ARP Request - does it update all hosts ARP tables on the LAN?

[wardwolfram]

Hello,

I see that 'arp request' frames include both the MAC & IP addresses of the sender. Since the arp request is a broadcast, do all the hosts connected to the LAN/VLAN update their arp tables with both the IP & MAC addresses of the sending arp request host?

Thanks in advance,

Ward

[balaji.bandi]

No, Only Switch has all the information, when the end device request, if the switch not aware it broadcast and get the information for device. (if this was not in the table)

[wardwolfram]

Thank you for your reply, but I do not think I follow your response...

A switch will forward or broadcast frames and is not aware of ARP tables or IP addresses.  But, since an ARP request is a broadcast, the switch will flood the arp request out to all hosts on the LAN.  Since the ARP is examined by all hosts, it would seem efficient to add the IP and MAC in this frame/packet to all devices (host or routers) arp tables.

[balaji.bandi]

Once switch aware based on arp time out setup it hold the database, it only query the one dont know,(make sense ?

)

[paul driver]

Hello
When one host wishes to speak to another, this sender needs a way to discover its destination host, and it does so by an arp request, this request will contain the SIP/MAC address of sender and DIP of its intended host.

The packet is then encapsulated into a frame with the source host mac address and destination address of all hosts (broadcast) and sent on its way, as it is a broadcast ALL hosts on the Lan will see it however as it is not for them they will drop the packet, Only the host that recognizes its own ip address will arp reply with its own mac-address.

So If the broadcast is not made how would the destination host be discovered within a large LAN?

[wardwolfram]

I desire to understand the effects of all host arp tables in a network (vlan) due to an arp broadcast from a host. I ran a simple test in Packet Tracer which resulted with :

1. The source host sending the arp request, his arp table was updated due to the arp reply.  Working as designed.

2. The destination host arp table was updated with the senders MAC and IP.

3. Arp tables from the remaining hosts in the network (vlan) were not updated.

Question:

1.Why would not all hosts in the vlan update their arp tables with the senders MAC and IP? The information in the arp request provides the senders MAC and IP addresses which is broadcasted. 

[EdgarMurray8920]

You can add unnecessary workload on the hosts if it's a big network. They will only know when they need it for something. Also, for that purpose are de routers and switches.