Configuring Ntp - 3Com Switch 7700 Configuration Manual

358 C 11: S
HAPTER YSTEM

Configuring NTP

M
ANAGEMENT
The system clocks are synchronized as follows:
Ethernet Switch A sends an NTP packet to Ethernet Switch B. The packet
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carries the timestamp 10:00:00am (T1) that tells when it left Ethernet Switch A.
When the NTP packet arrives at Ethernet Switch B, Ethernet Switch B adds a
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local timestamp 11:00:01am (T2) to it.
When the NTP packet leaves Ethernet Switch B, Ethernet Switch B adds
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another local timestamp 11:00:02am (T3) to it.
When Ethernet Switch A receives the acknowledgement packet, it adds a new
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timestamp 10:00:03am (T4) to it.
Next, Ethernet Switch A collects enough information to calculate the following
two important parameters:
The delay for a round trip of an NTP packet traveling between the Switch A and
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B: Delay= (T4-T1) - (T3-T2).
Offset of Ethernet Switch A clock relative to Ethernet Switch B clock: offset= (
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(T2-T1) + (T3-T4) ) /2.
Ethernet Switch A uses this information to set the local clock and to synchronize it
with the clock on Ethernet Switch B.
Configuring NTP is described in the following sections:
Configuring NTP
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NTP Configuration Examples
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NTP configuration includes the tasks described in the following sections:
Configuring NTP Operating Mode
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Configuring NTP ID Authentication
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Setting the NTP Authentication Key
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Setting the Specified Key to Be Reliable
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Designating an Interface to Transmit the NTP Message
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Setting the NTP Master Clock
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Enabling or Disabling an Interface to Receive an NTP Message
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Setting the Authority to Access a Local Switch
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Setting Maximum Local Sessions
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Displaying and Debugging NTP
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Configuring NTP Operating Mode
The Switch 7700 can only serve as an NTP client but not as an NTP server.
You can set the NTP operating mode of the Switch 7700 according to its location
in the network, and the network structure. For example, you can set a remote
server as the time server of the local equipment. In this case the local Ethernet
Switch works as an NTP client. If you set a remote server as a peer of the local
Ethernet Switch, the local equipment operates in symmetric active mode. If you
configure an interface on the local switch to transmit NTP broadcast packets, the