ARP
- Address Resolution Protocol (ARP) maps IP address to MAC addresses at Layer 2
- ARP requests and replies are Frames that include the target IP address, the sender's MAC Address, and either the Broadcast MAC address or the target's MAC Address
- If the Switch doesn't have the know the target MAC address, it broadcasts out the request to all ports
- Hosts that receive frames with mismatched target MAC addresses will drop the frame
- The source and destination IP addresses never change
- The MAC address changes at each hop
- At each hop, the ARP cache is updated to expedite future requests.
- Mapped addresses are saved to a host's ARP Cache and the Switch's MAC Address Table, which allows the host to send unicast Unicast packets directly to the destination
- When sending an ARP request outside of the subnet, the host will first contact its Default Gateway
- Sender wants to send ARP request to destination outside of its subnet
- It first sends an ARP request to its Default Gateway's IP address
- the DG replies with its own MAC address
- The sender then sends a request with the Target's IP, but uses the DG's MAC address
- The DG then forwards the ARP request to the appropriate subnet
- The target replies with its MAC address
- The DG then forwards to reply to the sender
OSI or TCP/IP Layer
CCNA Exam Topic
#extop-5-7
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