```text id="97dya4"
eno4            upstream toward RPi5 grandmaster
enp4s0/enp4s0d1 downstream toward N9K
```

This design is:

```text id="c1c9so"
RPi5 GM
  -> ptp4l-client on eno4
  -> eno4 PHC
  -> phc2sys-client
  -> CLOCK_REALTIME on WOLF-HUNTER
  -> phc2sys-downstream
  -> enp4s0/enp4s0d1 PHC
  -> ptp4l-downstream
  -> N9K / downstream clients
```

`ptp4l` can use multiple `-i` interfaces, `clientOnly` is the client/slave mode, and `serverOnly` prevents a port from becoming a client. `phc2sys` is the tool that syncs PHCs and `CLOCK_REALTIME`; `-w` waits for `ptp4l`, while `-O 37` provides the UTC/TAI offset explicitly. ([Linux PTP Project][1])

## 1. Upstream PTP client config: `eno4`

Create:

```bash id="o4uyiz"
sudo nano /etc/linuxptp/ptp4l-upstream-client.conf
```

```conf id="fxd4o4"
[global]
verbose                 1
time_stamping           hardware

domainNumber            0
network_transport       UDPv4
delay_mechanism         E2E

# Upstream side: only act as a PTP client/slave
clientOnly              1

summary_interval        1

# Separate UDS socket so multiple ptp4l instances do not collide
uds_address             /var/run/ptp4l-upstream

[eno4]
```

## 2. Downstream PTP server config: `enp4s0/enp4s0d1`

Create:

```bash id="zhy8l3"
sudo nano /etc/linuxptp/ptp4l-downstream-server.conf
```

```conf id="qqo3eb"
[global]
verbose                 1
time_stamping           hardware

domainNumber            0
network_transport       UDPv4
delay_mechanism         E2E

# Downstream side: serve time toward N9K/clients
serverOnly              1

# Make this preferred on the downstream PTP segment
priority1               128
priority2               128

# This host is fed by upstream PTP, not directly by GNSS
timeSource              0x40

# Conservative advertised quality for a PTP-fed downstream server.
# You can tune these later after measuring.
clockClass              6
clockAccuracy           0x23
offsetScaledLogVariance 0xFFFF

utc_offset              37
summary_interval        1

# Separate UDS socket
uds_address             /var/run/ptp4l-downstream

[enp4s0]

[enp4s0d1]
```

Small caveat: this split-service design works, but it is not a “pure” PTP boundary clock because the upstream and downstream `ptp4l` instances are separate. A single `ptp4l` boundary clock preserves PTP parent/stepsRemoved behavior better, but your split design avoids the mixed-PHC/JBOD issue.

## 3. `ptp4l` upstream client service

Create:

```bash id="l54yfe"
sudo nano /etc/systemd/system/ptp4l-upstream-client.service
```

```ini id="1pnwq3"
[Unit]
Description=PTP upstream client on eno4
After=network-online.target
Wants=network-online.target

[Service]
Type=simple
ExecStart=/usr/sbin/ptp4l -i eno4 -f /etc/linuxptp/ptp4l-upstream-client.conf -m
Restart=always
RestartSec=3

[Install]
WantedBy=multi-user.target
```

## 4. `phc2sys` upstream: `eno4 PHC -> CLOCK_REALTIME`

This syncs the **boundary server’s own Linux system clock**.

Create:

```bash id="r430d0"
sudo nano /etc/systemd/system/phc2sys-upstream-to-system.service
```

```ini id="eplzh9"
[Unit]
Description=Sync WOLF-HUNTER system clock from upstream eno4 PHC
After=ptp4l-upstream-client.service
Requires=ptp4l-upstream-client.service

[Service]
Type=simple
ExecStart=/usr/sbin/phc2sys -s eno4 -c CLOCK_REALTIME -w -z /var/run/ptp4l-upstream -m
Restart=always
RestartSec=3

[Install]
WantedBy=multi-user.target
```

## 5. `phc2sys` downstream: `CLOCK_REALTIME -> enp4s0 PHC`

First check whether `enp4s0` and `enp4s0d1` share the same PHC:

```bash id="ha7hlv"
readlink -f /sys/class/net/enp4s0/device/ptp
readlink -f /sys/class/net/enp4s0d1/device/ptp
ethtool -T enp4s0 | grep 'Hardware timestamp provider'
ethtool -T enp4s0d1 | grep 'Hardware timestamp provider'
```

If both are the same PHC, one downstream `phc2sys` service is enough.

