WAN Practice Exam Questions With 100% Correct Verified Answers.

WAN - correct answer A physical leases line WAN works a lot like an Ethernet crossover cable connecting 2 routers but with no distance limitations. Each router can send at any time full duplex. The speed is also symmetric meaning that both routers send bits at the same speed. WAN Links - correct answer Leased line provide a physical layer bit transmission facility routers also need to use a data link protocol on the WAN link to send bits over the link. LAN interfaces - correct answer Routers receive frames in LAN interfaces and then the router decapsulates the network layer packet. Before forwarding the packet the router encapsulates the packet inside a WAN data link High level data link control HDLC. Customer premise equipment CPE - correct answer This Telco term refers to the gear that sits at their customers sites on the end of the link. Channel service unit/data service unit. CSU/DSU - correct answer This device provides a function called clocking in which it physically controls the speed and timing at which the router serial interface sends and receives each bit over the serial cable. Serial cable - correct answer This is a short cable that connects the CSU and the router serial interface. Routers - correct answer Many routers today use serial interfaces. These serial interfaces usually exist as part of a removable card on the router called WAN interface cards WIC. CSU - correct answer Tells the router when to send and receive bits. The router attempts to send and receive bits only when the DCE creates the correct electrical impulses called clocking on the cable. Cisco type field - correct answer The type field allows Cisco routers to support multiple types of network layer packets to cross the HDLC link. An HDLC link between 2 Cisco routers can forward both IPv4 and IPv6 packets because the type field can identify which type of packet is encapsulated inside each HDLC frame. Enable HDLC - correct answer Enable HDLC using the encapsulation HDLC interface sub command. Configure the clocking rate using the clock rate speed interface sub command but only on the router with the DCE cable. PPP concepts - correct answer Definition of a header and trailer that allows delivery of a data frame over the link. Support for both synchronous and asynchronous links. A protocol type field in the header allowing multiple Layer 3 protocols to pass over the same link. PPP concepts - correct answer Built in authentication tools: password authentication protocol PAP and challenge handshake authentication protocol CHAP. Control protocols for each higher layer protocol that rides over PPP allowing easier integration and support of those protocols. PPP framing - correct answer PPP standard defines a protocol field. The protocol field identifies the type of packet inside the frame. Also defines a set of Layer 2 control protocols that perform various link control functions. PPP control protocols - correct answer Link control protocol - LCP. This one protocol has several different individual functions each focused on the data link itself ignoring the layer 3 protocol sent across the link. PPP control protocols - correct answer Network control protocol - NCP. This is a category of protocols one per network layer protocol. Each protocol does functions specific to its related layer 3 protocol. PPP authentication - correct answer WAN authentication is most often needed when dial lines are used. PAP sends passwords in clear text whereas CHAP uses a much more secure option, uses different messages and hides it passwords. CHAP sends a message called challenge which asks the other device to reply using MD5. Configuring PPP - correct answer Use the encapsulation PPP command on both ends of the link. Data link problems - correct answer Line status up-Protocol status down on both ends likely reason mismatched encapsulation commands. Show interface command list encapsulation type on about the 7th line of the output Data link problems - correct answer Line status up-Protocol status down on one end, up on the other likely reason keep alive disabled on the end in an up state when using HDLC. The router keep alive feature helps a router notice when a link is no longer functioning. Keep alive messages sent every 10 seconds. Keep alive messages - correct answer Regular keep alive keeps the link up, whereas a lack of keep alive makes the link fail. As long as both routers use keep alive or both routers disable keep alive the link works. Show interfaces s0/0/0 command identifies the problem. Data link problems - correct answer Line status up-Protocol status down on both ends likely reason PAP/CHAP authentication failure. PAP and CHAP authentication failure - correct answer To discover whether a PAP/CHAP failure exist you can use the debug PPP authentication command. HDLC link - correct answer With a HDLC link, if the IP addresses configured on the serial interfaces are in different subnets, a ping to the IP address will fail. With a PPP link, the ping will work but the IP subnet mismatch still prevents EIGRP and OSPF neighbor relationship