[技术分享] 剖析现在的核心路由操作系统

Introduction
The demands on Internet Protocol (IP) networks have evolved dramatically over the last
decade.  Nowhere is this more apparent than at the heart of service provider networks: the
core.  Service providers continue to make the transition from best-effort Internet to a
singular IP/MPLS infrastructure capable of delivering assured experiences for not only
data, but also voice and video.  This new network paradigm – an Infranet – only increases
the technical pressure on core routing hardware and software.  Today’s changing
environment is particularly demanding on the routing operating system (OS).  As many
service providers and vendors are finding, perhaps the greatest attribute of a core routing
OS is an intangible, rather than a technical one: foresight.  
In 1998, Juniper Networks launched the first purpose-built carrier-class router, the M40
Internet backbone router.  The JUNOS Software, which ran on the M40 router, was ground-
breaking given that it was the first operating system to have a modular architecture and be
purpose-built for service provider environments.  Since its initial introduction with the M40
router, JUNOS software has attained over 7 years operational experience in the world’s
largest service provider networks and now executes on all M-series, T-series, and J-series
routers.   
Recently, other router vendors have started to implement the router architecture and
modular software designs first introduced by Juniper Networks in 1998.  Although these
implementations emulate the fundamental design principles pioneered by Juniper
Networks, they are not equal to the Juniper Networks implementations.  The ASIC
hardware used in the Packet Forwarding Engine (PFE) of Juniper Networks routers
supports all features on all interfaces and has constantly demonstrated its merit in
production networks over the years.  JUNOS software is a full featured implementation,
providing regular and reliable updates while simplifying the software upgrade
management process.  While the initial success of JUNOS software demonstrates Juniper
Networks understanding of core requirements and design expertise, the subsequent
longevity and extensibility of JUNOS highlights Juniper Networks vision and foresight. Router Operating Systems
A router operating system is responsible for implementing and supporting the control
plane of the network.  The key functions performed by a router operating system include:
·  User interface management
·  Chassis management
·  Network interface management
·  Routing protocol management
·  Local packet management
·  Network management
Each router vendor releases periodic operating system updates that run on their hardware
platforms to introduce new features that service providers require to support growth and
provide revenue generating services.  Since the software upgrade process is an essential
part of network operations, it should be simple to manage and feature updates should not negatively impact the delivery of customer services.  
The operating system executes on the routing engine (i.e., computer) and is closely coupled
to the vendor’s custom processor hardware that implements the packet forwarding engine.  
Because the processor hardware implements the control plane that is defined by the
router’s configuration, it is very difficult to evaluate an operating system without also
evaluating the processor hardware that supports the packet forwarding process.  For
example, a feature rich operating system that is not efficiently and accurately supported by
hardware will provide inadequate network control.  If the processor hardware does not
provide adequate performance, then enabling certain features can severely compromise the
forwarding performance of the router.  The router hardware must scale with the operating
system if it is to sustain the intent of the software and provide feature consistency on both
low speed and high speed interfaces.

Implementation Requirements
The numerous requirements for a carrier-class operating system include:
·  A modular software design
·  Industrial strength routing protocols
·  Stability
·  Scalability
·  Security
·  Multiple platform support Protocols ......................................................................................5
Stability ..........................................................................................................................................5
Scalability.......................................................................................................................................6
Security...........................................................................................................................................6
Multiple Platform Support .........................................................................................................8
Dependable Software Update Schedule...................................................................................8
Engineering Discipline ................................................................................................................8
The Benefits of JUNOS Software........................................................................................................9
Conclusion ............................................................................................................................................10