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Routers repent - the end may be near.

Routers have a limited future in the corporate backbone because they lack scalability to Gigabit speeds and lack the processing power to handle a million packets per second on each Gigabit link. Routing switches will inherit the routing function as corporations move to Gigabit backbone speeds.

Routing switches are a new class of switch, bringing the high performance and low cost of Ethernet switching to IP routing. Routing switch technology provides scalability to Gigabit speeds and low-latency, wirespeed IP routing at costs significantly lower than today's routers.

In today's network, say your executive team has mandated deployment of centralized intranet servers to lower the cost of providing corporate information. Users accessing centralized servers drive an ever-increasing volume of traffic across the backbone and place a greater load on the routers. Network analyzers reveal backbone congestion. Consultants with traffic modeling tools predict network-wide gridlock.

The challenge before you is to expand the capacity of the backbone, and to do so within the constraints of a tight IS budget.

The challenge for routers is scaling to support multiple Gigabit Ethernet connections and reliably processing all the traffic (see Table).


A backbone router with five FDDI connections must scale to five Gigabit Ethernet connections. A single Gigabit Ethernet link can contain over 1 million packets per second (Mpps), yet high-end routers will only support 1 Mpps total.

In our example, the router with five Gigabit links will only process 20% of the generated traffic. This means that router technology will not support more than a single Gigabit link.

Many vendors have announced support for Gigabit routing switch ports, but there have been no announcements of Gigabit router ports. Is it even possible to create a router capable of processing 5 to 10 million packets per second?

Given that router vendors may announce Gigabit support tomorrow, bigger routers may be a solution for the scalability problem. Could a faster router help?

A higher performing router such as the proposed BFR (Big, Fast Router) is certainly one option to the scalability problem since it undoubtedly would support high-density Gigabit ports. But at what cost?

Comparing routing switch ports, currently you pay 3.5 times more for a Gigabit port than a Fast Ethernet port. Today's Fast Ethernet router ports cost around $5,000. If you apply the Fast Ethernet-to-Gigabit price difference to router ports, a single Gigabit router port would cost around $17,500.

Wow! Maybe BFR really stands for Best For Revenue. The point is, current routers cannot scale to support more than one Gigabit port, and the BFR-type solution will not fit the requirement for a low-cost solution -- at least at current rates.

Ethernet and token ring Layer 2 (L2) switches prevail throughout corporate America for wirespeed performance and low-cost network access. But L2 switches lack IP routing functionality.

Routing switches compensate for this by combining IP routing with L2 switching. The result is a single device performing Ethernet switching and IP routing at the speed and cost of switching.

Routing switches make sense throughout the corporate LAN to improve response time to mission-critical applications and to increase backbone capacity (see Figure). Initially, routing switches aggregate risers and connect to the backbone router. This offloads local IP traffic (source and destination within the building) from congested routers and improves performance between building subnets.


Switches differ from routers in basic technology and design goal. Routers use processors and software to make forwarding decisions for all traffic crossing subnet boundaries. They have very sophisticated protocol and filtering functionality and perform many other tasks such as network security, broadcast control, and connecting dissimilar network technologies. Performance is important in routers, but the primary goal is sophisticated functionality.

Switching technology deals with network connectivity in a completely different fashion. ASIC technology enables switches to do a few things extremely fast. The primary design goal of both L2 and routing switches is wirespeed performance.

There are two issues with Gigabit scalability. First, a switch must have a high-capacity switch fabric to support the high traffic demands of Gigabit ports. Current technology enables a single ASIC to process 2-3 Gbps and a typical routing switch line card to support 1-2 Gb ports.

Beginning early this year, vendors will ship switches with multi-Gigabit backplanes capable of supporting 10 or more Gb ports in a single switch. This makes routing switches an excellent solution for scaling the backbone to Gigabit Ethernet.

The second scalability issue concerns processing IP frames on multiple Gigabit links. In our example, the router needs five Gigabit ports. This means it must process more than 5 Mpps of IP traffic.

We have already seen that routers are limited to I Mpps or less. Routing switches, however. process IP frames at Gigabit speeds due to ASIC technology. Users can expect routing switches to ship with IP packet processing capacity starting at 3 Mpps.


Another issue is cost. Ethernet switch pricing has been significantly lower than Ethernet bridge pricing because of ASIC technology. Switch prices have fallen steadily, causing bridges to be eliminated as a viable network solution.

This same pricing pattern holds true for routing switches and routers. Today a Fast Ethernet routing switch port is around $700 and a Fast Ethernet router port is around $5,000.

In fact, a Gigabit routing switch port costs $2,500 and delivers 10 times the capacity, at half the cost of the 100-Meg router port. This is a big price difference, especially if you consider that a routing switch port processes all frames at wirespeed with near zero latency.

Does all this mean that routing switches will eliminate the need for routers? Not necessarily. With their sophisticated filtering capabilities, routers remain the best device for internal and external firewalls.

Essential in this age of Internet connectivity, external firewalls protect our networks from outside sources. But routers also protect confidential resources from individuals within the company, restricting access, for instance, between Human Resources or Finance and the rest of the corporate LAN.
COPYRIGHT 1998 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1998 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Technology Information; routing switches
Author:Lougee, Rick
Publication:Communications News
Date:Jan 1, 1998
Previous Article:Predicting performance.
Next Article:Take a second look at ISDN.

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