CCNA:ICND2 ?'s - sec 4

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  1. Are DLCI addresses defined by a Layer 2 or Layer 3 protocol?
    DLCI addresses are defined by a Layer 2 protocol. Frame Relay protocols do not define a logical addressing structure that can usefully exist outside a Frame Relay network; by definition, the addresses would be OSI Layer 2 equivalent.
  2. What is the name of the field that identifies, or addresses, a Frame Relay virtual circuit?
    Data-Link Connection Identifier (DLCI)
  3. True or False: “Frame Relay VCs provide a constant amount of bandwidth between two devices, typically routers—never more and never less.” Defend your answer.
    False. The provider assigns a guaranteed bandwidth, or CIR, for a VC, but the routers on either end of the VC can send more than the CIR of data. As long as the service provider has enough capacity to support it, the frames are forwarded over the VC.
  4. Explain how many DS0 channels fit into a T1, and why the total does not add up to the purported speed of a T1, which is 1.544 Mbps.
    Each DS0 channel runs at 64 kbps. With 24 in a T1, the T1 speed seemingly would be 24*64 kbps (1.536 Mbps). T1 also includes 8 kbps for management, which, when added to the 1.536 Mbps total, gives you the full T1 rate of 1.544 Mbps
  5. Define the term synchronous.
    The imposition of time ordering on a bit stream. Practically, a device will try to use the same speed as another device on the other end of a serial link. By examining transitions between voltage states on the link, the device can notice slight variations in the speed on each end and can adjust its speed accordingly.
  6. Imagine a drawing with two routers, each connected to an external CSU/DSU. Each CSU/DSU is connected with a four-wire circuit. Describe the role of the devices in relation to clocking and synchronization.
    The routers receive clocking from their respective CSU/DSUs. One of the two is configured as the master. The other (the slave), adjusts its clock to match the speed of the master.
  7. Imagine a drawing with two routers, each connected to an external CSU/DSU. Each CSU/DSU is connected with a four-wire circuit. List the words behind the acronyms DTE and DCE, and describe which devices in this imagined network are DTE and which are DCE.
    • Data Terminal Equipment
    • Data Communications Equipment
    • Routers are DTEs and the CSU/DSUs are DCEs
  8. Imagine a drawing with two routers, each connected to a Frame Relay switch over a local access link. Describe which devices in this imagined network are Frame Relay DTEs and which are Frame Relay DCEs.
    The routers are DTEs and the Frame Relay switches are the DCEs
  9. Imagine a point-to-point leased line between two routers, with PPP in use. What are the names of the protocols inside PPP that would be used on this link? What are their main functions?
    The PPP Link Control Protocol (LCP) controls and manages the link. The IP Control Protocol (IPCP) also would be used because you need a CP for each Layer 3 protocol. IPCP can assign IP addresses to devices on the other end of a link.
  10. Define the terms DCE and DTE in the context of the physical layer and a point-to-point serial link.
    At the physical later, DTE refers to the device that looks for clocking from the device on the other end of the cable on a link. The DCE supplies that clocking.
  11. Identify the command used to set the clock rate on an interface in which a DCE cable has been inserted. Compare and contrast the two styles of the command that may be entered in configuration mode versus which style shows up in the configuration.
    The "clock rate" command and the "clockrate" command both set the rate at which an interface clocks over a serial DCE cable.
  12. Name one WAN data-link protocol used on point-to-point leased lines that defines a method of announcing the interface’s IP addresses to other devices attached to the WAN.
    PPP uses an IP Control Protocol (IPCP) to announce, and sometimes assign, IP addresses to each end of the link.
  13. Define the terms PAP and CHAP. Which one sends passwords in clear-text format?
    • PAP = Password Authentication Protocol {Clear-text}
    • CHAP = Challenge Handshake Authentication Protocol {MD5 hashing}
  14. CHAP configuration uses names and passwords. Given Routers A and B, describe what names and passwords must match in the respective CHAP configurations.
    Router A has name B and corresponding password configured. Router B has name A and the same password configured. Unless changed, the names are hostnames of the routers.
  15. Create a CHAP configuration between two routers. Make up specific details as needed.
    • {local = Fred; Remote = Barney}
    • username Barney password Bedrock
    • !
    • interface serial 0
    • encapsulation ppp
    • ppp authentication chap
  16. What two WAN data-link protocols define a method of announcing the interface’s Layer 3 addresses to other devices attached to the WAN?
