all bits of the
Policy List Flags MUST be set to 0x0.
3.1. SRH and RFC2460 behavior o Length: 18.
o RESERVED: 8 bits. SHOULD be unset on transmission and MUST be
ignored on receipt.
o Flags: 8 bits. No flags are defined in this document.
o Ingress Node: 128 bits. Defines the node where the packet is
expected to enter the SR domain. In the encapsulation case
described in Section 2.2.1, this information corresponds to the SA
of the encapsulating header.
3.1.2. Egress Node TLV
The Egress Node TLV is optional and identifies the node this packet
is expected to traverse when exiting the SR domain. The Egress Node
TLV has 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 | RESERVED | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Egress Node (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: to be assigned by IANA (suggested value 2).
o Length: 18.
o RESERVED: 8 bits. SHOULD be unset on transmission and MUST be
ignored on receipt.
o Flags: 8 bits. No flags are defined in this document.
o Egress Node: 128 bits. Defines the node where the packet is
expected to exit the SR domain. In the encapsulation case
described in Section 2.2.1, this information corresponds to the
last segment of the SRH in the encapsulating header.
3.1.3. Opaque Container TLV
The Opaque Container TLV is optional and 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 | RESERVED | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Opaque Container (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: to be assigned by IANA (suggested value 3).
o Length: 18.
o RESERVED: 8 bits. SHOULD be unset on transmission and MUST be
ignored on receipt.
o Flags: 8 bits. No flags are defined in this document.
o Opaque Container: 128 bits of opaque data not relevant for the
routing layer. Typically, this information is consumed by a non-
routing component of the node receiving the packet (i.e.: the node
in the DA).
3.1.4. Padding TLV
The Padding TLV is optional and with the purpose of aligning the SRH
on a 8 octet boundary. The Padding 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 | Padding (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Padding (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: to be assigned by IANA (suggested value 4).
o Length: 1 to 7
o Padding: from 1 to 7 octets of padding. Padding bits have no
semantic. They SHOULD be set to 0 on transmission and MUST be
ignored on receipt.
The following applies to the Padding TLV:
o Padding TLV is optional and MAY only appear once in the SRH. If
present, it MUST have a length between 1 and 7 octets.
o The Padding TLV is used in order to align the SRH total length on
the 8 octet boundary.
o When present, the Padding TLV MUST appear as the last TLV before
the HMAC TLV (if HMAC TLV is present).
o When present, the Padding TLV MUST have a length from 1 to 7 in
order to align the SRH total lenght on a 8-octet boundary.
o When a router inspecting the SRH encounters the Padding TLV, it
MUST assume that no other TLV (other than the HMAC) follow the
Padding TLV.
3.1.5. HMAC TLV
HMAC TLV is optional and contains the HMAC information. The HMAC 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 | 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. SHOULD be unset on transmission and MUST be
ignored on receipt.
o HMAC Key ID: 4 octets.
o HMAC: 32 octets.
o HMAC and HMAC Key ID usage is described in Section 5
The Following applies to the HMAC TLV:
o When present, the HMAC TLV MUST be encoded as the last TLV of the
SRH.
o If the HMAC TLV is present, the SRH H-Flag (Figure 4) MUST be set.
o When the H-flag is set in the SRH, the router inspecting the SRH
MUST find the HMAC TLV in the last 38 octets of the SRH.
3.2. SRH and RFC2460 behavior
The SRH being a new type of the Routing Header, it also has the same The SRH being a new type of the Routing Header, it also has the same
properties: properties:
SHOULD only appear once in the packet. SHOULD only appear once in the packet.
Only the router whose address is in the DA field of the packet Only the router whose address is in the DA field of the packet
header MUST inspect the SRH. header MUST inspect the SRH.
Therefore, Segment Routing in IPv6 networks implies that the segment Therefore, Segment Routing in IPv6 networks implies that the segment
skipping to change at page 11, line 27 skipping to change at page 15, line 17
DA of the packet. DA of the packet.
The DA of the packet changes at each segment termination/completion The DA of the packet changes at each segment termination/completion
and therefore the final DA of the packet MUST be encoded as the last and therefore the final DA of the packet MUST be encoded as the last
segment of the path. segment of the path.
