DHCP Group of Four Questions

Refer to the exhibit. Using the information shown, answer the question

Question 1:

All hosts in the networks have been operational for several hours when the DHCP server goes down. What happens to the hosts that have obtained service from the DHCP server?

A – The hosts will not be able to communicate with any other hosts.
B – The hosts will continue to communicate normally for a period of time.
C – The hosts will be able to communicate with hosts outsides their own network
D – The hosts will only be able to communicate with other hosts by IP address not by hostname

Answer: B

Explanation:

DHCP often uses dynamic allocation mechanism to save IP addresses, which assigns an IP address to a client for a limited period of time. So when the DHCP server goes down, that client can still use the allocated IP address for a period of time

Question 2:

What is the purpose of the DHCP server?

A – to provide storage for email
B – to translate URLs to IP addresses
C – to translate IPv4 addresses to MAC addresses
D – to provide an IP configuration information to hosts

Answer: D

Explanation:

The main purpose of the DHCP server is to provide IP configuration parameters to hosts such as the default gateway, domain name, Domain Name System (DNS) server…

Question 3:

How is the message sent from a PC2 when is first powers on and attempts to contact the DHCP Server?

A – Layer 3 unicast
B – Layer 3 broadcast
C – Layer 3 multicast
D – Without any Layer 3 encapsulation

Answer: B

Explanation:

When a client boots up for the first time, it transmits a DHCPDISCOVER message on its local physical subnet. Because the client has no way of knowing the subnet to which it belongs, the DHCPDISCOVER is an all-subnets broadcast (destination IP address of 255.255.255.255, which is a layer 3 broadcast address). The client does not have a configured IP address, so the source IP address of 0.0.0.0 is used.

Question 4:

What is the default behavior of R1 when PC1 requests service from DHCP server?

A – Drop the request
B – Broadcast the request to R2 and R3
C – Forward the request to R2
D – Broadcast the request to R2, R3 and ISP

Answer: A

Explanation:

When PC1 requests service from DHCP server (for example, it requests an IP address), it sends a broadcast packet. But R1 router, by default, will not forward broadcast packet and drop it.

For your information, if you want to use the DHCP server from another network (like in this case) you can use the ip helper-address command which will make the router forward UDP broadcasts.

In the real exam you will be taken to a LAB simulation environment but it is, in fact, just a group of 4 multi-choice questions!

CCNA NAT SIM 1

Question

A network associate is configuring a router for the CCNA Training company to provide internet access. The ISP has provided the company six public IP addresses of 198.18.184.105 198.18.184.110. The company has 14 hosts that need to access the internet simultaneously. The hosts in the CCNA Training company LAN have been assigned private space addresses in the range of 192.168.100.17 – 192.168.100.30.

The task is to complete the NAT configuration using all IP addresses assigned by the ISP to provide Internet access for the hosts in the Weaver LAN. Functionality can be tested by clicking on the host provided for testing.

Configuration information
router name – Weaver
inside global addresses – 198.18.184.105 198.18.184.110/29
inside local addresses – 192.168.100.17 – 192.168.100.30/28
number of inside hosts – 14

The following have already been configured on the router： - The basic router configuration - The appropriate interfaces have been configured for NAT inside and NAT outside - The appropriate static routes have also been configured (since the company will be a stub network, no routing protocol will be required.) - All passwords have been temporarily set to “cisco”

Solution

The CCNA Training company has 14 hosts that need to access the internet simultaneously but we just have 6 public IP addresses from 198.18.184.105 to 198.18.184.110/29. Therefore we have to use NAT overload (or PAT)

Double click on the Weaver router to open it

Router>enable
Router#configure terminal

First you should change the router’s name to Weaver

Router(config)#hostname Weaver

Create a NAT pool of global addresses to be allocated with their netmask (/29 = 255.255.255.248). There were reports that the simulator in the real exam did not accept “prefix-length” keryword so you should use “netmask” keyword.

Weaver(config)#ip nat pool mypool 198.18.184.105 198.18.184.110 netmask 255.255.255.248

Create a standard access control list that permits the addresses that are to be translated

Weaver(config)#access-list 1 permit 192.168.100.16 0.0.0.15

Establish dynamic source translation, specifying the access list that was defined in the prior step

Weaver(config)#ip nat inside source list 1 pool mypool overload

This command translates all source addresses that pass access list 1, which means a source address from 192.168.100.17 to 192.168.100.30, into an address from the pool named mypool (the pool contains addresses from 198.18.184.105 to 198.18.184.110)

Overload keyword allows to map multiple IP addresses to a single registered IP address (many-to-one) by using different ports

The question said that appropriate interfaces have been configured for NAT inside and NAT outside statements.

