NA Lesson-8

Understanding TCP/IP-II

Address Resolution Protocol (ARP)

• Whereas IP routes packets to logical addresses that might be dozens of network segments away, ARP finds the physical computers for which IP packets are destined within each network segment. After using ARP to look up hardware addresses, TCP/IP hosts store known IP-to-MAC address mappings in a local ARP cache.
•  You can view this cache with arp –a command or clear it with the arp –d command.

Internet Protocol (IP)

• IP is primarily responsible for addressing and routing packets between hosts. An IP packet can be lost, delivered out of sequence, duplicated, or delayed, as can information in any other protocol. However, IP itself does not attempt to recover from these types of errors. 
• The acknowledgment of packets delivered, the sequencing of packets, and the recovery of lost packets are the responsibility of a higher-layer protocol, such as TCP.

Internet Control Message Protocol 

• With ICMP, hosts and routers that use IP can report errors and exchange limited control and status information. You can use the Ping command to send ICMP echo request messages and record the receipt of ICMP echo reply messages. 
• With these messages, you can detect communication failures and troubleshoot common TCP/IP connectivity problems.

Transmission Control Protocol

• TCP receives data from the application layer and processes the data as a stream of bytes. These bytes are grouped into segments that TCP then numbers and sequences for delivery to a network host. 
• When TCP receives a stream of data from a network host. it sends the data to the intended application.

UDP 

• Many network services (such as DNS) rely on UDP instead of TCP as a transport protocol. UDP enables fast transport of datagrams by eliminating the reliability features of TCP such as delivery guarantees and sequence verification. 
• Unlike TCP, UDP is a connectionless service that provides only best-effort datagram delivery to network hosts. A source host that needs reliable communication must use either TCP or a program that provides its own sequencing and acknowledgment services.