Address Resolution Protocol (ARP) is a required TCP/IP standard defined in RFC 826, "Address Resolution Protocol (ARP)." ARP resolves IP addresses used by TCP/IP-based software to media access control addresses used by LAN hardware. ARP provides the following protocol services to hosts located on the same physical network:

• Media access control addresses are obtained by using a network broadcast request in the form of the question "What is the media access control address for a device that is configured with the enclosed IP address?"
• When an ARP request is answered, both the sender of the ARP reply and the original ARP requester record each other's IP address and media access control address as an entry in a local table called the ARP cache for future reference.

The function of Spanning Tree Protocol (STP) is to prevent Layer 2 switching loop and broadcast storms in a Local Area Network (LAN). The Spanning Tree Protocol (STP) allows redundant links in a network to prevent complete network failure if an active link fails, without the danger of Layer 2 Switching loops.

The main difference between Rapid Spanning Tree Protocol (RSTP IEEE 802.1W) and Spanning Tree Protocol (STP IEEE 802.1D) is that Rapid Spanning Tree Protocol (RSTP) assumes the three Spanning Tree Protocol (STP) ports states Listening, Blocking, and Disabled are same (these states do not forward frames and they do not learn MAC addresses). Hence RSTP places them all into a new called Discarding state. Learning and forwarding ports remain more or less the same.

• In Spanning Tree Protocol (STP IEEE 802.1D), bridges would only send out a BPDU when they received one on their root port. They only forward BPDUs that are generated by the Root Bridge. Rapid Spanning Tree Protocol (RSTP IEEE 802.1W) enabled switches send out BPDUs every hello time, containing current information.
• Spanning Tree Protocol (STP IEEE 802.1D) includes two port types; Root Port and Designated Port. Rapid Spanning Tree Protocol (RSTP IEEE 802.1W) includes two additional port types called as alternate ports and backup ports. Analternate port is a port that has an alternative path or paths to the root but is currently in a discarding state (can be considered as an additional unused root port). A backup port is a port on a network segment that could be used to reach the root switch, but there is already an active designated port for the segment (can be considered as an additional unused designated port).

Broadcast Domain:

• A logical set of computer systems those are reachable without using a router.
• Broadcast Domain is limited to the specific IP sub network for all the IP broadcasts.
• Broadcast domain uses a switched environment to broadcast.
• The network systems will have 255 at the end of the IP addresses.

• It refers a set of devices in which packet collision could occur.
• The devices can include the devices of another IP sub networks.
• There is a potential packet collision as multiple devices transmit data on one wire / link.
• A collision can occur on cable , hub or repeater.

It is an arbitrary value, based on hop count, bandwidth, or another calculation, that is typically assigned by a network administrator and used by the routing protocol to compare different routes through an internetwork. Routing protocols use cost values to select the best path to a certain destination. The lowest cost identifies the best path. Also known as path cost.