SR Linux architecture overview

The kernel is the core of a computer operating system, with complete control over everything in the system. The kernel is loaded and executed by the boot loader, then handles the system startup as well as input/output requests from software, translating them into data-processing instructions for the CPU. The kernel handles memory and peripherals, as well as interactions with the switch ASIC.

SR Linux uses a mainline Linux kernel with no modifications or customization. This allows kernel upgrades to be performed using normal upgrade mechanisms (yum on CentOS/RHEL-based systems, and aptitude on Debian-based systems).

SR Linux is designed to be OS agnostic, with support for all enterprise-class Linux operating systems, with current deployments focused on CentOS.

To follow the Linux Filesystem Hierarchy Standard (FHS), SR Linux software is distributed and laid out as a closed-source, third-party application on the OS. The FHS clearly defines where configuration and binaries should be kept; for SR Linux, all application configuration is kept in the /opt/srlinux directory.

SR Linux is a suite of applications running like any others would in a Linux environment. The applications communicate with the IDB to process configuration and state. SR Linux applications and IDB shows the relationship between the IDB and the applications that run in SR Linux.

Messaging between applications is controlled by IDB, and configuration via supported APIs is controlled by the management server application.

SR Linux applications describes the key SR Linux applications. Use the show system application CLI command to display information about all applications running on the system.

Table 1. SR Linux applications

Application name	Description
IDB	Controls messaging between SR Linux applications.
mgmt_server	Controls interaction between external APIs and the IDB, handles application-specific YANG models, and translates them into protobufs for IDB. See SR Linux management server.
aaa_mgr	Performs AAA for end users connecting to the system.
fib_mgr	Responsible for route resolution and route selection.
lldp_mgr	Responsible for sending and receiving LLDP packets via XDP.
static_route_mgr	Creates/updates/deletes static routes.
arp_nd_mgr	Responsible for ARP resolution for IPv4 and Neighbor Discovery for IPv6.
bgp_mgr	Runs the BGP control plane.
chassis_mgr	Monitors interface/subinterface state and synchronizes interfaces between Linux and the ASIC.
xdp_mgr	Handles data path programming. The xdp_mgr runs on each line card and is split into two components: platform independent and platform dependent. The platform-independent component handles communication between IDB and the ASIC, and the platform-dependent component is an extensible framework for plugging in data plane programming software.
linux_mgr	Creates routes and neighbors in Linux. As control packets enter the Linux host (and kernel), the Linux network stack responds to them. Synchronizing routes and neighbors to Linux stops Linux from ARPing/routing via the default gateway when routes exist at the data plane but not within Linux.
plcy_mgr	Enforces routing policies.
app_mgr	Monitors the health of the processes running SR Linux applications, and restarts them if they fail.
net_inst_mgr	Synchronizes VRFs between the switch ASIC and Linux.
log_mgr	Controls the log infrastructure, implemented by rsyslog.
acl_mgr	Controls ACLs in the system, both on the Linux host and on the CPM.
bfd_mgr	Controls BFD sessions on the system.

IDB stores data as protobufs. Protobufs use a .proto file to define how data is structured. Protobufs are not human-readable, but an IDB client is provided with the IDB server, which allows you to read from different topics, decoding the protobuf in real time.