This is how to configure the NAT inside and NAT outside, just for your understanding:

Weaver(config)#interface fa0/0
Weaver(config-if)#ip nat inside

Weaver(config-if)#exit

Weaver(config)#interface s0/0
Weaver(config-if)#ip nat outside
Weaver(config-if)#end

Finally, we should save all your work with the following command:

Weaver#copy running-config startup-config

Check your configuration by going to “Host for testing” and type:

C:\>ping 192.0.2.114

The ping should work well and you will be replied from 192.0.2.114

CCNA Configuration SIM

Question:

To configure the router (R2-RC) click on the console host icon that is connected to a router by a serial console cable (shown in the diagram as a dashed black line)

CCNA Training Company recently installed a new router in their office. Complete the network installation by performing the initial router configurations and configuring RIPV2 routing using the router command line interface (CLI) on the R2-RC.

Name of the router is R2-RC
Enable-secret password is cisco1
The password to access user EXEC mode using the console is cisco2
The password to allow telnet access to the router is cisco3
IPV4 addresses must be configured as follows:
Ethernet network 209.165.202.128/27 – router has last assignable host address in subnet
Serial network is 192.0.2.16/28 – router has last assignable host address in the subnet. Interfaces should be enabled.
Router protocol is RIP V2

Attention : In practical examinations, please note the following, the actual information will prevail. 1. Name of the router is xxx 2. Enable-secret password is xxx 3. Password to access user EXEC mode using the console is xxx 4. The password to allow telnet access to the router is xxx 5. IP information

Solution

1) Name the router:

Router>enable
Router#configure terminal
Router(config)#hostname R2-RC

2) Set secret password:

R2-RC(config)# enable secret cisco1

3) Set password for the console:

R2-RC(config)#line console 0
R2-RC(config-line)#password cisco2
R2-RC(config-line)#login
R2-RC(config-line)#exit

4) Set the Telnet password:

R2-RC(config)#line vty 0 4
R2-RC(config-line)#password cisco3
R2-RC(config-line)#login
R2-RC(config-line)#exit

5) Assign IP address for Ethernet interface (Fa0/0):

The Ethernet network 209.165.202.128/27 has:

Increment:32 (/27 = 255.255.255.224 or 1111 1111.1111 1111.1111 1111.1110 0000)
Network address: 209.165.202.128
Broadcast address: 209.165.202.159 (because 128 + 32 – 1 = 159)

Therefore the last assignable host address in this subnet is 209.165.202.158 and we will assign it to Fa0/0 interface with these commands:

R2-RC(config)# interface fa0/0
R2-RC(config-if)#ip address 209.165.202.158 255.255.255.224
R2-RC(config-if)#no shutdown
R2-RC(config-if)#exit

6) Assign IP address for Serial interface (S0/0/0):

Serial network 192.0.2.16/28 has:

Increment:16 (/28 = 255.255.255.240 or 1111 1111.1111 1111.1111 1111.1111 0000)
Network address: 192.0.2.16
Broadcast address: 192.0.2.31 (because 16 + 16 – 1 = 31)

So the last assignable host address in this subnet is 192.0.2.30. Finally we assign it to s0/0/0 interface:

R2-RC(config)# interface s0/0/0
R2-RC(config-if)#ip address 192.0.2.30 255.255.255.240
R2-RC(config-if)#no shutdown
R2-RC(config-if)#exit

7) Configure RIP v2 routing protocol:

R2-RC(config)#router rip
R2-RC(config-router)#version 2
R2-RC(config-router)#network 209.165.202.128
R2-RC(config-router)#network 192.0.2.16
R2-RC(config-router)#end
R2-RC#copy running-config startup-config

CCNA Drag and Drop SIM

Question

You have been hired by Specialty Hardware Incorporated to document the layout of the network. Complete the following tasks: Complete the network topology shown in the graphic by dragging the labels below with the appropriate router types, interface types, and IP addresses to the graphic . Find the information you need by using the router console attached to the R-CENTER router.