4. SRH Procedures 4. SRH Procedures
In this section we describe the different procedures on the SRH. In this section we describe the different procedures on the SRH.
4.1. Segment Routing Node Functions 4.1. Source SR Node
SR packets are forwarded to segments endpoints (i.e.: the segment
endpoint is the node representing the segment and whose address is in
the segment list and in the DA of the packet when traveling in the
segment). The segment endpoint, when receiving a SR packet destined
to itself, does:
o Inspect the SRH.
o Determine the next active segment.
o Update the Segments Left field (or, if requested, remove the SRH
from the packet).
o Update the DA.
o Forward the packet to the next segment.
The procedures applied to the SRH are related to the node function.
Following nodes functions are defined:
Source SR Node.
SR Domain Ingress Node.
Transit Node.
SR Endpoint Node.
4.1.1. Source SR Node
A Source SR Node can be any node originating an IPv6 packet with its A Source SR Node can be any node originating an IPv6 packet with its
IPv6 and Segment Routing Headers. This include either: IPv6 and Segment Routing Headers. This include either:
A host originating an IPv6 packet A host originating an IPv6 packet.
A SR domain ingress router encapsulating a received IPv6 packet An SR domain ingress router encapsulating a received IPv6 packet
into an outer IPv6 header followed by a SRH into an outer IPv6 header followed by an SRH.
The mechanism through which a Segment List is derived is outside of The mechanism through which a Segment List is derived is outside of
the scope of this document. As an example, the Segment List may be the scope of this document. As an example, the Segment List may be
obtained through: obtained through:
Local path computation. Local path computation.
Local configuration. Local configuration.
Interaction with a centralized controller delivering the path. Interaction with a centralized controller delivering the path.
Any other mechanism. Any other mechanism.
The following are the steps of the creation of the SRH: The following are the steps of the creation of the SRH:
Next Header and Hdr Ext Len fields are set according to [RFC2460]. Next Header and Hdr Ext Len fields are set according to [RFC2460].
Routing Type field is set as TBD (SRH). Routing Type field is set as TBD (to be allocated by IANA,
suggested value 4).
The Segment List is built with the FIRST segment of the path The Segment List is built with the FIRST segment of the path
encoded in the LAST element of the Segment List. Subsequent encoded in the LAST element of the Segment List. Subsequent
segments are encoded on top of the first segment. Finally, the segments are encoded on top of the first segment. Finally, the
LAST segment of the path is encoded in the FIRST element of the LAST segment of the path is encoded in the FIRST element of the
Segment List. In other words, the Segment List is encoded in the Segment List. In other words, the Segment List is encoded in the
reverse order of the path. reverse order of the path.
The final DA of the packet is encoded as the last segment of the The final DA of the packet is encoded as the last segment of the
path (encoded in the first element of the Segment List). path (encoded in the first element of the Segment List).
skipping to change at page 13, line 11 skipping to change at page 16, line 20
The Segments Left field is set to n-1 where n is the number of The Segments Left field is set to n-1 where n is the number of
elements in the Segment List. elements in the Segment List.
The First Segment field is set to n-1 where n is the number of The First Segment field is set to n-1 where n is the number of
elements in the Segment List. elements in the Segment List.
The packet is sent out towards the first segment (i.e.: The packet is sent out towards the first segment (i.e.:
represented in the packet DA). represented in the packet DA).
HMAC and HMAC Key ID may be set according to Section 5. HMAC TLV may be set according to Section 5.
4.1.2. SR Domain Ingress Node
The SR Domain Ingress Node is the node where ingress policies are
applied and where the packet path (and processing) is determined.
After policies are applied and packet classification is done, the
result may be instantiated into a Segment List representing the path
the packet should take. In such case, the SR Domain Ingress Node
instantiate a new outer IPv6 header to which the SRH is appended
(with the computed Segment List). The procedures for the creation
and insertion of the new SRH are described in Section 4.1.1.
