BGP
BGP might be the most commonly used and important feature in switches. In this section, we take a deeper look at BGP-related workflows.
BGP Processes
SONiC uses FRRouting as its BGP implementation, responsible for handling the BGP protocol. FRRouting is an open-source routing software that supports multiple routing protocols, including BGP, OSPF, IS-IS, RIP, PIM, LDP, etc. When a new version of FRR is released, SONiC synchronizes it to the SONiC FRR repository: sonic-frr, with each version corresponding to a branch such as frr/8.2.
FRR mainly consists of two major parts. The first part includes the implementations of each protocol, where processes are named *d. When they receive routing update notifications, they inform the second part, the "zebra" process. The zebra process performs route selection and synchronizes the best routing information to the kernel. Its main structure is shown below:
+----+ +----+ +-----+ +----+ +----+ +----+ +-----+
|bgpd| |ripd| |ospfd| |ldpd| |pbrd| |pimd| |.....|
+----+ +----+ +-----+ +----+ +----+ +----+ +-----+
| | | | | | |
+----v-------v--------v-------v-------v-------v--------v
| |
| Zebra |
| |
+------------------------------------------------------+
| | |
| | |
+------v------+ +---------v--------+ +------v------+
| | | | | |
| *NIX Kernel | | Remote dataplane | | ........... |
| | | | | |
+-------------+ +------------------+ +-------------+
In SONiC, these FRR processes all run inside the bgp container. In addition, to integrate FRR with Redis, SONiC runs a process called fpmsyncd (Forwarding Plane Manager syncd) within the bgp container. Its main function is to listen to kernel routing updates and synchronize them to the APPL_DB. Because it is not part of FRR, its implementation is located in the sonic-swss repository.
References
- SONiC Architecture
- Github repo: sonic-swss
- Github repo: sonic-frr
- RFC 4271: A Border Gateway Protocol 4 (BGP-4)
- FRRouting