wdiff draft-ietf-6man-segment-routing-header-14.txt draft-ietf-6man-segment-routing-header-15.txt

Network Working Group C. Filsfils, Ed.
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track S. Previdi
Expires: December 30, 2018 Individual April 25, 2019 Huawei
J. Leddy
Comcast
Individual
S. Matsushima
Softbank
D. Voyer, Ed.
Bell Canada
June 28,
October 22, 2018

IPv6 Segment Routing Header (SRH)
draft-ietf-6man-segment-routing-header-14
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 December 30, 2018. April 25, 2019.

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 . . . . . . . . . . . . . . . . . . . . . . 8 7
3. SR Nodes . . . . . . . . . . . . . . . . . . . . . . . . . . 9 10
3.1. Source SR Node . . . . . . . . . . . . . . . . . . . . . 9 10
3.2. Transit Node . . . . . . . . . . . . . . . . . . . . . . 9 11
3.3. SR Segment Endpoint Node . . . . . . . . . . . . . . . . 9 11
4. Packet Processing . . . . . . . . . . . . . . . . . . . . . . 9 11
4.1. Source SR Node . . . . . . . . . . . . . . . . . . . . . 9 11
4.1.1. Reduced SRH . . . . . . . . . . . . . . . . . . . . . 10 12
4.2. Transit Node . . . . . . . . . . . . . . . . . . . . . . 10 12
4.3. SR Segment Endpoint Node . . . . . . . . . . . . . . . . 11 12
4.3.1. FIB Entry Is Locally Instantiated SRv6 END SID . . . 11 12
4.3.2. FIB Entry is a Local Interface . . . . . . . . . . . 13 14
4.3.3. FIB Entry Is A Non-Local Route . . . . . . . . . . . 13 15
4.3.4. FIB Entry Is A No Match . . . . . . . . . . . . . . . 13 15
4.3.5. Load Balancing and ECMP . . . . . . . . . . . . . . . 13 15
5. Illustrations . . . . . . . . . . . . . . . . . . . . . . . . 14 15
5.1. Abstract Representation of an SRH . . . . . . . . . . . . 14 15
5.2. Example Topology . . . . . . . . . . . . . . . . . . . . 15 16
5.3. Source SR Node . . . . . . . . . . . . . . . . . . . . . 15 17
5.3.1. Intra SR Domain Packet . . . . . . . . . . . . . . . 15 17
5.3.2. Transit Packet Through SR Domain . . . . . . . . . . 16 17
5.4. Transit Node . . . . . . . . . . . . . . . . . . . . . . 16 18
5.5. SR Segment Endpoint Node . . . . . . . . . . . . . . . . 16 18
6. Security Considerations . . . . . . . . . . . . . . Deployment Models . . . . . 17
6.1. Threat model . . . . . . . . . . . . . . . . . 18
6.1. Nodes Within the SR domain . . . . . 17
6.1.1. Source routing threats . . . . . . . . . . 18
6.2. Nodes Outside the SR Domain . . . . . 17
6.1.2. Applicability of RFC 5095 to SRH . . . . . . . . . . 18
6.1.3. Service stealing threat . . . . . . . .
6.2.1. SR Source Nodes Not Directly Connected . . . . . . . 19
6.1.4. Topology disclosure . . . . . . . .

