Border Gateway Protocol
The interdomain routing protocol of the internet — and the control plane of modern DC fabrics. OcNOS implements BGP-4 (RFC 4271) with the full extension set required for SP transit, IXP peering, and leaf-spine DC underlay.
BGP Peering Topology
Two autonomous systems exchanging routes via eBGP, with the local AS running iBGP through a Route Reflector to scale full-mesh peering.
BGP in Service Provider and DC Contexts
BGP-4 (RFC 4271) is a path-vector protocol that exchanges reachability information between autonomous systems. Its policy model — route maps, community tagging, AS-path filtering — gives operators precise control over traffic engineering across AS boundaries. The BGP multi-protocol extensions (RFC 4760) allow the same session to carry multiple address families: IPv4, IPv6, VPN, EVPN, SR-TE, and more.
In the data center, BGP has replaced OSPF and IS-IS as the de facto underlay in large-scale leaf-spine designs. RFC 7938 (Use of BGP for Routing in Large-Scale Data Centers) documents this shift: eBGP unnumbered sessions between leaf and spine, private ASNs per-device, and ADD-PATH for ECMP load distribution. OcNOS supports all three RFC 7938 design patterns.
BGP-LU (RFC 3107) distributes MPLS labels with BGP prefixes, enabling inter-AS MPLS LSP stitching without LDP. This is the foundation for BGP-signaled L3VPN Option C deployments across AS boundaries without exchanging full VPN routing tables at the border.
BGP FlowSpec
BGP FlowSpec (RFC 5575, RFC 8955) distributes traffic flow specifications as BGP routes. Each FlowSpec route matches a 5-tuple (or extended match criteria) and carries a REDIRECT or RATE-LIMIT action. This enables distributed DDoS mitigation at the network edge — a controller pushes a FlowSpec prefix to all PE routers simultaneously, black-holing or rate-limiting attack traffic without manual per-device configuration.
OcNOS Implementation
BGP-4 Base
RFC 4271 full compliance. 4-byte ASN (RFC 6793). MD5 TCP authentication (RFC 2385). Graceful Restart (RFC 4724). BGP NOTIFICATION reason codes.
Route Reflector
RR cluster support. Multiple RR clients per cluster. ORIGINATOR_ID and CLUSTER_LIST loop prevention. Confederation support (RFC 5065). On-demand RR for scaled deployments.