Port 2888 ZooKeeper peers · TCP

What runs on port 2888

ZooKeeper follower-to-leader port (2888) and leader election (3888). Internal to the ensemble; both must be open between members.

Software that uses it: ZooKeeper

Should port 2888 be open?

Private network or VPN only. Nothing good comes from this port being reachable from the internet. Keep it on an internal network, reach it over a VPN or an SSH tunnel, and firewall it from everything that does not need it.

• Firewall problems on 2888/3888 show as an ensemble that never gets a quorum.

Check port 2888

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :2888'
sudo lsof -i :2888

# from another machine: is it reachable?
nc -zv host 2888
nmap -p 2888 host
curl -v telnet://host:2888      # raw TCP connect test, Ctrl-C to leave

A port that answers from the internet when it should not is the finding; nmap from a machine outside your network (or a VPS) is the honest test, because scans from inside the LAN pass the firewall you are trying to verify.

Allow or block port 2888

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 2888 proto tcp
sudo ufw deny 2888/tcp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 tcp dport 2888 accept
nft add rule inet filter input tcp dport 2888 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 2888 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 2888 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=2888 protocol=tcp accept'

Replace 10.0.0.0/8 with the networks that need access. Allowing by source address is the rule that matters; "allow 2888" with no source is just "open".

Related ports

• 2181 ZooKeeper — Client port
• 3888 ZooKeeper election

Part of the port number reference. Ports are 16-bit numbers; see also the subnet calculator and the packet decoder, which shows ports inside TCP and UDP headers.

Questions