Address Resolution Protocol Flashcards
What is Address Resolution Protocol (ARP)?
ARP is a protocol used to discover the hardware address of a node with a certain IP address.
How does ARP work?
Once a IP datagram has been fully formed, it needs to be encapsulated inside an Ethernet frame. This means that the transmitting device needs a destination MAC address to complete the Ethernet frame header. Almost all network connected devices will retain a local ARP table. An ARP table is just a list of IP addresses an the Mac addresses associated with them.
What is an ARP Broadcast?
Let’s say we want to send some data to the IP address 10.20.30.40. It might be the case that this destination doesn’t have an entry in the ARP table. When this happens, the node that wants to send data send a broadcast ARP message to the Mac broadcast address, which is all F’s.
What is an ARP Response?
When the network interface that’s been assigned an IP of 10.20.30.40 receives an ARP broadcast, it sends back what’s known as an ARP response. This response message will contain the MAC address for the network interface in question. Now, the transmitting computer knows what MAC address to put in the destination hardware address field, and the Ethernet frame is ready for delivery.
Are ARP tables permanent?
No, ARP table entries generally expire after a short amount of time to ensure changes in the network are accounted for.