1. Introduction to the Junos Operating System
Chapter 2: Junos Operating System Fundamentals

2. Chapter Objectives
After successfully completing this chapter, you will be able to:
Describe the Junos operating system and its basic design architecture
Explain traffic processing for transit and exception traffic
Identify and provide a brief overview of Junos devices

3. Agenda: Junos Operating System Fundamentals
The Junos OS
Traffic Processing
Overview of Junos Devices

4. The Junos OS Robust, modular operating system
Provides industry-leading performance and scalability
Based on the FreeBSD UNIX operating system

5. Single Software Train
A single software train for all platforms running the Junos OS
Eases management overhead by providing a consistent set of features that are implemented in a consistent manner
12.0
12.1 …
J2320
TX Matrix

6. Separation of Control and Forwarding
All platforms running the Junos OS share a common design goal:
Clean separation of control and forwarding functions
Routing Engine RT FT
The Junos OS
Control Plane
Internal Link
Forwarding Plane FT
Frames/Packets In
Frames/Packets Out
Packet Forwarding Engine

7. Packet Forwarding Engine
Routing Engine
Maintains routing and forwarding tables
Controls and monitors the chassis
Manages the PFE
Routing Engine RT FT
The Junos OS
Control Plane
Forwarding Plane
Packet Forwarding Engine

8. Packet Forwarding Engine
Uses Layer 2 and Layer 3 forwarding tables, provided by the RE, to forward traffic toward its destination
Implements various services such as policing, stateless firewall filtering, and class of service
Routing Engine
Control Plane
Forwarding Plane FT
Frames/Packets In
Frames/Packets Out
Packet Forwarding Engine

9. Agenda: Junos Operating System Fundamentals
The Junos OS
Traffic Processing
Overview of Junos Devices

10. Transit Traffic Processing
Transit traffic is forwarded through the local system
PFE uses the forwarding table provided by the RE
Examples of transit traffic include unicast and multicast traffic
Routing Engine
CPU
Control Plane
Forwarding Plane FT
Frames/Packets In
Frames/Packets Out
Packet Forwarding Engine

11. Exception Traffic Processing (1 of 2)
Exception traffic is processed by the local system
Traffic destined for the local system is processed by RE CPU
In most cases, the PFE processes traffic requiring the generation of ICMP messages, such as TTL expired
Routing Engine
CPU
Control Plane
Forwarding Plane
Frames/Packets In
Frames/Packets Out
Packet Forwarding Engine

12. Exception Traffic Processing (2 of 2)
Exception traffic is rate-limited on the internal link to protect the RE from potential DoS attacks
Control traffic is given preference when congestion exists
Routing Engine
CPU
Control Plane
Built-In Rate Limiting
Forwarding Plane
Frames/Packets In
Packet Forwarding Engine

13. Agenda: Junos Operating System Fundamentals
The Junos OS
Traffic Processing
Overview of Junos Devices

14. Overview of Junos Devices
Platforms running the Junos OS span switching, routing, and security roles and are suited for small to large networks in both enterprise and service provider environments
Routing
Switching
Security

15. Junos Routing Devices M Series LN Series ACX Series PTX Series
MX Series
T Series

16. Junos Switching Devices
QFX Series
EX Series

17. Junos Security Devices
J Series
SRX Series

18. Summary In this chapter, we:
Described the Junos OS and its basic design architecture
Explained how transit and exception traffic is processed
Identified and provided a brief overview of Junos devices

19. Review Questions What are some advantages of the Junos OS?
What are the primary functions of the control plane and the forwarding plane on Junos devices?
How are transit and exception traffic processed?
Name three platforms that run the Junos OS.