Carrier Routing System

Carrier Routing System is a large-scale core router, developed by Cisco Systems, Inc. It runs IOS XR which is a train of IOS built upon the QNX microkernel. A single chassis holds a maximum of 16 line cards, and can run an OC-768 SONET interface. The system has the capability for combining multiple line card chassis using separate dedicated fabric chassis, allowing one system to replace a cluster of Internet core routers in a single site. In this multi-chassis configuration, each line card chassis (LCC) is connected over multiple fabric switching planes with one or more fabric card chassis (FCC). The chassis interconnections are achieved with PAROLI (parallel optical link) fiber optic bundles.

A fully populated CRS contains over 1000 linecards at 40 Gbit/s each and theoretically can scale to 92 Tbit/s bandwidth via multi-chassis configuration, although multichassis systems of such size were never delivered or shown to public. As of 2009, the largest production CRS-1 system is limited to eight line card chassis, for a total of 10 Tbit/s.

In both single- and multi-chassis configurations, the CRS-1 switch fabrics are based on a three-stage Beneš architecture. In a single-chassis system, the three switching stages—S1, S2, and S3—are all contained on one fabric card. In a multi-chassis system, the S2 stage is contained within the FCCs, with the S1 and S3 stages resident in the LCCs at the egress and ingress interfaces fabric plane interfaces, respectively.

While the device was in development, it was known by the code name of HFR, or Huge Fucking Router. The marketing group later maintained this actually meant Huge Fast Router. This code name was coined in the tradition of Cisco's previous service provider router, the GSR (12000-series), whose development code name was BFR, or Big Fucking Router. BFR even had a logo of a fist punching through a globe. On one of the fingers is a ring with the industry-standard blue router icon, and below the logo it says "BFR" on a banner. This same logo can be seen on the internals of some early GSR line cards. All CRS-1 software package file names start with "hfr-" (e.g., "hfr-fpd.pie-3.4.2" is the FPGA image).

At launch time in 2004, Cisco CRS-1 became the largest production router in existence, although it featured the same 40 Gbit/s/slot density as the first-generation T-series router (T640) launched by Cisco's archrival Juniper Networks two years earlier (2002). Effectively, CRS-1 16 delivered twice the capacity of competition in twice the space (non-standard full rack). Cisco's new Carrier Routing System included support for hardware-based virtual routers (SDRs) and remote process placement in IOS-XR. Other innovative features announced at launch (i.e. ISSU and self-healing) became significantly delayed. Multichassis version of CRS-1 16 as well as smaller chassis types (CRS-1 8 and CRS-1 4) became commercially available post-FRS.