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Port 33435 (mtrace)

IANA assigns port 33435 to mtrace: IP Multicast Traceroute.

Registered (user) port, 1024-49151 UDP

Port 33435 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
mtrace UDP IP Multicast Traceroute IESG RFC 8487

Registry dates for this port: registered 2017-12-13, last modified 2019-08-09.

Check what is listening on port 33435

Linux: UDP 33435
sudo ss -ulnp 'sport = :33435'
Linux / macOS: which process owns the port
sudo lsof -nP -i :33435
Windows (Command Prompt)
netstat -ano | findstr :33435
Windows (PowerShell)
Get-NetUDPEndpoint -LocalPort 33435

Test it from outside

UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 33435

Block port 33435 in the firewall

ufw
sudo ufw deny 33435/udp
iptables
sudo iptables -A INPUT -p udp --dport 33435 -j DROP
nftables
sudo nft add rule inet filter input udp dport 33435 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 33435' -Direction Inbound -Protocol UDP -LocalPort 33435 -Action Block

Related ports

33334speedtrace, speedtrace-disc33434traceroute33656snip-slave33890digilent-adept

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