| Internet-Draft | G-SRv6 for Cmpr | May 2023 |
| Cheng, et al. | Expires 5 November 2023 | [Page] |
This document proposes Generalized Segment Routing over IPv6 (G-SRv6) Networking Programming for SRv6 compression.¶
G-SRv6 can reduce the overhead of SRv6 by encoding the Generalized SIDs(G-SID) in SID list, and it also supports to program SRv6 SIDs and G-SIDs in a single SRH to support incremental deployment and smooth upgrade.¶
G-SRv6 is fully compatible with SRv6 with no modification of SRH, no new address consumption, no new route creation, and even no modification of control plane.¶
G-SRv6 for Compression is designed based on the Compressed SRv6 Segment List Encoding in SRH [I-D.ietf-spring-srv6-srh-compression] framework.¶
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This Internet-Draft will expire on 5 November 2023.¶
Copyright (c) 2023 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶
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 [RFC8754]. For support of SR, a new routing header called Segment Routing Header (SRH), which contains a list of SIDs and other information, has been defined in [RFC8754]. 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.¶
However, the size of SIDs (16 bytes per SID) in SRH proposes challenges for packet processing and payload efficiency [I-D.ietf-spring-compression-requirement]. In order to solve this problem, this document proposes Generalized Segment Routing over IPv6 (G-SRv6) Networking Programming for SRv6 compression.¶
G-SRv6 supports to encode multiple types of Segments in an SRH, called Generalized SRH (G-SRH). In SRv6 Compression, the G-SRH can carry multiple SRv6 SID and G-SID(Generalized Segment Identifier) containers in the SID list. A G-SID container may include an SRv6 SID or multiple G-SIDs and optional padding. A G-SID can be a 32-bits value of the original SRv6 SID, which contains the node ID and function ID. By carrying G-SIDs instead of 128 bits SRv6 SID, the problem of SRv6 header size can be solved, and the solution is compatible with SRv6.¶
This document makes use of the terms defined in [RFC8754], [RFC8402] and [RFC8200], and the reader is assumed to be familiar with that terminology. This document introduces the following terms:¶
Compressible SRv6 SID: It is the 128-bit SRv6 SID whose format can be compressed. It is composed by Common Prefix and Generalized Segment Identifier (G-SID) and optional arguments and padding.¶
Common Prefix: It is the same prefix shared by multiple SIDs.¶
G-SRv6: Generalized SRv6 Network Programming¶
G-SRH: Generalized Segment Routing Header. It keeps the same format and code point with original SRH, which can carry multiple G-SIDs and original SIDs.¶
G-SID: Generalized Segment Identifier.It is a Compressed SID(C-SID) [I-D.ietf-spring-srv6-srh-compression].¶
G-SID Container: Generalized Segment Identifier Container.It is a C-SID container [I-D.ietf-spring-srv6-srh-compression].¶
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.¶
This section describes the concepts of G-SRv6.¶
In an SRv6 domain, the SIDs are allocated from an address block, called SID space. Therefore, the SIDs allocated from the same SID space share the common prefix. Also, if the length of the SID is less than 128 bits, then padding is required. In an SID List, the common prefix and padding are redundant. Reducing the redundant information can reduce the overhead of SRv6.¶
This document defines a Generalized SID (G-SID) to carry the different part of the original SRv6 SID in the SRH to reduce the size of the SRH. The G-SID can be a 32-bits value following the common prefix in the original SRv6 SID. An SRv6 SID with this format is called compressible SRv6 SID. The format of a compressible SRv6 SID with 32-bits G-SID is shown in Figure 1.¶
0 Variable Length 32 bits 128 bits
+--------------------------------------------------------------+
| Common Prefix | G-SID | Args/padding |
+--------------------------------------------------------------+
|<-------- Locator ----------------->|
Figure 1. 32 bits G-SID in SRv6 SID
¶
In order to indicate the format of the SRv6 SID is compressible, control plane extension may be considered. This is out of scope of this document, and can be described in other documents.¶
In order to align with 128 bits, a 128 bit G-SID Container is defined. A G-SID Container is a 128 bits value, and it may contain different type of SIDs:¶
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| G-SID 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| G-SID 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| G-SID 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| G-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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| G-SID 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| G-SID 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(b)
Figure 2. G-SID Container for Compression
¶
In order to locate the G-SID within the G-SID Container, this section defines Generalized SID Index (SI) to indicate the location of the G-SID within the current G-SID Container.¶
