Dynamic ARP Inspection validates every ARP packet on untrusted ports against the DHCP snooping binding table — forged “I am the gateway” replies (ARP spoofing / MITM) are dropped. Trusted ports skip validation.

ip arp inspection vlan 10,20
interface Gi1/0/24
 ip arp inspection trust

IP Source Guard closes the other half: on untrusted ports, frames are only forwarded when source IP+MAC match the binding table — private-VLAN trickery and source-address spoofing die.

The trio: DHCP snooping builds the truth table, DAI polices ARP, ISG polices IP traffic. Each feature depends on the snooping bindings; enable them as a set. Verify: show ip arp inspection statistics, show ip source guard binding.