Huawei Quidway S3900 Series Operation Manual page 803

Operation Manual -- NTP
Quidway S3900 Series Ethernet Switches-Release 1510
Note:
To reduce the risk of being attacked by malicious users against opened socket and
enhance switch security, the S3900 series Ethernet switches provide the following
functions, so that a socket is opened only when it is needed:
Opening UDP port 123 (used for NTP) when NTP is enabled;
Close UDP port 123 when NTP is disabled.
The preceding functions are implemented as follows:
When you enable NTP by using the ntp-service unicast-server, ntp-service
unicast-peer, ntp-service broadcast-client, ntp-service broadcast-server,
ntp-service multicast-client, or ntp-service multicast-server command, UDP
port 123 is opened at the same time.
When you disable NTP from operating in any modes by using the undo forms of the
preceding six commands, UDP port 123 is closed at the same time.
I. NTP client mode
When an S3900 series switch operates in the NTP client mode,
The remote server identified by the remote-ip argument operates as the NTP time
server. The S3900 series switch operates as the client, whose clock is
synchronized to the NTP server. (In this case, the clock of the NTP server is not
synchronized to the local client.)
When the remote-ip argument is an IP address of a host, it cannot be a broadcast
or a multicast address, neither can it be the IP address of a reference clock.
II. NTP peer mode
When an S3900 series switch operates in NTP peer mode,
The remote server identified by the remote-ip argument operates as the peer of
the S3900 series switch, and the S3900 series switch operates as the active peer.
The clock of the S3900 series switch can be synchronized to the remote server or
be used to synchronize the clock of the remote server.
When the remote-ip argument is an IP address of a host, it cannot be a broadcast
or a multicast address, neither can it be the IP address of a reference clock.
III. NTP broadcast server mode
When an S3900 series switch operates in NTP broadcast server mode, it broadcasts a
clock synchronization packet periodically. The devices which are configured to be in the
NTP broadcast client mode will response this packet and start the clock
synchronization procedure.
Huawei Technologies Proprietary
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Chapter 1 NTP Configuration