CHAPTER 3
Configuring PTP
This chapter contains the following sections:
• Information About PTP, on page 7
• PTP Device Types, on page 8
• PTP Process, on page 9
• High Availability for PTP, on page 9
• Licensing Requirements for PTP, on page 10
• Guidelines and Limitations for PTP, on page 10
• Default Settings for PTP, on page 10
• Configuring PTP, on page 11
Information About PTP
PTP is a time synchronization protocol for nodes distributed across a network. Its hardware timestamp feature
provides greater accuracy than other time synchronization protocols such as the Network Time Protocol (NTP).
A PTP system can consist of a combination of PTP and non-PTP devices. PTP devices include ordinary clocks,
boundary clocks, and transparent clocks. Non-PTP devices include ordinary network switches, routers, and
other infrastructure devices.
PTP is a distributed protocol that specifies how real-time PTP clocks in the system synchronize with each
other. These clocks are organized into a master-slave synchronization hierarchy with the grandmaster clock,
which is the clock at the top of the hierarchy, determining the reference time for the entire system.
Synchronization is achieved by exchanging PTP timing messages, with the members using the timing
information to adjust their clocks to the time of their master in the hierarchy. PTP operates within a logical
scope called a PTP domain.
Starting from Cisco NXOS Release 6.0(2)A8(3), PTP supports configuring multiple PTP clocking domains,
PTP grandmaster capability, PTP cost on interfaces for slave and passive election, and clock identity.
All the switches in a multi-domain environment, belong to one domain. The switches that are the part of
boundary clock, must have multi-domain feature enabled on them. Each domain has user configurable
parameters such as domain priority, clock class threshold and clock accuracy threshold. The clocks in each
domain remain synchronized with the master clock in that domain. If the GPS in a domain fails, the master
clock in the domain synchronizes time and data sets associated with the announce messages from the master
clock in the domain where the GPS is active. If the master clock from the highest priority domain does not
meet the clock quality attributes, a clock in the subsequent domain that match the criteria is selected. The Best
Master Clock Algorithm (BMCA) is used to select the master clock if none of the domains has the desired
Cisco Nexus 3548 Switch NX-OS System Management Configuration Guide, Release 7.x
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