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Sample Exam -

Cisco & IP Addressing
Louis D. Rossi, Louis R. Rossi and Thomas Rossi
  Copyright © 1999 The McGraw-Hill Companies, Inc.

Answers
  Answer 1.
  b) show running-config
  d) write terminal
  Answer 2.
  a) show config
  c) show startup-config
  Answer 3.
  a) 255.255.255.224
  To calculate the number of host or networks using the formula 2n–2 where n is the number of bits that will be used to describe the host or the network.
  To answer this question we first have to determine how many host bits would we need to have at least 16 unique combinations.
  Using our formula we need to have 5 host bits 25–2 = 30.
  This would leave us with 3 network bits therefore the mask is 224 in the fourth octet.
  Answer 4.
  a) immediately
  After the configuration command is issued the change takes place immediately.
  There are times when the router needs to be bounced, but it is very rare.
  Answer 5.
  a) Activated by default
  Answer 6.
  a) ip address 192.82.4.7 255.255.255.252
  If you are not in the configuration mode, the IP address can also be set by using the setup mode.
Configuring interface Ethernet0/0:
  Is this interface in use? [yes]:
  Configure IP on this interface? [yes]:
     IP address for this interface [10.10.10.1]: 10.10.10.1
     Number of bits in subnet field [16]: 16
     Class A network is 10.0.0.0, 16 subnet bits; mask is /24
  Take note when using the setup mode the mask is configured by using the number of subnet bits.
  Answer 7.
  c. show ipx interface
Example
Router#sh ip interface
%SYS-5-CONFIG_I: Configured from console by console
Ethernet0 is administratively down, line protocol is down
Internet address is 10.10.1.1/24
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1500 bytes
Helper address is not set
Directed broadcast forwarding is enabled
Multicast reserved groups joined: 224.0.0.9
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
  All addresses that have IP configured will be displayed.
  Answer 8.
  a) Where an IP host resolves its IP address by broadcasting its MAC address to the network and a RARP server assigns it an IP address.
  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.
  Answer 9.
  b) OSPF
  A link state routing protocol advertises, to it’s neighbors, the state of the link when the state of the link changes.
  Answer 10.
  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 an IP RIP and an 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.
  Answer 11.
  d. ip nat outside
  Answer 12.
  e)
  router(config)#router ospf 69
  router(config-router)#area 0 range 172.16.24.0 255.255.248.0
  router(config-router)#area 0 range 172.16.32.0 255.255.224.0
  There is no way we can manipulate the first two octets. These 16 bits uniquely describe our network. Let’s examine the 3rd octet below. A 248 mask means DO NOT change the bit pattern of the most significant 5 bits. Which implies we can do what we want with the remaining 3 bits. The chart below list all the possibilities, I have also included the 36 address to show how the bit pattern will change.
THIRD OCTET
128
64
32
16
8
4
2
1
248
1
1
1
1
1
0
0
0
 24
0
0
0
1
1
0
0
0
 25
0
0
0
1
1
0
0
1
 26
0
0
0
1
1
0
1
0
 27
0
0
0
1
1
0
1
1
 28
0
0
0
1
1
1
0
0
 29
0
0
0
1
1
1
0
1
 30
0
0
0
1
1
1
1
0
 31
0
0
0
1
1
1
1
1
 32
0
0
1
0
0
0
0
0
 
