SPRING Working Group Z. Li
Internet-Draft C. Li
Intended status: Standards Track Huawei Technologies
Expires: August 14, 2020 W. Cheng
China Mobile
C. Xie
C. Li
China Telecom
H. Tian
F. Zhao
CAICT
February 11, 2020
Generalized Segment Routing Header
draft-lc-6man-generalized-srh-00
Abstract
Generalized SRv6 network programming defines the enhanced mechanisms
of SRv6 to encode SRv6 SIDs, Compressed SIDs and even the MPLS labels
or IPv4 tunnel information in a single SRH. This type of SRH is
called Generalized SRH (G-SRH), which can reduce the overhead of SRv6
and also provide more flexibility for network programming. This
document defines the encapsulation and packet processing of G-SRH.
Status of This Memo
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This Internet-Draft will expire on August 14, 2020.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. Generalized Segment Identifier . . . . . . . . . . . . . . . 4
3.1. SRv6 G-SID . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Compression G-SID . . . . . . . . . . . . . . . . . . . . 4
3.3. MPLS G-SID . . . . . . . . . . . . . . . . . . . . . . . 5
3.4. IPv4 G-SID . . . . . . . . . . . . . . . . . . . . . . . 6
4. Generalized Segment Routing Header (G-SRH) . . . . . . . . . 7
4.1. G-SRH for SRv6 Compression . . . . . . . . . . . . . . . 8
4.2. G-SRH for Crossing SR-MPLS Domains . . . . . . . . . . . 10
4.3. G-SRH for Crossing IPv4 Domains . . . . . . . . . . . . . 11
5. Packet Processing . . . . . . . . . . . . . . . . . . . . . . 14
5.1. Crossing SRv6 Compression Domains . . . . . . . . . . . . 14
5.2. Crossing SR-MPLS Domains . . . . . . . . . . . . . . . . 17
5.2.1. END.M . . . . . . . . . . . . . . . . . . . . . . . . 17
5.3. Crossing IPv4 Domains . . . . . . . . . . . . . . . . . . 17
5.3.1. END.4 . . . . . . . . . . . . . . . . . . . . . . . . 17
5.3.2. END.B4 . . . . . . . . . . . . . . . . . . . . . . . 18
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 19
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 19
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
10.1. Normative References . . . . . . . . . . . . . . . . . . 19
10.2. Informative References . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
Segment routing (SR) [RFC8402] is a source routing paradigm that
explicitly indicates the forwarding path for packets at the ingress
node by inserting an ordered list of instructions, called segments.
When segment routing is deployed on the IPv6 data plane, it is called
SRv6 [I-D.ietf-6man-segment-routing-header]. For support of SR, a
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new routing header called Segment Routing Header (SRH), which
contains a list of SIDs and other information, has been defined in
[I-D.ietf-6man-segment-routing-header]. In use cases like Traffic
Engineering, an ordered SID List with multiple SIDs is inserted into
the SRH to steer packets along an explicit path.
The overhead of SIDs (16 bytes per SID) in SRH proposes challenges
for packet processing and payload efficiency.
[I-D.li-spring-compressed-srv6-np] proposes a mechanism for reducing
the overhead of SRv6 by using the Compressed SID (C-SID) in SRH.
However it requires all the middle segment endpoint nodes to support
compression.
[I-D.cl-spring-generalized-srv6-np] proposes Generalized Segment
Routing over IPv6 (G-SRv6) Networking Programming, which supports to
encode multiple types of Segments in an SRH, called Generalized
SRH(G-SRH). These segments can be called Generalized Segment, and
the ID can be Generalized Segment Identifier(G-SID), which may
include an SRv6 SID(128 bits), C-SIDs, MPLS labels, or IPv4 tunnel
information. Therefore, G-SRv6 does not require all the nodes along
the path to be compression capable, which supports incremental
deployment, and brings benefits to the networks. Moreover it
provides more flexibilities for network programming. This document
defines the encapsulation and packet processing of Generalized SRH.
