CompTIA Security_ Deluxe Study Guide_ SY0-201 - Emmett Dulaney [72]
Because broadcasts don’t traverse routers, network segmentation decreases traffic.
FIGURE 3.6 A corporate network implementing routers for segmentation and security
Routers establish communication by maintaining tables about destinations and local connections. A router contains information about the systems connected to it and where to send requests if the destination isn’t known. These tables grow as connections are made through the router.
Routers communicate routing and other information using three standard protocols:
■ Routing Information Protocol (RIP) is a simple protocol that is part of the TCP/IP protocol suite. Routers that use RIP routinely broadcast the status and routing information of known routers. RIP also attempts to find routes between systems using the smallest number of hops or connections.
■ Border Gateway Protocol (BGP) allows groups of routers to share routing information.
■ Open Shortest Path First (OSPF) allows routing information to be updated faster than with RIP.
In the Cisco world, Interior Gateway Routing Protocol (IGRP) and Enhanced Interior Gateway Routing Protocol (EIGRP) are commonly used. These are distance vector protocols that automatically/mathematically compute routes and choose the best one.
Routers are your first line of defense, and they must be configured to pass only traffic that is authorized by the network administrators. In effect, a router can function as a firewall if it’s configured properly. The best approach is layered; a router shouldn’t take the place of a firewall but simply augment it.
The routes themselves can be configured as static or dynamic. If they are static, then they are edited manually and stay that way until changed. If they are dynamic, then they learn of other routers around them and use information about those to build their routing tables.
In the labs at the end of this chapter, you’ll check for the presence of a routing table and view the entries.
Switches
Switches are multiport devices that improve network efficiency. A switch typically has a small amount of information about systems in a network. Using switches improves network efficiency over hubs because of the virtual circuit capability. Switches also improve network security because the virtual circuits are more difficult to examine with network monitors. You can think of a switch as a device that has some of the best capabilities of routers and hubs combined.
The switch maintains limited routing information about systems in the internal network and allows connections to systems like a hub. Figure 3.7 shows a switch in action between two workstations in a LAN. The connection isn’t usually secure or encrypted; however, it doesn’t leave the switched area and become part of the overall broadcast traffic as typically happens on a star-based or bus-based LAN.
FIGURE 3.7 Switching between two systems
Telecom/PBX Systems
Telecommunications (or telecom) capabilities have undergone radical changes in the last 10 years. The telephone systems and technologies available to deal with communications have given many small businesses fully integrated voice and data services at reasonable prices.
These changes have complicated the security issues that must be handled. One of the primary tools in communications systems is the private branch exchange (PBX) system. PBX systems now allow users to connect voice, data, pagers, networks, and almost any other conceivable application into a single telecommunications system. In short, a PBX system allows a company to be its own phone company.
The technology is developing to the point where all communications occur via data links to phone companies using standard data transmission technologies, such as