    • PPP and Frame Relay
    • PPP uses control protocols specific to each Layer 3 protocol supported. Frame Relay uses Inverse ARP.
  17. Explain the purpose of Inverse ARP, as well as how it uses Frame Relay broadcasts.
    A router discovers the Layer 3 address(es) of a router on the other end of a VN when that other router sends an Inverse ARP message. The message is not a broadcast.
  18. Would a Frame Relay switch connected to a router behave differently if the IETF option were deleted from the encapsulation frame-relay ietf command on that attached router? Would a router on the other end of the VC behave any differently if the same change were made?
    The switch does not behave differently. The other router, however, must also use IETF encapsulation. Otherwise, the routers will not look at the correct fields to learn the packet type.
  19. What does NBMA stand for? Does it apply to X.25 networks or Frame Relay networks?
    • Nonbroadcast Multiaccess
    • X.25 and Frame Relay are NBMA networks. Multiaccess really means that more than two devices are connected to the data link, because many other devices may be reached by a single device. For instance, Router1 might have a PVC to Router2 and Router3, making it multiaccess.
  20. Which layer or layers of OSI are most closely related to the functions of Frame Relay? Why?
    • Layers 1 & 2.
    • Frame Relay refers to well-known physical layer specifications. Frame Relay defines headers for delivery across the Frame Relay cloud, but it provides no addressing structure to allow VCs among many different Frame Relay networks. Thus, it is not considered to match Layer 3 functions.
  21. When Inverse ARP is used by default, what additional configuration is needed to get IGRP routing updates to flow over each VC, assuming IGRP has already been configured correctly?
    No additional configuration is required. The forwarding of broadcasts as unicasts can be enable on each VC and protocol for which Inverse ARP is received.
  22. Define the attributes of a partial-mesh and full-mesh Frame Relay network.
    In a partial-mesh network, not all DTEs are directly connected with a VC. In a full-mesh network, all DTEs are directly connected with a VC.
  23. What key pieces of information are required in the frame-relay map statement?
    The pieces of information required are the Layer 3 protocol, the next-hop router's Layer 3 address, the DLCI to reach that router, and whether to forward broadcasts. Frame Relay maps are not required if Inverse ARP is in use.
  24. Create a configuration for Router1 that has Frame Relay VCs to Router2 and Router3 (DLCIs 202 and 203, respectively) on Router1’s Serial1 interface. Use any IP addresses you like. Assume that the network is not fully meshed.
    • interface serial 1
    • encapsulation frame-relay
    • interface serial 1.1 point-to-point
    • ip address
    • frame-relay interface dlci 202
    • interface serial 1.2 point-to-point
    • ip address
    • frame-relay interface dlci 203
  25. What show command tells you when a PVC became active? How does the router know what time the PVC became active?
    The "show frame-relay pvc" command lists the time since the PVC came up. You can subtract this time from the current time to derive the time at which the VC came up. The router learns about when PVCs come up and go down from LMI messages.
  26. What show command lists Frame Relay information about mapping? In what instances does the information displayed include the Layer 3 addresses of other routers?
    "show frame-relay map" lists Frame Relay information about mapping. The mapping information includes Layer 3 addresses when multipoint sub interfaces are used or when no sub interfaces are used. The two cases in which the neighboring routers' Layer 3 addresses are shown are the two cases in which Frame Relay acts like a multiaccess network. With point-to-point sub interfaces, the logic works like a point-to-point link, in which the next router's Layer 3 address is unimportant to the routing process.
  27. True or false: The no keepalive command on a Frame Relay serial interface causes no further Cisco-proprietary keepalive messages to be sent to the Frame Relay switch.
    False. This command stops LMI status inquiry messages from being sent. They are defined in Frame Relay Forum standards. Cisco sends proprietary keep alive messages on point-to-point serial and LAN interfaces.
  28. What debug option shows Inverse ARP messages?
    "debug frame-relay events" shows Inverse ARP messages
  29. What is the name of the field that identifies, or addresses, a Frame Relay virtual circuit?
    The data-link connection identifier (DLCI) is used to identify a VC. The number may be different on either side of the VC.
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CCNA:ICND2 ?'s - sec 4
2014-05-21 01:10:26

Open ended questions for section 4 of Cisco's CCNA ICND2
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