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 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.