101 · Question #533
A BIG-IP Administrator is trying to send traffic to a server on the same subnet and sees an incomplete in the BIG-IP devices ARP table. What could cause the incomplete status?
The correct answer is D. Server's switch connection is in the wrong VLAN. An incomplete ARP entry means an ARP request was sent but no reply was received, most commonly because a Layer 2 misconfiguration such as a wrong VLAN prevents the broadcast from reaching the server.
Question
A BIG-IP Administrator is trying to send traffic to a server on the same subnet and sees an incomplete in the BIG-IP devices ARP table. What could cause the incomplete status?
Options
- ABIG-IP device connection is half-duplex
- BRouter does not have a default gateway
- CFirewall is blocking ICMP
- DServer's switch connection is in the wrong VLAN
How the community answered
(26 responses)- A8% (2)
- B15% (4)
- C4% (1)
- D73% (19)
Why each option
An incomplete ARP entry means an ARP request was sent but no reply was received, most commonly because a Layer 2 misconfiguration such as a wrong VLAN prevents the broadcast from reaching the server.
A half-duplex mismatch causes collisions and throughput degradation but does not prevent ARP reply frames from being returned.
A missing default gateway on a router is irrelevant for same-subnet communication, which relies entirely on ARP and Layer 2 switching with no routing required.
A firewall blocking ICMP affects ping reachability but has no effect on ARP, which operates at Layer 2 below the IP stack.
If the server's switch port is assigned to the wrong VLAN, the BIG-IP's ARP broadcast will not reach the server because VLANs segment Layer 2 broadcast domains. Without a reply, the ARP entry remains incomplete and all traffic destined for that server is dropped at Layer 2.
Concept tested: BIG-IP ARP incomplete status caused by VLAN misconfiguration
Source: https://support.f5.com/csp/article/K14135
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