Wide Area Networks Questions and Answers

Answer: C

Correct answer: 3, 4 and 5

The question mark lists the available keywords, which are lmi, pvc and map - the local management interface statistics, the state and counters of each virtual circuit, and the mappings of protocol address to DLCI. There is no show frame-relay dlci or neighbors; the DLCI information appears within the pvc and map output.

Answer: D

Correct answer: Cable

HFC stands for hybrid fibre-coaxial, the plant a cable operator uses: fibre from the head end to a neighbourhood node, then coaxial cable to the individual premises. It is specific to cable broadband. DSL runs over the existing telephone pair, and Frame Relay and a dedicated T1 are carrier services with no such plant of their own.

Answer: C

Correct answer: Non-broadcast multi-access

Many sites are reachable over one interface, which makes it multi-access, but a frame sent once does not reach them all - it must be replicated onto each virtual circuit, which makes it non-broadcast. That combination is what breaks routing protocols relying on broadcast or multicast hellos, and it is why Frame Relay needs neighbour statements, subinterfaces or careful mapping.

Answer: C

Correct answer: VPN

A VPN builds a private network across a shared public one, tunnelling traffic so that it is private in transit and so that protocols the intervening network does not carry can be encapsulated within IP. IPSec is one suite used to secure such tunnels rather than the concept itself, and HDLC, cable and xDSL are link technologies.

Answer: D

Correct answer: IPSec

IPSec is the standardised suite - AH, ESP and IKE with their associated algorithms - that provides authentication, integrity and encryption at the Network layer, so it protects any traffic carried over IP without the applications needing to know. That layer 3 position is exactly what distinguishes it from TLS, which secures individual transport connections.

Answer: A

Correct answer: DSL

A DSL line carries ATM cells over the copper pair to the DSLAM at the exchange, where the subscriber lines are aggregated onto the provider’s network. That is why PPPoA exists alongside PPPoE - PPP over ATM is the natural encapsulation for a link whose data link layer is ATM.

Answer: A

Clocking on a serial interface is always provided by the CSU/DSU (DCE device). However, if you do not have a CSU/DSU in your nonproduction test environment, then you need to supply clocking with the clock rate command on the serial interface of the router with the DCE cable attached.

Answer: B

Correct answer: frame-relay map

Inverse ARP normally discovers which DLCI reaches which remote IP address automatically. Where it is not operating - because it has been disabled, or the far end does not support it - the mapping must be entered by hand with frame-relay map ip <address> <dlci>, optionally with the broadcast keyword so that routing updates are replicated onto that circuit.

Answer: A

If you have a serial port configured with multiple DLCIs connected to multiple remote sites, split horizon rules, stop route updates received on an interface from being sent out the same interface. By creating subinterfaces for each PVC, you can avoid the split horizon issues when using Frame Relay.

Answer: C

Correct answer: PPPoE

PPPoE carries PPP frames inside Ethernet frames, which lets a provider keep PPP’s per-subscriber authentication, accounting, encryption and compression while delivering service over an Ethernet-style access network. It is the usual arrangement for DSL and fibre broadband, and PPPoA is its counterpart where the access link is ATM.