SONiC SRv6 VPN Deployment for Predictable WAN

Author: Shuan Shuan, Software Engineer, Alibaba; Jason Boss, Principal Software Engineer, Cisco Collection: 2023 Global Summit - Networking

Summary

Alibaba and Cisco presented their joint effort to build a predictable global WAN using SRv6 VPN on SONiC-based white box routers. Alibaba's predictable network framework is an end-to-end Ethernet architecture spanning hyperscale data centers, edge networks (with programmable smart NICs and DPUs), and a global network interconnecting regions. The global network is simplified to a single protocol stack (IPv6/SRv6), single-chip white box routers, and SONiC as the NOS for all devices. SRv6's programmability enables fine-grained quality-of-service differentiation by encoding different VPN SIDs for different service tiers within the same tenant.

The deployment uses two key device roles: Elastic Service Routers (ESR) as PE (provider edge) routers supporting SRv6 VPN head-end functionality, and Elastic Core (EC) as P (provider) routers. For each tenant, four VRFs are configured on the ESR -- a root VRF receiving routes from CE devices, and three service-quality VRFs (green/yellow/red) with different VPN SIDs. Users select service quality either via DSCP marking (matched by ACL PBR) or by using specific UIDT46 SRv6 service SIDs. The second use case deploys SONiC white box routers as an Elastic Peering Fabric (EPF) for south-north traffic with service providers, using SRv6 TE for traffic steering within a spine-leaf fabric controlled by a local BGP controller.

Cisco extended the SAI specification to properly support SRv6 VPN encapsulation by decoupling VPN SIDs from traffic engineering SID lists, solving a combinatorial explosion problem. Additional SAI extensions include SBfD (Seamless BFD) with SRv6 encapsulation for tunnel path monitoring, SRv6 path tracing for telemetry, and tunnel maps for flexible VPN SID assignment per VRF or per prefix. The platform supports 2 million routes and was designed to overcome SONiC's original data center switch focus for router use cases.