7. Security Considerations . . . . . . . . . 19
6.1.5. ICMP Generation . . . . . . . . . . 20
7.1. Source Routing Attacks . . . . . . . . . 19
6.2. Security fields in SRH . . . . . . . . 21
7.2. Service Theft . . . . . . . . . 19
6.2.1. Selecting a hash algorithm . . . . . . . . . . . . . 21
6.2.2. Performance impact of HMAC . . . . . . . .
7.3. Topology Disclosure . . . . . 21
6.2.3. Pre-shared key management . . . . . . . . . . . . . . 22
6.3. Deployment Models . . . . . . . . . . . .
7.4. ICMP Generation . . . . . . . . 22
6.3.1. Nodes within the SR domain . . . . . . . . . . . . . 22
6.3.2. Nodes outside of the SR domain . . . . . . . .
8. IANA Considerations . . . 22
6.3.3. SR path exposure . . . . . . . . . . . . . . . . . . 23
6.3.4. Impact of BCP-38 . . . . . . . .
8.1. Segment Routing Header Flags Register . . . . . . . . . . 23
7. IANA Considerations . . . . . .
8.2. Segment Routing Header TLVs Register . . . . . . . . . . 23
9. Implementation Status . . . . . 24
7.1. Segment Routing Header Flags Register . . . . . . . . . . 24
7.2. Segment Routing Header TLVs Register . . . . . 23
9.1. Linux . . . . . 24
8. Implementation Status . . . . . . . . . . . . . . . . . . . . 25
8.1. Linux . 24
9.2. Cisco Systems . . . . . . . . . . . . . . . . . . . . . . 24
9.3. FD.io . . . 25
8.2. Cisco Systems . . . . . . . . . . . . . . . . . . . . . . 25
8.3. FD.io . 24
9.4. Barefoot . . . . . . . . . . . . . . . . . . . . . . . . 24
9.5. Juniper . 25
8.4. Barefoot . . . . . . . . . . . . . . . . . . . . . . . . 25
8.5. Juniper 24
9.6. Huawei . . . . . . . . . . . . . . . . . . . . . . . . . 26
9. 25
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 26
10. 25
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26
11. 25
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
11.1. 25
12.1. Normative References . . . . . . . . . . . . . . . . . . 26
11.2. 25
12.2. Informative References . . . . . . . . . . . . . . . . . 27 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29 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 [I-D.ietf-spring-segment-routing] [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
[I-D.ietf-spring-segment-routing].
[RFC8402]. Specifically, these terms: Segment Routing, SR Domain,
SRv6, Segment ID (SID), SRv6 SID, Active Segment, and SR Policy.

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.

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.

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.

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

HMAC

The keyed Hashed Message Authentication Code (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. MUST be 0 on transmission and ignored on
receipt.

o HMAC Key ID: A 4 octets. 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.

o 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 usage is described

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)
* SRH: Segments Left (1 octet)

* SRH: Last Entry (1 octet)

* SRH: Flags (1 octet)

* SRH: HMAC Key-id (4 octets)

* SRH: all addresses in Section 6 the Segment List (variable octets)

The Following applies HMAC digest is truncated to 32 octets and placed in the HMAC TLV:

o
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.

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.

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 6. 7.

The packet is forwarded toward the packet's Destination Address
(the first segment).

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.

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.
}
}
}
}

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 destination unreachable 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.

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.

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
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)

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. Security Considerations

This section analyzes the security threat model, the security issues
and proposed solutions related to the new Segment Routing Header.

The Segment Routing Header (SRH) is simply another type of Deployment Models

6.1. Nodes Within the
Routing Header as described in [RFC8200] and is:

o Added by an SR edge router when entering the segment routing domain or by the originating host itself. The source host can
even be outside the

SR domain;

o inspected and acted upon when reaching the destination address of
the IP header per [RFC8200].

Per [RFC8200], routers on the path that simply forward Source Nodes within an IPv6 packet
(i.e. the IPv6 destination address is none of theirs) will never
inspect and process the content of the SRH. Routers whose FIB
contains a locally instantiated SRv6 SID equal to the destination
address field of the IPv6 packet MUST parse the SRH if present, and
if supported and if the local configuration allows it, MUST act
accordingly SR Domain are trusted to the SRH content.

As specified in [RFC8200], the default behavior of a non SR-capable
router upon receipt of an generate IPv6 packet
packets with SRH destined to an address SRH. SR segment endpoint nodes receiving packets on
interface that are part of its, is to:

o ignore the SRH completely if the Segment Left field is 0 and
proceed to SR Domain may process the next header in the IPv6 packet;

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
Address.

6.1. Threat model

6.1.1. Source routing threats

Using an SRH is similar to source routing, therefore it has some
well-known security issues as described in [RFC4942] section 2.1.1
and [RFC5095]:

o amplification attacks: where a any packet could be forged in such a
way
destined to cause looping among a set of SR-enabled routers causing
unnecessary traffic, hence a Denial of Service (DoS) against
bandwidth;

o reflection attack: where a hacker could force local segment, containing an intermediate node SRH.