4.1.3. Transit Node 4.2. Transit Node
According to [RFC2460], the only node who is allowed to inspect the According to [RFC2460], the only node who is allowed to inspect the
Routing Extension Header (and therefore the SRH), is the node Routing Extension Header (and therefore the SRH), is the node
corresponding to the DA of the packet. Any other transit node MUST corresponding to the DA of the packet. Any other transit node MUST
NOT inspect the underneath routing header and MUST forward the packet NOT inspect the underneath routing header and MUST forward the packet
towards the DA and according to the IPv6 routing table. towards the DA and according to the IPv6 routing table.
In the example case described in Section 2.2.2, when SR capable nodes In the example case described in Section 2.2.2, when SR capable nodes
are connected through an overlay spanning multiple third-party are connected through an overlay spanning multiple third-party
infrastructure, it is safe to send SRH packets (i.e.: packet having a infrastructure, it is safe to send SRH packets (i.e.: packet having a
Segment Routing Header) between each other overlay/SR-capable nodes Segment Routing Header) between each other overlay/SR-capable nodes
as long as the segment list does not include any of the transit as long as the segment list does not include any of the transit
provider nodes. In addition, as a generic security measure, any provider nodes. In addition, as a generic security measure, any
service provider will block any packet destined to one of its service provider will block any packet destined to one of its
internal routers, especially if these packets have an extended header internal routers, especially if these packets have an extended header
in it. in it.
4.1.4. SR Segment Endpoint Node 4.3. SR Segment Endpoint Node
The SR segment endpoint node is the node whose address is in the DA. The SR segment endpoint node is the node whose address is in the DA.
The segment endpoint node inspects the SRH and does: The segment endpoint node inspects the SRH and does:
1. IF DA = myself (segment endpoint) 1. IF DA = myself (segment endpoint)
2. IF Segments Left > 0 THEN 2. IF Segments Left > 0 THEN
decrement Segments Left decrement Segments Left
update DA with Segment List[Segments Left] update DA with Segment List[Segments Left]
3. IF Segments Left == 0 THEN 3. IF Segments Left == 0 THEN
IF Clean-up bit is set THEN remove the SRH IF Clean-up bit is set THEN remove the SRH
skipping to change at page 14, line 23 skipping to change at page 17, line 23
5. Forward the packet out 5. Forward the packet out
5. Security Considerations 5. Security Considerations
This section analyzes the security threat model, the security issues This section analyzes the security threat model, the security issues
and proposed solutions related to the new Segment Routing Header. and proposed solutions related to the new Segment Routing Header.
The Segment Routing Header (SRH) is simply another type of the The Segment Routing Header (SRH) is simply another type of the
routing header as described in RFC 2460 [RFC2460] and is: routing header as described in RFC 2460 [RFC2460] and is:
o inserted by a SR edge router when entering the segment routing o inserted by an SR edge router when entering the segment routing
domain or by the originating host itself. The source host can domain or by the originating host itself. The source host can
even be outside the SR domain; even be outside the SR domain;
o inspected and acted upon when reaching the destination address of o inspected and acted upon when reaching the destination address of
the IP header per RFC 2460 [RFC2460]. the IP header per RFC 2460 [RFC2460].
Per RFC2460 [RFC2460], routers on the path that simply forward an Per RFC2460 [RFC2460], routers on the path that simply forward an
IPv6 packet (i.e. the IPv6 destination address is none of theirs) IPv6 packet (i.e. the IPv6 destination address is none of theirs)
will never inspect and process the content of SRH. Routers whose one will never inspect and process the content of the SRH. Routers whose
interface IPv6 address equals the destination address field of the one interface IPv6 address equals the destination address field of
IPv6 packet MUST to parse the SRH and, if supported and if the local the IPv6 packet MUST parse the SRH and, if supported and if the local
configuration allows it, MUST act accordingly to the SRH content. configuration allows it, MUST act accordingly to the SRH content.
According to RFC2460 [RFC2460], the default behavior of a non SR- According to RFC2460 [RFC2460], the default behavior of a non SR-
capable router upon receipt of an IPv6 packet with SRH destined to an capable router upon receipt of an IPv6 packet with SRH destined to an
address of its, is to: address of its, is to:
o ignore the SRH completely if the Segment Left field is 0 and o ignore the SRH completely if the Segment Left field is 0 and
proceed to process the next header in the IPv6 packet; proceed to process the next header in the IPv6 packet;
o discard the IPv6 packet if Segment Left field is greater than 0, o discard the IPv6 packet if Segment Left field is greater than 0,
it MAY send a Parameter Problem ICMP message back to the Source it MAY send a Parameter Problem ICMP message back to the Source
Address. Address.
