2.1.3 WAN Standards WANs use the OSI reference model, but focus mainly on Layer 1 and Layer 2. WAN standards typically describe both physical layer delivery methods and data link layer requirements, including physical addressing, flow control, and encapsulation. WAN standards are defined and managed by a number of recognized authorities. The physical layer protocols describe how to provide electrical, mechanical, operational, and functional connections to the services provided by a communications service provider. Some of the common physical layer standards are listed in Figure , and their connectors illustrated in Figure . The data link layer protocols define how data is encapsulated for transmission to remote sites, and the mechanisms for transferring the resulting frames. A variety of different technologies are used, such as ISDN, Frame Relay or Asynchronous Transfer Mode (ATM). These protocols use the same basic framing mechanism, high-level data link control (HDLC), an ISO...
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2.1.2 WAN devices WANs are groups of LANs connected together with communications links from a service provider. Because the communications links cannot plug directly into the LAN, it is necessary to identify the various pieces of interfacing equipment. LAN-based computers with data to transmit send data to a router that contains both LAN and WAN interfaces. The router will use the Layer 3 address information to deliver the data on the appropriate WAN interface. Routers are active and intelligent network devices and therefore can participate in network management. Routers manage networks by providing dynamic control over resources and supporting the tasks and goals for networks. Some of these goals are connectivity, reliable performance, management control, and flexibility. The communications link needs signals in an appropriate format. For digital lines, a channel service unit (CSU) and a data service unit (DSU) are required. The two are often combined into a single piece of equi...
2.1 WAN Technologies Overview 2.1.1 WAN Technology A WAN is a data communications network that operates beyond the geographic scope of a LAN. One primary difference between a WAN and a LAN is that a company or organization must subscribe to an outside WAN service provider in order to use WAN carrier network services. A WAN uses data links provided by carrier services to access the Internet and connect the locations of an organization to each other, to locations of other organizations, to external services, and to remote users. WANs generally carry a variety of traffic types, such as voice, data, and video. Telephone and data services are the most commonly used WAN services. Devices on the subscriber premises are called customer premises equipment (CPE). The subscriber owns the CPE or leases the CPE from the service provider. A copper or fiber cable connects the CPE to the service provider’s nearest exchange or central office (CO). This cabling is often called the local ...
Module 2: WAN Technologies/Overview As the enterprise grows beyond a single location, it is necessary to interconnect the LANs in the various branches to form a wide-area network (WAN). This module examines some of the options available for these interconnections, the hardware needed to implement them, and the terminology used to discuss them. There are many options currently available today for implementing WAN solutions. They differ in technology, speed, and cost. Familiarity with these technologies is an important part of network design and evaluation. If all data traffic in an enterprise is within a single building, a LAN meets the needs of the organization. Buildings can be interconnected with high-speed data links to form a campus LAN if data must flow between buildings on a single campus. However, a WAN is needed to carry data if it must be transferred between geographically separate locations. Individual remote access to the LAN and connection of the LAN to the Internet are...
Summary Module 1 Before students begin Module 2, they must be able to explain the concepts of NAT, PAT, and DHCP. Online assessment options include the end-of-module online quiz in the curriculum and the online Module 1 exam. From memory, students should be able to fill in Drag and Drop assessments for Basic NAT Operation and NAT with Overload. Students should also be able to complete a Checkbox activity for the advantages and disadvantages of NAT. A comprehension of the following key points should have been achieved: Private addresses are for private, internal use and should never be routed by a public Internet router. NAT alters the IP header of a packet so that the destination address, the source address, or both addresses are replaced with different addresses. PAT uses unique source port numbers on the inside global IP address to distinguish between translations. NAT translations can occur dynamically or statically and can be used for a ...
Verifying the Catalyst switch default configuration Switch name Command Explanation SydneySwitch# show version Displays the configuration of the system hardware, software version, names, and sources of configuration files and boot images SydneySwitch# show running-configuration Displays the current active configuration file of the switch SydneySwitch# show interfaces Displays the statistics for all interfaces configured on the switch SydneySwitch# show ip Displays the IP address, subnet mask, and default gateway
1.2.8 DHCP Relay DHCP clients use IP broadcasts to find the DHCP server on the segment. What happens when the server and the client are not on the same segment and are separated by a router? Routers do not forward these broadcasts. DHCP is not the only critical service that uses broadcasts. Cisco routers and other devices may use broadcasts to locate TFTP servers. Some clients may need to broadcast to locate a TACACS server. A TACACS server is a security server. Typically, in a complex hierarchical network, clients do not reside on the same subnet as key servers. Such remote clients will broadcast to locate these servers. However, routers, by default, will not forward client broadcasts beyond their subnet. Because some clients are useless without services such as DHCP, one of two choices must be implemented. The administrator will need to place servers on all subnets or use the Cisco IOS helper address feature. Running services such as DHCP or DNS on several c...
1.2.6 Verifying DHCP operation To verify the operation of DHCP, the command show ip dhcp binding can be used. This displays a list of all bindings created by the DHCP service. To verify that messages are being received or sent by the router, use the command show ip dhcp server statistics . This will display count information regarding the number of DHCP messages that have been sent and received. 1.2.7 Troubleshooting DHCP To troubleshoot the operation of the DHCP server, the command debug ip dhcp server events can be used. This command will show that the server periodically checks to see if any leases have expired. Also displayed are the processes of addresses being returned and addresses being allocated.