destination mac address in the arp request packet

[Not_light]

why the destination mac addrss in the arp request packet can either be 0000-0000-0000 or FFFF-FFFF-FFFF? 

[Seb Rupik]

Hi there,

An ARP request with all zero's is used when the sender is sending a packet for which it only knows the destination IP. You will find this in the ARP packet (Target MAC) itself.

An frame with all F's in the destination MAC is used when the sender is broadcasting to the local segment, ie, gratuitous ARP.

Cheers,

Seb.

[Not_light]

hello, I learned that the target mac with all zero's in gratuitious arp packet in Huawei's document, is there any difference between the two scenario ?

[Seb Rupik]

The Ethernet frame must always use all F's for the destination MAC address to function as a broadcast.

The Target MAC address specified in the ARP packet itself can be either all 0's or F's, it can vary depending on vendor implementation.

cheers,

Seb.