What is an ARP cache and why is it important?

• A. A table of recently resolved IP-to-MAC mappings used to speed forwarding.
• B. A cache of DNS records used to resolve domain names.
• C. A memory pool for storing packet headers to reduce memory churn.
• D. A log of ignored ARP requests for security auditing.

Answer: (A)

An ARP cache is a table that stores recently learned mappings between IP addresses and MAC (hardware) addresses. When a device on a local network needs to send a frame to another host, it must place the destination’s MAC address in the Ethernet header. ARP translates the destination IP to that MAC address. Instead of asking every time, the device checks its ARP cache first; if a valid entry exists, it can forward the frame immediately using the stored MAC address. If not, it broadcasts an ARP request, the owner replies with its MAC, and the mapping is added to the cache. This caching speeds forwarding and reduces ARP traffic. Entries age out after a timeout, so the cache stays current; stale entries can cause delivery failures if not refreshed. On some networks static ARP entries are used to reduce spoofing risks.

DNS caches map domain names to IPs, not MAC addresses. A memory pool for packet headers is unrelated to ARP. A log of ignored ARP requests is for auditing, not the ARP cache itself.