5.1. Threat model 5.1. Threat model
5.1.1. Source routing threats 5.1.1. Source routing threats
Using a SRH is similar to source routing, therefore it has some well- Using an SRH is similar to source routing, therefore it has some
known security issues as described in RFC4942 [RFC4942] section 2.1.1 well-known security issues as described in RFC4942 [RFC4942] section
and RFC5095 [RFC5095]: 2.1.1 and RFC5095 [RFC5095]:
o amplification attacks: where a packet could be forged in such a o amplification attacks: where a packet could be forged in such a
way to cause looping among a set of SR-enabled routers causing way to cause looping among a set of SR-enabled routers causing
unnecessary traffic, hence a Denial of Service (DoS) against unnecessary traffic, hence a Denial of Service (DoS) against
bandwidth; bandwidth;
o reflection attack: where a hacker could force an intermediate node o reflection attack: where a hacker could force an intermediate node
to appear as the immediate attacker, hence hiding the real to appear as the immediate attacker, hence hiding the real
attacker from naive forensic; attacker from naive forensic;
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Routing Type and not limited to SRH packets. So, it is not specific Routing Type and not limited to SRH packets. So, it is not specific
to SRH and the usual rate limiting for ICMP generation is required to SRH and the usual rate limiting for ICMP generation is required
anyway for any IPv6 implementation and has been implemented and anyway for any IPv6 implementation and has been implemented and
deployed for many years. deployed for many years.
5.2. Security fields in SRH 5.2. Security fields in SRH
This section summarizes the use of specific fields in the SRH. They This section summarizes the use of specific fields in the SRH. They
are based on a key-hashed message authentication code (HMAC). are based on a key-hashed message authentication code (HMAC).
The security-related fields in SRH are: The security-related fields in the SRH are instantiated by the HMAC
TLV, containing:
o HMAC Key-id, 8 bits wide; o HMAC Key-id, 16 bits wide;
o HMAC, 256 bits wide (optional, exists only if HMAC Key-id is not o HMAC, 256 bits wide (optional, exists only if HMAC Key-id is not
0). 0).
The HMAC field is the output of the HMAC computation (per RFC 2104 The HMAC field is the output of the HMAC computation (per RFC 2104
[RFC2104]) using a pre-shared key identified by HMAC Key-id and of [RFC2104]) using a pre-shared key identified by HMAC Key-id and of
the text which consists of the concatenation of: the text which consists of the concatenation of:
o the source IPv6 address; o the source IPv6 address;
o First Segment field; o First Segment field;
o an octet whose bit-0 is the clean-up bit flag and others are 0; o an octet whose bit-0 is the clean-up bit flag and others are 0;
o HMAC Key-id; o HMAC Key-id;
o all addresses in the Segment List. o all addresses in the Segment List.
The purpose of the HMAC field is to verify the validity, the The purpose of the HMAC TLV is to verify the validity, the integrity
integrity and the authorization of the SRH itself. If an outsider of and the authorization of the SRH itself. If an outsider of the SR
the SR domain does not have access to a current pre-shared secret, domain does not have access to a current pre-shared secret, then it
then it cannot compute the right HMAC field and the first SR router cannot compute the right HMAC field and the first SR router on the
on the path processing the SRH and configured to check the validity path processing the SRH and configured to check the validity of the
of the HMAC will simply reject the packet. HMAC will simply reject the packet.
The HMAC field is located at the end of the SRH simply because only The HMAC TLV is located at the end of the SRH simply because only the
the router on the ingress of the SR domain needs to process it, then router on the ingress of the SR domain needs to process it, then all
all other SR nodes can ignore it (based on local policy) because they other SR nodes can ignore it (based on local policy) because they
trust the upstream router. This is to speed up forwarding operations trust the upstream router. This is to speed up forwarding operations
because SR routers which do not validate the SRH do not need to parse because SR routers which do not validate the SRH do not need to parse
the SRH until the end. the SRH until the end.