A SR Source Node connected to appear as the immediate attacker, hence hiding the real
attacker from naive forensic;

o bypass attack: where an intermediate node could be used as a
stepping stone (for example in SR Domain via a De-Militarized Zone) to attack
another host (for example in the datacenter secure tunnel, e.g.
IPSec tunnel mode [RFC4303] or any back-end
server).

6.1.2. Applicability of RFC 5095 to SRH

First of all, the reader must remember this specific part of section
1 of [RFC5095], "A side effect is that this also eliminates benign
RH0 use-cases; however, such applications Ethernet pseudowire [RFC4448], may be facilitated by
future Routing Header specifications.". In short, it is not
forbidden to create new secure type
considered trusted and directly connected. Some types of Routing Header; for example,
[RFC6554] (RPL) also creates a new Routing Header type for a specific
application confined tunnels may
result in a single network.

In the segment routing architecture described additional processing overhead that should be considered in
[I-D.ietf-spring-segment-routing] there are basically two kinds of
nodes (routers and hosts):

o nodes within
a deployment.

6.2. Nodes Outside the SR domain, which is within one single
administrative domain, i.e., where all nodes are trusted anyway
else the damage caused by those nodes could be worse than
amplification attacks: traffic interception, man-in-the-middle
attacks, more server DoS by dropping packets, and so on.

o nodes Domain

Nodes outside of the SR domain, which is outside of the
administrative segment routing domain hence they Domain cannot be trusted
because there is no physical security for those nodes, i.e., they
can be replaced by hostile nodes or can be coerced in wrong
behaviors.

The main use case for trusted. SR consists of Domain Ingress
routers SHOULD discard packets destined to SIDs within the single administrative domain
where only trusted nodes with SR enabled and configured participate
in SR: this is Domain
(regardless of the same model presence of an SRH) to avoid attacks on the SR
Domain as described and referenced in [RFC6554]. All non-trusted [RFC5095]. As an additional
layer of protection, SR Segment Endpoint nodes
do SHOULD discard packets
destined to local SIDs from source addresses not participate as either part of the SR processing is not enabled by default
or because they only process SRH
Domain.

For example, using the example topology from nodes within their domain.

Moreover, section 5, all SR nodes ignore SRH created by outsiders based on
topology information (received on a peering or internal interface) or
on presence and validity of SIDs in
the HMAC field. Therefore, if
intermediate nodes ONLY act on valid and authorized SRH (such as SR Domain (SIDS S1-S9) are assigned within a single administrative domain), then there is no security
threat similar IPv6 prefix,
Prefix-S. All SIDs assigned to RH-0. Hence, the [RFC5095] attacks a node k are not
applicable.

6.1.3. Service stealing threat

Segment routing is used for added value services, there is also assigned within a
need single
IPv6 prefix Prefix-Sk, all addresses permitted to prevent non-participating nodes source packets
destined to use those services; this
is called 'service stealing prevention'.

6.1.4. Topology disclosure

The SRH may also contains SIDs of some intermediate SR-nodes in the
path towards the destination, this obviously reveals those addresses
to the potentially hostile attackers if those attackers SR Domain are able to
intercept packets containing SRH. On the other hand, if the attacker
can do assigned within a traceroute whose probes will be forwarded along the SR
Policy, then there is little learned by intercepting single IPv6
prefix Prefix-A.

An Infrastructure Access List (IACL), applied to the SRH itself.

6.1.5. ICMP Generation

Per Section 4.4 external
interfaces of [RFC8200], when destination SR Domain ingress nodes (i.e. where the
destination address is one of theirs) receive a Routing Header with
unsupported Routing Type, the required behavior is:

o If Segments Left is zero, the node must ignore the Routing Header 3 and proceed 4, that discards packets
destined to process the next header in the packet.

o If Segments Left a SID covered by Prefix-S is non-zero, the node must discard the packet and
send an ICMP Parameter Problem, Code 0, message used to the packet's
Source Address, pointing discard packets
destined to SIDs within the unrecognized Routing Type.

