D-Link DES-3250TG User Manual page 69

DES-3250TG Layer 2 Fast Ethernet Switch User's Guide
UDP uses port numbers in a way that is directly analogous to
TCP. There are well-known UDP port numbers for servers that
use UDP.
Figure 5- 11. UDP Packet Header
The UDP header is shorter than a TCP header. UDP also uses
a checksum to verify that data is received uncorrupted.
The Internet Control Message Protocol (ICMP) is also a
simplified protocol used for error messages and messages used
by TCP/IP. ICMP, like UDP, processes messages that will fit
into a single packet. ICMP does not, however use ports because
its messages are processed by the network software.
Internet Group Management Protocol (IGMP)
End users that want to receive multicast packets must be able
to inform nearby routers that they want to become a multicast
group member of the group these packets are being sent to.
The Internet Group Management Protocol (IGMP) is used by
multicast routers to maintain multicast group membership.
IGMP is also used to coordinate between multiple multicast
routers that may be present on a network by electing one of the
multicast routers as the 'querier'. This router then keep track
of the membership of multicast groups that have active
61