PTP / IEEE 1588 (Precision Time Protocol)
PTP is clock synchronization, not media transport. In AV, it is the timing layer underneath systems such as AES67, SMPTE ST 2110, AVB/Milan, Q-LAN, and Dante interoperability modes. For IT/firewall work, do not treat "PTP" as one generic allow rule: identify the profile, transport mapping, domain, intended grandmaster / time transmitter, multicast/unicast behavior, and whether switches only forward PTP or actively participate as boundary / transparent clocks.
Scope: PTP / IEEE 1588 (Precision Time Protocol) — select the deployed product/version; optional services require separate selection.
protocol · Catalog reviewed 2026-10-21
Infrastructure Requirements
- One explicit clocking strategy per domain
- an intended grandmaster / time transmitter
- managed switching that forwards the chosen PTP profile correctly
- hardware timestamping where accuracy actually matters
- boundary-clock or transparent-clock support where the profile and scale justify it
- disciplined QoS and multicast/unicast policy documented before deployment
Network & Physical Requirements
| Port / allocation | Transport | Connection / signal flow | Feature and requirement | Evidence |
|---|---|---|---|---|
| 319 | UDP Multicast: Profile-specific; commonly 224.0.1.129 | Clock participant → Clock participant | Profile requirement · Core PTP event messages IEEE 1588 UDP service mapping; version/profile selected separately This source confirms the assigned UDP service port, not profile compatibility. Match domain, version, multicast/unicast mode and clock roles. UDPv4 P2P profiles also use 224.0.0.107 for peer-delay messages; profile selection is required. LinuxPTP ptp4l p2pdstipv4 documents this default. | Source checked 2026-09-27 ptp-event / UDP registration |
| 320 | UDP Multicast: Profile-specific | Clock participant → Clock participant | Profile requirement · Core PTP general messages IEEE 1588 UDP service mapping; version/profile selected separately This source confirms the assigned UDP service port, not profile compatibility. Match domain, version, multicast/unicast mode and clock roles. UDPv4 P2P profiles also use 224.0.0.107 for peer-delay messages; profile selection is required. LinuxPTP ptp4l p2pdstipv4 documents this default. | Source checked 2026-09-27 ptp-general / UDP registration |
Physical, link and configuration requirements
link-layer · Optional · Layer 2 timing
Native Ethernet PTP uses ordinary-message and peer-delay multicast MAC addresses.
LinuxPTP L2 defaults; IEEE 1588 profile selection
These are Ethernet multicast addresses, not IP groups. 802.1AS/gPTP profile behavior must be selected separately.
EtherType: 0x88F7
Source checked 2026-09-27
Default Transport Options: ptp_dst_mac and p2p_dst_mac
Gotchas & IT Notes
- ⚠Select one compatible version, domain and profile (for example AES67, ST 2059-2, Dante or 802.1AS). Identical port numbers do not imply clock interoperability.
- ⚠Multicast addresses, TTL, QoS and boundary/transparent clock support are profile-specific. Peer-delay IP multicast may use 224.0.0.107; its octets are not port numbers.