This required behavior could be used by an attacker SR Domain.

An IACL, applied to force the
generation each interface of ICMP message by any node. The attacker could send
packets with SRH (with SR Segment Left not set to 0) Endpoint Nodes k,
that discards packets destined to a node
not supporting SRH. Per [RFC8200], the destination node could
generate an ICMP message, causing a local CPU utilization and if the
source of the offending packet SID covered by Prefix-Sk with SRH was spoofed could lead to a
reflection attack without any amplification.

It must be noted that this is a required behavior for any unsupported
Routing Type and
source address not limited covered by Prefix-A.

Failure to SRH packets. So, it is not specific implement a method of ingress filtering, as defined above,
exposes the SR domain to SRH and source routing attacks from nodes outside
the usual rate limiting for ICMP generation is required
anyway for any IPv6 implementation and has been implemented SR Domain, as described and
deployed for many years.

6.2. Security fields referenced in SRH

This section summarizes [RFC5095].

6.2.1. SR Source Nodes Not Directly Connected

Nodes outside the use of specific fields in SR Domain may request, by some trusted means
outside the SRH. They
are based on scope of this document, a key-hashed message authentication code (HMAC).

The security-related fields in the complete SRH are instantiated by the HMAC
TLV, containing:

o HMAC Key-id, 32 bits wide;

o HMAC, 256 bits wide (optional, exists only if HMAC Key-id is not
0).

The including an HMAC field
TLV which is computed correctly for the output of the SRH.

SR Domain ingress routers permit traffic destined to select SIDs with
local policy requiring HMAC computation (per [RFC2104])
using TLV processing for those select SIDs,
i.e. those SIDs provide a pre-shared key identified by HMAC Key-id and of the text
which consists of the concatenation of:

o gateway to the source IPv6 address;

o Last Entry field;

o an octet SR Domain for a set of bit flags;

o
segment lists.

If HMAC Key-id;

o all addresses in the Segment List.

The purpose of verification is successful, the HMAC TLV packet is forwarded to verify the validity, the integrity
and the authorization of
next segment. Within the SRH itself. SR Domain no further HMAC check need be
performed.

If HMAC verification fails, an outsider of the SR
domain does not have access ICMP error message (parameter problem,
error code 0, pointing to a current pre-shared secret, then it
cannot compute the right HMAC field TLV) SHOULD be generated (but rate
limited) and SHOULD be logged.

For example, extending the first SR router on the
path processing the SRH and configured topology defined in Figure 3, consider
node 3 offering access to check the validity of the
HMAC will simply reject the packet.

The HMAC TLV is located at the end of the SRH simply because only the
router on the ingress of the SR domain needs a premium SLA service to process it, then all
other SR nodes can ignore it (based on local policy) because they
trust the upstream router. This node 20. Node 20
is to speed up forwarding operations
because a trusted SR routers which do Source not validate directly connected to the SRH do not need SR Domain.

+ * * * * * * * * * * * * * * * * * * * * +

* [8] [9] *
| |
* | | *
[20]--[11]--[3]--------[5]----------------[6]---------[4]---[2]
* | | *
| |
* | | *
+--------[7]-------+
* *

+ * * * * * * * SR Domain * * * * * * * +

In order to parse access the SRH until SLA service, node 20 must be able to access
segments within the end.

The HMAC Key-id field allows SR Domain. To provide a secure entry point for
the simultaneous existence of
several hash algorithms (SHA-256, SHA3-256 ... or future ones) as
well as pre-shared keys. The SLA service, SIDs with local policy requiring HMAC Key-id field is opaque, i.e., it
has neither syntax nor semantic except verification
at node k are defined as an index to the right
combination of pre-shared key and hash algorithm Hk and except that assigned from a
value of 0 means that there prefix Prefix-H.
Prefix-H is no HMAC field. Having an HMAC Key-id
field allows for pre-shared key roll-over when two pre-shared keys
are supported for a while when all SR 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 converged access to it.

