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User Datagram Protocol
UDP is a connectionless oriented transport protocol for use when the upper layers provide error-
recovery and reliability. UDP does not sequence data or re-assemble it into any order after transmis-
sion. This protocol uses Port 17.
TCP/IP network layer protocols
TCP/IP Network Layer (OSI) or Internet (DOD) protocols are IP, ARP, RARP, BOOTP, and ICMP.
Internet protocol
IP provides routing and a single interface to the upper layers. No upper layer protocol and no lower
layer protocol have any functions relating to routing. IP receives segments from the transport layer and
fragments them into packets including the host's IP address.
Address Resolution Protocol
ARP is responsible for resolving IP addresses to MAC addresses. It stores these in its arp cache for
later use. It does this to inform a lower layer of the destination's MAC address.
Reverse Address Resolution Protocol
RARP resolves MAC addresses to IP addresses on diskless workstations.
Boot Strap Protocol
BootP is used also for diskless workstations when it requires an IP address.
Internet Control Message Protocol
ICMP is a management protocol and messaging service provider for IP. Its messages are carried as IP
datagrams. ICMP is used in to perform the following functions:
·
Destination Unreachable - If a router cannot send an IP packet any further it uses an ICMP
echo to send a message back to the sender notifying it that the remote node is unreachable.
·
Buffer Full - If a routers memory buffer is full ICMP will send out a message to the originator.
·
Hops - Each IP datagram is assigned a path. This consists of hops. If it goes through the
maximum number of hops the packet is discarded and the discarding router sends an ICMP
echo to the host.
·
Ping - Ping uses ICMP echo messages to check connectivity.
*Keypoints:Know the above 4 functions of ICMP.ICMP commands can be executed from USER EXEC and PRIVILEGED EXEC modes.TCP/IP networks use ARP requests to determine a destination's MAC address.ICMP is implemented by all TCP/IP hosts.TCP is a reliable connection oriented protocol that acknowledges receipt of packets.Know that all reliable connections use acknowledgments.Know that Reverse ARP (RARP) maps Ethernet addresses to IP address and is implemented at thedata link layer.Novell IPXEnable IPX protocol
The IPX protocol uses SAP advertisements to update the network servers. IPX addresses are com-
posed of a network number (32 bit number) and a node address (48 bit MAC address) represented by
dotted triplets of 4 hexadecimal numbers. For example, 0000004a.0000.0c00.23fe, where 4a is the