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Port 5786 (cisco-redu)

IANA assigns port 5786 to cisco-redu: redundancy notification.

Registered (user) port, 1024-49151 UDP

Port 5786 is normally used over UDP; the checker tests TCP only, so a "filtered" result does not mean the UDP service is down.

IANA assignment

Service nameProtoDescriptionAssigneeReference
cisco-redu UDP redundancy notification Ming Zhang -

Registry dates for this port: registered 2010-02-04.

Check what is listening on port 5786

Linux: UDP 5786
sudo ss -ulnp 'sport = :5786'
Linux / macOS: which process owns the port
sudo lsof -nP -i :5786
Windows (Command Prompt)
netstat -ano | findstr :5786
Windows (PowerShell)
Get-NetUDPEndpoint -LocalPort 5786

Test it from outside

UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 5786

Block port 5786 in the firewall

ufw
sudo ufw deny 5786/udp
iptables
sudo iptables -A INPUT -p udp --dport 5786 -j DROP
nftables
sudo nft add rule inet filter input udp dport 5786 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 5786' -Direction Inbound -Protocol UDP -LocalPort 5786 -Action Block

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