SID H3 is a fresher
pre-shared key. It could also allow for interoperation among
different SR domains if allowed SID covered by local policy Prefix-H at node 3.

Node 20 requests the premium SLA service to node 2 and assuming is provided a
collision-free
pre-computed SRH and HMAC Key Id allocation.

When with destination address H3.

Node 20 sends a specific SRH is linked packet with destination addresses set to a time-related service (such as
turbo-QoS for a 1-hour period) where the DA, Segment ID (SID) H2, SRH and
HMAC TLV are
identical, then it is important to refresh the shared-secret
frequently as provided for the HMAC validity period expires only when premium SLA service.

Node 3 receives the HMAC
Key-id packet and its associated shared-secret expires.

6.2.1. Selecting a hash algorithm

The verifies the HMAC field as defined in
section 4.3, forwarding the HMAC TLV is 256 bit wide. Therefore, packet to the HMAC
MUST be next segment in the segment
list or dropping it based on a hash function whose output is at least 256 bits.
If the output HMAC result.

This use of the hash function an HMAC is 256, then this output particularly valuable within an enterprise
based SR Domain to authenticate a host which is simply
inserted using SRv6 segment
routing as documented in [SRN]. In that example, the HMAC field. If the output of the hash function is
larger than 256 bits, then the output value used to
validate a source node is truncated using a permitted segment list.

7. Security Considerations

This section reviews security considerations related to 256 by
taking the least-significant 256 bits and inserting them in SRH,
given the HMAC
field. SRH implementations can support multiple hash functions but MUST
implement SHA-2 [FIPS180-4] processing and deployment models discussed in its SHA-256 variant.

NOTE: SHA-1 this
document.

As describe in Section 6, it is currently used by some early implementations used for
quick interoperations testing, necessary to filter packets ingress
to the 160-bit hash value must then be
right-hand padded with 96 bits set SR Domain destined to 0. The authors understand that
this segments within the SR Domain. This
ingress filtering is not secure but via an IACL at SR Domain ingress border nodes.
Additional protection is ok for limited tests.

6.2.2. Performance impact of HMAC

While adding applied via an HMAC to IACL at each and every SR packet increases the
security, it has a performance impact. Nevertheless, it must be
noted that:

o the HMAC field is used only when SRH is added by a device (such as
a home set-top box) which is outside of the segment routing
domain. If Segment
Endpoint node, filtering packets not from within the SRH is added by a router SR Domain,
destined to SIDs in the trusted segment
routing domain, then, there is no need SR Domain. ACLs are easily supported for an HMAC field, hence no
performance impact.

o when present, the HMAC field need only be checked and validated by
the first router
small numbers of prefixes, making summarization important, and when
the segment routing domain, this router prefixes requiring filtering is
named 'validating SR router'.

o this validating SR router can also have kept to a cache seldom changing set.

Additionally, ingress filtering of <IPv6 header +
SRH, HMAC field value> to improve the performance. It is not the
same use case IPv6 source addresses as
recommended in IPsec where HMAC value was unique per packet,
in SRH, BCP38 SHOULD be used.

SR Source Nodes not directly connected to the HMAC value is unique per flow.

o hash functions such as SHA-2 have been optimized for security and
performance and there are multiple implementations with good
performance.

With SR Domain may access
specific sets of segments within the above points in mind, SR Domain when secured with the performance impact of using
SRH HMAC
is minimized.

6.2.3. Pre-shared key management TLV. The field SRH HMAC Key-id allows for:

o key roll-over: when there is a need to change the key (the hash
pre-shared secret), then multiple pre-shared keys can be used
simultaneously. The validating SR router can have TLV provides a table means of
<HMAC Key-id, pre-shared secret> for the currently active and
future keys.

o different algorithms: by extending verifying the previous table
validity of ingress packets SRH, limiting access to <HMAC
Key-id, hash function, pre-shared secret>, the validating SR
router can also support several hash algorithms (see section
Section 6.2.1)

The pre-shared secret distribution can be done:

o segments in
the configuration of the validating SR routers, either by
static configuration or any SDN oriented approach;

o dynamically using Domain to only those source nodes with permission.

