3Com 10014298 manual Configuring NTP Operating Mode

NTP 279

■Ethernet Switch B serves as an NTP time server and Ethernet Switch A synchronizes the local clock with the clock of B.

■It takes 1 second to transmit a data packet from either A or B to the opposite end.

The system clocks are synchronized as follows:

■Ethernet Switch A sends an NTP packet to Ethernet Switch B. The packet 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 local timestamp 11:00:01am (T2) to it.

■When the NTP packet leaves Ethernet Switch B, Ethernet Switch B adds another local timestamp 11:00:02am (T3) to it.

■When Ethernet Switch A receives the acknowledgement packet, it adds a new 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 B: Delay= (T4-T1) - (T3-T2).

■Offset of Ethernet Switch A clock relative to Ethernet Switch B clock: offset= ( (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

■NTP Configuration Examples

Configuring NTP NTP configuration includes the tasks described in the following sections:

■Configuring NTP Operating Mode

■Configuring NTP ID Authentication

■Setting the NTP Authentication Key

■Setting the Specified Key to Be Reliable

■Designating an Interface to Transmit the NTP Message

■Setting the NTP Master Clock

■Enabling or Disabling an Interface to Receive an NTP Message

■Setting the Authority to Access a Local Switch

■Setting Maximum Local Sessions

■Displaying and Debugging NTP

Configuring NTP Operating Mode

The Switch 7750 can serve as an NTP client but not as an NTP server.