3Com 5500-EI PWR Install Manual page 757

Neighbor Discovery Protocol (NDP)
Neighbor Topology Discovery Protocol (NTDP)
Cluster
A cluster configures and manages the devices in it through the above three protocols.
Cluster management involves topology information collection and the establishment/maintenance of a
cluster. Topology information collection and cluster establishment/maintenance are independent from
each other. The former, as described below, starts before a cluster is established.
All devices use NDP to collect the information about their neighbors, including software version,
host name, MAC address, and port name.
The management device uses NTDP to collect the information about the devices within specific
hops and the topology information about the devices. It also determines the candidate devices
according to the information collected.
The management device adds the candidate devices to the cluster or removes member devices
from the cluster according to the candidate device information collected through NTDP.
Introduction to NDP
NDP is a protocol used to discover adjacent devices and provide information about them. NDP operates
on the data link layer, and therefore it supports different network layer protocols.
NDP is able to discover directly connected neighbors and provide the following neighbor information:
device type, software/hardware version, and connecting port. In addition, it may provide the following
neighbor information: device ID, port full/half duplex mode, product version, the Boot ROM version and
so on.
An NDP-enabled device maintains an NDP neighbor table. Each entry in the NDP table can
automatically ages out. You can also clear the current NDP information manually to have neighbor
information collected again.
An NDP-enabled device regularly broadcasts NDP packet through all its active ports. An NDP
packet carries a holdtime field, which indicates how long the receiving devices will keep the NDP
packet data. The receiving devices store the information carried in the NDP packet into the NDP
table but do not forward the NDP packet. When they receive another NDP packet, if the information
carried in the packet is different from the stored one, the corresponding entry in the NDP table is
updated, otherwise only the holdtime of the entry is updated.
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 switches within the specified hop
count, so as to provide the information of which devices can be added to 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, and the management device triggers its NTDP to
perform specific topology collection, so that its NTDP can discover topology changes timely.
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