2. Terminology
This document makes use of the terms defined in
[I-D.ietf-6man-segment-routing-header], [RFC8402] and [RFC8200], and
the reader is assumed to be familiar with that terminology. This
document introduces the following new terms:
C-SRH: Compressed Segment Routing Header
C-SID: Compressed Segment Identifier
G-SRH: Generalized Segment Routing Header
G-SID: Generalized Segment Identifier.
2.1. 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.
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3. Generalized Segment Identifier
A G-SID is a 128 bits value, and it can be used for carry multiple
types of Segment ID or segment information, so may contain:
o an SRv6 SID
o a compression G-SID
o an MPLS G-SID
o an IPv4 G-SID
3.1. SRv6 G-SID
SRv6 SID is a type of G-SID. A G-SID contains a single SRv6 SID, and
does not change anything of SRv6 SID.
3.2. Compression G-SID
As per [I-D.li-spring-compressed-srv6-np], a C-SID is a sub-set of a
compressable SRv6 SID, which can be used for routing the packets in
compressed SRv6 network programming. The format of compressable SID
and C-SID is shown below. The argument part is specified by use
cases, and it is zero by default. It is shared by the compressable
SRv6 SIDs in a C-SRv6 sub-path.
0 Variable Length 32 bits 128 bits
+--------------------------------------------------------------+
| Common Prefix | C-SID | Argument |
+--------------------------------------------------------------+
|<-------- Locator ---------------->|<-FuncID->|<--Argument -->|
|<--->|
|
Different part of Locator
Figure 1. 32 bits C-SID in Compressable SRv6 SID
A compression G-SID shown in Figure 2 may contain several C-SIDs and
optional padding. when C-SID is a 32 bits value, a compression G-SID
can consist of 4 C-SIDs. If the length of C-SIDs in a G-SID is less
than 128 bits, then padding is required.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-SID 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-SID 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-SID 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-SID 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-SID 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-SID 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(b)
Figure 2. Compression G-SID
3.3. MPLS G-SID
An MPLS G-SID shown in Figure 3 can contain 4 MPLS Label
Encapsulations, if number of MPLS Label Encapsulations is less than
4, then padding is required in G-SID to align with 128 bits.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label 0 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label 1 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label 2 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label 3 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label 0 | TC |1| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label 1 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(b)
Figure 3. MPLS G-SID
3.4. IPv4 G-SID
An IPv4 G-SID shown in Figure 4 can contain 128 bits information of
IPv4 tunnel. The format of the IPv4 G-SID is shown below.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Tunnel Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Src Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Dest Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tunnel Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4. IPv4 G-SID
4. Generalized Segment Routing Header (G-SRH)
Generalized Segment Routing Header (G-SRH) is an enhancement of the
SRH, and it supports to encode different types of G-SIDs in a single
SRH. The format of G-SRH is shown as below.
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 | Flag |CL | Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Generalized Segment List[0] (128 bits value) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Generalized Segment List[n] (128 bits value) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
// Optional Type Length Value objects (variable) //
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5. Generalized Segment Routing Header
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Where:
o Next Header, Hdr Ext Len, Routing Type, Segments Left, Last Entry
and Tag are the same as those defined in
[I-D.ietf-6man-segment-routing-header].
o CL (C-SID Left): 2-bit unsigned integer to indicate the index of
C-SID in the Compression G-SID. There can be four 32-bit C-SIDs
within a Compression G-SID.
o Segment List[n]: 128-bit G-SID representing the nth Generalized
Segment in the Segment List. In G-SRH, the Generalized Segment
can be an SRv6 SID, Compression G-SID, MPLS G-SID, or IPv4 G-SID,
etc.
o Type Length Value (TLV): It is the same as that defined in
[I-D.ietf-6man-segment-routing-header].
