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tech juniper ijaut > 11: Introduction to Junos
Junos OS is modular. Processes have their own memory spaces. The control and forwarding planes are separated. This separation is how the Junos OS supports such a wide variety of platforms from the same codebase. The Routing Engine is the control plane. It has an internal link to the Packet Forwarding Engine which is in the forwarding plane. The Packet Forwarding Engine forwards packets, frames or both with high stability and deterministic performance.
The Routing Engine maintains routing and forwarding tables, provides user interfaces, controls and monitors the chassis, and manages the PFE.
Transit traffic is forwarded through the local system. It is processed by the PFE and is not seen by the RE. Transit traffic may be unicast or multicast.
Exception traffic does not pass through the local device, but requires special handling by the RE. Exception traffic includes traffic addressed to the local device, IP packets with IP options, traffic requiring ICMP responses. Exception traffic is rate limited to prevent denial of service attacks. Control traffic (addressed to the local device) is given preference when congestion exists.
RJ-45 RS-232 @ 9600bps, 8/1/N
The root user is logged in to the Unix shell by default, and must use the ‘cli’ command to get a Junos prompt. Other users go straight to the Junos CLI and can access the Unix shell with the ‘start shell’ command if their permissions allow.