Port 8551 (Ethereum Engine API)

Authenticated API between execution and consensus clients after the Merge (JWT).

Registered (user) port, 1024-49151 TCP Peer-to-peer Localhost or LAN only

What port 8551 is used for

Authenticated API between execution and consensus clients after the Merge (JWT).

Localhost or LAN only. Localhost or private network only.

Port 8551 is in the registered range and has no IANA assignment. The usage above is unofficial but widespread.

Linux: is anything listening on TCP 8551?

sudo ss -tlnp 'sport = :8551'

Linux / macOS: which process owns the port

sudo lsof -nP -i :8551

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':8551 '

Windows (Command Prompt)

netstat -ano | findstr :8551

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 8551 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 8551

From Windows

Test-NetConnection HOST -Port 8551

ufw

sudo ufw deny 8551/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 8551 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 8551 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 8551' -Direction Inbound -Protocol TCP -LocalPort 8551 -Action Block

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