7.1. Source Routing Attacks

[RFC5095] deprecates the Type 0 Routing header due to a trusted key distribution such as [RFC6407]

The intent 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 NOT to define yet-another-key-
distribution-protocol.

6.3. Deployment Models

6.3.1. Nodes for use within the an SR
domain protected by ingress filtering via IACLs, and by
cryptographically authenticated SR Source Nodes within source nodes not directly
connected to the SR Domain; such attacks cannot be mounted from
outside an SR Domain are trusted to generate IPv6
packets with SRH. Domain. As specified in this document, SR segment endpoint Domain
ingress edge nodes receiving drop packets on
interface that are part of entering the SR Domain may process any packet destined to a local segment, containing an SRH.

6.3.2. Nodes outside of
segments within the SR domain

Nodes outside Domain.

Aditionally, this document specifies the use of IACL on SR Domain cannot be trusted. Segment
Endpoint nodes within the SR Domain Ingress
routers SHOULD discard to limit the source addresses
permitted to send packets destined to SIDs within a SID in the SR Domain
(regardless of Domain.

Such attacks may, however, be mounted from within the presence of an SRH) SR Domain, from
nodes permitted to avoid source traffic to SIDs in the domain. As such,
these attacks and other known attacks on the 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. This

7.2. Service Theft

Service theft is accomplished via infrastructure Access Lists (iACLs)
applied on domain ingress nodes. However defined as the SR Domain may be
extended to nodes outside of it via use of the SRH HMAC.

Nodes outside a service offered by the SR
Domain may request, by some trusted means
outside the scope of this document, a complete SRH including an HMAC
TLV which node not authorized to use the service.

Service theft is computed correctly for not a concern within the SRH (see Section 6.2). SR Domain ingress routers permit traffic destined as all SR Source
nodes and SR segment endpoint nodes within the domain are able to select SIDs with
local policy requiring HMAC TLV processing for those select SIDs,
i.e. these SIDs provide
utilizing the services of the Domain. If a gateway to node outside the SR
Domain for a set learns of
segment lists.

If HMAC validation is successful, segments or a topological service within the packet is forwarded SR
domain, IACL filtering denies access to the next
segment. Within those segments.

Nodes outside the SR Domain no further HMAC check need be
performed. However, other segments in Domain, capable of intercepting packets from SR
Source nodes not directly connected to the SR domain MAY verify Domain utilizing the
HMAC TLV when
SRH HMAC, may steel the outer IP header SRH is processed, dependent on local policy.

If HMAC validation fails an ICMP error message (parameter problem)
SHOULD be generated (but rate limited) and SHOULD be logged.

6.3.3. SR path exposure

The SRH contains a Segment List. HMAC TLV. If such an observer outside the SR
Domain
attacker is able to inspect capable of spoofing the SRH, they source address of the original
sender it may use the segments in the
Segment List IP header and HMAC to launch an attack on the SR Domain or obtain knowledge access services of the topology within the SR Domain. When
Domain intended for the original SR Source node is
outside node.

Frequent rekeying of the SR Domain and 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 packet traverses risk of service threat is of minimum concern and the public internet HMAC TLV is
used primarily to validate that the SR Domain ingress router it source is likely that others will have
access permitted to use the Segment List
segment list in the SRH.

IPSec Encapsulating Security Payload (ESP), [RFC4303], cannot be use
to protect the

7.3. Topology Disclosure

The SRH as may contains SIDs of some intermediate SR-nodes in the ESP header must appear after path
towards the routing
header (including SRH).

Exposure of segments and TLV content destination, this reveals those addresses to observers outside the SR
Domain should be considered in any deployment. There attackers if
they are two methods able to limit exposure, and attacks on segments intercept packets containing SRH.

This is applicable within the an SR Domain from
outside but the disclosure is less
relevant as an attacker has other means of learning topology.

For an SR Domain:

Limit Source node not directly connected to the SR Domain this
disclosure is applicable. While the number of segments and within the TLV data exposed SR domain
disclosed in SRH from
nodes outside the SR Domain.

