清華大學 計算機網路 第7週小考

(+10)	(10%)1. Assume LAN1 and LAN2 are connected by a router R, stations A,B are connected to LAN1, and stations C, D are connected to LAN2. Thus, A,B －－－－ LAN1 －－－－ R －－－－LAN2 －－－－ C,D  Which of the following statements are correct ? (多選)
		(a) When station A wants to send a packet to station C, it can send the packet to station C directly by putting the MAC address of station C into the frame.
		(b) When station A wants to send a packet to station B, it can send the packet to station B directly by putting the MAC address of station B into the frame.
		(c) Station A needs to know the MAC addresses of stations B,C,D in order to send frames to them directly.
		(d) When station A wants to send a packet to station D, it needs to send the packet to Router R first by putting the MAC address of Router R into the frame.
		(e) When station A wants to send a packet to station B, it needs to send the packet to Router R first by putting the MAC address of Router R into the frame.

(+16)	(16%)2. Consider the following internetwork configuration. Assume that “1” represents the interface of router R3 to network 3, “2” represents the interface of router R3 to network 4, “3” represents router R1, “4” represents router R2, “5” represents the interface of router R1 to network 2, “6” represents the interface of R1 to network 1, and “7” represents router R3, Then for routing tables of routers R1 and R3, what is the value of each of  the “next hop” entries ? (每個空格填入一個數字(1-7), 每格兩分)
	a	ANS:6
	b	ANS:5
	c	ANS:4
	d	ANS:4
	e	ANS:4
	f	ANS:4
	g	ANS:1
	h	ANS:2

(+8)	(8%) 3. Consider the case that a datagram of 1280 bytes are fragmented into four fragments and each fragment contains 320 bytes of data. What is the offset value for each of the four fragments ? Thus, (每格兩分)
	Offset of 1st fragment	ANS:0
	Offset of 2nd fragment	ANS:40
	Offset of 3rd fragment	ANS:80
	Offset of 4th fragment	ANS:120

(+12)	(12%)4. Consider the following internetwork configuration with subnet setting. Assume that “1” represents the interface of router R1 to network 1, “2” represents the interface of router R1 to network 2, “3” represents router R2, “4” represents router R1, “5” represents the interface of router R2 to network 2, and “6” represents the interface of R2 to network 3. Then for router R1, what is the “next hop” for the following received packets ? (每個空格填入一個數字(1-6), 每格兩分)
	(a) Destination IP = 128.96.34.16, Nexthop	ANS:1
	(b) Destination IP = 128.96.33.126, Nexthop	ANS:3
	(c) Destination IP = 128.96.33.20, Nexthop	ANS:3
	(d) Destination IP = 128.96.34.235, Nexthop	ANS:2
	(e) Destination IP = 128.96.34.12, Nexthop	ANS:1
	(f) Destination IP = 128.96.34.252, Nexthop	ANS:2

(+8)	(8%)5. Which of the following statements are correct for “Classless Inter-Domain Routing (CIDR)” ? (多選)
		(a)A technique that deal with the size problem of backbone routing table
		(b)It uses aggregate routes. Thus, uses a single entry in the forwarding table to tell the router how to reach a lot of different networks.
		(c)The convention is to place a “/X” after the prefix where X is the prefix length in bits
		(d)The “prefix” for all the networks 192.4.16 through 192.4.31 is represented as 192.4.16/24
		(e)A single class C network number 192.4.16 is represented as 192.4.16/20

(+6)	(6%)6. With the CIDR, what is the “prefix” for all the networks 192.4.16 through 192.4.31 ? Assume the prefix is represented as 192.4.a/b, and therefore (每格三分, 填入數字)
	a	ANS:16
	b	ANS:20

(+6)	(6%)7. With the CIDR, what is the “prefix” for all the networks 192.4.0 through 192.4.127 ? Assume the prefix is represented as 192.4.a/b, and therefore (每格三分, 填入數字)
	a	ANS:0
	b	ANS:17

(+5)	(5%)8. Which of the following statements is NOT correct for “Address Resolution Protocol (ARP)” ? (單選)
		(a) It is used to map IP addresses into physical (MAC) addresses
		(b) Each host has an IP/MAC mapping table to binding the IP address to physical (MAC) address
		(c) For a host, if an IP address is not in its IP/MAC table, it sends an ARP request to the network by using broadcast packet.
		(d) When the targeted host receives an ARP request, it will respond with its physical (MAC) address.
		(e) Every host receives an ARP request will respond with its physical (MAC) address.

(+5)	(5%)9. The Internet Message Control Protocol (ICMP) defines a collection of error messages that will be sent back to the source host whenever a router or host is unable to process an IP datagram successfully. Which of the following conditions will be reported by the ICMP protocol ? (多選)
		(a) Destination host unreachable
		(b) Reassembly process failed
		(c) Host received an out of order packet
		(d) Host received a delayed packet
		(e) A packet dropped by router due to network congestion

(+8)	(8%)10. Which of the following statements is correct for “Distance Vector” routing protocol ? Assume that each node knows the cost of the link to each of its directly connected neighbors. (單選)
		(a) Each node constructs a one dimensional array (a vector) containing the “distances” (costs) to its immediate neighbors and distributes that vector to all other nodes.
		(b) Each node constructs a one dimensional array (a vector) containing the “distances” (costs) to all other nodes and distributes that vector to all other nodes.
		(c) Each node constructs a one dimensional array (a vector) containing the “distances” (costs) to all other nodes and distributes that vector to its immediate neighbors.
		(d) Each node constructs a one dimensional array (a vector) containing the “distances” (costs) to its immediate neighbors and distributes that vector to its immediate neighbors.
		(e) fast response to “bad news” and slow response to “good news”

(+8)	(8%)11.  Which of the following statements is correct for “split horizon with poison reverse” scheme ? (單選)
		(a) When a node sends a routing update to its neighbors, it only sends those routes it learned from each neighbor back to that neighbor.
		(b) When a node sends a routing update to its neighbors, it does not send those routes it learned from each neighbor back to that neighbor
		(c) When a node sends a routing update to its neighbors, it sends those routes it learned from each neighbor back to that neighbor with negative information (such as ∞).
		(d) When a node sends a routing update to its neighbors, it sends all routes it learned to those neighbors.
		(e) When a node sends a routing update to its neighbors, it sends all routes it learned to those neighbors with negative information (such as ∞).

(+8)	(8%)12. Which of the following statements are correct for “Link State” routing protocol ? Assume that each node knows the cost of the link to each of its directly connected neighbors. (多選)
		(a) Each node constructs a one dimensional array (a vector) containing the “distances” (costs) to all other nodes and distributes that vector to its immediate neighbors.
		(b) Each node constructs a one dimensional array (a vector) containing the “distances” (costs) to all other nodes and distributes that vector to all other nodes.
		(c) Each node constructs a one dimensional array (a vector) containing the “distances” (costs) to its immediate neighbors and distributes that vector to its immediate neighbors.
		(d) Each node constructs a one dimensional array (a vector) containing the “distances” (costs) to its immediate neighbors and distributes that vector to all other nodes.
		(e) The link state packets (LSP) are sent to all other nodes by using reliable flooding algorithm.