SI is a location argument of the G-SID, which is the least bits in the argument part. When G-SID is a 32 bits value, the SI is the least 2 bits in Argument.¶
0 Variable Length 32 bits 128 bits
+--------------------------------------------------------------+
| Common Prefix | G-SID |SI| Padding |
+--------------------------------------------------------------+
Figure 4. SI in the IPv6 DA
¶
In order to indicate the SRv6 compression processing, updating the next 32-bits G-SID to the IPv6 DA, this section defines COC(Continue of Compression) Flavor.¶
When a node receives an SID with COC Flavor, it indicates to update the G-SID part in IPv6 DA with the next 32 bits G-SID.¶
When a node receives an SID without COC Flavor, the node processes the packet as a normal SRv6 packet [RFC8986], for example, update the IPv6 DA with the next 128 bits SID if SL >0.¶
Therefore, if the behavior of the last G-SID in the G-SID list has no COC Flavor, then the next 128 bits SID will be updated to the DA, so it indicates the end of the compression sub-path.¶
When COC Flavor applies to END, END.X and END.T, the SIDs can be advertised via the IS-IS [I-D.ietf-lsr-isis-srv6-extensions], and the SRv6 SID Structure Sub-Sub-TLV MUST be carried to indicate the format of the SRv6 SID. The Locator.Block length indicates the length of the common prefix, and the G-SID is the following 32-bits value after the Block, which contains the Node ID and Function ID.¶
G-SRH supports to encode different types of segment in a single SRH without modifying the encapsulation format of SRH.¶
When an SRv6 path travels normal SRv6 nodes and compressed SRv6 nodes, the SRv6 SID and G-SIDs can be encoded in a single G-SRH.¶
For easier understanding, this document assumes that the Compressible SRv6 SID consists of 64 bits common prefix and 32 bits G-SID. 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 | Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Other G-SID Container |
. ... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| Optional Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| G-SID 0 | G-SID Container 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ... . ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| G-SID 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| G-SID 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| G-SID 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| G-SID 2 | G-SID Container j
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| G-SID 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| Common Prefix |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ G-SID Container k
| G-SID 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Generalized Segment List[n] (128 bits SRv6 SID) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Optional Type Length Value objects (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3. G-SRH for SRv6 Compression
¶
Where:¶
This section describes the pseudo code of COC Flavor, and it replaces the S13 and S14 of End, End.X, and End.T's pseudo code [RFC8986]. The pseudo code is shown below.¶
When N receives a packet whose IPv6 DA is S and S is a local SID with COC Flavor, N does:¶
1. If (DA.SI != 0) { //ref1
2. Decrement DA.SI by 1.
3. } Else {
4. Decrement Segments Left by 1.
5. Set DA.SI to 3 in the IPv6 Destination Address
6. }
7. Copy Segment List[Segments Left][DA.SI] into the bits //ref2
[B..B+31] of the IPv6 Destination Address.
¶
Ref1: an SID with COC flavor indicates the SRv6 compression processing that the node needs to update the next 32 bits G-SID to the IPv6 DA.¶
An SID without COC Flavor will be processed following the SRv6 processing. The node will update the next 128 bit SID to the IPv6 DA if the SL > 0.¶
This section describes a simple example of G-SRv6 for compression.¶
The reference topology is shown below.¶
*--------------------*
* SRv6 Domain *
* *
Tenant10 CE1--0-1-2-3-4-5-6-7-8-9-10--CE2 Tenant10
* *
*--------------------*
Figure 5. Reference topology
¶
Nodes 0 - 10 are G-SRv6 enabled nodes within the SRv6 domain, and node 0 is the ingress node of the G-SRv6 path while the node 10 is the egress node.¶
Nodes CE1 and CE2 are tenants of VPN 10, and they are outside of the SRv6 domain.¶
In order to ease the reading of the example, this section introduces a simplified SID allocation schema.¶
Therefore, the SID 2001:db8:0:0:1:1::, 2001:db8:0:0:2:1::, 2001:db8:0:0:3:1::, 2001:db8:0:0:4:1::, 2001:db8:0:0:5:1::, 2001:db8:0:0:6:1::, 2001:db8:0:0:7:1::, 2001:db8:0:0:8:1:: are SRv6 End.X SIDs with COC Flavor, and 2001:db8:0:0:9:2:: is a Compressible SRv6 End.X SID.¶
The SID list [2001:db8:0:0:1:1::, 2001:db8:0:0:2:1::, 2001:db8:0:0:3:1::, 2001:db8:0:0:4:1::, 2001:db8:0:0:5:1::, 2001:db8:0:0:6:1::, 2001:db8:0:0:7:1::, 2001:db8:0:0:8:1::, 2001:db8:0:0:9:2::, 2001:db8:0:0:10:10::] is calculated for a strict TE path from Node 1 to Node 10 for the VPN traffic of tenant 10.¶
