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Port 9991 (osm-oev)

IANA assigns port 9991 to osm-oev: OSM Event Server.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
osm-oev TCP OSM Event Server Vinay Gupta -
osm-oev UDP OSM Event Server Vinay Gupta -

Registry dates for this port: registered 2003-08.

Check what is listening on port 9991

Linux: is anything listening on TCP 9991?
sudo ss -tlnp 'sport = :9991'
Linux: UDP 9991
sudo ss -ulnp 'sport = :9991'
Linux / macOS: which process owns the port
sudo lsof -nP -i :9991
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':9991 '
Windows (Command Prompt)
netstat -ano | findstr :9991
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 9991 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 9991
From Windows
Test-NetConnection HOST -Port 9991
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 9991

Block port 9991 in the firewall

ufw
sudo ufw deny 9991/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 9991 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 9991 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 9991' -Direction Inbound -Protocol TCP -LocalPort 9991 -Action Block
ufw
sudo ufw deny 9991/udp
iptables
sudo iptables -A INPUT -p udp --dport 9991 -j DROP
nftables
sudo nft add rule inet filter input udp dport 9991 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 9991' -Direction Inbound -Protocol UDP -LocalPort 9991 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.