RPi5 Grandmaster
      │
      \/
Linux Boundary Clock
      │
      \/
Nexus Boundary Clock
      │
      \/
Linux client NIC PHC
      │
   phc2sys
      │
      \/
CLOCK_REALTIME (UTC)

Each direct client normally needs only:

ptp enabled on its physical NEXUS switch port;
ptp4l to synchronize the NIC PHC from NEXUS; and
phc2sys to synchronize Linux CLOCK_REALTIME from that PHC.

Files in this directory

File	Install as	Purpose
`ptp4l-client.conf`	`/etc/linuxptp/ptp4l-client.conf`	Ordinary-clock/client-only PTP configuration
`ptp4l-client.service`	`/etc/systemd/system/ptp4l-client.service`	Runs `ptp4l` on the client NIC
`phc2sys-client.service`	`/etc/systemd/system/phc2sys-client.service`	Synchronizes `CLOCK_REALTIME` from the client NIC PHC

The bundled files currently use enp4s0 as the client interface. Change that name everywhere if the target server uses another interface.

1. Enable PTP on the corresponding Nexus port

On NEXUS:

configure terminal

interface Ethernet1/<clientPort>
  ptp

end
copy running-config startup-config

Example:

interface Ethernet1/10
  ptp

Once the client is online, the Nexus port should normally become Master in:

show ptp brief

2. Install LinuxPTP

On the client:

sudo apt update
sudo apt install linuxptp ethtool

3. Identify the PTP NIC

Find the interface connected to NEXUS:

ip -br link

The examples below assume:

enp4s0

If your interface has a different name, replace enp4s0 in all three files before installing them.

For example, search the bundled files with:

grep -Rni 'enp4s0' .

4. Verify hardware timestamping

ethtool -T enp4s0

The NIC should expose hardware transmit, receive, and raw hardware timestamping plus a PTP Hardware Clock.

You can map it to the PHC device with:

readlink -f /sys/class/net/enp4s0/device/ptp/ptp*

If the NIC does not support hardware timestamping, do not use the bundled time_stamping hardware configuration unchanged.

5. Disable competing system-clock synchronization

phc2sys-client.service will discipline CLOCK_REALTIME. Disable services that would compete for the same system clock:

sudo systemctl disable --now chrony 2>/dev/null || true
sudo systemctl disable --now systemd-timesyncd 2>/dev/null || true
sudo systemctl disable --now ntp 2>/dev/null || true
sudo systemctl disable --now ntpd 2>/dev/null || true

6. Install the client files

If the interface really is enp4s0, install the files directly:

sudo install -D -m 0644 ptp4l-client.conf /etc/linuxptp/ptp4l-client.conf
sudo install -D -m 0644 ptp4l-client.service /etc/systemd/system/ptp4l-client.service
sudo install -D -m 0644 phc2sys-client.service /etc/systemd/system/phc2sys-client.service

If the interface name is different, edit the local copies first and replace enp4s0 in:

ptp4l-client.conf
ptp4l-client.service
phc2sys-client.service

The PTP client config intentionally uses:

domainNumber      0
network_transport UDPv4
delay_mechanism   E2E
clientOnly        1

clientOnly 1 prevents a downstream server from ever trying to become the grandmaster.

7. Enable the services

sudo systemctl daemon-reload
sudo systemctl enable --now ptp4l-client.service
sudo systemctl enable --now phc2sys-client.service

The data flow is:

ptp4l:    NEXUS -> NIC PHC
phc2sys:  NIC PHC -> CLOCK_REALTIME

The bundled phc2sys service uses:

phc2sys -s enp4s0 -c CLOCK_REALTIME -w -m

-w waits for ptp4l and obtains the PTP/UTC offset from it, so the client does not need a hard-coded -37 offset.

8. Verification

Check service state:

systemctl status ptp4l-client
systemctl status phc2sys-client

Follow the logs:

journalctl -fu ptp4l-client
journalctl -fu phc2sys-client

ptp4l should progress into the synchronized client/slave state and its master offsets should settle near zero.

Query PTP datasets:

sudo pmc -u -b 0 'GET PORT_DATA_SET'
sudo pmc -u -b 0 'GET CURRENT_DATA_SET'
sudo pmc -u -b 0 'GET PARENT_DATA_SET'
sudo pmc -u -b 0 'GET TIME_STATUS_NP'

For a client directly downstream from NEXUS, expect approximately:

portState             CLIENT/SLAVE
stepsRemoved          3
grandmasterIdentity   <same RPi5 grandmaster identity>

In the current topology the RPi5 grandmaster identity observed on NEXUS is:

88a29efffe826ce6

If the RPi5 NIC or grandmaster identity changes later, use the currently advertised identity instead of treating that value as permanent.

Also verify the Nexus side:

show ptp brief

The client-facing Nexus port should normally be Master.

9. Quick deployment checklist for another server

NEXUS:
  interface Ethernet1/X
    ptp

Linux server:
  1. install linuxptp + ethtool
  2. verify `ethtool -T <NIC>`
  3. replace `enp4s0` in the three bundled files if needed
  4. install the config and two systemd units
  5. disable chrony/timesyncd/ntpd if they discipline CLOCK_REALTIME
  6. enable ptp4l-client and phc2sys-client
  7. verify logs + pmc output

10. Troubleshooting

If ptp4l stays in LISTENING:

sudo tcpdump -ni enp4s0 'udp port 319 or udp port 320'
journalctl -u ptp4l-client -n 100 --no-pager

Then check NEXUS:

show ptp brief
show ptp packet

If the NIC PHC synchronizes but Linux system time does not, inspect:

journalctl -u phc2sys-client -n 100 --no-pager
systemctl status chrony systemd-timesyncd ntp ntpd

Only one service should be responsible for disciplining CLOCK_REALTIME on the client.