The HMAC Key-id field allows for the simultaneous existence of The HMAC Key-id field allows for the simultaneous existence of
several hash algorithms (SHA-256, SHA3-256 ... or future ones) as 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 well as pre-shared keys. The HMAC Key-id field is opaque, i.e., it
has neither syntax nor semantic except as an index to the right has neither syntax nor semantic except as an index to the right
combination of pre-shared key and hash algorithm and except that a combination of pre-shared key and hash algorithm and except that a
value of 0 means that there is no HMAC field. Having a HMAC Key-id value of 0 means that there is no HMAC field. Having an HMAC Key-id
field allows for pre-shared key roll-over when two pre-shared keys field allows for pre-shared key roll-over when two pre-shared keys
are supported for a while when all SR nodes converged to a fresher are supported for a while when all SR nodes converged to a fresher
pre-shared key. It could also allow for interoperation among pre-shared key. It could also allow for interoperation among
different SR domains if allowed by local policy and assuming a different SR domains if allowed by local policy and assuming a
collision-free HMAC Key Id allocation. collision-free HMAC Key Id allocation.
When a specific SRH is linked to a time-related service (such as When a specific SRH is linked to a time-related service (such as
turbo-QoS for a 1-hour period) where the DA, Segment ID (SID) are turbo-QoS for a 1-hour period) where the DA, Segment ID (SID) are
identical, then it is important to refresh the shared-secret identical, then it is important to refresh the shared-secret
frequently as the HMAC validity period expires only when the HMAC frequently as the HMAC validity period expires only when the HMAC
Key-id and its associated shared-secret expires. Key-id and its associated shared-secret expires.
5.2.1. Selecting a hash algorithm 5.2.1. Selecting a hash algorithm
The HMAC field in the SRH is 256 bit wide. Therefore, the HMAC MUST The HMAC field in the HMAC TLV is 256 bit wide. Therefore, the HMAC
be based on a hash function whose output is at least 256 bits. If MUST be based on a hash function whose output is at least 256 bits.
the output of the hash function is 256, then this output is simply If the output of the hash function is 256, then this output is simply
inserted in the HMAC field. If the output of the hash function is inserted in the HMAC field. If the output of the hash function is
larger than 256 bits, then the output value is truncated to 256 by larger than 256 bits, then the output value is truncated to 256 by
taking the least-significant 256 bits and inserting them in the HMAC taking the least-significant 256 bits and inserting them in the HMAC
field. field.
SRH implementations can support multiple hash functions but MUST SRH implementations can support multiple hash functions but MUST
implement SHA-2 [FIPS180-4] in its SHA-256 variant. implement SHA-2 [FIPS180-4] in its SHA-256 variant.
NOTE: SHA-1 is currently used by some early implementations used for NOTE: SHA-1 is currently used by some early implementations used for
quick interoperations testing, the 160-bit hash value must then be quick interoperations testing, the 160-bit hash value must then be
right-hand padded with 96 bits set to 0. The authors understand that right-hand padded with 96 bits set to 0. The authors understand that
this is not secure but is ok for limited tests. this is not secure but is ok for limited tests.
5.2.2. Performance impact of HMAC 5.2.2. Performance impact of HMAC
While adding a HMAC to each and every SR packet increases the While adding an HMAC to each and every SR packet increases the
security, it has a performance impact. Nevertheless, it must be security, it has a performance impact. Nevertheless, it must be
noted that: noted that:
o the HMAC field is used only when SRH is inserted by a device (such o the HMAC field is used only when SRH is inserted by a device (such
as a home set-up box) which is outside of the segment routing as a home set-up box) which is outside of the segment routing
domain. If the SRH is added by a router in the trusted segment domain. If the SRH is added by a router in the trusted segment
routing domain, then, there is no need for a HMAC field, hence no routing domain, then, there is no need for an HMAC field, hence no
performance impact. performance impact.
o when present, the HMAC field MUST only be checked and validated by o when present, the HMAC field MUST only be checked and validated by
the first router of the segment routing domain, this router is the first router of the segment routing domain, this router is
named 'validating SR router'. Downstream routers may not inspect named 'validating SR router'. Downstream routers may not inspect
the HMAC field. the HMAC field.
o this validating router can also have a cache of <IPv6 header + o this validating router can also have a cache of <IPv6 header +
SRH, HMAC field value> to improve the performance. It is not the SRH, HMAC field value> to improve the performance. It is not the
same use case as in IPsec where HMAC value was unique per packet, same use case as in IPsec where HMAC value was unique per packet,
skipping to change at page 20, line 9 skipping to change at page 23, line 9
o dynamically using a trusted key distribution such as [RFC6407] o dynamically using a trusted key distribution such as [RFC6407]
The intent of this document is NOT to define yet-another-key- The intent of this document is NOT to define yet-another-key-
distribution-protocol. distribution-protocol.