4.1. G-SRH for SRv6 Compression
When an SRv6 path travels normal SRv6 domains and compressed SRv6
domains, the SRv6 SID and Compression G-SID(containing C-SIDs) can be
encoded in a single G-SRH. For easier understanding, this document
assumes that the compressable consists of 96 bits common prefix and
32 bits C-SID, while actually the length of common prefix can be
configured as less than 96 to fit the address planning of the
networks. The encoding can be shown 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 | Flag |CL | Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Generalized Segment List[0] (128 bits value) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. ... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| Optional Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Compression
| C-SID [0] | G-SID 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ... . ...
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-SID 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| C-SID 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-SID 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Compression
| C-SID 2 | G-SID k
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-SID 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| Common Prefix |
| | Compressable
| | SRv6 SID
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| C-SID 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| |
| Generalized Segment List[n1] (128 bits value) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Generalized Segment List[n] (128 bits SRv6 SID) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
// Optional Type Length Value objects (variable) //
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6. G-SRH for SRv6 Compression
Where:
o Common Prefix: 96-bit value for the common prefix shared by a
group of Compressable SRv6 SIDs. Operators are free to configure
the length and the value of the common prefix based on the address
planning of their networking. In a Compressable SRv6 SID, when
the length of Common prefix is less than 96, and the length of the
C-SID is less than 32 bits, the the rest bits can be used as
arguments.
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o C-SID: 32-bit compressed SID of a Compressable SRv6 SID.
o Padding: Must be zero. When the length of C-SIDs within G-SID is
less than 128 bits within a compression G-SID, then padding is
needed.
4.2. G-SRH for Crossing SR-MPLS Domains
The G-SRH support to encode the MPLS labels and SRv6 SID or
Compression G-SID within a G-SRH. The G-SRv6 path for crossing SR-
MPLS domains can be encoded in the G-SRH 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 | Flag |CL | Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Generalized Segment List[0] (128 bits value) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. ... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| Optional Padding | MPLS
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ G-SID 0
| Label 0 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label 3 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| Label 0 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label 1 | TC |S| TTL | MPLS
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ G-SID n
| Label 2 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label 3 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| |
| Generalized Segment List[n2] (128 bits value) | End.M
| | SRv6 SID
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
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| |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Generalized Segment List[n2] (128 bits value) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
// Optional Type Length Value objects (variable) //
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7. G-SRH for Crossing SR-MPLS Domains
Where:
o Label: 32-bit MPLS label.
o TC: 3-bit value for traffic class of MPLS label encapsulation.
o S: 1-bit flag to indicate the bottom of MPLS label stack. It can
be used for indicating the end of the MPLS label stack.
o TTL: 8-bit value for TTL of MPLS label encapsulation.
o Padding: When the number of MPLS labels is less than 4 in an MPLS
G-SID, then padding is required to align with 128 bits.
4.3. G-SRH for Crossing IPv4 Domains
The G-SRv6 path for crossing IPv4 domains can be encoded in the G-SRH
as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type | Segments Left|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Entry | Flag |CL| Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Generalized Segment List[0] (128 bits value) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Generalized Segment List[n3] (128 bits value) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| Type | Tunnel Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Src Address | IPv4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ G-SID
| IPv4 Dest Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tunnel Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| |
| Generalized Segment List[n1] (128 bits vlaue) | End.4
| | SRv6 SID
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Generalized Segment List[n2] (128 bits value) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
// Optional Type Length Value objects (variable) //
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8. G-SRH for Crossing IPv4 Domains
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Where:
o Type: 4-bit value to indicate the types of IPv4 tunnel.
o IPv4 Src Address: 32-bit value for the source address of the IPv4
tunnel.
o IPv4 Dest Address: 32-bit value for the destination address of the
IPv4 tunnel.
o Tunnel Parameters: tunnel parameters of the IPv4 tunnel except the
source address and destination address.
This document defines the encoding for IPv4 UDP tunnel and VxLAN
tunnel.
