思科认证考试（ＣＣＮＡ）考试模拟题０１—１９及答案(5)
添加时间: 2007-9-3 22:06:40 作者: Cisco认证考试 阅读次数:43 来源: http://www.d9soft.com
Answer
d) The process where a router will prioritize routing protocols so that in the event two routing protocols have conflicting next hop addresses, the routing protocol with the lowest administrative distance will take priority.
Cisco uses administrative distances (AD) to measure the reliability of the routing protocol. The lower the (AD) the more reliable the protocol.
Router_C#sh ip route
Codes: C - connected, S - static,
I - IGRP, R - RIP,
M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF,
IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF
NSSA external type 2
E1 - OSPF external type 1,
E2 - OSPF external type 2,
E - EGP
i - IS-IS, L1 - IS-IS level-1,
L2 - IS-IS level-2, * -
candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
172.16.0.0/24 is subnetted, 2 subnets
C 172.16.1.0 is directly connected,
Serial1
C 172.16.2.0 is directly connected,
Serial0
I 10.0.0.0/8 [100/8576] via 172.16.1.1,
00:00:09, Serial1
[100/8576] via 172.16.2.1, 00:00:19,
Serial0
The 100 in bold is the administrative
distance for IGRP.
A partial list of administrative distances is included below:
Protocol AD
EIGRP 90
IGRP 100
OSPF 110
RIP 120
BGP 180
If a router hears a IP RIP and a IGRP update for the same network the router will discard the rip information. IP RIP uses hop count as it’s metric, while IGRP uses a composite metric including bandwidth and load, speed is the primary consideration.
11. [ExNx] Collisions occur when
a) multiple packets are placed on a serial link
b) multiple stations listen for traffic and transmit at the same time
c) when multiple tokens are on a ring simultaneously
d) beaconing process takes place
Answer
b) multiple stations listen for traffic and transmit at the same time
Collisions is a term that is used in an ethernet environment. Ethernet can be described as a listen then transmit scenario. First a station will listen for traffic if no traffic is sensed then a transmission will take place. If two stations transmit at the same time collisions will occur. The first station to detect the collision sends out a jamming signal to alert all stations a collision has occurred. At this point these stations set up a random interval timer when the timer expires re-transmission will occur.
Token ring is a token passing process a station can transmit only when he has the token. There never can be multiple tokens on the ring. Early token release allows up to two data frames to be transmitted on a token ring LAN at the same time. Collisions do not occur on a token ring.
Because of the point to point nature of serial links collisions do not occur.
Beaconing is a term used in a token passing environment.
12. [RINx] How many subnets are possible with a Class C address and a subnet mask of 255.255.255.252?
a) 32
b) 30
c) 60
d) 62
e) 4
Answer
d) 62
The above mask is using 6 bits to describe subnets. The formula used to determine the number of subnets (not including the all 0’s or all 1’s subnet) is 2n - 2 were n is the number of subnet bits. This is the number to use when configuring a ip address with the setup dialog.
13. [RxNx] What commands will list all protocols that are currently being routed? (Choose all that apply.)
a) show ip protocol
b) show protocol
c) show run
d) show start
e) All of the above
Answer
b) show protocol
c) show run
Show ip protocol will show just the ip routing protocols that are currently configured. Show start may or may not show the current routed protocols.
Below is the output of show protocol
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