5.3. Deployment Models 5.3. Deployment Models
5.3.1. Nodes within the SR domain 5.3.1. Nodes within the SR domain
A SR domain is defined as a set of interconnected routers where all An SR domain is defined as a set of interconnected routers where all
routers at the perimeter are configured to insert and act on SRH. routers at the perimeter are configured to insert and act on SRH.
Some routers inside the SR domain can also act on SRH or simply Some routers inside the SR domain can also act on SRH or simply
forward IPv6 packets. forward IPv6 packets.
The routers inside a SR domain can be trusted to generate SRH and to The routers inside an SR domain can be trusted to generate SRH and to
process SRH received on interfaces that are part of the SR domain. process SRH received on interfaces that are part of the SR domain.
These nodes MUST drop all SRH packets received on an interface that These nodes MUST drop all SRH packets received on an interface that
is not part of the SR domain and containing a SRH whose HMAC field is not part of the SR domain and containing an SRH whose HMAC field
cannot be validated by local policies. This includes obviously cannot be validated by local policies. This includes obviously
packet with a SRH generated by a non-cooperative SR domain. packet with an SRH generated by a non-cooperative SR domain.
If the validation fails, then these packets MUST be dropped, ICMP If the validation fails, then these packets MUST be dropped, ICMP
error messages (parameter problem) SHOULD be generated (but rate error messages (parameter problem) SHOULD be generated (but rate
limited) and SHOULD be logged. limited) and SHOULD be logged.
5.3.2. Nodes outside of the SR domain 5.3.2. Nodes outside of the SR domain
Nodes outside of the SR domain cannot be trusted for physical Nodes outside of the SR domain cannot be trusted for physical
security; hence, they need to request by some trusted means (outside security; hence, they need to request by some trusted means (outside
of the scope of this document) a complete SRH for each new connection of the scope of this document) a complete SRH for each new connection
(i.e. new destination address). The received SRH MUST include a HMAC (i.e. new destination address). The received SRH MUST include an
Key-id and HMAC field which is computed correctly (see Section 5.2). HMAC TLV which is computed correctly (see Section 5.2).
When an outside node sends a packet with an SRH and towards a SR When an outside node sends a packet with an SRH and towards an SR
domain ingress node, the packet MUST contain the HMAC Key-id and HMAC domain ingress node, the packet MUST contain the HMAC TLV (with a
field and the the destination address MUST be an address of a SR Key-id and HMAC fields) and the the destination address MUST be an
domain ingress node . address of an SR domain ingress node .
The ingress SR router, i.e., the router with an interface address The ingress SR router, i.e., the router with an interface address
equals to the destination address, MUST verify the HMAC field with equals to the destination address, MUST verify the HMAC TLV.
respect to the HMAC Key-id.
If the validation is successful, then the packet is simply forwarded If the validation is successful, then the packet is simply forwarded
as usual for a SR packet. As long as the packet travels within the as usual for an SR packet. As long as the packet travels within the
SR domain, no further HMAC check needs to be done. Subsequent SR domain, no further HMAC check needs to be done. Subsequent
routers in the SR domain MAY verify the HMAC field when they process routers in the SR domain MAY verify the HMAC TLV when they process
the SRH (i.e. when they are the destination). the SRH (i.e. when they are the destination).
If the validation fails, then this packet MUST be dropped, an ICMP If the validation fails, then this packet MUST be dropped, an ICMP
error message (parameter problem) SHOULD be generated (but rate error message (parameter problem) SHOULD be generated (but rate
limited) and SHOULD be logged. limited) and SHOULD be logged.
