Quick question: routers and switches

[Wingless]

What's the difference between, say, a 4-port router, and a 4-port switch? Or, what is a router, and what is a switch?

[guthmund]

Ah, I knew I remembered Mr. Mephisto doing an excellent write up about this....

Check out this thread...

http://www.tfproject.org/tfp/showthr...uters+switches

It don't get any better than that....

[Lasereth]

While Mr. Mephisto's guide is extremely useful, it's hard to understand for folks who don't even know what each component does. So here's my extremely simple, way-too-layman's definitions:

A 4-port hub can be used to connect PC's together through a decent connection. A switch can be used to do the same thing but is simply faster than a hub for various reasons that Mr. Mephisto explained. So basically, a hub and a switch are sort of the same thing with a switch allowing much faster connections.

A router can be attached to a hub or switch. Some routers have built in 4-port switches which is really useful. What does a router do? It simply allows an ethernet Internet connection to be shared across a network to multiple computers. If you have dial-up, a router isn't necessary (you can share dial-up Internet across a hub to multiple PCs). If you have Cable or DSL, a router is needed. Without a router, only one computer on a hub or switch network can use the broadband Internet connection without paying extra. If you buy a router and connect it to your network, multiple computers on the network can share the broadband Internet connection by means of DHCP and other neat acronyms.

In summary: a hub is a device that allows computers to connect to each other on a network. A switch does the same thing only faster due to various technological upgrades. A router can be used to allow a broadband Internet connection to be shared across a switch or hub network.

I know this is a simple explanation but I don't think further explanation is needed for someone who just wants to know what each device is.

-Lasereth

A hub is like a pool where all the machines on the network share their communication.

A switch allows the machines to communicate more directly with one another (i.e. they don't all share the same 'pool' of information)

A router is a thing that connects different and often distant networks together i.e. Many people connect to their ISP via a broadband router.

[bendsley]

Also, please be advised that some switches are Layer 3 switches.
=============================================================
A Layer 3 Switch Is a Router
Vendors and the trade press alike have tried to apply the term "Layer 3 switch" to various products of the day, succeeding only in confusing IT decision makers. A Layer 3 switch does everything to a packet that a traditional router does:

* Determines forwarding path based on Layer 3 information
* Validates the integrity of the Layer 3 header via checksum
* Verifies packet expiration and updates accordingly
* Processes and responds to any option information
* Updates forwarding statistics in the Management Information Base (MIB)
* Applies security controls if required

Because it is designed to handle high-performance LAN traffic, a Layer 3 switch can be placed anywhere within a network core or backbone, easily and cost-effectively replacing the traditional collapsed backbone router. The Layer 3 switch communicates with the WAN router using industry-standard routing protocols like RIP and OSPF.

Router Interfaces as Layer 2 Switching Domains
The Layer 3 switch has inherent Layer 2 switching domains per interface, allowing for individual subnet bandwidth allocation, along with broadcast containment. Not all interfaces are created equal, so the ability to group ports together, whether based on physical characteristics or protocol information, is an extremely powerful tool for network designers concerned with capacity planning. This architecture is inherently scalable, capable of supporting numerous external Layer 2 switches that reside either in the data center or the wiring closet.

Such a design model preserves the subnetted infrastructure, concurrently boosting performance of those subnets and enabling the deployment of switched 10, 100, or 1000 Mbps right to the desktop if so desired. The concept of "subnet preservation" is the key to effective and trouble-free network migration—it allows gradual migration, helping IT managers to work within their staffing constraints without the need to renumber and reassign their entire network.

Effective Application of Policy
As previously stated, contemporary Layer 3 switches perform their forwarding—whether Layer 2, Layer 3, unicast, multicast, or broadcast—in hardware. Software is deployed to handle network administration, table management, and exception conditions. Some technologists view the hardware component of a Layer 3 switch as inflexible. In fact, hardware provides the ultimate flexibility not only in performance, but in parallel processing as well. The parallel processing model allows the network device to perform far more operations on packets than previously imagined, especially with respect to the application of policy.

