R3303-HP HSR6800 Routers Network Management and Monitoring Configuration Guide

The client continues listening to broadcast messages and synchronizes its local clock based on the

received broadcast messages.

Multicast mode

Figure 24 Multicast mode

In multicast mode, a server periodically sends clock synchronization messages to the user-configured

multicast address, or, if no multicast address is configured, to the default NTP multicast address 224.0.1.1,

with the Mode field in the messages set to 5 (multicast mode). Clients listen to the multicast messages

from servers. When a client receives the first multicast message, the client and the server start to

exchange messages with the Mode field set to 3 (client mode) and 4 (server mode), to calculate the

network delay between client and server. Then, the client enters multicast client mode. It continues

listening to multicast messages and synchronizes its local clock based on the received multicast

messages.

In symmetric peers mode, broadcast mode and multicast mode, the client (or the symmetric active peer)

and the server (the symmetric passive peer) can operate in the specified NTP working mode only after

they exchange NTP messages with the Mode field being 3 (client mode) and the Mode field being 4

(server mode). During this message exchange process, NTP clock synchronization can be implemented.

NTP for VPNs

The device supports multiple VPN instances when it functions as an NTP client or a symmetric active peer

to realize clock synchronization with the NTP server or symmetric passive peer in an MPLS VPN network.

For more information about MPLS L3VPN, VPN instance, and PE, see MPLS Configuration Guide.

As shown in Figure 25, u

sers in VPN 1 and VPN 2 are connected to the MPLS backbone network through

PE devices, and services of the two VPNs are isolated. If you configure the PEs to operate in NTP client

or symmetric active mode, and specify the VPN to which the NTP server or NTP symmetric passive peer

belongs, the clock synchronization between PEs and CEs of the two VPNs can be realized.