Answer and explanation

This is the simplest lab question in four labs you see in the real CCNA exam. First we should identify the types of these routers by using the show cdp neighbors command:

There are 3 columns we should pay more attention to:

+ Local Interface: the interface on the device you are using “show cdp neighbors” command. In this case it is the interface of R-CENTER router

+ Platform: the platform of neighbor device

+ Port ID: the neighbor device’s port or interface on which the CDP packets are multicast

From the exhibit, the “Local Interface”, “Platform” and “Port ID” columns, we can identify where these four routers should be placed and their corresponding associated ports

Finally, use the show running-config command to find out the ip addresses of four interfaces on R-CENTER

And we can easily assign corresponding ip addresses to four neighbor routers, which are on the same network with R-CENTER router’s interfaces

Please remember in the real CCNA Exam the routers’ types, ip addresses and interfaces may be different! So make sure you understand how it works.

CCNA EIGRP LAB

Question

After adding R3 router, no routing updates are being exchanged between R3 and the new location. All other inter connectivity and Internet access for the existing locations of the company are working properly.

The task is to identify the fault(s) and correct the router configuration to provide full connectivity between the routers.

Access to the router CLI can be gained by clicking on the appropriate host. All passwords on all routers are cisco.

IP addresses are listed in the chart below.

R1 Fa0/0: 192.168.77.33 S1/0: 198.0.18.6 S0/1: 192.168.60.25	R2 Fa0/0: 192.168.60.97 Fa0/1: 192.168.60.113 S0/0: 192.168.36.14
R3 Fa0/0: 192.168.77.34 Fa0/1: 192.168.60.65 Fa1/0: 192.168.60.81	R4 Fa0/0: 192.168.60.129 Fa0/1: 192.168.60.145 S0/1: 192.168.60.26

Answer and explanation

We should check the configuration of the new added router first because it does not function properly while others work well. From the command line interface of R3 router, enter the show running-config command

From the output above, we know that this router was wrongly configured with an autonomous number (AS) of 22. When the AS numbers among routers are mismatched, no adjacency is formed.

(You should check the AS numbers on other routers for sure)

To solve this problem, we simply re-configure router R3 with the following commands:

R3>enable (you have to enter cisco as its password here)

R3#configure terminal

R3(config)#no router eigrp 22

R3(config)#router eigrp 212

R3(config-router)#network 192.168.60.0

R3(config-router)#network 192.168.77.0

R3(config-router)#no auto-summary

R3(config-router)#end

R3#copy running-config startup-config

Check R1 router with the show running-config command:

Notice that it is missing a definition to the network R3. Therefore we have to add it so that it can recognize R3 router

R1>enable (you have to enter cisco as its password here)

R1#configure terminal

R1(config)#router eigrp 212

R1(config-router)#network 192.168.77.0

R1(config-router)#end

R1#copy running-config startup-config

Now the whole network will work well. You should check again with ping command from router R3 to other routers!

Modifications:

Maybe in this EIGRP Sim you will see the “passive-interface …” command somewhere in R1 configuration. If the link between R1 to R2 (or R3, r4) routers has the “passive interface” then we have to remove it with the “no passive-interface …” command because it prevents EIGRP update from being sent on that interface. But if the “passive interface” is applied to the link between R1 and ISP router then we just leave it. Don’t use the “no passive-interface s1/0″ on R1 because the link between R1 & ISP doesn’t need EIGRP to run on it. A static route from R1 to ISP & “ip default-network” command in R1 are the correct answers.

(Note: The “ip default-network” command in R1 will advertise the static route of R1 (to go to the Internet) to other routers (R2,R3,R4) so that they can access the Internet too). In the exam you will see these lines in R1 configuration:

!
ip default-network 198.0.18.0
ip route 0.0.0.0 0.0.0.0 198.0.18.5
!

CCNA Implementation SIM

This topology contains 3 routers and 1 switch. Complete the topology.

Drag the appropriate device icons to the labeled Device
Drag the appropriate connections to the locations labeled Connections.
Drag the appropriate IP addresses to the locations labeled IP address

(Hint: use the given host addresses and Main router information)
To remove a device or connection, drag it away from the topology.

Use information gathered from the Main router to complete the configuration of any additional routers. No passwords are required to access the Main router. The config terminal command has been disabled for the HQ router. The router does not require any configuration.

