Giáo trình CCNA - Chương 4

CCNA – Semester4 Module 1 Scaling IP Address Objectives • Scaling networks with NAT and PAT • Dynamic Host Configuration Protocol Scaling networks with NAT and PAT Introducing NAT • NAT is designed to conserve IP addresses and enable networks to use private IP addresses on internal networks. • These private, internal addresses are translated to routable, public addresses. NAT terms • Inside local address – The IP address assigned to a host on the inside network (not a legitimate IP address-RFC 1918 private address). • Inside global address – A legitimate IP address represents one or more inside local IP addresses to the outside world. • Outside local address – The IP address of an outside host as it is known to the hosts on the inside network. • Outside global address – The IP address assigned to a host on the outside network. The owner of the host assigns this address. Major NAT and PAT features • NAT translations can be used for a variety of purposes and can be either dynamically or statically assigned. • Dynamic NAT is designed to map a private IP address to a public address. • Overloading, or Port Address Translation (PAT), maps multiple private IP addresses to a single public IP address. • Realistically, the number of ports that can be assigned a single IP address is around 4000. Major NAT and PAT features NAT advantages • Eliminates reassigning each host a new IP address when changing to a new ISP. • Conserves addresses through application port- level multiplexing. • Protects network security. • Reduce address overlap occurrence. NAT disadvantages • Translation introduces switching path delays and processing overhead. • Loss of IP end-to-end traceability. • Certain application will not function with NAT enabled. Cisco IOS NAT Configure static NAT Static translation Configure dynamic NAT Configure dynamic NAT Configure dynamic NAT Dynamic NAT example Configure PAT Clear NAT table Show NAT translation Troubleshooting NAT and PAT configuration • Use the following steps to determine whether NAT is operating as expected: – Based on the configuration, clearly define what NAT is supposed to achieve. – Verify that correct translations exist in the translation table. – Verify the translation is occurring by using show and debug commands. – Review in detail what is happening to the packet and verify that routers have the correct routing information to move the packet along. [...]... relatively long connection time, not proper for voice or video traffic ISDN • The connection uses 64 kbps bearer channels (B) for carrying voice or data and a signaling, delta channel (D) for call set-up • ISDN is used to provide additional capacity or backup for leased-line • ISDN tariffs are based on a per-B channel basis and are similar to those of analog voice connections ISDN • Basic Rate Interface... capable of transferring voice, video, and data • It is built on a cell-based architecture rather than on a frame-based architecture ATM cells are always a fixed length of 53 bytes including 5 bytes header DSL • • • • Digital Subscriber Line (DSL) technology is a broadband technology Use existing twisted-pair telephone lines to transport high-bandwidth data Broadband refers to a technique which uses multiple... field is not needed for WAN links, which are almost always point-to-point The control field indicates the frame type: – Unnumbered frames carry line setup messages – Information frames carry network layer data – Supervisory frames control the flow of information frames and request data retransmission in the event of an error WAN Data-link Protocols Circuit Switching • Fixed capacity may not be efficient... Packet Switching • Two approaches: connectionless or connection-oriented • Connectionless systems carry full addressing information in each packet • Connection-oriented systems predetermine the route for a packet, and each packet need only carry an identifier WAN link options WAN Technologies Analog dialup • • • • When intermittent, low-volume data transfers are needed, modems and analog dialed telephone... forward client broadcasts beyond their subnet IP helper-address • Remote clients will broadcast to locate servers while routers, by default, will not forward client broadcasts beyond their subnet • When possible, administrators should use the ip helperaddress command to relay broadcast requests for these key UDP services • By default, the ip helper-address command forwards the following eight UDP services:... PAT configuration and troubleshooting • Comparison between DHCP and BOOTP • Cisco Router DHCP configuration • DHCP relay with ip helper-address Module 2 WAN Technologies Objectives • Identify the devices used in a WAN and list standards • Differentiate between packet-switched and circuitswitched WAN technologies • Describe equipment involved in the implementation of various WAN services • Compare and... managing an IP network when DHCP is used • The DHCP protocol is described in RFC 2131 Easy IP • Cisco routers can use a Cisco IOS feature set, Easy IP, to offer an optional, full-featured DHCP server • Easy IP leases configurations for 24 hours by default • The DHCP service is enabled by default on versions of Cisco IOS that support it • To disable DHCP service, use the no service dhcp command BOOTP and... dedicated capacity gives no latency or jitter between the endpoints • These dedicated circuits are generally priced based on bandwidth required and distance between the two connected points X.25 • • • Packet-switched networks using shared lines to reduce costs, tariffs are based on the amount of data Switched or permanent virtual circuits can be established through the network and data packets are subject... are called data terminal equipment (DTE) WAN Line Types and Bandwidth WAN Devices WAN Devices: Modem • • A modem is needed if the local loop is analog rather than digital Modems transmit data over voice-grade telephone lines by modulating and demodulating the signal WAN Devices: CSU/DSU • The communications link needs signals in an appropriate format • For digital lines, a channel service unit (CSU)... the type and condition of its cabling Cable modem • Network access is available from some cable television networks allows greater bandwidth than telephone local loop • Enhanced cable modems enable two-way, highspeed data transmissions up to 6.5 times that of T1 leased lines • It is an attractive medium for transferring large amounts of digital information quickly, including video clips, audio files, . CCNA – Semester4 Module 1 Scaling IP Address Objectives • Scaling networks with NAT and PAT • Dynamic