5.3.3. SR path exposure 5.3.3. SR path exposure
As the intermediate SR nodes addresses appears in the SRH, if this As the intermediate SR nodes addresses appears in the SRH, if this
SRH is visible to an outsider then he/she could reuse this knowledge SRH is visible to an outsider then he/she could reuse this knowledge
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5.3.4. Impact of BCP-38 5.3.4. Impact of BCP-38
BCP-38 [RFC2827], also known as "Network Ingress Filtering", checks BCP-38 [RFC2827], also known as "Network Ingress Filtering", checks
whether the source address of packets received on an interface is whether the source address of packets received on an interface is
valid for this interface. The use of loose source routing such as valid for this interface. The use of loose source routing such as
SRH forces packets to follow a path which differs from the expected SRH forces packets to follow a path which differs from the expected
routing. Therefore, if BCP-38 was implemented in all routers inside routing. Therefore, if BCP-38 was implemented in all routers inside
the SR domain, then SR packets could be received by an interface the SR domain, then SR packets could be received by an interface
which is not expected one and the packets could be dropped. which is not expected one and the packets could be dropped.
As a SR domain is usually a subset of one administrative domain, and As an SR domain is usually a subset of one administrative domain, and
as BCP-38 is only deployed at the ingress routers of this as BCP-38 is only deployed at the ingress routers of this
administrative domain and as packets arriving at those ingress administrative domain and as packets arriving at those ingress
routers have been normally forwarded using the normal routing routers have been normally forwarded using the normal routing
information, then there is no reason why this ingress router should information, then there is no reason why this ingress router should
drop the SRH packet based on BCP-38. Routers inside the domain drop the SRH packet based on BCP-38. Routers inside the domain
commonly do not apply BCP-38; so, this is not a problem. commonly do not apply BCP-38; so, this is not a problem.
6. IANA Considerations 6. IANA Considerations
This document makes the following registrations in the Internet This document makes the following registrations in the Internet
Protocol Version 6 (IPv6) Parameters "Routing Type" registry Protocol Version 6 (IPv6) Parameters "Routing Type" registry
maintained by IANA: maintained by IANA:
Suggested Description Reference Suggested Description Reference
Value Value
---------------------------------------------------------- ----------------------------------------------------------
4 Segment Routing Header (SRH) This document 4 Segment Routing Header (SRH) This document
In addition, this document request IANA to create and maintain a new
Registry: "Segment Routing Header Type-Value Objects". The following
code-points are requested from the registry:
Registry: Segment Routing Header Type-Value Objects
Suggested Description Reference
Value
-----------------------------------------------------
1 Ingress Node TLV This document
2 Egress Node TLV This document
3 Opaque Container TLV This document
4 Padding TLV This document
5 HMAC TLV This document
7. Manageability Considerations 7. Manageability Considerations
TBD TBD
8. Contributors 8. Contributors
Dave Barach, John Leddy, John Brzozowski, Pierre Francois, Nagendra Dave Barach, John Leddy, John Brzozowski, Pierre Francois, Nagendra
Kumar, Mark Townsley, Christian Martin, Roberta Maglione, James Kumar, Mark Townsley, Christian Martin, Roberta Maglione, James
Connolly, Aloys Augustin contributed to the content of this document. Connolly, Aloys Augustin contributed to the content of this document.
skipping to change at page 23, line 15 skipping to change at page 26, line 33
[RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain [RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain
of Interpretation", RFC 6407, DOI 10.17487/RFC6407, of Interpretation", RFC 6407, DOI 10.17487/RFC6407,
October 2011, <http://www.rfc-editor.org/info/rfc6407>. October 2011, <http://www.rfc-editor.org/info/rfc6407>.
10.2. Informative References 10.2. Informative References
[I-D.ietf-isis-segment-routing-extensions] [I-D.ietf-isis-segment-routing-extensions]
Previdi, S., Filsfils, C., Bashandy, A., Gredler, H., Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
Litkowski, S., Decraene, B., and J. Tantsura, "IS-IS Litkowski, S., Decraene, B., and J. Tantsura, "IS-IS
Extensions for Segment Routing", draft-ietf-isis-segment- Extensions for Segment Routing", draft-ietf-isis-segment-
routing-extensions-05 (work in progress), June 2015. routing-extensions-06 (work in progress), December 2015.
