ARP & layer 3 switch [closed]

Question

Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.

---

We don’t allow questions about professional server or networking-related infrastructure administration on Stack Overflow. You can edit the question so it’s on-topic for Stack Overflow.

Closed 6 years ago.

Improve this question

The following is based on my understanding of network, if there's anything wrong, please point it out.

Considering the following scenario. A host (sender) is to send a IP packet:

1. sender fills in the destination IP address
2. sender fills in the destination MAC address (may use ARP)
3. switch forwards the packet based on the MAC address.

Here's my question:

Can we get rid of ARP, if we are using a layer 3 switch? because a layer 3 switch forwarding the packets based on IP address.

Answer 1

Switches don't really use ARP in the meaning they don't send out out ARPs but they do utilise their functions when a pc sends out an arp.

Switches with IP interfaces's use ARP in the same way any other device uses ARP to communicate. This can be on a L2 switch as the management interface, or a layer 3 switch with IP VLAN interfaces.

An ARP is broadcasted, and so switches do flood it out all ports. Once the device which the ARP is intended to reach see's the ARP, it replies directly to the device which sent the ARP with it's MAC address. The original device then sends the traffic (which caused it to send an ARP) directly to the MAC of the responder. It's at this point the switch uses it's MAC table to forward the frames out the correct port.

source techexams.

Answer 2

You still need ARP. A layer-3 switch is basically a laer-3 router and a layer-2 switch combination. The layer-3 switch is a layer-2 switch for the purposes of forwarding traffic on the same layer-2 domain, but a layer-3 router for traffic destined for a different subnet.

Any host-to-host (a router is just a host, too) traffic still needs layer-2 to first deliver it, and that requires a layer-2 address to forward it to the destination (another host on the same layer-2 domain, including a router if the IP address is not in the same subnet). ARP gets a layer-2 address based on a layer-3 address, so it is still necessary.