Port 27018 MONGODB SHARD
Port 27018 is the community default for MongoDB shard, using TCP.
What is port 27018 used for?
Port 27018 is widely used by MongoDB shard (TCP), a community convention rather than an IANA assignment. Conventional MongoDB shard server port, one above the default 27017 (community convention). It sits above the registered range, where most numbers are transient client ports. A fixed high port is worth documenting precisely because tooling often assumes the default.
Ports are the transport-layer address a service listens on. A client that wants to reach MongoDB shard connects to port 27018. If nothing is listening, the connection is refused. That is why a port conflict appears whenever two processes try to bind the same number.
Use the commands below to confirm whether port 27018 is actually in use before you change firewall rules. Blocking the port stops new inbound traffic at the firewall, but it does not stop a local process from listening, and it does not remove the service from the machine.
Because this number is not IANA-assigned, a different application may legitimately use it on a machine you do not control. Always identify the actual listening process before deciding that the port belongs to this technology.
This port number is not assigned by IANA. The entry documents a widely adopted community convention.
Check and block port 27018
Copy-ready commands for the protocols assigned to this port. Run the check first, then block only what should not be reachable.
Check on Linux
sudo ss -tlpn 'sport = :27018'Check on Windows
Get-NetTCPConnection -LocalPort 27018 -State Listen -ErrorAction SilentlyContinueBlock with UFW
sudo ufw deny 27018/tcpBlock with iptables
sudo iptables -A INPUT -p tcp --dport 27018 -j DROPThese commands are examples for a typical host. Check the listener before you change firewall rules, and persist iptables rules with iptables-save or netfilter-persistent. On Windows, use Windows Defender Firewall or New-NetFirewallRule for persistent blocks. The iptables rules here cover IPv4; mirror them with ip6tables if IPv6 is enabled.
Is port 27018 safe to expose?
MongoDB shard servers are often left unauthenticated like the main service. Enable auth, TLS and private networking. Treat this port as sensitive. Restrict it to trusted networks or a VPN, require authentication and logging, and never expose it directly to the public internet without a hardened gateway in front.
Where port 27018 is usually used
Most traffic on port 27018 falls into these scenarios. The demo below is a safe way to confirm the listener before you change anything.
- Application servers opening pooled connections to the database on port 27018.
- Migrations, backups and reporting jobs run from a trusted bastion host.
- Local Docker or test environments that publish the database on the host.
Probe the shard listener
Shard servers are internal; query the mongos router instead of opening a client session here.
nc -vz 127.0.0.1 27018Common problems with port 27018
Connection refused or timed out
Refused usually means the host is reachable but nothing is listening on port 27018. A timeout more often means a firewall drop, a wrong host or a service bound to a different interface.
Port already in use
Find the process holding the port with sudo ss -tlpn 'sport = :27018' or sudo lsof -i :27018. Stop that process or configure it to bind another port; killing it without identifying it can take down a production service.
Firewall rule did not survive a reboot
UFW and Windows Firewall keep rules across restarts. Raw iptables rules do not: save them with iptables-save or the netfilter-persistent package, and re-apply after upgrades that reset the ruleset.
The port is blocked but still reachable
A firewall rule filters inbound traffic; it does not close the listener. Confirm with the check command above and bind the service to 127.0.0.1 when only local clients need it.
Port 27018 at a glance
| Port number | 27018 |
|---|---|
| Service name | MongoDB shard |
| Transport protocol | TCP |
| Category | Databases |
| Range | High port (10001–65535) |
| Risk level | High |
| Reference | Community convention (not IANA-assigned) |
| Registry description | Conventional MongoDB shard server port, one above the default 27017 (community convention) |
| Source | Community convention |
Frequently asked questions
What is port 27018 used for?
Port 27018 (MONGODB SHARD) uses TCP. Conventional MongoDB shard server port, one above the default 27017 (community convention) (community convention, not an IANA assignment).
How do I check if port 27018 is open?
On Linux run `sudo ss -tlpn 'sport = :27018'`. On Windows run `Get-NetTCPConnection -LocalPort 27018 -State Listen -ErrorAction SilentlyContinue` in PowerShell. If the port is open, the output shows a process listening on port 27018; empty output usually means nothing is bound to it.
How do I block port 27018?
With UFW run `sudo ufw deny 27018/tcp`. With iptables run `sudo iptables -A INPUT -p tcp --dport 27018 -j DROP`. Persist the iptables rules with your distribution's netfilter-persistent or iptables-save tooling so they survive a reboot.
Is port 27018 safe to expose?
MongoDB shard servers are often left unauthenticated like the main service. Enable auth, TLS and private networking. Nevertheless, treat this port as sensitive. Restrict it to trusted networks or a VPN, require authentication and logging, and never expose it directly to the public internet without a hardened gateway in front.
Related ports
Primary data: IANA Service Name and Transport Protocol Port Number Registry. This number is a community convention, not an IANA assignment.
Last reviewed 2026-10-30 · Methodology · About · Privacy