The command area 0 range 172.16.24.0 255.255.248.0 will include the networks 24-31.
The command area 0 range 172.16.32.0 255.255.224.0 will include the networks 32-63.
THIRD OCTET
128
64
32
16
8
4
2
1
224
1
1
1
0
0
0
0
0
 32
0
0
1
0
0
0
0
0
 40
0
0
1
0
1
0
0
0
 48
0
0
1
1
0
0
0
0
 56
0
0
1
1
1
0
0
0
 64
0
1
0
0
0
0
0
0
  Notice again how we have maintained the bit pattern of the first 3 bits up to a value of 64.
  Answer 13.
  b) EIGRP would then allow discontinuous networks to be configured
  The “no auto-summary command” will force EIGRP to act as a Classless Routing Protocol. EIGRP would then have the ability to communicate a mask other than the default.
  Cisco defines EIGRP as a advanced distance vector routing protocol. Mask information is communicated between hosts and therefore allows discontinuous networks to be defined.
  The command “no auto-summary” is required to support discontinuous networks.
  EIGRP is a internal routing protocol which means it is used to route within a autonomous system.
  BGP4 is an example of a exterior routing protocol.
  EIGRP also allows Variable Length Subnet Masking (VLSM) which means you can have different masks for the same major network number.
  Answer 14.
  e) 124
  The above mask is using 6 bits to describe subnets. The formula used to determine the number of subnets is  26 – 2 = 62 subnets and on each of these subnets we can have 2 hosts, there for we would have a total of 124 hosts.
  Answer 15.
  d) Area 0 is always required
  Area 0 is not required if only one area is configured.
  Answer 16.
  e. Workstation A could not successfully ping Workstation B
  Since Router_A is directly connected to network 10.0.0.0. Router_A will ignore the updates received from Router_C pertaining to 10.0.0.0  because the metric is higher.
  Classful routing protocols only use the set prefixes of 8 bits for a Class A, 16 bits for a Class B and 24 bits for a Class C address.
  IGRP is a classful routing protocol and does not communicate the subnet across different major networks. As a result there is no way Router_A can distinguish between the subnets 10.0.1.0 and 10.0.4.0.
  When Workstation A pings the 10 address of Workstation B or Router_B the ICMP echo request will remain on the subnet 10.0.1.0.
  Answer 17.
  e) Workstation A could not successfully ping Workstation B
  Since Router_A is directly connected to network 10.0.0.0 Router_A will ignore the updates received from Router_C that say’s network 10.0.0.0 is 1 hop away. Classful routing protocols only use the set prefixes of 8 bits for a Class A, 16 bits for a Class B and 24 bits for a Class C address.
  IP RIP is a classful routing protocol and does not communicate the subnet across different major networks. As a result there is no way Router_A can distinguish between the subnets 10.0.1.0 and 10.0.4.0.
  When Workstation A pings the 10 address of Workstation B or Router_B the ICMP echo request will remain on the subnet 10.0.1.0.
  Answer 18.
  b) Workstation A could successfully ping the ethernet interface of Router_B
  d) Workstation A could successfully ping Workstation B
  A classless routing protocol can set the prefix at any length.
  OSPF is a classless routing protocol and does communicate the subnet across different major networks therefore Router_A can distinguish between subnets 10.0.1.0 and 10.0.4.0.
Routing Table of Router_A
  172.16.0.0/24 is subnetted, 2 subnets
C   172.16.1.0 is directly connected, Serial0/0
O   172.16.2.0 [110/128] via 172.16.1.2, 00:01:06, Serial0/0
  10.0.0.0/24 is subnetted, 2 subnets
C    10.0.1.0 is directly connected, Ethernet0/0
     10.0.4.0 [110/138] via 172.16.1.2, 00:01:06, Serial0/0
  Any packet with a destination address of 10.0.4.x will be sent out the Serial0/0 interface.
  Answer 19.
  b. Router_C would ping Workstation B with a 50% success rate
  Classful routing protocols only use the set prefixes of 8 bits for a Class A, 16 bits for a Class B and 24 bits for a Class C address.
  IGRP is a clssful routing protocol and does not communicate the subnet across different major networks as a result Router_C  hears routing updates relating to network 10.0.0.0 from Router_A and Router_B. These updates are sent with the same metric. Therefore Router_C assumes that it can reach the 10 network by going out S0 or S1. When a ping is initiated from Router_C or Workstation C, Router_C will load balance the packets.
  Refer to the routing table of Router_C below:
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
  Two pings are shown below:
Router_C#ping 10.0.4.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.4.1, timeout is 2 seconds:
U!.!U
Success rate is 40 percent (2/5), round-trip min/avg/max = 4/4/4 ms
Router_C#ping 10.0.4.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.4.1, timeout is 2 seconds:
U!.!U
Success rate is 60 percent (3/5), round-trip min/avg/max = 4/4/4 ms
  10 ping probes were successful 5 times or 50%.
  Answer 20.
  b) Router_C would ping Workstation B with a 50% success rate
  Classful routing protocols only use the set prefixes of 8 bits for a Class A, 16 bits for a Class B and 24 bits for a Class C address.
  IP RIP is a classful routing protocol and does not communicate the subnet across different major networks.  Router_C  hears routing updates relating to network 10.0.0.0 from Router_A and Router_B. These updates are sent with the same metric of 1 hop. Therefore Router_C assumes that it can reach the 10 network by going out S0 or S1. When a ping is initiated from Router_C or Workstation C, Router_C will load balance the packets.
  Refer to the routing table of Router_C below:
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
R   10.0.0.0/8 [120/1] via 172.16.1.1, 00:00:09, Serial1
       [120/1] via 172.16.2.1, 00:00:19, Serial0
  Two pings are shown below:
Router_C#ping 10.0.4.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.4.1, timeout is 2 seconds:
U!.!U
Success rate is 40 percent (2/5), round-trip min/avg/max = 4/4/4 ms
Router_C#ping 10.0.4.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.4.1, timeout is 2 seconds:
!U!.!
Success rate is 60 percent (3/5), round-trip min/avg/max = 4/4/4 ms
  10 ping probes were successful 5 times or 50%.
  Answer 21.
  d)
  172.16.10.112/3
  172.16.10.116/30
  172.16.10.120/30
  172.16.10.124/30
  All of the above addresses can be summarized because the pattern of the first four bits is the same for each address; as shown below.
FOURTH OCTET
128
64
32
16
8
4
2
1
Value
0
1
1
1
0
0
0
0
112
0
1
1
1
0
1
0
0
116
0
1
1
1
1
0
0
0
120
0
1
1
1
1
1
0
0
124
 
