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Configuration Guide - Device Management

CloudEngine 8800, 7800, 6800, and 5800 V200R005C10

This document describes the configurations of IP multicast, including IP multicast basics, IGMP, MLD, PIM (IPv4), PIM (IPv6), MSDP, multicast VPN, multicast route management (IPv4), multicast route management (IPv6), IGMP snooping, MLD snooping, static multicast MAC address, multicast VLAN, multicast network management.

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NTP Network Architecture

NTP Network Architecture

The NTP network architecture involves the following concepts:
  • Synchronization subnet consists of the primary time server, secondary time servers, PC clients, and interconnecting transmission paths, as shown in Figure 4-2.
  • Primary time server directly synchronizes its clock with a standard reference clock using a cable or radio. The standard reference clock is usually a radio clock or the Global Positioning System (GPS).
  • Secondary time server synchronizes its clock with the primary time server or other secondary time servers on the network. A secondary time server transmits the time information to other hosts on a LAN through NTP.
  • Stratum is a hierarchical standard for clock synchronization. It represents precision of a clock. The value of a stratum ranges from 1 to 16. A smaller value indicates higher precision. The value 1 indicates the highest clock precision, and 16 indicates that the clock is not synchronized.
Figure 4-2 NTP network architecture

Under normal circumstances, the primary time server and the secondary time servers in a synchronization subnet are arranged in a hierarchical master-slave structure. In this structure, the primary time server is located at the root, and the secondary time servers are arranged close to leaf nodes. As their strata increase, the precision decreases accordingly. The extent to which the precision of the secondary time servers decreases depends on the stability of network paths and the local clock. The decreased precision of the secondary time servers varies depending on network paths and local clock stability.

When the synchronization subnet has multiple primary time servers, the optimal server can be selected using an algorithm.

Such a design ensures that:
  • When faults occur in one or more primary/secondary time servers or network paths interconnecting them, the synchronization subnet will automatically be reconstructed into another hierarchical master-slave structure to obtain the most precise and reliable time.
  • When all primary time servers in the synchronization subnet become invalid, a standby primary time server runs.
When all primary time servers in the synchronization subnet become invalid, other secondary time servers are synchronized among each other. These secondary time servers become independent of the synchronization subnet and automatically run at the last determined time and frequency. When a switch with a stable oscillator becomes independent of the synchronization subnet for an extended period of time, its timing error can be kept to within several milliseconds in a day because of highly precise calculations.
Updated: 2020-01-07

Document ID: EDOC1100075362

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