Computer Network Homework3’ s hard question
Computer Network Homework3’ s hard question
1. Which kind of protocol does CSMA belong to?
A. Random Access Protocol
B. Take Turns Protocol
C. Centralized Protocol
(2 points)??
Answer:
A
6. Which provides connection-oriented service?
A. LLC1
B. LLC2
C. LLC3
(2 points)??
Answer:
B
-
unacknowledged connectionless service(LLC1)
-
connection-oriented service(LLC2)
-
acknowledged connectionless service(LLC3)?
17. A host connected by hub works on which method?
A. full duplex
B. half duplex
C. simplex
(2 points)??
Answer:
B
Explanation:
集線器(hub)用電子線路模擬總線方式，每次只允許一個站點發(fā)送。
18. In an Ethernet, four stations have one longest frame (1520 bytes) to send when the channel is busy. When all these frames are sent successfully, how many collisions will happen at least?
A. 1
B. 2
C. 3
D. 4
(2 points) ??
Answer:
C
Explanation:
第一次是在當(dāng)前站點發(fā)送完畢后四個站點同時發(fā)送會產(chǎn)生沖突。然后，一個選擇0t，另三個選擇1t，結(jié)果沖突一次，然后這三個沖突站點分別選擇從四個時間長度選三個，無論如何還會沖突一次，因為如果無沖突，則有一個站點先發(fā)送（幀很長），另外兩個站點都會檢測到信道忙，結(jié)果信道一空閑，它們立即發(fā)送，造成沖突。
After aborting, NIC enters exponential backoff: after mth collision, NIC chooses K at random from
{0,1,2,...,2m-1}. NIC waits K·512 bit times.
19. Which of the following Ethernet LAN has most collision domains?
A. all the hosts are connected to one switch by UTP cables
B. all the hosts are connected to one hub by UTP cables
C. all the hosts are connected by thin coax (10base-2)
(2 points)
?Answer:
A
?
Explanation:
交換機(jī)每個接口一個形成沖突域。不過只有在這個接口接hub時才會有沖突發(fā)生，接口全雙工工作時不會沖突。
20. Which field does not belong to an Ethernet Frame?
A. destination MAC address
B. source MAC address
C. type
D. frame check sequence
E. control
(2 points)??
Answer:
E
DIXv2? -- type >=1536
802.3(original)? -- length
802.3 (1997 edition) -- type/length
21. What is the maximum length of the data field of an Ethernet Frame?
A. 46
B. 512
C. 1000
D. 1500
(2 points)?
Answer:
D
23. When is a SNAP frame required in Ethernet?
A. The header of an Ethernet frame lacks length.
B. The header of an Ethernet frame lacks premeable.
C. The header of an Ethernet frame lacks source address.
D. The length of the playload field of an Ethernet frame is less than 46 bytes.
Answer:
D
?
Explanation:
使用長度字段主要是當(dāng)Data中有填充字節(jié)時確定Data中payload的長度。
24. The Ethernet (802.3), fast Ethernet (802.3u) and Gigabit Ethernet standard are different mainly in the layer of OSI.
A. Physical
B. data link
C. network
D. transport
(2 points)??
Answer:
A
?
Explanation:
10M/100M/1000Mbps以太網(wǎng)主要不同點是在物理層：物理介質(zhì)不同、調(diào)制和編碼方法不同、速率不同。
29. In spanning tree algorithm，how many bridges will be designated for a LAN segment?
A. 1
B. 2
C. 3
D. varied
(2 points)??
Answer:
A
33. In spanning tree algorithm，which port will be selected as the root port for a bridge if two shortest paths from the bridge to the root bridge have the same neighboring bridge on the paths?
A. the port of the bridge with the highest port ID
B. the port of the bridge with the lowest port ID
C. the port of the neighboring bridge with the highest port ID
D. the port of the neighboring bridge with the lowest port ID
(2 points)??
Answer:
D
?
Explanation:
不采用自己的端口號而采用鄰居的端口號打破平衡。
35. In spanning tree algorithm，a data frame cannot be forwarded between which port pair of a bridge?
A. the designated port and root port
B. the designated port and the designated port
C. the blocked port and the root port
(2 points)??
Answer:
C
37. What is one benefit of PVST+?
A. PVST+ supports Layer 3 load balancing without loops.
B. PVST+ reduces the CPU cycles for all the switches in the network.
C. PVST+ allows the root switch location to be optimized per VLAN.
D. PVST+ automatically selects the root bridge location, to provide optimized bandwidth usage.
(2 points)??
Answer:
C
38. If a switch (802.1Q) receives a frame without VLAN ID tagged from trunk port, what will it do?
A. regard it as default VLAN
B. regard it as native VLAN
C. drop it
(2 points)??
Answer:
B
40. Which of the following VLANs is static?
A. based on MAC address
B. based on subnets
C. based on network protocol
D. based on ports
(2 points)??
Answer:
D
42. Which of the following spanning trees is most flexible for load balancing and computational complex?
A. PVST
B. CST
C. MST
(2 points)??
Answer:
C
?
Explanation:
MST為多生成樹算法，可以設(shè)置生成樹的個數(shù)和每個VLAN采用哪顆生成樹。
46. How does a switch differ from a hub?
A. A switch does not induce any latency into the frame transfer time.
B. A switch tracks MAC addresses of directly-connected devices.
C. A switch operates at a lower, more efficient layer of the OSI model.
D. A switch decreases the number of broadcast domains.
E. A switch decreases the number of collision domains.
(2 points)??
Answer:
B
?
Explanation:
使用交換機(jī)會增加沖突域的數(shù)量
48. If host A sends an IP packet to host B, what will the source physical address be in the frame when it reaches host B?
The connections are: [host A]--[Router R1]--[Router R2]--[host B]
A. host A's MAC Address
B. host B's MAC Address
C. R1's MAC Address
D. R2's MAC Address
Answer:
D
?
Explanation:
在這里，每對路由器和主機(jī)之間采用一種數(shù)據(jù)鏈層協(xié)議，通過每一跳的源MAC地址和目的MAC都不同。IP分組被封裝在幀中，通過最后一段數(shù)據(jù)鏈路層協(xié)議時，源MAC為路由器R2的，目的MAC地址為主機(jī)B的。
8. How many collision domains are there in the following Ethernet?? How many broadcast domains?
?
Answer:
7,1
?
Explanation:
Switch每個端口一個沖突域（只有接hub時會沖突）。集線器所有端口位于同一個沖突域。一個廣播幀可以到達(dá)的地方屬于同一個廣播域。??
12. In the following figure, S1~S3 are switches, A~E are hosts,which of following statements will be true? (select two)
A. If host A sends a frame to host D, D will receive it.
B. If host B sends a frame to host D, D will receive it.
C. If host D sends a frame to host A, A will receive it.
D. If host D sends a frame to host B, B will receive it.
E. If host E sends a frame to host A, A will receive it.
F. If host E sends a frame to host B, B will receive it.
G. If host A sends a frame to host E, E will receive it.
Answer:
EG
轉(zhuǎn)載于:https://www.cnblogs.com/instant7/p/4127848.html
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