An example of the OSPF command that would summarize these addresses is as follows:
area 0 range 172.16.10.112 255.255.255.240
  Answer 22.
  d) None of the above
  This is a good question to illustrate the importance of understanding the wildcard mask. A wildcard mask tells the router which bits to check (compare against the given IP) and which bits to ignore. A wildcard mask with an octet value of 0 means to check all eight bits against the corresponding octet of the given IP. A wildcard mask with an octet value of 255 means to ignore all eight bits in the corresponding octet of the given IP.
  It appears that the administrator wanted to permit the entire 207.239.71.0 network, but deny a single host.  Unfortunately, the mask 255.255.255.0 was used as a WILDCARD mask against the address 207.239.71.0.  The result of this access list is to permit all traffic from hosts whose fourth octet value is zero. It is possible for a host to have a fourth octet value of 0 (e.g. consider a class B network with a subnet mask of 255.255.252.0).
  Answer 23.
  d) 10.6.160.1 to 10.6.191.254
  A mask value in the third octet means that network addresses will be a multiple of 32. Therefore network 10.6.160.0 is the wire address for this host. The next wire address is 10.6.192.0. Of course if all host bits have a value of 1 this identifies the broadcast address, therefore c) is not correct.
  Answer 24.
  b) allows a single network addresses to carry multiple subnet masks
  c) allows the definition of subnets that contain only two host addresses
  Answer 25.
  d) broadcast
  The /27 represents the 255.255.255.224 mask. All networks will be multiples of 32. This address represents the last address on the 32 wire it is therefore a broadcast address.
  Answer 26.
  c) measures the “reliability” of an IP routing protocol
Administrative Distance (AD)
Protocol
AD
EIGRP
 90
IGRP
100
OSPF
110
RIP
120
BGP
180
EIGRP would be considered the most reliable protocol.
  Answer 27.
  d) this is an illegal command
  The 50 represents a standard IP access list. Therefore only a source address can be identified.
  If there is a need to identify both source and destination an access list number would have to be in the range of 100–199.
  Answer 28.
  b) access-list 1 deny 172.16.16.16
  a) is incorrect because an extended access list must identify a protocol
  c) is incorrect because it does not identify the source address
  d) is incorrect because the syntax used is an extended access list yet the number 1 identifies a standard list.
  b) will prevent all IP traffic from 172.16.16.16 including TFTP.
  Answer 29.
  d) Depends on the routing protocol configured
  The major network address has been variably subnetted if we were using a Classless routing protocol there would be no problem and we should expect 100% pings. If a Classful protocol were configured then we would have a problem.
  If IP RIP were configured for example the RIP updates would not be advertised out the serial interfaces due to split horizon. There fore the remote router would never “learn” about the remote subnet.
  The router output below shows the update being suppressed.
Router_B#
debug ip rip
RIP: sending v1 update to 255.255.255.255 via Ethernet0 (172.16.2.32) - suppressing null update
RIP: sending v1 update to 255.255.255.255 via Serial0 (172.16.4.5) - suppressing null update
</routerio>
  Answer 30.
  b) OSPF
  c) EIGRP
  Because the major network address is variably subnetted we must use a classless routing protocol.

 


 
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