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What is gratuitous ARP packet?
A ‘Gratuitous ARP’ is an AddressResolutionProtocol request packet where the source and destination IP are both set to the IP of the machine issuing the packet and the MAC is the broadcast address ff:ff:ff:ff:ff:ff. One function is to help detect IP conflicts.
What do you know about ARP and gratuitous ARP?
A Gratuitous ARP is an ARP Response that was not prompted by an ARP Request. The Gratuitous ARP is sent as a broadcast, as a way for a node to announce or update its IP to MAC mapping to the entire network.
How does an ARP reply know the Ethernet address?
An ARP reply will know the ethernet address, so it will be a unicast. It then causes this packet to be broadcast to all stations on the Ethernet cable originally determined by the routing mechanism. The way the ARP cache works is OS-dependent, and there is nothing requiring a host to maintain an ARP cache.
How many ARP requests does a host send?
The host sends 3 ARP requests. These requests will ask about its own IP (as you’ve correctly assumed), but will present himself as 0.0.0.0 so other hosts don’t log its IP address yet. If there’s no reply after those 3 requests, it will send a GARP packet effectively updating everyone else in the network*.
What do you mean by Gratuitous ARP request?
Gratuitous ARP could mean both Gratuitous ARP request and Gratuitous ARP reply, but not needed is all cases. Gratuitous ARP request is a packet where source and destination IP are both set to IP of the machine issuing the packet and the destination MAC is the broadcast address ff:ff:ff:ff:ff:ff ; no reply packet will occur.
How to send a unicast message in ARP-cache?
Now, this receiver will send a unicast packet with its MAC address (ARP-reply) to the sender of ARP-discovery packet. After the original sender receives the ARP-reply, it updates ARP-cache and start sending unicast message to the destination. Example – GATE CS 2005, Question 24 (ARP Based).