Computer Networks ARP and RARP Presented By: Ahasana Sultana(1741103) Meghna Sen(1741133) Pooja Shah(1741137) Sweta Panigrahi(1741156) 1

Static Mapping Creates a table that associates a logical address with a physical address and store in each machine Physical addresses may change A machine could change its NIC resulting in a new physical address In some LANs, such as LocalTalk, the physical address changes every time the computer is turned on A mobile station can move from one physical network to another, resulting in a change in its physical address

Dynamic Mapping Uses a protocol to find another address ARP: Address Resolution Protocol Maps a logical address to a physical address RARP: Reverse Address Resolution Protocol Maps a physical address to a logical address

ARP (Address Resolution Protocol)

Address Resolution Protocol A communication protocol used for discovering physical address associated with given network address. A network layer to data link layer mapping process, which is used to discover MAC address for given Internet Protocol Address.

ARP is beneficial only if its reply is cached. Otherwise,every packet that is supposed to be sent would have to be broadcasted.

ARP PACKET

ARP Spoofing ARP replies can come from systems other than the one with the required Layer 2 address An ARP proxy is a system which answers the ARP request on behalf of another system for which it will forward traffic as a part of the network's design ARP spoofing the answering system, or spoofer, replies to a request for another system's address with the aim of intercepting data bound for that system. A malicious user may use ARP spoofing to perform a man-in-the-middle or denial-of-service attack on other users on the network. Various software exists to both detect and perform ARP spoofing attacks, though ARP itself does not provide any methods of protection from such attacks.(prank call ex)

Proxy ARP Proxy ARP is the technique in which one host, usually a router, answers ARP requests intended for another machine. By "faking" its identity, the router accepts responsibility for routing packets to the "real" destination.

Advantages of Proxy ARP It can be added to a single router on a network and does not disturb the routing tables of the other routers on the network. Proxy ARP must be used on the network where IP hosts are not configured with a default gateway or do not have any routing intelligence.

Disadvantages of Proxy ARP Hosts have no idea of the physical details of their network and assume it to be a flat network in which they can reach any destination simply by sending an ARP request. It increases the amount of ARP traffic on your segment. Hosts need larger ARP tables in order to handle IP-to-MAC address mappings. Security can be undermined. A machine can claim to be another in order to intercept packets, an act called "spoofing." It does not work for networks that do not use ARP for address resolution. It does not generalize to all network topologies. For example, more than one router that connects two physical networks.

RARP (Reverse Address Resolution Protocol)

Adapted from ARP Protocol Reverse Address Resolution Protocol is a communication protocol that obtains the logical address of the host from the server, when provided with the host’s physical address.

Encapsulation of ARP Packets

Encapsulation of RARP Packets

Ethernet Header Type: Ethernet A cyclic redundancy check (CRC) is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data.

RARP PACKET

Important Questions What is ARP Packet? Provide the frame format of ARP Packet. How encapsulation of ARP Packet is done? Discuss four cases of using ARP. (Marks : 10) Why address mapping required? (Marks : 2) What is ARP? (Marks : 2) What is logical address? (Marks :2) What is static mapping? (Marks : 2)