Task 1

IPv4

For IPv4, address ranges from the private IP address space (RFC 1918) have been chosen. Based on the diagram and the VLAN sizes provided, the approach can include the following:

• Class A (10.0.0.0/8) for large VLANs
• Class B (172.16.0.0/12) for medium VLANs
• Class C (192.168.0.0/16) for smaller VLANs

In this case, the IPv4 Scheme Table should look like this:

Table 1: IPv4 Scheme Table
(Source: Self-Created)

The IPv4 scheme includes the functionalities of appropriate Class A, B, and C which range from the VLAN size and start to optimise the address space usage. For IPv4, larger subnets use Class A and B networks such as VLANs 10 and 8. On the other hand, VLANs like VLANs 5 and 3 try to implement Class B or Class C ranges.

IPv6

For IPv6, the use of the Global Unicast Address (GUA) range can be identified. These are assigned from the 2000::/3 space, while the Link-Local Address (FE80::/10) is automatically assigned for the duration of system users. As a large address space is available in the IPv6, every VLAN can be allocated a unique /64 prefix.
In this case, the IPv4 Scheme Table should look like this:

Table 2: IPv6 Scheme Table
(Source: Self-Created)

The IPv6 can be identified as highly scalable. This is why the network is trying to assign a /64 subnet to each VLAN and the smallest VLAN. The best practices for IPv6 addressing can be achieved for ample growth. IPv6 is mostly known for providing a vast address space that can enable unique subnets for each VLAN without needing subnetting complexity like IPv4. IPv6 has also been accepted to allow automatic address configuration and hierarchical routing improvements.

Task 2

Technical Overview

The simulation involves using Cisco Packet Tracer to design and configure a network. To manage internal network/IP traffic between the internal network and ISP, the configuration is required to have the default routes (Chen et al., 2020). This network simulation provides a complete network setup over several routers and switches connected with PCs across several VLANs, mimicking both the physical and logical segmentation of an enterprise network.

Analysis of Network Components

Routers and Switches

Some of these are in the 2911, 4331, and 2901 series models router and connected by GigabitEthernet (G0/0, G0/1) and Serial (S0/0/0, S0/2/0) interfaces in the diagram. These routers are used to connect the various VLANs across the network. The 3650 and 3560 multilayer switches, with Layer 3 routing features, are needed for routing within VLANS and OSPF routing adjacency between VLANS.

VLAN Assignment

• VLANs are mostly applied extensively throughout the network which is applied for logical segmentation.
• VLAN 100, VLAN 200 and VLAN 300 are used on one set of switches.
• VLANs 2, VLAN 4, VLAN 5, and others are deployed that can separate other network segments.
• Each VLAN has its IP addressing scheme, such as 192.168.x.x/24 for VLAN 2 or 172.16.x.x/16 for VLAN 5.
• VLAN DHCP scopes are set up for automatic IP address assignment across different VLANs.

Figure 1: Simulation Diagram
(Source: Self-Created)

IP Address Scheme

The above diagram has also provided subnetting and IP addresses made particularly such as 5.0.0.5/30 for point-to-point links and 192.168.2.0/24 for VLAN 2 DHCP.

Routing Protocol (OSPFv2)

For the IPv4 network, OSPFv2 will be used by the internal routers and Layer 3 switches to exchange routing information and to calculate the best data packet paths. It is the configuration of routers on some OSPF areas, setting up router IDS, and announcing a suitable network range for the OSPF process.

BGP and Default Routes

The black devices are connected to the ISP and are preconfigured using BGP. To allow internal traffic to flow through these BGP routers, the ISP-BGP routers have to receive outbound traffic directed at them on a default route attached to the routers configured with OSPF (Jain et al., 2021). Using IP 9.9.9.9, the external networks can be reached as represented by the ISP.

Task 3

In Task 3, 10 faults have been found and fixed in the network simulation so that the network works appropriately. These two processes involve analysing each network segment and device configuration to locate where the errors arise, correcting those errors and naturally working with the network. It has been performed so that the errors are not propagated across the network.

Fault 1: Incorrect IP Address Configuration on Router Interfaces

Figure 2: Incorrect IP Address Configuration
(Source: Self-Created)

The first fault concerned assigning incorrect IP addresses on the interfaces of more than one router. In the diagram, the routers had IPs which did not fit the subnet configuration or they had a conflicting address. Using the show IP interface brief command, the verification of the IP addressing scheme for each interface was done. Using the IP scheme from Task 1, the wrong IPs were reconfigured with the correct addresses in such a way that there was no IP conflict or misalignment. The IP addresses such as 10.100.0.0/18 are also not accurate.