Restrict which SIDs are protected by ingress filtering, they may accept traffic from outside be
learned by an attacker external to the SR Domain
to only those enforcing HMAC verification by using iACLs (as Domain.

As described in Section 6.3.2).

6.3.4. Impact of BCP-38

BCP-38 [RFC2827], also known as "Network Ingress Filtering", checks
whether 6.2.1, there exist use cases where the source address risk
of packets received on an interface topology disclosure is
valid for this interface. The use of loose minimum concern when the HMAC TLV is
used primarily to validate that the source routing such as
SRH forces packets is permitted to follow a path which differs from use the expected
routing. Therefore, if BCP-38 was implemented
segment list in all routers inside the SR domain, SR packets could SRH.

7.4. ICMP Generation

The generation of ICMPv6 error messages may be received used to attempt
denial-of-service attacks by sending an interface which is
not the expected one, and the packets could be dropped.

As BCP-38 is only deployed at the ingress routers of an
administrative domain, and as Packets arriving at those ingress
routers have been forwarded using the routing information, then there
is no reason why this ingress router should drop the error-causing destination
address or SRH packet based
on BCP-38. Routers inside in back-to-back packets. An implementation that
correctly follows Section 2.4 of [RFC4443] would be protected by the domain commonly do not apply BCP-38;
so, this is not a problem.

7.
ICMPv6 rate-limiting mechanism.

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"

7.1.

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

7.2.

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.

8.1.

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]

8.2.

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]

8.3.

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]

8.4.

9.4. Barefoot

Name: Barefoot Networks Tofino NPU

Status: Prototype

Implementation: performs END processing, no TLV processing

Details: [I-D.filsfils-spring-srv6-interop]

8.5.

9.5. Juniper

Name: Juniper Networks Trio and vTrio NPU's

Status: Prototype & Experimental
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.

10.

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.

11.

12. References

11.1.

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>.

[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing
Architecture", draft-ietf-spring-segment-routing-15 (work
in progress), January 2018.

[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>.

[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.

[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>.

[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>.

11.2.

[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-00
srv6-interop-01 (work in progress), March September 2018.

[I-D.filsfils-spring-srv6-network-programming]
Filsfils, C., Li, Z., Camarillo, P., Leddy, J.,
daniel.voyer@bell.ca, d.,
daniel.bernier@bell.ca, d., Steinberg, D., Raszuk, R., Matsushima, S., Lebrun, D., Decraene, B., Peirens, B.,
Salsano, S., Naik, G., Elmalky, H., Jonnalagadda, P., and
M. Sharif, Z. Li, "SRv6
Network Programming", draft-filsfils-
spring-srv6-network-programming-04 draft-filsfils-spring-srv6-network-
programming-05 (work in progress),
March 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>.

[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
May 2000, <https://www.rfc-editor.org/info/rfc2827>.

[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>.

[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>.

[RFC4942] Davies, E., Krishnan,

[RFC4303] Kent, S., and P. Savola, "IPv6 Transition/
Co-existence "IP Encapsulating Security Considerations", Payload (ESP)",
RFC 4942, 4303, DOI 10.17487/RFC4942, September 2007,
<https://www.rfc-editor.org/info/rfc4942>. 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>.

[RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
Routing Header for Source Routes with the Routing Protocol
for Low-Power and Lossy Networks (RPL)", RFC 6554,
DOI 10.17487/RFC6554, March 2012,
<https://www.rfc-editor.org/info/rfc6554>.

[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
Clarence Filsfils (editor)
Cisco Systems, Inc.
Brussels
BE

Email: cfilsfil@cisco.com

Stefano Previdi
Individual
Huawei
Italy

Email: stefano@previdi.net

John Leddy
Comcast
4100 East Dry Creek Road
Centennial, CO 80122
Individual
US

Email: John_Leddy@comcast.com john@leddy.net

Satoru Matsushima
Softbank

Email: satoru.matsushima@g.softbank.co.jp

Daniel Voyer (editor)
Bell Canada

Email: daniel.voyer@bell.ca