Wednesday, November 11, 2020


Introducing DENT OS, switchdev NOS for the rest of us talk, presented at the recent Open Source Summit, describes the Linux Foundation DENT project. The slides from the presentation are available.

Linux switchdev is an in-kernel driver model for switch devices which offload the forwarding (data) plane from the kernel. Integrating switch ASIC drivers in the Linux kernel makes switch ports appear as additional Linux network interfaces that can be configured and managed using standard Linux tools. 

DENT is an Ubuntu based Linux distribution that packages the drivers for switch hardware (fans, temperature sensors, ASIC, etc) along with the open source FRRouting routing protocol suite which includes protocol daemons for BGP, IS-IS, LDP, OSPF, PIM, and RIP. The FRRouting software uses the Linux netlink API to program Linux kernel packet forwarding, which on a hardware switch platform is offloaded by the switchdev driver to the ASIC for line rate forwarding.

A major benefit of DENT's approach to making Linux into the network operating system is that the same tools used to configure, manage and monitor Linux servers can also be used to manage network switches. In addition, a DENT virtual machine behaves in exactly the same way as DENT running on a physical switch, allowing configurations to be validated in virtual environments before being pushed into the production network.

The open source Host sFlow agent streams standard sFlow telemetry from Linux hosts. On a switchdev based network switch, hardware counters are gathered using standard Linux API's for monitoring network interfaces. The Host sFlow agent also supports Linux psample and drop_monitor APIs that provide visibility into packet flows and dropped packets. On hardware switches, the switchdev driver offloads these measurements to the switch ASIC which provides line rate visibility into packet forwarding. 
Installing Host sFlow agents on DENT OS based switches activates the standard sFlow hardware instrumentation in switch ASICs to stream network telemetry to an sFlow collector, for example sFlow-RT, for the real-time network-wide view of performance needed to drive automation.

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