The IPv4 UDP tunnel information encapsulated in the G-SRH is 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Src Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Dest Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Src Port | Dest Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9. G-SID for IPv4 UDP Tunnel
Where,
o Reserved: It is the reserved field and MUST be set as 0.
o Src Port: 16-bit value for the source port of the IPv4 UDP tunnel.
o Dest Port: 16-bit value for the destination port of the IPv4 UDP
tunnel.
The IPv4 VXLAN tunnel information encapsulated in the G-SRH is as
follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Resv | VN ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Src Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Dest Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Src Port | Dest Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10. G-SID for IPv4 VXLAN Tunnel
Where,
o Resv: It is the reserved field and MUST be set as 0.
o VN ID: 24-bit value for the VN ID of the IPv4 VXLAN tunnel.
o Src Port: 16-bit value for the source port of the IPv4 VXLAN
tunnel.
o Dest Port: 16-bit value for the destination port of the IPv4 VXLAN
tunnel.
The other types of IPv4 tunnel information will be described in the
future.
5. Packet Processing
This section describes the packet processing of G-SRH.
5.1. Crossing SRv6 Compression Domains
There are several cases when encoding the SRv6 SID and Compressable
SRv6 SID in a single G-SRH.
o SRv6 path
o Compressed SRv6 path
o SRv6 path -> Compressed SRv6 path
o Compressed SRv6 path -> SRv6 path
o Combination of the above options.
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The ingress node of G-SRv6 encodes the G-SID list in G-SRH based on
the type of path and the order of SIDs.
If the beginning of the G-SRv6 path is a Compressed SRv6 sub-path,
the CL MUST be initiated accordingly.
If the first Compressable SRv6 SID is inserted in the G-SRH, then the
CL MUST be set as 0. If the first Compressable SRv6 SID is reduced,
the the CL MUST set to 3, which points to the first C-SID in the
first G-SID.
If the beginning of the G-SRv6 path is a SRv6 sub-path, and there is
any compressable SRv6 SID in the list, the CL MUST be set to 0.
If the G-SRv6 path is a SRv6 path , then the CL SHOULD be set to 0,
and it MUST be ignored in G-SRH processing.
When a compression G-SID is encoded in the G-SRH, new actions should
be defined for processing it. When the SL >0, the pseudo code is
shown below:
01. If ipv6 DA is a normal local SRv6 SID, //Ref1
02. SL- -; DA = SRH [SL];
03. Process the packet based on the type of SID
04. Forward the packet to the new DA;
05. if ipv6 DA is a local Compressable SRv6 SID //Ref2
06. If CL = 0
07. SL- -; CL = 3;
08. DA[CP..CP+31] = SRH[SL][CL] ;
09. Else
10. CL --;
11. DA[CP..CP+31] = SRH[SL][CL]
12. Process the packet based on the type of SID
13. Forward the packet to the new DA;
14. if ipv6 DA is a local Compressable SRv6 SID with EOC flavor //Ref3
15. SL --
16. CL = 0
17. DA = SRH[SL]
18. Process the packet based on the type of SID
19. Forward the packet to the new DA
20. else
21. other G-SIDs processing;
o Ref1: nothing is changed when the IPv6 DA is an SRv6 SID, the SID
will be processed as per
[I-D.ietf-spring-srv6-network-programming], so G-SRH is compatible
with SRH.
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o Ref2: when the IPv6 DA is a local compressable SRv6 SID, the node
should process it based on the type of SID and update the IPv6 DA
based on the value of CL. If the CL is 0, the next C-SID should
be selected from the first C-SID in the next compression G-SID and
updated to the IPv6 DA. If the CL is greater than 0, then the
next C-SID in this G-SID should be updated to the IPv6 DA.
o Ref3: If the IPv6 DA is a local Compressable SRv6 SID with EOC
flavor, means this is the last C-SID of the C-SIDs list of this
compression SRv6 sub-path. The next G-SID should be updated to
the IPv6 DA, and the CL is set to 0 in order to help the process
of the next Compression SRv6 SID.