[I-D.ietf-ospf-ospfv3-segment-routing-extensions] [I-D.ietf-ospf-ospfv3-segment-routing-extensions]
Psenak, P., Previdi, S., Filsfils, C., Gredler, H., Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
Shakir, R., Henderickx, W., and J. Tantsura, "OSPFv3 Shakir, R., Henderickx, W., and J. Tantsura, "OSPFv3
Extensions for Segment Routing", draft-ietf-ospf-ospfv3- Extensions for Segment Routing", draft-ietf-ospf-ospfv3-
segment-routing-extensions-03 (work in progress), June segment-routing-extensions-04 (work in progress), December
2015. 2015.
[I-D.ietf-spring-ipv6-use-cases] [I-D.ietf-spring-ipv6-use-cases]
Brzozowski, J., Leddy, J., Leung, I., Previdi, S., Brzozowski, J., Leddy, J., Leung, I., Previdi, S.,
Townsley, W., Martin, C., Filsfils, C., and R. Maglione, Townsley, W., Martin, C., Filsfils, C., and R. Maglione,
"IPv6 SPRING Use Cases", draft-ietf-spring-ipv6-use- "IPv6 SPRING Use Cases", draft-ietf-spring-ipv6-use-
cases-05 (work in progress), September 2015. cases-06 (work in progress), March 2016.
[I-D.ietf-spring-problem-statement] [I-D.ietf-spring-problem-statement]
Previdi, S., Filsfils, C., Decraene, B., Litkowski, S., Previdi, S., Filsfils, C., Decraene, B., Litkowski, S.,
Horneffer, M., and r. rjs@rob.sh, "SPRING Problem Horneffer, M., and R. Shakir, "SPRING Problem Statement
Statement and Requirements", draft-ietf-spring-problem- and Requirements", draft-ietf-spring-problem-statement-07
statement-05 (work in progress), October 2015. (work in progress), March 2016.
[I-D.ietf-spring-resiliency-use-cases] [I-D.ietf-spring-resiliency-use-cases]
Francois, P., Filsfils, C., Decraene, B., and r. Francois, P., Filsfils, C., Decraene, B., and R. Shakir,
rjs@rob.sh, "Use-cases for Resiliency in SPRING", draft- "Use-cases for Resiliency in SPRING", draft-ietf-spring-
ietf-spring-resiliency-use-cases-02 (work in progress), resiliency-use-cases-02 (work in progress), December 2015.
December 2015.
[I-D.ietf-spring-segment-routing] [I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Decraene, B., Litkowski, S., Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
and r. rjs@rob.sh, "Segment Routing Architecture", draft- and R. Shakir, "Segment Routing Architecture", draft-ietf-
ietf-spring-segment-routing-06 (work in progress), October spring-segment-routing-07 (work in progress), December
2015. 2015.
[I-D.ietf-spring-segment-routing-mpls] [I-D.ietf-spring-segment-routing-mpls]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., rjs@rob.sh, r., Tantsura, Litkowski, S., Horneffer, M., Shakir, R., Tantsura, J.,
J., and E. Crabbe, "Segment Routing with MPLS data plane", and E. Crabbe, "Segment Routing with MPLS data plane",
draft-ietf-spring-segment-routing-mpls-02 (work in draft-ietf-spring-segment-routing-mpls-03 (work in
progress), October 2015. progress), February 2016.
[RFC1940] Estrin, D., Li, T., Rekhter, Y., Varadhan, K., and D. [RFC1940] Estrin, D., Li, T., Rekhter, Y., Varadhan, K., and D.
Zappala, "Source Demand Routing: Packet Format and Zappala, "Source Demand Routing: Packet Format and
Forwarding Specification (Version 1)", RFC 1940, Forwarding Specification (Version 1)", RFC 1940,
DOI 10.17487/RFC1940, May 1996, DOI 10.17487/RFC1940, May 1996,
<http://www.rfc-editor.org/info/rfc1940>. <http://www.rfc-editor.org/info/rfc1940>.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997, DOI 10.17487/RFC2104, February 1997,
 End of changes. 72 change blocks. 
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