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Cork Institute of Technology
Bachelor of Science (Honours) in Software Development & Computer Networking – Stage 2
(Bachelor of Science in Software Development and Computer Networking)
(NFQ – Level 8)
Autumn 2005
Computer Networks II
(Time: 3 Hours)
Instructions Answer any FOUR questions. All questions carry equal marks.
Examiners: Mr. D. Chambers Mr. E. A. Parslow Mr. P. O Connor Mr. T. Horgan
Q1. Distant Vector Routing
a. Describe how routing loops can be avoided when using a Distance Vector routing protocol such as RIP. (^) (5 marks) b. Assuming that RIP has now been configured, draw the routing tables for all three routers when the internetwork has converged. (5 marks)
c. List the advantages and disadvantages of static routing. (5 marks)
d. Define the following routing terms: Autonomous System, Administrative Distance, Default Route and Interior Gateway Protocol (IGP). (5 marks) e. Why does the Data Link layer address changes each time a packet is routed through a router? (5 marks)
RTA#show ip route C 172.16.0.0/16 is directly connected, Serial0/ C 192.168.2.0/24 is directly connected, FastEthernet0/
RTA RTB RTC
e0 s0 s0 s1 s1 e
Q2. OSPF
a. Describe the operation of the OSPF routing protocol from the exchange of Hello packets through to the creation of the routing table. (10 marks) b. What is the function of the OSPF Hello Protocol? (5 marks) c. What is a Designated Router (DR)? How are the DR and Backup Designated Router (BDR) selected? (5 marks) d. When a router detects a link failure, the router sends an LSA to its neighbours. Describe what happens next. (5 marks)
Q3. TCP/IP
a. ARP resolves IP addressed to the machines network adapter (MAC) addresses for outgoing packets. Describe in detail how this protocol operates. (5 marks) b. Why is ICMP required as a companion of IP? Give three examples of when ICMP messages are used. (^) (5 marks) c. Four fields in the IP header are used to control the fragmentation and reassembly of packets. Write a brief note about these fields. (5 marks) d. How does TCP negotiate a connection with a destination host? Describe how this system works. (^) (5 marks) e. Explain the use of the destination port field in the Transport layer’s header as shown in the diagram below. (5 marks)
Source Port Number Destination Port Number Sequence Number Acknowledgement Number HLEN Reserved URGACKPSHRSTSYNFIN Window Size Checksum Urgent Pointer TCP Segment Diagram
Q5. ACLs & DNS
a. Design an IP access list that permits FTP traffic to FTP servers that have host addresses ending in even numbers, denies Telnet traffic to Telnet servers that have host addresses ending in even numbers, permits traffic to other Telnet servers, and denies all other IP traffic. Activate your list inbound on interface f0/1. (5 marks)
b. Design an ACL that permits all IP traffic except pings in either direction between networks 172.32.0.0/16 and 192.168.10.0/24. (5 marks) c. What is the result of the following Access Control List (ACL)? int s0/ ip access-group 1 in access-list 1 permit host 192.168.10. access-list 1 deny 192.168.44.11 0.0.255. access-list 1 deny 192.168.55.45 0.0.255. access-list 1 permit any Show how this ACL could be written more concisely. (5 marks) d. List the various types of DNS resource records and describe each type. (^) (5 marks) e. Describe the role of a DNS resolver? (5 marks)
Q6. Spanning Tree & VLANs
a. Using the Spanning Tree Protocol (STP), Bridge A is elected as the root bridge because it has the lowest MAC address. Describe what happens next and outline how STP achieves a loop free environment. (10 marks)
b. Bridges or switch ports configured for STP are in one of five different states: Blocking, Listening, Learning, Forwarding and Learning. Briefly describe each one of these states. (5 marks c. What advantages are provided by VLANs? Name the three types of VLANs and explain their differences. (5 marks) d. IEEE 802.1q states that frame tagging is the way to implement VLANs. What is VLAN frame tagging and how does it operate? (5 marks)
