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Appendix E: Understanding IP and IP addressing 161
DMS-100 Family EIU User Guide TELECOM12
Internet control message protocol
The Internet control message protocol (ICMP) provides feedback from an IP
router or gateway to a source host. ICMP messages are sent in several
situations—for example, to report resource or routing problems or to report a
shorter available route to a destination. The DMS-100 switch uses ICMP
echoes and echo replies to verify the reachability of routers or end systems.
ICMP supports redirect messages to provide routine table updates.
ICMP is defined in RFC792.
Transmission control protocol
Transmission control protocol (TCP) is a connection-oriented transport-layer
protocol. It provides reliable, robust, and adaptable data transfer between end-
system upper layer protocols. TCP assumes that simple, potentially unreliable,
datagram services are available from lower-level protocols.
TCP is defined in RFC793.
User datagram protocol
User datagram protocol (UDP) defines the use of unacknowledged datagrams.
UDP packets are often used for very low-priority data or on very high-
reliability networks. UDP is also used when an application already provides an
integrity function and does not need to duplicate that function by using TCP.
UDP is defined in RFC768.
Address resolution protocol
The address resolution protocol (ARP) is a mechanism for mapping 32-bit IP
addresses to 48-bit Ethernet hardware addresses. The hardware address is a
concatenation, or joining, of two numbers:
• a vendor ID number, centrally assigned by the IEEE
• a unique serial number, the media access control (MAC) address, is
assigned by the hardware vendor (see “Appendix I: Obtaining a MAC
address”).
The MAC address usually has significance only on the local LAN wire.
The EIU implementation of ARP supports the following features:
• removal of out-of-date ARP cache data
• configurable cache data time-out
• encapsulation between Ethernet and IEEE 802.3 networks
ARP is supported on Ethernet, FDDI, token ring and frame relay media.