27018
MongoDB shard server for horizontally scaled clusters
MongoDB Shard Server
What is port 27018?
Port 27018 is used by MongoDB shard servers within sharded clusters. MongoDB sharding enables horizontal scaling by distributing data across multiple servers (shards). This port must be accessible only between MongoDB cluster nodes on a private network and must never be exposed to the internet.
Quick checks
$
nc -zv example.com 27018
$
nmap -p 27018 example.com
$
telnet example.com 27018