3Com Switch 4800G 24-Port Configuration Manual page 908

908 C 73: C
HAPTER LUSTER
M C
ANAGEMENT ONFIGURATION
Introduction to NDP
NDP is used to discover the information about directly connected neighbors,
including the device name, software version, and connecting port of the adjacent
devices. NDP works in the following ways:
A device running NDP periodically sends NDP packets to its neighbors. An NDP
■
packet carries NDP information (including the device name, software version,
and connecting port, etc.) and the holdtime, which indicates how long the
receiving devices will keep the NDP information. At the same time, the device
also receives but does not forward the NDP packets from its neighbors.
A device running NDP stores and maintains an NDP table. The device creates an
■
entry in the NDP table for each neighbor. If a new neighbor is found, meaning
the device receives an NDP packet sent by the neighbor for the first time, the
device adds an entry in the NDP table. When another NDP packet is received, if
the NDP information carried in the NDP packet is different from the stored
information, the corresponding entry in the NDP table is updated; otherwise,
only the holdtime of the entry is updated. If no NDP information from the
neighbor is received within the holdtime, the corresponding entry is removed
from the NDP table.
NDP runs on the data link layer, and therefore supports different network layer
protocols.
Introduction to NTDP
NTDP is a protocol used to collect network topology information. NTDP provides
information required for cluster management: it collects topology information
about the devices within the specified hop count, to identify candidate devices for
a cluster.
Based on the neighbor information stored in the neighbor table maintained by
NDP, NTDP on the management device advertises NTDP topology collection
requests to collect the NDP information of each device in a specific network range
as well as the connection information of all its neighbors. The information
collected will be used by the management device or the network management
software to implement required functions.
When a member device detects a change on its neighbors through its NDP table, it
informs the management device through handshake packets. Then the
management device triggers its NTDP to perform specific topology collection, so
that its NTDP can discover topology changes timely.
The management device collects topology information periodically. You can also
administratively launch a topology information collection with commands. The
process of topology information collection is as follows:
The management device periodically sends NTDP topology collection request
■
from the NTDP-enabled ports.
Upon receiving the request, the device sends NTDP topology collection
■
response to the management device, copies this response packet on the
NTDP-enabled port and sends it to the adjacent device. Topology collection
response includes the basic information of the NDP-enabled device and NDP
information of all adjacent devices.