Explain the three different address allocation mechanisms used by DHCPv4:
Manual: A permanent address is manually assigned by the administrator. This is used for devices that need to have a fixed address, such as servers and printers.
Automatic: A permanent address is assigned from the DHCP pool automatically. This is used in stable networks where the devices rarely change.
Dynamic: An address from the DHCP pool is temporarily leased to a client device. This is used most of the time.
Describe the DHCP operations for lease origination and lease renewal. Include all the steps
required:
The client broadcasts a DHCPDISCOVER message on the network.
A server replies with a DHCPOFFER, with the proposed IP address, and other information like the default gateway and lease length. It marks the offered address as temporarily reserved. If the client does not respond to the offer, the offered address returns to the pool.
The client broadcasts a DHCPREQUEST message, letting all the servers on the network know that it has accepted the offer.
The server responds with a DHCPACK message to finalise the lease. It adds the new address and the host's MAC address to its lease table.
When the lease has expired, the client sends another DHCPREQUEST to the server. If it doesn't get a response, the client broadcasts the message so that another server can renew its lease.
Question 2
List the four main reasons for subnetting an IP network address:
Security: Subnets are kept seperate and limit unauthorised access.
Organisation: Networks can be organised logically by location, function, or department.
Management: Smaller networks are easier to manage, and issues can be identified more quickly
Performance: Subnetting creates smaller broadcast domains, which reduces congestion
As a network administrator you are given the following network address: 172.34.0.0/16
You want to have the maximum possible number of subnets, but you need to accommodate at least 3000 hosts per subnet.
12 bits are needed for host (212 is 4096), leaving 20 for network. The subnet mask is /20, or 255.255.240.0
First four networks:
Subnet #
Network address
First host address
Last host address
Broadcast address
0
172.34.0.0
172.34.0.1
172.34.15.254
172.34.15.255
1
172.34.16.0
172.34.16.1
172.34.31.254
172.34.31.255
2
172.34.32.0
172.34.32.1
172.34.47.254
172.34.47.255
3
172.34.48.0
172.34.48.1
172.34.63.254
172.34.63.255
What is the function of a subnet mask?
Subnet masks show how to seperate the network and host portions of an IP address, so that you can find the network address and identify which hosts are on the same network
Question 3
Explain three basic functions of a router:
Connect networks
Read IP addresses
Determine the best path to send traffic
Write the commands to add the IP address 172.54.60.48/26 to the Serial interface S2/0:
en
conf t
int s2/0
ip addr 172.54.60.48 255.255.255.192
no shut
What show command has input shown below and define what the 120 represents:
198.45.120.0/28 is subnetted, 10 subnets
R 198.45.120.0 [120/1] via 198.45.120.97, 00:00:01, Serial2/0
R 198.45.120.16 [120/2] via 198.45.120.97, 00:00:01, Serial2/0
[120/2] via 198.45.120.145, 00:00:01, Serial3/0
This is the output of the command show ip route. The number 120 is the administrative distance (trustworthiness) of the source the network was discovered by (in this case, RIP).
What is wrong with the command below for IP address 220.34.56.0/26 and how would you correct it?
Router# conf t
Router(config)# ip addr 220.34.56.0 255.255.255.0
This command should be executed in interface config mode (int g0/0), not global config mode.
This is a network address (use 220.34.56.1)
The subnet mask is wrong for /26. It should be 255.255.255.192
Explain the phrase ‘time to convergence’:
How long it takes for all the routers on the network to be up-to-date with the same information.
Question 4
What is the difference between classless and classful IPv4 addressing?
Classful addressing is the older system. A network could only have one subnet mask, and routers didn't send subnet mask information in routing updates. Classless addressing means that more than one subnet mask can be used on a network (e.g. a /22 LAN and a /30 point-to-point connexion between routers).
Complete the table below:
IP Address/Prefix
Network address
Broadcast address
196.48.200.50/20
192.48.192.0
192.48.207.255
200.61.84.190/12
200.48.0.0
200.63.255.255
10.10.10.196/25
10.10.10.128
10.10.10.255
172.16.31.187/22
172.16.28.0
172.16.31.255
156.78.92.5/18
156.78.64.0
156.78.127.255
Question 5
Explain in detail how switches can be used to reduce traffic loads on a network:
While hubs create large collision domains, switches create lots of small ones (one for each device; this is called microsegmentation). This greatly reduces the number of collisions. Switches can also be used to create VLANs, which make smaller broadcast domains, reducing the load of broadcast traffic.
Describe the 3 types of Inter-VLAN routing:
Type
Description
Pros
Cons
Legacy inter-vlan routing
One physical connexion between router and switch for each VLAN
Easy to configure
Works on old devices
Wastes ports
Large routers needed
Poor scalability
Router-on-a-stick
One trunk link between switch and router that connects all VLANs
Saves cabling and ports
Cost-effective
Lower performance as routing handled by CPU instead of hardware
Traffic bottleneck as all going through same link
Layer 3 switches
An L3 switch performs routing and switching through hardware
Quick
Highly scalable
No routers needed
Expensive
Difficult to configure
2023
Question 1
List the four main reasons for subnetting an IP network address:
To organise a network by location, function, or department
To keep subnetworks seperate and manage access
To make management and troubleshooting easier by reducing the size of networks
To improve network performance by decreasing broadcast traffic
As a network administrator you are given the following network address: 172.31.0.0 /16
You want to have the maximum possible number of subnets, but you need to accommodate at least 1000 hosts per subnet.
The new subnet mask is /22 (255.255.252.0), as 10 bits are needed for the host portion (210 = 1024), leaving 22 for the network portion.
First five networks:
Subnet #
Network address
First host address
Last host address
Broadcast address
0
172.31.0.0
172.31.0.1
172.31.3.254
172.31.3.255
0
172.31.4.0
172.31.4.1
172.31.7.254
172.31.7.255
0
172.31.8.0
172.31.8.1
172.31.11.254
172.31.11.255
0
172.31.12.0
172.31.12.1
172.31.15.254
172.31.15.255
0
172.31.16.0
172.31.16.1
172.31.19.254
172.31.19.255
Question 2
Question 3
Explain three basic functions of a router:
Read IP addresses
Connect networks
Determine the best path to send traffic
What is wrong with the command below for IP address 192.168.10.0/29 and how would you correct it?Router(config)# ip address 192.168.10.0 255.255.255.0
Wrong mode: use interface config mode (int g0/0)
Incorrect subnet mask: use 255.255.255.248
Network address: use a host address, e.g. 192.168.10.1
Write the commands to see the routing table of a router and see the full routing configuration: