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Network Devices Transcription

Welcome to our Common Networking Devices module. There are several types of devices used in LANs, or local area networks, metropolitan area networks, or MANs, and wide area networks, or WANs, to allow for communication between computers and networks. The differences between these devices depend on their intelligence, network placement, functionality, and capabilities.

Some of the most common devices are hubs, which operate at layer one of the OSI model, switches, which operate at layer two of the OSI model, routers, which operate at layer three of the OSI model, and gateway devices, which operate at multiple layers of the OSI model. You should remember for the CISSP examination that a gateway is a device that operates at multiple layers of the OSI model.

Ethernet hubs are layer one, or physical layer devices, that are no longer commonly used. They were used to connect multiple local area network devices in a star topology. A hub is simply a multi-port repeater. It rebuilds binary data, 0s and 1s, from one system and then transmits it to all of the other ports on the device.

So all of the devices on the network receive the same traffic. The problem with hubs is a security issue, in that anyone who is able to plug a device into the Ethernet port of a hub is able to receive all of the traffic destined for other devices using a packet capturing device.

And this can compromise the confidentiality of your data. An Ethernet switch is a layer two or data link layer device. This is a multi-port repeater similar to a hub, but is much more intelligent. These devices often may look like hubs, but they are very different. When they receive a frame, it forwards that frame only to the correct network segment or device on the network.

It builds a table which maps MAC addresses to port numbers. A MAC address is a Media Access Control address or hardware address for a network interface card. So this device is smart enough to know which devices are plugged into which ports. And if it receives a piece of traffic for a computer plugged into the fourth port, for example, it will only send that data to port four rather than sending it to the entire network.

Ethernet switches can be affected by MAC flooding attacks, as well as spoofing attacks. Ethernet technology uses the IEEE 802.3 standard for local area networking. And this is the most popular LAN technology in use today. Networks very large as well as very small networks with only two computers utilize Ethernet switches and network interface cards.

And these devices operate at layer two of the OSI Model. Most Ethernet networks use a star topology, and now are commonly supporting gigabit speeds. We discussed MAC addresses, and here is an example of what a MAC address would look like. MAC addresses are 48 bits in length, and they are commonly written in six groups of two hexadecimal characters, separated by either dashes or colons.

Protocols like Ethernet will define rules for how systems are addressed, how collisions are dealt with, and how data is segmented before it is transmitted over the network. Routers are devices that operate at the network layer, or layer three of the OSI model. These devices will forward packets based on IP or Internet Protocol address information that is found in the header.

These devices often act as a gateway between an Ethernet LAN and a WAN or wide area network, taking traffic off of the Ethernet LAN and moving it onto the WAN. They're able to convert traffic from Ethernet format to WAN format, and they typically act as firewalls and they're able to implement security through packet filtering using access control lists.

These access control lists will tell the router whether or not certain types of traffic is permitted. Routers will also block broadcast data to prevent data from being broadcast from a local area network to the entire Internet. If data is being transmitted to the same subnet or segment of the network, this is considered local traffic and will not be forwarded through the router.

If data is intended to leave the local network, it will move to the router, where the access control list will be checked. And if rules permit, then the data will be forwarded outside of the subnet, based on a routing table which is used to keep information about how to forward data.

There are two common interior routing protocols, Routing Information Protocol, or RIP, and OSPF, or Open Shortest Path First. There is two versions of the routing information protocol, RIP and RIP version two. And this protocol uses an algorithm based on the distance and the number of hops or stops along a certain route.

Routing tables commonly have a list of destination networks, with direction and distance in hops, and typically try to remain within a 15 hop limit. The more common technology is Open Shortest Path First, or OSPF. Routers keep a topology map of networks, and are able to identify all routers and sub-networks.

The route is then determined using the shortest path based on speed or bandwidth to the ultimate destination. You should remember for the CISSP examination that OSPF is the newer and more commonly used technology compared to RIP. Exterior routing protocols include the Internet Border Gateway Protocol or BGP. This is commonly used by Internet service providers to route traffic on the Internet.

For the CISSP examination, you should remember that border gateway protocol is commonly used by Internet service providers. A gateway is a device that connects two unlike environment or systems and is able to convert data from one protocol to another. These devices are commonly Cisco routers with expansion cards installed. It is important to remember for the CISSP examination that this is the only device that works at multiple layers of the OSI model. Gateways are basically translators that allow computers with different transport protocols or media types to communicate with each other. A modem used on your home network is considered a gateway because Ethernet traffic comes into the device, and it is then converted to flow out, either over a phone line using DSL technology, or over the cable network with a cable modem using DOCSIS technology.

Gateway devices should not be confused with a default gateway, which is used to describe a router at the perimeter of your network. This concludes our Common Networking Devices module. Thank you for watching.