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Juniper Networks Router Architecture

Learn how routing takes place through a Juniper Networks router, the function of the ASICs, and how fan trays and impellers keep the system components cool. Also, examine the router startup process and the order in which the boot image locations are searched.
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When the routers produced by Juniper Networks first hit the market in 1998, they brought simplicity of design, a logical UNIX-style CLI, and robust troubleshooting tools. The engineers who designed the routers wanted to build a device that made sense. In doing so, they filled a void in the market and appealed to other engineers who wanted a router that moved packets through as quickly as possible.

Juniper Networks' product offerings come in the form of the M-Series routers. The M40 was the first router of its kind capable of scaling to meet current Internet needs. The initial M40 release was based on the Internet Processor I. The Internet Processor I was the fundamental core of the packet forwarding engine (PFE). The PFE consisted of a shared memory, a single forwarding table, and a one-write, one-read architecture. The entire PFE was capable of forwarding 40Mbps, more than 100 times the capacity of other available router architectures at the time.

Although the M40 was quite progressive, Juniper Networks was able to improve on its available functionality by upgrading the processor, raising the available memory, adding redundancy, and including the ability to filter traffic through ACLs in later iterations of the product.

This chapter introduces you to the router models and architectural differences of each product. In addition, we will describe each hardware and software piece of the router and explain how that piece contributes to the overall logic of the device. This will include the routing engine, the PFE, the switching fabrics and control boards, the interfaces available, and the differences between the available router models. It will also include an explanation of the router's boot process and how to upgrade the JUNOS software.

Since the architecture and operating-system commands of these routers differs from those of other vendors, such as Cisco, with which you may already be quite familiar, the material covered here should help you to understand the rest of the material in this book. It will also undoubtedly help in your pursuit of Juniper Networks career certifications.

3.1 Juniper Networks Router Models

This section describes the different models of Juniper Networks routers. The physical dimension, performance statistics, and some information about the internal architecture of the router itself are provided for each model.

3.1.1 M5 and M10

The M5 and M10 routers were introduced in September 2000 as the latest additions to the router family. With their introduction, Juniper Networks hoped to gain a larger marketshare by appealing to networks needing a smaller footprint router. Due to its minimal physical requirements—5.25 3 17.4 3 24 in., or 13.33 3 44.2 3 60.96 cm—single rack can hold 15 M5s, which creates a bandwidth-to-footprint-to-price ratio that is hard to beat.

The M5 and M10 were released at the same time because they had similar architectures with two different throughput capabilities (5Gbps on the M5 and 10Gbps on the M10). Both routers employ the Internet Processor II ASIC, providing forwarding table lookups at 40Mpps.The M10's chassis looks the same as the M5's; however, there are two forwarding engine boards (FEBs) in the M10, allowing for a maximum of eight physical interface cards (PICs) to be used.

3.1.2 M20

The second router introduced by Juniper Networks was the M20, released in December 1999. The M20 also uses the Internet Processor II ASIC and is capable of throughput in excess of 20Gbps.

With physical dimensions of 14 3 19 3 21 in., or 35.56 3 48.26 3 53.34 cm, a network administrator can stack five chassis in a single equipment rack. The M20 was the first Juniper Networks router available with redundancy (power supply, routing engine, and system and switch board [SSB]). This greatly increased the appeal of the Juniper Networks routers to the marketplace. Component failure in an operational network can be disastrous. By addressing the need for component redundancy, Juniper Networks was able to allay this fear in the minds of potential customers.

3.1.3 M40

The M40 router was the first product launched by Juniper Networks. With a chassis size of 35 3 19 3 23.5 in., or 88.9 3 48.26 3 59.69 cm, deployment is limited to two chassis per equipment rack. However, the router's architecture provides over 40Gbps throughput. The M40 supports the same PICs as the M20. The PICs are compatible between both platforms. Although initially deployed with the Internet Processor I and without ACL capability, the M40 now runs on the Internet Processor II and has addressed the need for filtering. This platform, however, does not provide for the same component redundancy as the M20 and M160 models, an important distinction for most customers.

3.1.4 M40e

To answer the need for the throughput of the M40 coupled with redundant-component capability, Juniper Networks introduced the M40e platform in February 2002. The M40e router has the same footprint and port density as the M40, but it provides the optional redundancy that the M40 does not. This model is compatible with most of the PICs from the M20, M40, and M160 models.

3.1.5 M160

The M160 was introduced in March 2000 as the third box in the M-Series. It is a formidable router, both in size and capacity. The M160 chassis is 35 3 19 3 29 in., or 88.9 3 48.26 3 73.66 cm. This allows for two per equipment rack.

The M160, to date, is the highest-rated core router on the market. Independent testing has shown that the M160 outperforms the competition in areas of BGP table capacity, MPLS LSP capacity, route flapping recovery at OC-192 speeds, convergence at both OC-192 and OC-48 speeds, and filtering at both OC-192 and OC-48 speeds. In additional tests, the M160 has matched or exceeded the competition in the areas of CoS at OC-48 and OC-192 speeds and IP and MPLS baseline testing at OC-48 and OC-192 speeds.

The M160 platform provides the maximum throughput and port density necessary for the next generation of Internet architectures.

3.1.6 G10

In November 2001, Juniper Networks announced its intent to acquire Pacific Broadband Communications and its CMTS. Subsequently, Juniper Networks rereleased that CMTS as its G10 router. This product is aimed at the growing broadband-remote-access-service (BRAS) market that delivers Internet service into private homes and small businesses primarily through cable modems.

A chief complaint of cable Internet subscribers is that as more subscribers join in a given area, the amount of bandwidth available to each end user can drop dramatically. The G10 uses a custom-built ASIC that has the capability of 20 legacy CMTS chips. The end result is that this device is capable of supporting greater numbers of subscribers using less bandwidth.

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