In G-SRv6, the SID list can be encoded as [2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:2, 2001:db8:0:0:10:10::] in reduced mode. The G-SID Container encoding is shown 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ----
| |
| 2001:db8:0:0:10:10:: | G-SID Container 0
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ----
| 9:2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8:1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ G-SID Container 1
| 7:1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 6:1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ----
| 5:1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4:1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ G-SID Container 2
| 3:1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2:1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ----
Figure 6. G-SID Container Encoding for G-SRv6
¶
The packets forwarding procedures:¶
This illustration shows that 70 % overhead of SID list is removed in G-SRv6(10 x 16 Bytes to 3 x 16 Bytes), also, it shows the capabilities of encoding G-SIDs and SRv6 SIDs in a single G-SRH.¶
G-SRv6 is fully compatible with SRv6¶
G-SRv6 reduces the SRv6 encapsulation size.¶
G-SRv6 has efficient address consumption and easy to deploy¶
G-SRv6 is hardware friendly¶
The G-SRv6 mechanism has been implemented on the following 10+ hardware devices, software implementations and SDN controllers.¶
They had also successfully participated in the series of joint interoperability testing events hosted by China Mobile from June 2020 to November 2020.¶
The following hardware devices and software implementations had successfully passed the series of G-SRv6 dataplane interoperability testing (in alphabetical order).¶
The following hardware devices and software implementations had successfully passed the series of G-SRv6 with control plane interoperability test (in alphabetical order).¶
Regarding open-source implementations, G-SRv6 has been implemented on Linux Kernel.¶
In addition, China Mobile had come up with China Unitechs, Huawei, ZTE and H3C to successfully deploy trial of G-SRv6 (with control plane) in their three province branch networks in November 2020, respectively.¶
The details are listed below (in alphabetical order).¶
More information of G-SRv6 interop-test and deployment status will be updated as the work progresses.¶
This section describes the protocol extension requirements.¶
REQ1-01: An SRv6 compression path can be represented as a G-SID Container list consists of a compressible SRv6 SID and G-SID Containers.¶
REQ1-02: A G-SID Container consists of at most 4 (32-bits) G-SIDs, if the number of G-SID is less than 4, then padding is required to align with 128 bits.¶
REQ1-03: If the first Compressible SRv6 SID is copied to the IPv6 DA, then following G-SIDs should be updated to the IPv6 DA by the nodes along the SRv6 compression sub-path accordingly.¶
REQ1-04: The last G-SID in the G-SID Container for the SRv6 compression sub-path is the a G-SID without COC flavor.¶
REQ1-05: When process the G-SID with COC flavor in the IPv6 DA, the next G-SID is updated to the IPv6 DA.¶
REQ1-11: ISIS/OSPF/BGP-LS/PCEP extensions for advertising the capabilities of supporting G-SRv6 for SRv6 compression.¶
REQ1-12: ISIS/OSPF/BGP-LS/BGP extensions for advertising Compressible SRv6 SIDs.¶
REQ1-13: ISIS/OSPF/BGP-LS/BGP extensions for advertising the Continue-of-compression(COC) flavor SID.¶
REQ1-21: BGP SR Policy extensions for programming a G-SRv6 path combining with Compressible SRv6 SIDs and SRv6 SIDs.¶
REQ1-31: PCEP SR Policy extensions for programming a G-SRv6 path combining with G-SIDs and SRv6 SIDs.¶
REQ1-32: PCEP extensions for programming a G-SRv6 path combining with G-SIDs and SRv6 SIDs.¶
This document requests IANA to allocate the following codepoints for COC flavor behaviors within the "SRv6 Endpoint Behaviors" sub-registry under the top-level "Segment Routing Parameters" registry.¶
+-------+--------+----------------------------+-----------+
| Value | Hex | Endpoint behavior | Reference |
+-------+--------+----------------------------+-----------+
| 101 | 0x0065 | End with COC | [This.ID] |
| 102 | 0x0066 | End with PSP&COC | [This.ID] |
| 104 | 0x0068 | End with PSP&USP&COC | [This.ID] |
| 105 | 0x0069 | End.X with COC | [This.ID] |
| 106 | 0x006A | End.X with PSP&COC | [This.ID] |
| 108 | 0x006C | End.X with PSP&USP&COC | [This.ID] |
| 109 | 0x006D | End.T with COC | [This.ID] |
| 110 | 0x006E | End.T with PSP&COC | [This.ID] |
| 112 | 0x0070 | End.T with PSP&USP&COC | [This.ID] |
| 130 | 0x0082 | End with PSP&USD&COC | [This.ID] |
| 131 | 0x0083 | End with PSP&USP&USD&COC | [This.ID] |
| 133 | 0x0085 | End.X with PSP&USD&COC | [This.ID] |
| 135 | 0x0087 | End.X with PSP&USP&USD&COC | [This.ID] |
| 137 | 0x0089 | End.T with PSP&USD&COC | [This.ID] |
| 139 | 0x008B | End.T with PSP&USP&USD&COC | [This.ID] |
+-------+--------+----------------------------+-----------+
Table 1: IETF - SRv6 Endpoint Behaviors
¶
The security considerations described in [RFC8754], and [RFC8402] are applicable to this specification. No additional security measure is required.¶
TBD¶
TBD¶