3Com Switch 4500 26-Port, Configuration Manual

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298 C
HAPTER
18: NTP C
ONFIGURATION
ITo reduce the risk of being attacked by malicious users against opened socket and
enhance switch security, the Switch 4500 Ethernet switches provides 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.
NTP client mode
The remote server specified by the remote-ip or server-name argument serves as
the NTP server. The local Switch 4500 serves as the client. The clock of the client is
synchronized to the NTP server, while the clock of the NTP server is not
synchronized to the client. The IP address specified by the remote-ip argument
cannot be a broadcast address, a multicast address, or the IP address used by the
local reference clock.
NTP peer mode
The remote server specified by the remote-ip or peer-name argument serves as the
peer of the local Ethernet switch, and the local Ethernet switch operates in the
active peer mode. The clock of the local switch can be synchronized to the remote
server or used to synchronize the clock of the remote server. The IP address
specified by the remote-ip argument cannot be a broadcast address, a multicast
address, or the IP address used by the local reference clock.
Configure the switch to
operate in the NTP
broadcast client mode ntp-service
broadcast - client
Optional
By default, no Ethernet switch
operates in NTP broadcast client
mode.
Configure the switch to
operate in NTP broadcast
server mode ntp-service
broadcast-server [
authentication-keyid
key-id | version number ]*
Optional
By default, no Ethernet switch
operates in NTP broadcast server
mode.
Configure the switch to
operate in NTP multicast
client mode ntp-service
multicast - client [
ip-address ]
Optional
By default, no Ethernet switch
operates in NTP multicast client
mode.
Configure the switch to
operate in NTP multicast
server mode ntp-service
multicast-server [
ip-address ] [
authentication-keyid keyid
| ttl ttl-number | version
number ]*
Optional
By default, no Ethernet switch
operates in NTP multicast server
mode.
Operation Command Description