When SL = 0, the pseudo code is shown below.
01. If ipv6 DA is a local SRv6 SID //Ref1
02. SRv6 processing based on the type of SID
03. If ipv6 DA is a local compressable SID //Ref2
04. If CL = 0
05. SRv6 processing based on the type of SID
06. Else
07. CL --;
08. DA[CP..CP+31] = SRH[SL][CL];
09. Process the packet based on the type of SID
09. Forward the packet to the new DA;
10. If ipv6 DA is a local compressable SID with EOC Flavor //Ref 3
11. Process the packet based on the type of SID
12. Else
13. Other G-SIDs processing;
o Ref1: nothing is changed when the IPv6 DA is an SRv6 SID, the SID
will be processed as per
[I-D.ietf-spring-srv6-network-programming], so G-SRH is compatible
with SRH.
o Ref2: when the IPv6 DA is a local compressable SRv6 SID, the node
should process it based on the type of SID and update the IPv6 DA
based on the value of CL. If the CL is 0, meaning this C-SID is
the last segment, the node should process the SID and the G-SID
processing should be finished. If the CL is greater than 0, the
next C-SID in the G-SID should be updated to the IPv6 DA.
o Ref3: If the IPv6 DA is a local Compressable SRv6 SID with EOC
flavor, meaning this is the last C-SID in the C-SIDs list of this
compression SRv6 sub-path, the node should process the SID and the
G-SID processing should be finished.
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5.2. Crossing SR-MPLS Domains
In some scenarios such as SD-WAN, an SRv6 packet may cross MPLS
networking. Usually, the packet can be steered into an SR-MPLS
policy based on END.BM SID
[I-D.ietf-spring-srv6-network-programming]. For reducing
configuration in the middle nodes, this document proposes END.M (End
function with SR-MPLS path instantiation) to indicate the SR-MPLS/
MPLS path by the MPLS label stack carried after it.
5.2.1. END.M
An End.M SID indicates the beginning of the SR-MPLS SID list/MPLS
Label stack, and the S-bit in MPLS label indicates the end of the
MPLS label stack.
When a node processes an END.M SID, it copies the SR-MPLS SID list/
MPLS labels to the outer MPLS header, and updates the SL pointing to
the next G-SID after these MPLS G-SIDs, set the IPv6 DA as the
G-SRH[SL], and then forwards the packet based on the active MPLS
label.
The pesudo code is shown below:
01. Copy the MPLS labels to MPLS header //Ref1
02. Update the SL point to next G-SID after the MPLS G-SID
03. Set the IPv6 DA as the SRH[SL]
04. Forward the packet based on the active MPLS label
Ref1. The Node will copy the MPLS labels within the MPLS G-SID to
the outer MPLS header. The end of the MPLS labels is indicated by
the S-bit in the MPLS label.
The MPLS G-SID MUST NOT be the last G-SID in the G-SID list.
5.3. Crossing IPv4 Domains
In some scenarios such as SD-WAN, an SRv6 packet may cross IPv4
networking. Usually, the packet will be transported by an IPv6 over
IPv4 tunnel. This document proposes END.4 (End with IPv4 tunnel
instantiation) and END.B4 (End binding to an IPv4 tunnel) behaviors
for indicating the IPv4 tunnel.
5.3.1. END.4
The End.4 indicates the instantiation of an IPv4 Tunnel, and the
parameter of this IPv4 Tunnel is carried by the IPv4 G-SID. An End.4
SID is never the last segment in a G-SID list.
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When a node processes a END.4 SID, it will encapsulate an outer IPv4
tunnel header according to the tunnel information in the associated
IPv4 G-SID, and set the SL point the next G-SID after the IPv4
G-SIDs, update the inner IPv6 DA by G-SRH[SL], and then forward the
packet based on the outer IPv4 DA.
