ARP

What is Dynamic ARP Inspection (DAI) ?

Dynamic ARP inspection is a security feature which validates ARP packet in a network. Dynamic ARP inspections validates the packet by performing IP to MAC address binding inspection stored in a trusted database (the DHCP snooping database) before forwarding the packet. Dynamic ARP intercepts, logs, and discards ARP packets with invalid IP-to-MAC address bindings. This capability protects the network from certain man-in-the-middle attacks.

Dynamic ARP inspection ensures that only valid ARP requests and responses are relayed.

The switch performs these activities:·        

Intercepts all ARP requests and responses on untrusted ports ·        

Verifies that each of these intercepted packets has a valid IP-to-MAC address binding before it updates the local ARP cache or before it forwards the packet to the appropriate destination·        

Drops invalid ARP packets

Most Commonly used Network Layer Utilities

I was just thinking about the most commonly used Network Layer utilities in day to day business. Here are they which are useful to guys who are aspiring for their CCNA.
1) Address Resolution Protocol (ARP)
2) Domain Name Systems (DNS)
3) Dynamic Host Configuration Protocol (DHCP)
4) Ping.

You can find more details about  Network Layer Utilities  in detail, how they work etc.