Create:

```bash id="m3hpvj"
sudo nano /etc/systemd/system/phc2sys-system-to-downstream.service
```

```ini id="j9tgaw"
[Unit]
Description=Sync downstream enp4s0 PHC from WOLF-HUNTER system clock
After=phc2sys-upstream-to-system.service ptp4l-downstream-server.service
Requires=phc2sys-upstream-to-system.service ptp4l-downstream-server.service

[Service]
Type=simple
ExecStart=/usr/sbin/phc2sys -s CLOCK_REALTIME -c enp4s0 -O 37 -m
Restart=always
RestartSec=3

[Install]
WantedBy=multi-user.target
```

If `enp4s0d1` is on a **different** PHC from `enp4s0`, create a second downstream PHC sync service too:

```bash id="tlsjdk"
sudo nano /etc/systemd/system/phc2sys-system-to-downstream-d1.service
```

```ini id="70k638"
[Unit]
Description=Sync downstream enp4s0d1 PHC from WOLF-HUNTER system clock
After=phc2sys-upstream-to-system.service ptp4l-downstream-server.service
Requires=phc2sys-upstream-to-system.service ptp4l-downstream-server.service

[Service]
Type=simple
ExecStart=/usr/sbin/phc2sys -s CLOCK_REALTIME -c enp4s0d1 -O 37 -m
Restart=always
RestartSec=3

[Install]
WantedBy=multi-user.target
```

## 6. `ptp4l` downstream server service

Create:

```bash id="nl7f0c"
sudo nano /etc/systemd/system/ptp4l-downstream-server.service
```

```ini id="46l106"
[Unit]
Description=PTP downstream server on enp4s0 and enp4s0d1
After=network-online.target phc2sys-upstream-to-system.service
Wants=network-online.target
Requires=phc2sys-upstream-to-system.service

[Service]
Type=simple
ExecStart=/usr/sbin/ptp4l -i enp4s0 -i enp4s0d1 -f /etc/linuxptp/ptp4l-downstream-server.conf -m
Restart=always
RestartSec=3

[Install]
WantedBy=multi-user.target
```

## 7. Enable in order

```bash id="ze5i6s"
sudo systemctl daemon-reload

sudo systemctl enable --now ptp4l-upstream-client.service
sudo systemctl enable --now phc2sys-upstream-to-system.service
sudo systemctl enable --now ptp4l-downstream-server.service
sudo systemctl enable --now phc2sys-system-to-downstream.service
```

Only enable this one if `enp4s0d1` has a different PHC:

```bash id="e1i9bw"
sudo systemctl enable --now phc2sys-system-to-downstream-d1.service
```

## 8. Disable other system-clock discipliners on WOLF-HUNTER

On this boundary host, do not let chrony/NTP/timesyncd also adjust `CLOCK_REALTIME` while `phc2sys-upstream-to-system` is doing it:

```bash id="zzbz88"
sudo systemctl disable --now chrony 2>/dev/null
sudo systemctl disable --now systemd-timesyncd 2>/dev/null
sudo systemctl disable --now ntp 2>/dev/null
```

## 9. Verify

```bash id="j1o8oo"
systemctl status ptp4l-upstream-client.service
systemctl status phc2sys-upstream-to-system.service
systemctl status ptp4l-downstream-server.service
systemctl status phc2sys-system-to-downstream.service
```

Logs:

```bash id="s3klj9"
journalctl -u ptp4l-upstream-client.service -f
journalctl -u phc2sys-upstream-to-system.service -f
journalctl -u ptp4l-downstream-server.service -f
journalctl -u phc2sys-system-to-downstream.service -f
```

Expected behavior:

```text id="a8sadn"
ptp4l-upstream-client:
  eno4 should go SLAVE / UNCALIBRATED -> SLAVE

phc2sys-upstream-to-system:
  CLOCK_REALTIME phc offset ... s2 ...

ptp4l-downstream-server:
  enp4s0/enp4s0d1 should assume MASTER/server role

phc2sys-system-to-downstream:
  enp4s0 sys offset ... s2 ...
```

Also useful:

```bash id="n0wowv"
pgrep -a ptp4l
pgrep -a phc2sys
```