Wide Area Networks Questions and Answers

Answer: A

The issue that becomes most significant is propagation delay.

The defining change from a LAN to a WAN is distance. In a LAN, signals cross a building in well under a microsecond, but over a WAN they travel hundreds or thousands of kilometres, at roughly 5 microseconds per kilometre in fibre, so a cross-country round trip takes tens of milliseconds. That delay cannot be engineered away, and protocols must be designed around it, with larger windows, longer timeouts and fewer round trips.

Bandwidth on WAN links is costlier, but it can be bought, whereas propagation delay is set by physics. Duplex mismatch and connector differences are local cabling and configuration faults that occur in a LAN as much as in a WAN.

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

If you have a Cisco router on one side of a Frame Relay network and a non-Cisco router on the other side, you would need to use the Frame Relay encapsulation type of IETF. The default is Cisco encapsulation, which means that a Cisco router must be on both sides of the Frame Relay network.

Answer: A

Please do not freak out because ATM is an answer to this question. ATM is not covered in depth on the CCNA exam. PPP is mostly used for dial-up (async) services, but ATM could be used as well, though it typically is not used anymore since PPP is so efficient.

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: 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: 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: C

Correct answer: Frame Relay

Frame Relay carries many permanent virtual circuits over one physical connection, so twelve branches can be reached through a single serial interface at headquarters using subinterfaces. That directly solves the stated problem of having no free ports, and it costs far less than twelve leased lines. PPP and HDLC are point-to-point and would need a port each, and ISDN is dial-up rather than an always-on branch link.

Answer: C

Correct answer: An IP address on the physical interface

With point-to-point subinterfaces each subinterface is a separate network and carries its own IP address, so the physical interface must not have one. What the physical interface does carry is the Frame Relay encapsulation; the subinterfaces then take the point-to-point type and each is assigned its local DLCI with frame-relay interface-dlci.

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.