Configure each additional router with the following:

Configure the interfaces with the correct IP address and enable the interfaces.
Set the password to allow console access to consolepw
Set the password to allow telnet access to telnetpw
Set the password to allow privilege mode access to privpw

Note: Because routes are not being added to the configurations, you will not be able to ping through the internetwork.
All devices have cable autosensing capabilities disabled.
All hosts are PC’s

Answer and explanation

Specify appropriate devices and drag them on the “Device” boxes

For the device at the bottom-right box, we notice that it has 2 interfaces Fa0/2 and Fa0/4; moreover the link connects the PC on the right with the device on the bottom-right is a straight-through link -> it is a switch

The question stated that this topology contains 3 routers and 1 switch -> two other devices are routers

Place them on appropriate locations as following:

(Host D and host E will be automatically added after placing two routers. Click on them to access neighboring routers)

Specify appropriate connections between these devices:

+ The router on the left is connected with the Main router through FastEthernet interfaces: use a crossover cable
+ The router on the right is connected with the Main router through Serial interfaces: use a serial cable
+ The router on the right and the Switch: use a straight-through cable+ The router on the left and the computer: use a crossover cable

(To remember which type of cable you should use, follow these tips:

- To connect two serial interfaces of 2 routers we use serial cable
– To specify when we use crossover cable or straight-through cable, we should remember:
Group 1: Router, Host, Server
Group 2: Hub, Switch
One device in group 1 + One device in group 2: use straight-through cable
Two devices in the same group: use crossover cable

For example: we use straight-through cable to connect switch to router, switch to host, hub to host, hub to server… and we use crossover cable to connect switch to switch, switch to hub, router to router, host to host… )

Assign appropriate IP addresses for interfaces:

From Main router, use show running-config command:

(Notice that you may see different IP addresses in the real CCNA exam, the ones shown above are just used for demonstration)

From the output we learned that the ip address of Fa0/0 interface of the Main router is 192.168.152.177/28. This address belongs to a subnetwork which has:

Increment: 16 (/28 = 255.255.255.240 or 1111 1111.1111 1111.1111 1111.1111 0000)
Network address: 192.168.152.176 (because 176 = 16 * 11 and 176 < 177)
Broadcast address: 192.168.152.191 (because 191 = 176 + 16 – 1)

And we can pick up an ip address from the list that belongs to this subnetwork: 192.168.152.190 and assign it to the Fa0/0 interface the router on the left

Use the same method for interface Serial0/0 with an ip address of 192.168.152.161

Increment: 16
Network address: 192.168.152.160 (because 160 = 16 * 10 and 160 < 161)
Broadcast address: 192.168.152.175 (because 176 = 160 + 16 – 1)

-> and we choose 192.168.152.174 for Serial0/0 interface of the router on the right

Interface Fa0/1 of the router on the left

IP (of the computer on the left) : 192.168.152.129/28

Increment: 16
Network address: 192.168.152.128 (because 128 = 16 * 8 and 128 < 129)
Broadcast address: 192.168.152.143 (because 143 = 128 + 16 – 1)

-> we choose 192.168.152.142 from the list

Interface Fa0/0 of the router on the right

IP (of the computer on the left) : 192.168.152.225/28

Increment: 16
Network address: 192.168.152.224 (because 224 = 16 * 14 and 224 < 225)
Broadcast address: 192.168.152.239 (because 239 = 224 + 16 – 1)

-> we choose 192.168.152.238 from the list

Let’s have a look at the picture below to summarize

Configure two routers on the left and right with these commands:

Router1 = router on the left

Assign appropriate IP addresses to Fa0/0 & Fa0/1 interfaces:

Router1>enable
Router1#configure terminal
Router1(config)#interface fa0/0
Router1(config-if)#ip address 192.168.152.190 255.255.255.240
Router1(config-if)#no shutdown

Router1(config-if)#interface fa0/1
Router1(config-if)#ip address 192.168.152.142 255.255.255.240
Router1(config-if)#no shutdown

Set passwords (configure on two routers)

+ Console password:

Router1(config-if)#exit
Router1(config)#line console 0
Router1(config-line)#password consolepw
Router1(config-line)#login
Router1(config-line)#exit

+ Telnet password:

Router1(config)#line vty 0 4
Router1(config-line)#password telnetpw
Router1(config-line)#login
Router1(config-line)#exit

+ Privilege mode password:

Router1(config)#enable password privpw

Save the configuration:

Router1(config)#exitRouter1#copy running-config startup-config

Configure IP addresses of Router2 (router on the right)

Router2>enable
Router2#configure terminal
Router2(config)#interface fa0/0
Router2(config-if)#ip address 192.168.152.238 255.255.255.240
Router2(config-if)#no shutdown

Router2(config-if)#interface serial0/0
Router2(config-if)#ip address 192.168.152.174 255.255.255.240
Router2(config-if)#no shutdown

and set console, telnet and privilege mode passwords for Router2 as we did for Router1, remember to save the configuration when you finished

Brijesh Patel (CCNP)