If you are aware of device ip address then we can process commands to get mac -address
In layer3 devices enter command
Assuming your device ip address is 192.168.X.X
Switch (config)#sh ip arp | I 192 .168.X.X
Output of command = mac address for specific ip address is showen
So further even we can find on which L2 interface this end device is connected by ...
In addition to the timeout described by Ron, devices changing their IP addresses often send out a gratuitous ARP (GARP - usually a request for self) as broadcast to notify the network of the MAC address change.
GARP is especially important when you use virtual IP addresses without virtual MAC addresses.
Entries in an ARP table on modern OSes will time out. This is not an official part of RFC 826, An Ethernet Address Resolution Protocol, although the RFC does discuss it at the end:
It may be desirable to have table aging and/or timeouts. The
implementation of these is outside the scope of this protocol. Here is
a more detailed description (...
I was told that MAC address are unique for each device and they don't
That is partially true. MAC addresses need to be unique only on the same LAN, and it is pretty easy to change the MAC address of most devices.
Does this mean that my computer allows unicast communications but not
multicast? So each device depending on the least significant bit of
Does this mean that my computer allows unicast communications but not multicast?
That indicates that your NIC's MAC is a unicast address - that's what it's supposed to be. The NIC also accepted broadcast and those multicasts that it is subscribed to - regardless of its hardware MAC.
Think of the hardware MAC of the NIC's default address. It only accepts ...
The data will get lost. At the very latest, the last router in the chain will send a "Who has X" ARP request and get no answer, so it will not be able to deliver the packet. Or, if it still has the MAC address in its ARP cache, it will send the frame to a MAC address that no longer exists on the network, and the frame will just end up being ignored ...