Chapter 3 Address Resolution Protocol

ARP Reply - The ARP Reply message is used to reply to the ARP requester. The node whose IP address matches the requested IP address in the arp request message sends the arp reply. The arp reply is a

unicast MAC frame sent to the destination MAC address of the ARP requester.

ARP is used to resolve

the next hop IP address of a node to its corresponding media access control address

The node sending the ARP request is knkown as the

ARP requester

the node sending the ARP reply is known as the

ARP responder

ARP

Address Resolution Protocol

when an arp exchange for address resolution is complete, both the arp requester and the arp responder have each others

IP address-to-MAC address mappings in their ARP caches

Hubs bridges and layer 2 switches propagate the ARP request. however

IP routers do not propagate ARP frames

What is MAC

Media access control

All nodes within the same broadcast domain receive the ARP request. A broadcast domain is

a portion of a network over which the broadcast frame is propagated.

Windows server 2008 uses ARP for

address resolution, duplicate address detection, and neighbor unreachability detection.

If a routing table entry contains an invalid next hop ip address, and the address is not directly reachable for the interface

arp will fail to resolve the next hop ip address

Subsequent packets forwarded to the previously resolved IP addresses use the ARP cache entry's MAC address The ARP cache is always

checked before an ARP request is sent

For direct deliveries to destinations on the same subnet, the next hop IP aaddress is the

datagram's destination ip address

The next hop IP address is not necessarily the same as the

destination IP address of the IP datagram

Because the ARP request message is a MAC level broadcast, all next hop IP addresses to be resolved must be directly reachable (on the same subnet) from the

interface used to send the ARP Request

for indirect deliveries to remote destinations, the next-hop ip address is the IP address of a

neighboring router on the same subnet as the forwarding host

As is common in many tcp ip implementatons, tcp ip for windows server 2008 and windows vista maintains a

ram based table of ip and mac address mappings

ARP request - the forwarding node uses the ARP request message to request the MAC address for a specific next hop IP address. The ARP Request is a MAC-level broadcast frame intented to

reach all the nodes on the physical subnet to which the interface sending the ARP request is attached.

ARP is used by TCP/IP nodes on

shared access, broadcast based networking technologies such as Ethernet and Token Ring

the arp cache is also known as

the neighbor cache