While troubleshooting why a Linux file server cannot be reached from any workstation, a junior administrator runs the command:
ip addr show dev enp0s25
The relevant output is:
2: enp0s25: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000 link/ether 3c:8c:f8:12:34:56 brd ff:ff:ff:ff:ff:ff inet 169.254.23.42/16 brd 169.254.255.255 scope link enp0s25 valid_lft forever preferred_lft forever
No additional addresses are listed for the interface, and the default gateway does not respond to pings. Based on this information, which issue is MOST likely preventing clients from connecting to the server?
The switchport connected to the server is administratively shut down.
The subnet mask delivered by DHCP is incorrect, limiting routing to the local host.
The DHCP service on the subnet is unavailable or not reachable.
The server's NIC is set to half-duplex, causing excessive collisions.
The 169.254.23.42/16 address shown by ip addr is an IPv4 link-local (APIPA) address that a host self-assigns only when it cannot obtain a lease from a DHCP server. Because the interface is up and showing carrier, the physical link and switch port are working, and speed/duplex problems would not trigger automatic link-local addressing. An incorrect subnet mask provided by DHCP would still require the server to have received a lease, which has not happened. Therefore the most probable cause of the outage is that the server's DHCP requests are not being answered or are being blocked, leaving the host with only the self-assigned link-local address and no route to the gateway.
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