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Questions a) 96 Answer Here is a sampling of other port numbers and the application they are associated with. The first 8 of these protocols are automatically forwarded through the router by using the helper-address command Trivial File Transfer (TFTP) (port
69)
2. [CxNx] What is the standard encapsulation method used by Cisco routers for the Internet Protocol (IP) on it’s Ethernet interfaces? a) SNAP Answer SNAP is the default encapsulation for a token ring interface NOVELL-ETHER is the default encapsulation for a ipx interface.
a) ip address 1.1.1.1 255.255.255.0 Answer If you are not in the configuration mode, the ip address can be set by using the setup mode. Configuring interface Ethernet0/0:
4. [CxNx] Which commands will display the IP addresses of all interfaces on a Cisco Router? (Choose all that apply) a) show ip route Answer Examples of each of these commands are shown below: Router_A#sh int e0/0
Ethernet0/0 is up, line protocol is up
Hardware is AmdP2, address is
0010.7b15.bd41
(bia 0010.7b15.bd41)
Internet address is 10.10.10.1/24
MTU 1500 bytes, BW 10000 Kbit,
DLY 1000 usec,
rely 255/255, load 1/255
Encapsulation ARPA, loopback not set,
keepalive set (10 sec)
ARP type: ARPA, ARP Timeout 04:00:00
Last input never, output 00:00:06,
output hang never
Last clearing of "show interface"
counters never
Queueing strategy: fifo
Output queue 0/40, 0 drops;
input queue 0/75,
0 drops
5 minute input rate 0 bits/sec,
0 packets/sec
5 minute output rate 0 bits/sec,
0 packets/sec
0 packets input, 0 bytes,
0 no buffer
Received 0 broadcasts, 0 runts,
0 giants,
0 throttles, 0 input errors, 0 CRC,
0 frame, 0 overrun, 0 ignored,
0 abort
0 input packets with dribble
condition detected
127 packets output, 11802 bytes,
0 underruns
0 output errors, 0 collisions,
2 interface resets
0 babbles, 0 late collision,
0 deferred
0 lost carrier, 0 no carrier
0 output buffer failures, 0 output
buffers swapped out
Router_A#sh ip int e0/0 Ethernet0/0 is up, line protocol is up Internet address is 10.10.10.1/24 Broadcast address is 255.255.255.255 Address determined by non-volatile memory MTU is 1500 bytes Helper address is not set Directed broadcast forwarding is enabled Outgoing access list is not set Inbound access list is not set Proxy ARP is enabled Security level is default Split horizon is enabled ICMP redirects are always sent ICMP unreachables are always sent ICMP mask replies are never sent IP fast switching is enabled IP fast switching on the same interface is disabled IP multicast fast switching is enabled Router Discovery is disabled IP output packet accounting is disabled IP access violation accounting is disabled TCP/IP header compression is disabled Probe proxy name replies are disabled Gateway Discovery is disabled Policy routing is disabled Network address translation is disabled
5. [CxNx] Which of the following commands will display the contents of the ARP cache of your Cisco router? a) show ip arp cache Answer
6. [CxNx] Reverse Address Resolution Protocol (RARP) is the process: a) Where an IP host resolves
it’s IP address by broadcasting it’s MAC address to the network and a RARP
server assigns it an IP address. Answer Choice C describes Address Resolution Protocol (ARP). A host never has to resolve it’s own MAC address. The MAC address is burned into the Network Interface card. When the host is booted the MAC address will be loaded into memory.
7. [OxNx] Which of the following applications requires the connection-oriented layer four protocol, TCP? (Choose all that apply) a) Telnet Answer TFTP and SNMP use layer 4 UDP.
8. [RxNx] Which of the following are link state Routing Protocols. a) IP Answer A link state routing protocol advertises, to it’s neighbors, the state of the link when the state of the link changes. A distance vector routing protocol advertises its routing table periodically.
9. [CxNx] Of the following commands, identify the correct one for clearing the IP arp table in memory of the router. a) clear ip arp-cache Answer If you have changed an ip address or a NIC card on a host you might use this command to reset the cache.
10. [CxNx] Which of the following explains the correct definition of administrative distance as it pertains to Cisco’s IOS? a) The process by which routers
select an administrator for an autonomous system. Answer 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 Answer 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 Answer 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 Answer 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 Router_B#show protocol
14. [xxNx] Which of the following are true of access lists? a) Access list should have at least
one permit statement. Answer Every access list has an implicit deny all at the end. What would the need be to create a access list with just deny statements. Access-list are processed from the top down therefore the order of each statement could be critical, for instance suppose you created an access list and the first line was a permit any and the next line was a deny. Since it’s top down processing a packet would be permitted to pass on the first line and the second line would never be executed. An extended list will give you a "match count" that will help in determining what the most efficient order should be.
15. [xxNx] If the access-group command is configured on an interface and there is no access-list created which of the following is most correct? a) An error message will appear. Answer There are two steps to use an access list . 1. Create the list 2. Place the access list on a interface The analogy I use in class is: Suppose you reside in a gated community. The community is not protected until you hire the guard and then place him at the gate. If you hire the guard and never place him at the gate all traffic will be permitted. When there is no access list on an
interface it is implicit permit any
16. [xxNx] What is the result of the command? " access-list 101 permit tcp any 172.16.0.0 0.0.255.255 established" a) telnet sessions will be permitted
regardless of the source address Answer The secret to this question is the key word "established." Established means that the packet will be permitted unless it is the first part of the three way handshake. Recall that when we initiate a TCP connection we have no ACK. How can we acknowledge a sequence number from the other side when we have not established a session with him?
17. [xxNx] Which is generally true of the location of access-lists? (Choose all that apply.) a) Standard lists will most likely
be placed close to the destination. Answer A standard list will only check the source address. It makes no difference where the packet is going. If you place a standard list close to the source you could very well be denying that traffic to go to other destinations. An extended list can be placed close to the source because we can permit or deny traffic based upon the source and destination address. This insures that only traffic we wish to have denied is denied.
18. [RxNx] Which of the following is most correct? a) IP is to TCP. as IPX is to SPX. Answer 19. [ExNx] If Host A sends a packet to Host B over ethernet and Host B is not active: a) The packet will time out. Answer
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