Intel and Alibaba Bring Simplified Network Control to Telecom Networks by adding SRv6 into SONiC
By Reshma Sudarshan, Director Applications Engineering, Intel
Introduction
Enabling network operators to gain control of their networks and making the network programmable are the answers to some of the top challenges that many communications service providers (CoSPs) face today. One of the main issues is that traditional protocols do not give CoSPs the ability to change or modify the behavior of their networks to deliver on service level agreements (SLAs) and engineer the deterministic latency needed for user applications.
Bridging Different Network Domains
Another challenge CoSPs face today is that IP backbone, metro, and mobile bearer networks are all independent network domains that are isolated from each other. Applications, however, require packets to traverse these network boundaries. In order to extend services across domains, complex inter-autonomous system (AS) VPNs and the associated protocols need to be enabled on switching devices adding to management burden and deployment complexity.
Network Control using SDN and SRv6
The solution to these challenges involves software defined networking (SDN), which provides network control to solve this business need for better control of large networks and IPv6 which allows for extending services across isolated network domains. CoSPs embrace SDN and IPv6 networks because this combination allows them to build large networks and cater to SLA guarantees and future proof 5G requirements. The controller-based SDN solution provides a network-wide view of the live data traffic and network operators can now dynamically steer packet flows around areas of congestion to most efficient paths in a network.
Segment routing for IPv6 (SRv6) is an SDN solution for source routing that provides powerful programming ability and a flexible solution for traffic engineering with efficient traffic steering. SRv6 is a segment routing technology based on the IPv6 forwarding plane which is easy to deploy because it does not require complex MPLS protocols or hardware support, while also ensuring quality of service and maintaining network resiliency.
Expanding the Scope of SONiC with SRv6
SONiC is an open source network operating system (NOS) developed by Microsoft and the OCP community that is widely deployed in data centers and supported by most switch ASIC vendors. Implementing SRv6 in SONiC enables CoSPs to have a single management interface with fine grained network control while using existing telemetry features for analytics, fault isolation and to achieve intelligent proactive O&M.
Intel, working together with leading CoSP Alibaba and Microsoft, helped add SRv6 to SONiC, creating a powerful traffic engineering tool that would restore control to the network operators and natively bridge network domains.
How SRV6 achieves Network Programming
SRv6 creates a network domain with predefined network segments that can be set up within an IPv6 network where segment-based traffic steering is desired. The SRv6 domain is composed of three types of SRv6 nodes:
- The ingress head-end node, which encodes SRv6 Header data into each packet.
- The transit node that routes a packet based on the information in that added segment routing header (SRH).
- The egress end node that removes the SRH and forwards the packet using the packet’s original protocol.
Packets are forwarded along an ordered list of up to 16 segments — with each segment consisting of one or multiple network hops — that define the journey from the ingress head-end node to the egress END node. The segments can be changed by the controller based on network dynamics. In this way, SRv6 can be used to steer traffic in certain parts of the network.
SRv6 also supports service function chaining to enable the creation of composite network services (CG-NAT, SLB etc) that consist of an ordered set of service functions. SRv6 provides a simple scalable way to chain service functions by assigning a segment ID (SID) to each service function and sequencing these service SIDs in a segment list.
SRv6 features are supported in the Intel® Tofino™ 2 programmable Ethernet switch ASIC. Intel Tofino 2 features a P4-programmable Match-Action Pipeline architecture that can support SID-based forwarding as well as host value-added services such as load balancing and CG-NAT. These capabilities mean a wide range of SRv6 use cases such as H.Encaps, END.DT46 and uSID are supported in Intel Tofino 2.
Alibaba’s SRv6 Use Case
The diagram below illustrates a basic use case implemented by Alibaba. The SDN controller uses gRPC to communicate with the switches to install segment routing (SR) policy. The head-end node encodes the path information in the segment routing header (SRH). The SRH contains the SRv6 path as an ordered sequence of SIDs. Each SID contained by that field is 128 bits long. The transit nodes are not required to maintain the path information, they process the segment-IDs and forward the packet to the next segment. Alibaba uses SRv6 SIDs as service anchor point for scaling a service mapping mechanism. They use SR policy and auto steering in the backbone network to provide agile and predictable network service to meet customer end-to-end SLA guarantees and to reduce the cost of operation achieved through SID mapping.
Conclusion
Through software development work done by Intel, along with Alibaba and Microsoft, and many community members, the latest SONiC release (SONiC.202111) supports SRv6 to address use cases such as H.Encaps.Red and END.DT46. This milestone opens the doors for the SONiC community to experiment and move towards production deployment of SONiC in CoSP networks using SRv6. In more general terms, this development facilitates SDN features onto SONiC. Another feature adding controller-based SDN management of switches was introduced in 2021 through the addition of P4 integrated networking stack (PINS) that can be used in tandem with SRv6 to enhance SDN capabilities for managing the allocation and distribution of SR policies. The result is more intelligence to network traffic steering using a simplified protocol stack that is still native IP compatible.
Intel continues work on SRv6 together with Alibaba and Microsoft along with other partners in the SONiC community to add features like END.X with SRv6 FRR integration into SONiC, sBFD and uSID. Other possible features may include service-proxy using PINS.
Try out SRv6 in the SONiC.202111 release! Comment and contribute to SRv6 HLDs –
https://github.com/opencomputeproject/SAI/pull/1231
https://github.com/Azure/SONiC/pull/795
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