A policy is a mechanism to alter the normal forwarding of a packet through a networking device. Familiar examples include security, load balancing, and protocol option processing. Newer policies include QoS, a way to allocate bandwidth and control propagation delay, in addition to CoS, a way to manage packet prioritization. QoS and CoS policies are not only meant to enable new multimedia applications, such as LAN telephony, but to ensure network response time for mission-critical applications, such as telemedicine. Policy implemented by intelligent networking devices, such as Layer 3 switches, enables the integration of voice, video, and data onto the same infrastructure, a process 3Com calls convergence.

Software-based architectures cannot seamlessly administer policy controls at even moderate rates of speed (beyond 10 Mbps). The Layer 3 switch solves the problem, enabling policies to be applied at the same performance levels as ordinary Layer 2 and 3 forwarding. Further innovation allows the Layer 3 switch to apply policy based on Layer 4 information, such as TCP and UDP port information. Forward thinkers refer to this as "Layer 4 switching." The FIRE architecture supports all these policies, all the way to Layer 4.

Even with the massive capacity additions being planned for many networks, effective policy management enabled by Layer 3 switching is key to the protection and availability of critical resources.

Ease of Management
One of the critical success factors for the Layer 2 switch was its implementation and operational simplicity. Deployment was often as easy as powering on the switch, assigning it an IP address, and making the physical network connections. Routers, on the other hand, required extensive training and forced users to sift through a multitude of arcane commands. Layer 3 switches remove such complexity. Setting up a routed environment is as simple as setting up a Layer 2 switch, defining the routed interface, and enabling the routing protocols. IT managers concerned about their investment in training staff on traditional router platforms must assess whether this is truly an investment, or simply a sunk cost based upon vendor lock-in schemes.

For the network management application perspective, a Layer 3 switch behaves exactly as a legacy router does. Because of its Layer 2 component, extensive Remote Monitoring (RMON) capabilities are available. However, since Layer 3 and Layer 4 capabilities are present in the Layer 3 switch, higher-layer monitoring is available with RMON2 technology. RMON and RMON2 have historically been deployed with expensive external devices known as probes. Moving the RMON/RMON2 capability into the Layer 3 switch is a major benefit for IT administrators.

Layer 3 Switching vs. Traditional Routing
By now, it should be clear that a Layer 3 switch can be deployed anywhere in the LAN where a traditional router can be or has been used.
Table 2 compares the two types of devices. The Layer 3 switch has been optimized for high-performance LAN support and is not meant to service wide area connections (although it could easily satisfy the requirements for high-performance MAN connectivity, such as SONET). This optimization boosts the performance of a Layer 3 switch to as much as ten times that of a legacy router, while driving the price down to as little as a tenth. This cost comparison does not include the lower training costs for Layer 3 switch administrators or the increased productivity of a high-performance network.

There is another major architectural difference between a Layer 3 switch and a router. A traditional router organizes bridging (Layer 2) and routing (Layer 3) as peers. A Layer 3 switch layers routing on top of switching, permitting a more natural networking architecture while greatly facilitating scalability.


Characteristic Layer 3 Switch Legacy Router
Routes core LAN protocols: IP, IPX, AppleTalk Yes Yes
Subnet definition Layer 2 switch domain Port
Forwarding architecture Hardware Software
RMON support Yes No
Price Low High
Forwarding performance High Low
Policy performance High Low
WAN support No Yes

Layer 3 Switch vs. Legacy Router

The Business Case for a Layer 3 Switch
Some IT managers may be concerned about deploying a "new" technology such as Layer 3 switching to their network. But Layer 3 switching is really an integration of two proven technologies: switching and routing. In fact, some Layer 3 switches are running the exact same routing software that has been fully tested and used in mission-critical networks for nearly a decade. So whether the decision maker is an early adopter of technology or more conservative, the Layer 3 switch can satisfy both needs.

