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entry and holdtime in the NDP table are updated; otherwise, only the holdtime of the entry is
updated. If no NDP information from the neighbor is received when the holdtime times out, the
corresponding entry is removed from the NDP table.
NDP runs on the data link layer, and supports different network layer protocols.
Introduction to NTDP
NTDP provides information required for cluster management; it collects topology information about the
devices within the specified hop count. 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 all devices 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
collect specific topology information, 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. Topology information collection includes the following process:
• 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.
• The adjacent device performs the same operation until the NTDP topology-collection request is sent
to all devices within specified hops.
When the NTDP topology-collection request is advertised in the network, large numbers of network
devices receive the NTDP topology-collection request and send NTDP topology-collection response at the
same time, which may cause congestion and the management device busyness. To avoid such case, use
the following methods to control the speed of the NTDP topology-collection request advertisement:
• Upon receiving an NTDP topology-collection request, each device does not forward it, instead, it
waits for a period of time and then forwards the NTDP topology-collection request on the first NTDP-
enabled port.
• On the same device, except the first port, each NTDP-enabled port waits for a period of time and
then forwards the NTDP topology-collection request after its prior port forwards the NTDP topology-
collection request.
Cluster management maintenance
1. Adding a candidate device to a cluster
You should specify the management device before creating a cluster. The management device discovers
and defines a candidate device through NDP and NTDP protocols. The candidate device can be
automatically or manually added to the cluster.
After the candidate device is added to the cluster, it can obtain the member number assigned by the
management device and the private IP address used for cluster management.
2. Communication within a cluster
In a cluster the management device communicates with its member devices by sending handshake
packets to maintain connection between them.
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