The pesudo code is shown below:
01. Encapsulate the outer IPv4 tunnel header according to the
information in IPv4 G-SID(IPv4 DA, SA, etc.) //Ref1
02. Update the SL point to next G-SID after the IPv4 G-SID
03. Set the inner IPv6 DA as the SRH[SL]
04. Forward the packet based on the outer IPv4 DA.
Ref1: When encapsulating the outer IPv4 tunnel header, the source
address and destination address and tunnel related parameters are
learned from the IPv4 G-SID.
The IPv4 G-SID MUST NOT be the last G-SID in the G-SID list.
5.3.2. END.B4
This is a variation of the End behavior, and it will be bound to an
IPv4 tunnel initiated at endpoint node, while the parameters of this
tunnel are not carried by SRH but maintained by node.
The parameters of the IPv4 tunnel associated to the END.B4 SID can be
configured and advertised in SID instantiation. This is out of scope
of this document, and will be described in other documents.
An End.B4 SID is never the last segment in a SID list.
When a node processes an END.B4 SID, it will encapsulate an outer
IPv4 tunnel header based on the parameters binding to the End.B4 SID,
and set the SL point the next G-SID, update the inner IPv6 DA by
G-SRH[SL], and then forward the packet based on the outer IPv4 DA.
The pseudo code is shown below.
01. Encapsulate the outer IPv4 tunnel header according to
the parameters binding to the End.B4 SID //Ref1
02. Update the SL point to next G-SID after the IPv4 G-SID
03. Set the inner IPv6 DA as the SRH[SL]
04. Forward the packet based on the outer IPv4 DA.
Ref1: When encapsulating the outer IPv4 tunnel header, the source
address and destination address and tunnel related parameters are
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learned from the parameters binding to the SID, the information is
maintained at the node.
6. IANA Considerations
TBD
7. Security Considerations
TBD
8. Contributors
Zhibo Hu
Huawei Technologies
huzhibo@huawei.com
Yang Xia
Huawei Technologies
yolanda.xia@huawei.com
9. Acknowledgements
10. References
10.1. Normative References
[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>.
[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>.
[]
Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", draft-ietf-6man-segment-routing-header-26 (work in
progress), October 2019.
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[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>.
[I-D.li-spring-compressed-srv6-np]
Li, Z., Li, C., Xie, C., Voyer, D., LEE, K., Tian, H.,
Zhao, F., Guichard, J., Cong, L., and S. Peng, "Compressed
SRv6 Network Programming", draft-li-spring-compressed-
srv6-np-01 (work in progress), January 2020.
10.2. Informative References
[I-D.ietf-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
Matsushima, S., and Z. Li, "SRv6 Network Programming",
draft-ietf-spring-srv6-network-programming-09 (work in
progress), February 2020.
[I-D.filsfils-spring-srv6-net-pgm-illustration]
Filsfils, C., Camarillo, P., Li, Z., Matsushima, S.,
Decraene, B., Steinberg, D., Lebrun, D., Raszuk, R., and
J. Leddy, "Illustrations for SRv6 Network Programming",
draft-filsfils-spring-srv6-net-pgm-illustration-01 (work
in progress), August 2019.
Authors' Addresses
Zhenbin Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: lizhenbin@huawei.com
Cheng Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: chengli13@huawei.com
Li, et al. Expires August 14, 2020 [Page 20]
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Weiqiang Cheng
China Mobile
Email: chengweiqiang@chinamobile.com
Chongfeng Xie
China Telecom
China Telecom Information Science&Technology Innovation park, Beiqijia Town,Changping District
Beijing
China
Email: xiechf.bri@chinatelecom.cn
Cong Li
China Telecom
China Telecom Information Science&Technology Innovation park, Beiqijia Town,Changping District
Beijing
China
Email: licong.bri@chinatelecom.cn
Hui Tian
CAICT
Beijing
China
Email: tianhui@caict.ac.cn
Feng Zhao
CAICT
Beijing
China
Email: zhaofeng@caict.ac.cn
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