- Functionality
While the all-in-1 networking device meets the needs of the home user or the tiny one-man (person?) business network, it rarely provides enough functionality for more sophisticated networks. For instance, few all-in-1 switch-routers properly support Demilitarized Zones (DMZs) or provide an 'application layer' or 'stateful' firewall, which inspects the contents of data packets and data streams rather than just filtering on IP address information. - Availability and Reliability
If you put all your networking eggs into a single basket, and that basket fails, the entire network fails with it. To keep costs low, most all-in-1 devices use a cheap, external 'wall-wart' power supply and a small plastic case. Rarely do they have any form of active cooling or any resilience: they are built down to a cost and if a part fails, the entire unit fails.
You may be happy with this situation if your network is not business-critical or you can quickly replace a failed unit, but most businesses need their network to work, and may lose significant amounts of money if it fails.
Also, most businesses have significant internal network traffic that is functionally independent of Internet traffic. If you want to make sure that your internal traffic continues even if your Internet Access router fails, then the Internet Access router and your network switch-hub need to be separate devices.
In addition, many business-level devices are built to a specification rather than to a price (although, of course, price is significant) and have internal power supplies and active cooling (although see a later article concerning cooling fans!) and so are inherently more reliable than the domestic all-in-1 devices. - Versatility
If you think that, later, you may need to enhance your network, then you may decide that the domestic all-in-1 device is not versatile enough. For instance, few of them are modular, their capabilities may be very limited and they may not be upgradeable.
Business-level devices are often modular, and have expandability built-in, as well as supporting 'firmware' upgrades that allow them to adapt to changing standards. They also support many of the more sophisticated networking protocols that provide resilience in high-availability systems.
Buying business-grade devices may seem extravagant at first, but will enable you to significantly enhance your network without having to replace them as you enhance your network and thus wasting some of the initial investment.
When do I use a hub, when a switch and when a router?
- Hubs
Hubs are dead. Nobody much uses them any more. What is a hub? It is a device that allows data from any attached device to pass unhindered to any other attached device. There is no filtering and every data packet on the segment is visible to every attached device. What does this mean? It means that the file the Financial Director is copying from his PC to the server could be intercepted by any PC on the segment. The video download the salesman is watching clogs up the connections of all the devices on the segment.
All the devices connected to a hub are in the same 'collision domain'. Hence, if two devices try to send data at the same time, there will be a data collision and the data will be corrupted. The devices detect this and will wait for a random period before trying again. Once the total traffic on the segment exceeds about 70% of the bandwidth of the slowest spoke, then users will start to notice that the network is slowing down. Originally, all the spokes of a hub had to use the same data speed (the speed of the slowest device) although 'two-speed hubs' were developed that contained a switch that allowed devices of different speeds to connect to the same hub.
Generally, a hub does not require an IP address to be assigned to it and has no, or very limited, management capabilities. Two-speed hubs are more flexible. Since they include a switch, many of the switch management functions may be available in a limited fashion. - Switches
Switches add (limited) intelligence to the hub function. They route traffic between spokes based on the IP source and destination addresses. There is little sophistication to this. All it means is that traffic between two attached devices is blocked from appearing on any spoke that does not form part of that direct link. This keeps the traffic on each spoke to a minimum, and you could have two devices transferring data at almost the full speed of the spoke without significantly slowing traffic on other spokes. Of course, if one of the spokes is connecting to the central file server, or to the Internet, then the total traffic between all the attached devices and the server/internet will pass down that spoke.
Another function performed by a switch is to bridge Ethernet segments that operate at different speeds. It does this by buffering the data and retransmitting it at the speed of the outgoing spoke. This means that devices of different speeds can be connected to a switch. Each switch-device spoke is a separate collision domain so overall throughput is improved as collisions are less frequent. If full duplex is used (the default) then there will never be a collision on a segment linking a single device to a switch. Data loss can occur in a switch if the incoming data rate is much higher than the outgoing and the protocol does not implement any form of high-level data transmission control. Once the buffer in the switch fills up, data will be dumped. The switch will normally indicate this either to the sending device or on its panel indicators.
Generally, a switch does not require an IP address to be assigned to it. If the switch has a management capability, then it may need an IP address either from the switched subnets or on a dedicated management port. Management capabilities may include:
- Enabling/disabling specific ports
- Assigning a port to a specific subnet (if the switch supports multiple subnets)
- setting port configuration (speed, duplex, priority, MAC filtering, port mirroring and aggregation etc)
- Routers
A router adds an additional rule-based layer to the switch fuction. Traffic can be routed or blocked based on data type, protocol and IP address. A hub or a switch can only deal with data traffic between nodes that are directly connected to it, but a router contains instructions (called a routing table) that tells it what to do with data to and from IP addresses that are not on a directly-connected network. Unlike (most) switches, the rule set can be altered to meet the requirements of the user.
Since a router is, as far as a switch is concerned, an end-point for traffic passing through it to other subnets, it needs an IP address on each attached port. These addresses will be assigned by the system admin from the pool of addresses assigned to each subnet.
So, when to use a hub, switch or router?
Generally, within a simple home or SME network, there is no need for internal routing. A switch or a hub is all that's necessary to allow the devices attached to your network to communicate. Originally, hubs were cheap and switches expensive, but now switches are often cheaper than hubs, so use switches. In this arrangement, all the devices in your network use IP addresses from the same subnet.
Where you want to exchange data with someone else's network or your internal network has more than one subnet, you will need to use a router. Hence, to connect to the Internet, you will need a suitable Internet Access router.
You may hear talk of bridges, repeaters and gateways. What are they an what do they do?
- Bridge
A network bridge is, effectively, a switch. The terms switch and network bridge are often used interchangeably although use of the term network bridge normally indicates that the transport layer is different either side of the bridge (such as Apple Localtalk to Ethernet). A network bridge does not convert the protocol carried on the two media.
A Protocol Bridge (or protocol converter) interconnects two otherwise incompatible network protocols. This is a more complex function than network bridging and is often carried out on a general-purpose computer. An example of a protocol bridge was where a Novell Netware server could be used to provide a bridging function between a network using IPX/SPX and one using TCP/IP. If you stick to TCP/IP, you won't need to worry about protocol bridging.
- Repeater
A repeater is a two-port network hub. It is used to regenerate Ethernet signals so that the normal 100 meter range of a single network spoke can be extended. There are strict limits on how far a single spoke can be extended without using a switch or router due to the timing constraints of the Ethernet specification. - Gateway
Another name for a router. Often used to indicate a router plus a modem for Internet access
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