HP LaserJet Pro MFP 4101 network autodiscovery problem

[jshafer817]

I wanted to share a solution to an HP LaserJet Pro MFP 4101 network autodiscovery problem that took considerable troubleshooting to isolate.

**Problem:**

1. HP's printer installation software was unable to discover the printer on the local network and reported:

"A firewall appears to be blocking autodiscovery."

2. Twain also stops working after being installed if you don't go through auto-discovery, printing still works.

**Environment:**
- HP LaserJet Pro MFP 4101
- Latest available printer firmware
- Printer connected via Ethernet
- Windows PC joined to an Active Directory domain
- Windows Defender Firewall disabled for testing
- Bitdefender completely uninstalled
- Unmanaged Ethernet switches
- Computer and printer on the same subnet

**Troubleshooting performed:**

1. Confirmed the printer was reachable by IP address.
2. Verified TCP ports 80 and 9100 were accessible.
3. Confirmed Windows discovery services (fdPHost, FDResPub, SSDPSRV, upnphost) were running.
4. Confirmed WS-Discovery, Bonjour/mDNS, and SLP were enabled on the printer.
5. Captured network traffic using Wireshark during printer autodiscovery.

6. Rebooted the Printer (didn't fix the issue to get the installer to recognize the printer)

**Wireshark findings:**

The Windows computer transmitted WS-Discovery multicast probes to 239.255.255.250:3702.

However, no corresponding UDP WSD responses were observed from the printer.

Interestingly, the printer was still transmitting mDNS multicast traffic on UDP port 5353. Its WSD HTTP endpoint was also accessible and responding successfully.

This suggested that the issue was specific to the printer's WS-Discovery responder rather than general network connectivity or UDP communication.

**SOLUTION – No reboot required:**

1. Open the printer's embedded web server by entering its IP address in a browser.
2. Sign in as administrator if prompted.
3. Navigate to the printer's network protocol settings.
4. Disable WS-Discovery.
5. Click Apply/Save.
6. Re-enable WS-Discovery.
7. Click Apply/Save again.

**Printer autodiscovery immediately started working without rebooting the printer or computer.**

**Conclusion:**

Based on the packet captures and the immediate recovery after toggling WS-Discovery, this appears to be a stuck or malfunctioning WS-Discovery service within the printer's firmware.  Rebooting the printer did not fix the issue. We had to restart WS-Discovery AFTER a reboot of the printer.

The printer was already running the latest firmware.

HP should investigate whether the WS-Discovery responder can stop answering multicast discovery probes while the printer's other network services remain operational.

Hopefully this saves someone else from wasting hours troubleshooting firewalls, antivirus software, switches, and Windows services when the actual workaround takes less than a minute.