CS4500 Test 3 Study Guide

KSU CS4500
Test 3 Study Guide/Test Sample

Note: Some questions have answers, some don't not all answers are correct, this is a study guide.
True/False and fill in blank questions.

  2. Router B receives an update from ROUTER A that indicates NET1 is two hops away. The next update from A says NET1 is five hops away. What value is entered in B’s routing table for NET1? Assume the basic RIP is being used. 6
  3. If a host needs a synchronize its clocks with another host, it sends a timestamp request message.
  4. The purpose of echo requests and echo reply is to check node-to-node communications.
  5. Errors in the header or option fields of an IP datagram requires a parameter-problem error message.
  6. In calculating the time difference between two clocks, a negative value indicates the destination clock lags behind the source clock.
  7. If routing table contains four new entries, how many update messages must the router send to its one neighbor router? ONE
  8. A periodic update message goes out at time = 37s. A triggered update follows at time = 57s. Assuming a period of 30s, when does the next regular periodic update message go out? 30s + 37s = 67s
  9. In an autonomous system with n areas, how many areas are connected to the backbone? n-1
  10. Which IP address is need in the hello message? Designed router, neighbor router and backup designated router
  11. Path vector routing has instability and looping problem. False
  12. MBONE is used for multicasting between two non-contiguous multicast routers. True
  13. PIM is used in a dense multicasting environment which DM is used in a sparse multicast environment.
  14. When a multicast router is not directly connected to another multicast router, a logical tunnel can be formed to connect the two.
  15. A graft message tells an upstream router to start sending multicast messages for a specific group through a specific router.
  16. MOSPF uses multicast links state routing concepts to create source-based trees.
  17. An multicast message is sent from one source to multiple destinations.
  18. A tree is a data structure with nodes & edges & a hierarchical structure.
  19. In unicasting, the Internet, or part of it, can be represented by a graph.
  20. A router has four interfaces: A, B, C and D. It receives a packet from interface A. To flood, the network with this packet, the router sends the packet through interfaces? B,C and D
  21. A system uses source-based trees for multicasting. If there are 100 sources and 5 groups, there is a max of 5x100 = 500 different trees.
  22. In networks that do not support physical multicasting addressing, multicasting can be accomplished through tunneling.
  23. If four hosts on a network belong to the same group, a total of two membership reports are sent in a response to general query message.
  24. A prune message tells an upstream router to stop sending multicast messages for a specific group through a specific router.

Essay Questions.
  1. Do OSPF messages propagate faster than RIP messages?
  2. A classful routing table has four buckets in the table and a single entry for default routing. The first bucket is for host-specific routing with 10 entries. The second bucket is for class A blocks with 50 entries. The third bucket is for class B block with 400 entries. The fourth bucket is for class C with 2000 entries. Find the average number of table lookups for each of the following cases:
  1. A packet with host-specific route has arrived 5 lookups
  2. A packet with class A address has arrived 25 lookups
  3. A packet with class B address has arrived 200 lookups
  4. A packet with class C address has arrived  1000 lookups

  1. Router A sends a unicast RIP update packet to router B that says is 7 hops away. Network B sends an update packet to router A that says is 4 hops away. If these two routers are connected to the same network, which one is designated to parent router?
The designated parent router is router B.
  1. A Router has the following RIP routing table: NET1   4    B
                                                                                  NET2   2     C
                                                                                  NET3   1     F
                                                                                   NET4   5     G
What would be the contents of the table if the router receives the following RIP message from router C:  NET1   2
                                       NET2   1
                                       NET3   3
                                       NET4    7
NET1   3    C
NET2   2    C
NET3   1     F
NET4   5    G

  1. A computer receives a timestamp request from another computer at 2:34.20 pm. The value of the original timestamp is 54,453,000. If the sender clock is 5ms slow, what is the one-way time?
         -------no answer ------

  1. An ICMP message has arrived with header (in hex) 05 00 11 12 11 0B 03 02
  1. What is the type of the message? Redirect Message
  2. What is the code? Redirect Datagram for the Network
  3. What is the purpose of the message? Error Message
  4. What is the value of the last 4 bytes? 2
  5. What do the last bytes signify?
  1. A computer sends a timestamp request to another computer. It receives the corresponding timestamp reply at 3:46.07 am. The value of the original timestamp and transmit timestamp are 13,560,000  13,562,000 and 13,560,300 respectively.
  1. What is the sending trip time?
  2. What is the receiving trip time?
  3. What is the round trip time?
  4. What is the difference between the sender clock and the receiver clock?
  1. A router using DVMRP receives a packet with source address from interface 2. If the router forwards the packet, what are the contents of the entry related to this address in the unicast routing table?

  1. The contents of an IGMP message in hex notation are 16 00 F9 C0 E1 2A 13 14
  1. What is the type? Membership Report
  2. What is the checksum? 249
  3. What is the groupid?

Application Problems

  1. For the network below, create a routing table for router R1. Smallest number of hops is desired. All network elements of importance to router R1 are illustrated in the diagram and each network contains 30 assigned hosts. Consider the internet as a default. Network addresses are outlined with box-based on information provided, determine feasible masks for each table entry.

Next Hop
Specific Host
Specific Host
Network Specific
Network Specific
Network Specific

  1. A network diagram has been translated to the graph below. The link cost in the graph represents both directions. Using Dijkstra’s algorithm and calculating the least cost routes from node A, answer the following questions:
  1. Not counting the initial node, which nodes were the 3rd and 5th nodes selected? What were the cummaltive costs for the 3rd and 5th selected nodes?
3rd node => E    5th node => D     Costs: 14 + 18 = 32
  1. List all the least-cost-routes and associated costs per least-cost-route for node A in hyphen form  - will lose points for not using hyphen form for answer?
A-> B 13     A-> C 10    A->D 18    A->E 14   A->F 16    A->G 23
  1. What is the least cost route from node F to node A? Can you use the existing results?
F => A    F->E->C->A    Cost: 2 + 4 + 10 = 16
Yes, we can use existing.
Node      Rate     Cost
B          A-C-B      13
C           A-C         10
D       A-C-E-D      18
E       A-C-E          16
F      A-C-E-F        16
G     A-C-E-D-G     22

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