SK0-004 · Question #26
A technician is troubleshooting an issue with a new server, which is unable to download OS patches from the Internet. The technician reviews the following configuration: Ethernet Adapter Local Area…
The correct answer is A. Incorrect default gateway. With a /25 subnet mask (255.255.255.128), the host at 192.168.10.20 is in the 192.168.10.0/25 subnet (range .0-.127), but the configured gateway 192.168.10.129 falls in the second /25 subnet (.128-.255), making it unreachable.
Question
A technician is troubleshooting an issue with a new server, which is unable to download OS patches from the Internet. The technician reviews the following configuration:
Ethernet Adapter Local Area Connection:
Connection-specific DNS Suffix . : comptia.org Link-local IPv6 Address . . . . : fe80::c95:3f59:1a01:c050%11 IPv4 Address . . . . . . . . . . : 192.168.10.20 Subnet Mask . . . . . . . . . . : 255.255.255.128 Default Gateway . . . . . . . . : 192.168.10.129 Which of the following is the reason that the server is unable to connect to the Internet?
Options
- AIncorrect default gateway
- BInvalid IPv6 address
- CWrong subnet mask
- DMisconfigured DNS suffix
How the community answered
(47 responses)- A62% (29)
- B13% (6)
- C4% (2)
- D21% (10)
Why each option
With a /25 subnet mask (255.255.255.128), the host at 192.168.10.20 is in the 192.168.10.0/25 subnet (range .0-.127), but the configured gateway 192.168.10.129 falls in the second /25 subnet (.128-.255), making it unreachable.
The mask 255.255.255.128 splits 192.168.10.0 into two /25 subnets: 192.168.10.0-127 and 192.168.10.128-255. The server IP 192.168.10.20 is in the first subnet while the gateway 192.168.10.129 is in the second, placing them on different logical networks. Because the gateway is unreachable at Layer 3, the server cannot forward packets to the Internet regardless of DNS or IPv6 configuration.
The address fe80::c95:3f59:1a01:c050%11 is a valid link-local IPv6 address; link-local addresses always begin with fe80::/10 and are auto-configured, so this is not an error.
The mask 255.255.255.128 is itself a valid subnet mask; the problem is not the mask value but that the configured gateway IP falls outside the subnet defined by that mask for this host.
The DNS suffix 'comptia.org' affects name resolution only and does not prevent the server from establishing IP-layer connectivity to the Internet.
Concept tested: Default gateway reachability within /25 subnet boundaries
Source: https://learn.microsoft.com/en-us/troubleshoot/windows-server/networking/tcpip-addressing-and-subnetting
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