The first step toward the deployment of next-generation IT infrastructures is to ignore the networking element. Although this may seem absurd, it allows managers to focus on the end users, services, and data without being bound by historical network deficiencies. The network should be transparent. When the requirements for information transfer are known, capacity planning techniques will determine the necessary client and server interconnects. Organizational and security mandates are then applied, yielding the policy and subnetted infrastructure. Cost is then factored in. Finally, the decision is made regarding the appropriate networking products to satisfy these requirements.

Layer 3 switching technology must be considered from two perspectives. First, as a migration tool to move users forward to higher-performance networking, or surprisingly, to squeeze more performance out of what is currently installed. Many users complain about FDDI performance, only to discover that the network is running at less than 20 percent of capacity. The problem is not the network, but rather the devices attached to it. The second perspective addresses what can be done when network performance bottlenecks are removed. A high-performance network enables a variety of steps to reduce costs and enhance security and business operations. The following are examples of several such steps.

* Server farms. Today, the viability of many organizations is closely related to their intellectual property, often stored on databases or server devices. The security and protection of these servers has been a major goal of IT managers, who have been at odds with the users of those servers. The point of contention has been the dependence of server performance on the network topology. The response has been to move servers within the same subnet or Layer 2 switching domain as users. With data traffic patterns becoming more distributed, this approach was breaking down. The Layer 3 switch allows servers to be centralized with no performance penalty, eliminating the cost of numerous server repositories while keeping end users satisfied.
* Intranets. Because of its secure nature, along with its higher capacity, the intranet is becoming a viable corporate communications vehicle with usage that includes HR record retrieval, major announcements, computer-based training, and live video broadcasts. Delivering a wide variety of services, some requiring a huge amount of bandwidth, can wreak havoc on the old router. The Layer 3 switch, because of its higher performance, traffic prioritization, and subnet preservation, is ideally suited for the deployment of intranets.
* Converged networks. For some time, technological prognosticators have been extolling the virtues of multimedia and warning of the excessive demand it will place on IT infrastructures. But many network managers have been disinclined to integrate their voice, video, and data traffic, concerned not only with the bandwidth requirements, but fearing the degraded quality of the respective elements. The ability to recognize and respond to the unique attributes of voice, data, and video not only makes their integration viable, but also attractive from a cost and management perspective. The inherent flow recognition capabilities of Layer 3 switching enable practical deployment of converged networks without performance uncertainties.


Q: Layer 3 switches vs. routers
Q: What is the difference between Layer 3 switching and regular routing?

A: Not much. Layer 3 switches were designed to provide greater performance at a lower price than traditional routers.
Q: Will Layer 3 switches always improve the performance of your network?

A: No. They will improve performance if your router is too slow to support the speed of the LANs your company uses.
Q: Do Layer 3 switch management systems differ from systems used to manage routers?

A: Yes. There are a lot of variations in management packages for Layer 3 switches just as there are lots of variations in router packages. IS managers need to look at each Layer 3 switch management package before deciding.
Q: Do Layer 3 switch vendors plan support for protocols beyond IP?

A: Yes. The major players, Nortel, Cisco, 3Com and Juniper either have support or plan support for Novell IPX. Cisco already supports additional protocols, but many vendors will likely stop after IPX support because they feel user companies will eventually phase out additional protocols.

[Crack]

That might be a little bit more indepth than he/she needs...

[guthmund]

Christ.

I thought by linking to another post we could avoid bringing out the chalkboard and pontificating on the virtues of the argument "The Switch Vs. Router conundrum."

Guess that wasn't going to happen, eh?

If it was a quick and dirty answer one was looking for I would imagine a quick search on Google would net the simple answer one was looking for. However, since we are simplifying the response let me give it a try....

Switch good, Router better.

4 words. "So simple, even a caveman could understand."