思科认证考试（ＣＣＮＡ）考试模拟题２０—３９及答案(4)
添加时间: 2007-9-3 22:11:00 作者: Cisco认证考试 阅读次数:57 来源: http://www.d9soft.com
Common Name Novel Name Cisco Name
Ethernet 2 Ethernet_II arpa
IEEE 802.3 Ethernet_802.2 sap
IEEE 802.3 with SNAP Ethernet_SNAP snap
Ethernet Ethernet_802.3 Novell ether
IEEE 802.5 with SNAP Token_ring snap
Note that Cisco can use the name snap to define two different frame types because these names are assigned to either a Token Rring or an Ethernet interface. In doing this the frame type name means something different to the router depending upon the interface type it is assigned to.
31. [RxNx] In order to communicate throughout an internetwork, which of the following are required. Choose Two.
a) The use of a routable protocol such as NetBEUI or LAT
b) A hierarchical naming scheme server such as DNS
c) A host file at each communicating device
d) A two part network addressing scheme such as Network/Host
e) The use of a routable protocol such as IP or IPX
f) The use of a routable protocol such as TCP or IPX
Answer
d) A two part network addressing scheme such as Network/Host
e) The use of a routable protocol such as IP or IPX
Explanation: Since an internetwork is made up of multiple logical networks with hosts on each of those networks, a two-part addressing scheme is required so that each can be identified. For example, IP uses a 32-bit number, which is really at least two separate numbers, one part for the network and one part for the host on that network. In an IP number such as 131.108.25.165, the major network portion is 131.108, and, assuming we are not subnetting, the host portion is 25.165. Both IP and IPX provide such a two part addressing scheme.
But protocols such as NetBEUI or LAT do not provide addressing at layer 3 and therefore are unable to distinguish between different logical networks. As a result they are not routable.
32. [CxNx] What is the default route on an IP network? Choose one.
a) This is the route that will be chosen first by IP for delivery of a datagram.
b) The address of the nearest downstream neighbor in a Token ring network.
c) At the router, it is the route used to direct frames for which the next hop has not been explicitly listed in the routing table.
d) Any static route listing in a routing table.
e) When all conditions are equal, the best route for delivery of IP datagrams.
Answer
c) At the router, it is the route used to direct frames for which the next hop has not been explicitly listed in the routing table.
The purpose of a default route is to route frames for which a next hop has not been explicitly listed in the routing table. To say it another way is to say that the default route points the way to go when there is no known path to follow. At a router, the default route is the address of the next hop if no other route is known or specified. Often the default route is set as a path to the Internet, where any unknown destination can hopefully be resolved.
33. [CxNx] A caret symbol (^) inserted into a failed command indicates which of the following. Choose one.
a) Numeric data is required for this command.
b) The point in a command where you can simply press return to complete the syntax string.
c) The point in a command where you have entered an incorrect command, keyword or argument.
d) The point in a command where you must enter a required value.
e) This is a normal indicator for any failed command.
Answer
c) The point in a command where you have entered an incorrect command, keyword or argument.
An example follows:
R2#sh clack
^% Invalid input detected at ^
marker.Router_B>sh cl?
WORD clock
34. [RXNx] The metric used by IPX RIP is:
a) hops
b) ticks
c) cost
d) ticks and hops
e) None of the above.
Answer
d) ticks and hops
Ticks are used initially if there is a tie then hops are used. Default tick count is 1 for a LAN connection and 6 for a serial connection.
35. [xINx] Which one of the following masks has the nickname of the "serial mask"?
a) 255.255.255.192
b) 255.255.255.224
c) 255.255.255.240
d) 255.255.255.248
e) 255.255.255.252
Answer
e) 255.255.255.252
The 255.255.255.252 provides two host addresses. This is the exact number of host addresses we need for a serial connection. In the example below the two host addresses are shown in bold. The chart represents the fourth octet of a class C address. The mask is 255.255.255.252. The network number is 4. The broadcast address is 7.
36. [SxNx] The following statement would deny traffic from what subnets?
Router_B(config)#access-list 101 deny
tcp 10.1.8.0 0.0.7.255
192.16.5.0 0.0.0.255
a) 10.1.8.0
b) 10.1.15.0
c) 10.1.0.0
d) 10.1.16.0
e) choice a and b
Answer
a) 10.1.8.0
b) 10.1.15.0
e) choice a and b
The type of mask used here is an inverse mask meaning that when the mask has a bit value of 0 the access list must match the corresponding bits. If the inverse mask has a value of 1 it s "don t care," meaning the access list does not care about the corresponding bit.
Since the inverse mask has a value of 0 in the first and second octet the access list must match the first 16 bits. Since the value of the fourth octet is 255 that means all the bits are ones, so the access list does not care about the value of the fourth octet.
10 1 8 0
0 0 7 255
The octet that is not so obvious is the third octet. The inverse mask of 7 gives us 0 s for the most significant 5 bits and 1 s for the last 3. Refer to the chart below.
Since the least 3 significant bits are 1 s they can be anything, which gives us the subnets 8-15.
37. [SxNx] Name three reasons why VLAN s should be created.
a) Moves, Adds and Changes are made simpler.
b) There is less administrative overhead.
c) The switch can route between VLANS.
d) It limits broadcasts domains.
e) The router can switch faster.
Answer
a) Moves, Adds and Changes are made simpler.
b) There is less administrative overhead.
d) It limits broadcasts domains.
If a workstation moves there is a good chance the move is within the same VLAN. If we have a good design of a single subnet within each VLAN there will be no need to reconfigure the workstation with a new layer 3 address. Each VLAN defines a broadcast domain.
38. [SxNx] The Catalyst 5000 uses which switching mode?
a) Cut-through
b) Store and forward
c) Fast switching
d) Choice a and b
e) Choice a and c
Answer
b) Store and forward
Store and forward mode receives the complete frame before forwarding takes place. After the destination and source addresses are read the cyclic redundancy check is performed, the frame is forwarded. Switch latency is dependent upon frame size.
Cut-through, on the other hand, starts forwarding the frame as soon as the destination address is read. This mode reduces latency in the switch.
39. [OxNx] Which of the following layers defines data representation?
a) Application Layer 7
b) Presentation Layer 6
c) Session Layer 5
d) Transport Layer 4
e) Network Layer 3
f) Data Link Layer 2
g) Physical Layer 1
Answer
b) Presentation Layer 6
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