1. SRv6 concept

Segment Routing (SR) is a source routing technology that assigns Segment IDs to each node or link. The head node combines these Segment IDs to form a Segment sequence (Segment List), which directs packets to be forwarded according to the Segment sequence. Implement network programming capabilities.

Currently, Segment Routing technology mainly has two implementations: SR-MPLS and SRv6. Among them, SR-MPLS is a Segment Routing implementation based on the MPLS data plane, and its SID is the MPLS label (Label); SRv6 (Segment Routing over IPv6, segment routing based on IPv6) is a Segment Routing implementation based on the IPv6 data plane, and its SID is an IPv6 address.

SRv6 combines the source routing advantages of Segment Routing with all the characteristics of IPv6, and has multiple network programming spaces, conforming to the idea of ​​SDN (Software Defined Network, Software Defined Network).

2. SRv6 implementation principle

2.1 SRH package

SRv6 implements segment routing by inserting a routing extension header SRH (Segment Routing Header) into the IPv6 packet header to carry segment transmission information. The SRH contains a Segment List represented by a SID list with IPv6 address characteristics. The destination address of the message will be updated segment by segment based on the Segment List, thereby completing segment-by-segment forwarding.

The message format of SRv6 is shown in Figure 1.

Figure 1 SRv6 message format

The fields contained in SRH are explained below:

Figure 2 Meaning of SRH extended header field

2.2 SID definition

The routable 128-bit SID is usually divided into three parts: Locator, Function and Arguments. The respective lengths of the three parts are flexibly defined according to actual needs.

• Locator is a network location identifier assigned to a network node and is used for routing and forwarding data packets.
• Function is used to express the forwarding behavior to be performed by the SID. In SRv6 network programming, different forwarding behaviors are expressed by different Functions.
• Arguments are optional parameters that can carry parameters required for instruction execution. For example, user ID, application type, quality requirements and any other relevant information.

Figure 3 Segment ID format

2.3 Segment type

SRH directly uses IPv6 addresses to represent segments, which can flexibly support many types. Different types of segments can be used together to complete specific functions. Generally speaking, Segments can be divided into two categories: Segments representing path information; Segments representing business information.

Figure 4 segment type

3. SRv6 forwarding process

Figure 5 SRv6 forwarding topology diagram

P1 and P2 simulate backbone network equipment, PE1 and PE2 simulate backbone network edge equipment, and CE1 and CE2 customer access devices Host1 and Host2 act as clients and servers. During the forwarding process, changes in destination IP, Segment list encapsulation, SL, Last Entry and other fields can be seen in the pcap packet.

3.1 Client accesses the server upstream path

Host1->CE1->PE1->P1->CE2->Host2

CE1:

PE1:

P1:

PE2:

CE2:

3.2 Client accesses the server downstream path

Host2>CE2->PE2->P2->CE1->Host1

CE2:

PE2:

P2:

PE1:

CE1:

4. Advantages of SRv6

• Simple deployment: only need to deploy SRv6 policies end-to-end, without operating intermediate transmission nodes.
• Intelligent: By interacting with the SDN controller through the MP-BGP protocol, the entire network can be automatically scheduled intelligently.
• Programmable: Segments can be programmed according to business needs.
• Aware applications: Bring application information into the network so that the network can sense application types and needs in real time to provide intelligent and customized services.
• Multiple tunnel capabilities: can support SRv6 BE, L2VPN, L3VPN

5. SRv6 application scenarios

5.1 Main application scenarios of SRv6

5.2 SRv6 home application scenario

The traffic is APN6 encapsulated through the cloud gateway, and the customized service traffic is imported into the SRv6 acceleration network through the traffic diversion policy to realize intelligent scheduling of home broadband services.

6. Summary and outlook

IPv6 has always been an issue of great concern to various countries. It is also the basis for the development of the next generation of the Internet. It is also an important new technological application of the new generation of information technology in my country's strategic emerging industries. As SRv6 technology matures, the application and deployment of IPv6 in existing networks will be accelerated.

As a new generation IP bearer protocol, SRv6 can simplify and unify traditional complex network protocols and will be widely used in home broadband business scenarios in terms of computing power networks, intelligent network scheduling, and service orchestration.