How do ARP requests work

Question

So I may have a stupid question that mainly comes from me getting weird results to say the least while experimenting.

I'm a bit unsure how do ARP requests work.

For example how can I arp my entire local net 192.168.0.1/24. Must I send an arp request to each individual ip or does the arp request get sent to the router or switch who in turn replies to which host is up and its corresponding ip and MAC address.

I'm trying to do this programmatically using python, with a module called scapy... I was watching a tutorial and they arpinged the entire local network by giving their local ip address and mask to scapy.all.arping if I'm not mistaken

Answer 1

Must I send an arp request to each individual ip

Yes.

or does the arp request get sent to the router

An ARP request is never forwarded by a router (apart from very exotic cases).

or switch

A switch does forward ARP requests just like any other broadcasts (to all ports but the one the broadcast was received on).

who in turn replies to which host is up and its corresponding ip and MAC address.

No - the one replying is the host itself.

An ARP request is sent as a broadcast (=destination MAC address FF:FF:FF:FF:FF:FF) to the whole layer-2 network (connected by switches, hubs). All hosts receive the request but all but the one asked for simply ignore/drop it. The one host with the requested IP address replies to the request to the source host, informing it of the associated MAC address.

ARP is defined in RFC 826.