ARP - the Address Resolution Protocol - is the unsung mechanism that makes Layer 3 routing actually work over Layer 2 Ethernet. Every time your router forwards a packet on a LAN, ARP is what tells it which MAC address to write in the frame header. This lab inspects the ARP table on R1, generates traffic to watch entries populate, and configures a static ARP entry to see how it differs from a dynamic one.
What you will learn
- What the ARP table actually contains and what each column means
- How dynamic entries get learned and how long they live (the ARP aging timer)
- How to configure a static ARP entry and when you would want to
- The difference between an "interface" entry (the router's own address) and a learned dynamic entry
- The
show arp summarycommand and why it is the fastest way to spot ARP-table problems
What this lab does NOT cover
- Dynamic ARP Inspection (DAI), the security feature that validates ARP packets against a binding table. Lab sec-05 covers it.
- ARP poisoning and gratuitous-ARP attacks. Mentioned briefly here, covered in depth in the 802.1X pillar and the sec-05 lab.
- Proxy ARP, beyond a brief mention.