Fault 2: VLAN Mismatch on Trunk Links

Figure 3: Invalid IP Address and Subnet
(Source: Self-Created)

A switch uses VLAN mismatch on trunk links between switches as a differentiator. That happens when trunk ports in different switches do not allow the same VLANs and the communication between VLANs across switches frequently. Commands like show interface trunk and show vlan spotted the issue. The solution involved updating the trunk to its configuration by using the switchport trunk allowed vlan command to make sure all required VLANs were allowed across the trunk links. No subnets were properly mentioned. The subnet getaway such as /10 and /14 are not appropriate.

Fault 3: Misconfigured Routing Protocol

There were some issues with the routers not routing correctly, this was due to specific or non-configured routes. The routing table represents the show IP route and for some routers, there is no forwarding routing information. The issue was fixed by correcting the OSPF configuration. Each router has been put in the right OSPF area and has network statements for the correct subnets on its network statements.

Fault 4: Missing Default Gateway on PCs

The default gateways on some end devices (PCs) were either missing or configured incorrectly and some of the end devices (PCs) themselves were not able to communicate with external networks. There is not any ping delivered from a PC to an external network which is why it was identified. The misconfiguration was revealed by the config command on each PC. All affected devices had default gateways fixed correctly so traffic beyond the local network was routed properly.

Fault 5: Incorrect Access Control Lists (ACLs)

Figure 4: Incorrect ACLs
(Source: Self-Created)

On routers several ACLs were improperly configured, blocking certain traffic. It turned out that certain denied statements were blocking traffic that should have been permitted, and that was discovered using the show access lists command. The ACLs were modified to allow the requisite traffic, particularly between VLANs and across subnets. This IP address of 10.100.0.0/18 does not match with ACL 2960.

Fault 6: DHCP Server Misconfiguration

The network's DHCP was improperly configured, refusing to assign dynamic IP addresses to devices. The IP addresses on PCs have been renewed but it was failing. When issuing the show running-config command on the router that is acting as the DHCP server, it provided an error in the DHCP pool configuration. By using the correct network and default router parameters the pool was corrected.

Fault 7: Switchport Misconfigurations

Figure 5: Switchport Misconfigurations
(Source: Self-Created)

The access ports were incorrectly configured on certain switches as trunk ports, preventing devices from talking to the network at all. In some cases, there are 2 IP addresses assigned in a single line which is also an error. This was detected by examining the output of the show interfaces command from the affected switches. The solution was to configure the access mode correctly on these ports with the switchport mode access command and give them to the correct VL. Connection and packet sending are successful from PCS to router R3.

Fault 8: Duplex Mismatch

Some switch and router interfaces showed a duplex mismatch consistent with performance degradation and communication problems. An error has been observed in the interface errors during the "show interface" command, where high collision and late collision counts were reported. For duplex settings, both ends have been aligned by either duplex auto or forced full duplex where necessary.

Fault 9: Static Route Configuration Issues

Figure 6: Static Route Configuration Issues
(Source: Self-Created)

Static routes on some routes are incorrect or missing which is another error. These routers cannot communicate with the rest of the network. Because of all the missing routes, the routing table (show Ip route) showed that some networks were unreachable. For example, it is not possible to include 2 IP addresses at G0/0. 2 IP addresses can be assigned in 2 static routes such as 1 can be assigned on G0/0 and another can be assigned on G0/1. Adding or correcting the static routes with the Ip route command ensured full connectivity from one network site to the next.

Fault 10: Missing or Incorrect NAT Configuration

The NAT (Network Address Translation) issues on the routers connecting to the internet were the final thing that was failing the network. If not properly configured NAT, internal devices could not see external networks. Show Ip Nat translations showed no active NAT translations which means a configuration issue. The Ip Nat inside and Ip Nat outside commands were used to configure NAT properly securing the internal network by the use of the correct ACLs.

All 10 faults were identified through a systematic examination of the network devices, with show IP interface brief, show vlan, show IP route, show access lists and show interfaces being used to identify the faults. This troubleshooting process illustrates the necessity of systematic network analysis and the significance of (network) protocols and device configurations. This allows the successful operation of the final simulation with all devices communicating with each other as expected.

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