Default Gateway

When some users are unable to reach external network resources while others can, it is most likely due to the affected users not having the correct default gateway set up. The default gateway is the path that data takes when it needs to leave the local network to another network (like the internet). If users have an incorrect gateway, their data can't leave the local network thus they are unable to reach external network resources. The other options are less likely because: checking the network cable for damage would mostly result in no internet connection at all rather than just some users being affected, checking the firewall configuration might be a step to take if no users can access the external network resources as the firewall could be blocking access, and inspecting for malware on affected devices would typically only be done if the devices showed other signs of infection, simply not being able to access external network resources is usually not an indicator of malware.

The most plausible issue might be 'Incorrect default gateway on the problematic computer'. This is because a gateway is needed for a network device to communicate with devices on a different network; in this case, the web server. If it's incorrectly set, the problematic computer can't communicate with the web server while all others in the same network can access it, suggesting an issue specific to this computer. The 'Faulty network cable' would also create a communication problem but would likely affect more than just the ability to access the web server. 'Outdated web browser' is less likely because it would generally result in difficulty to load certain websites or features, rather than preventing access to the server altogether. The answer 'No internet access' can't be correct since the problem is specifically tied to accessing the web server, not the internet in general. Moreover, other computers on the same network have internet access.

Computers in a network need a default gateway configuration in order to communicate beyond their local network, or subnet. In this case, since the company branch can communicate locally but not with the headquarters, it suggests that the computers lack a default gateway to route their data to different subnets or networks. Adding a default gateway to the DHCP settings would resolve this issue. The other potential answers are incorrect: Changing the IP address range or subnet mask could disrupt local communication without necessarily fixing the issue with connecting to headquarters, and adding a DNS server to the DHCP is irrelevant to this problem as it refers to the resolution of domain names to IP addresses, not to intra-network communication.