Essential Protocols: Quick Guide for SREs & SysAdmins
Updated
•2 min read
In infrastructure, you don't guess—you verify. Whether you're debugging a Kubernetes CNI or a cloud-native database, knowing the underlying protocol is the key to faster troubleshooting.
Here is a cheat sheet of the 25 most important protocols and the commands to test them directly from your terminal.
| Protocol | Role in Infrastructure | Command to Test |
| HTTPS | Secure web traffic & API entry points. | curl -I https://google.com |
| SSH | Secure remote server management. | ssh -v user@host |
| DNS | The backbone of service discovery. | dig +short google.com |
| TCP | Connection-oriented, reliable delivery. | nc -zv host 443 |
| UDP | Fast delivery for VoIP, VPN, & DNS. | nc -zuv host 1194 |
| ICMP | Network reachability & latency testing. | ping -c 4 8.8.8.8 |
| BGP | Internet-scale routing (AS path). | mtr --aslookup 8.8.8.8 |
| NTP | Log & certificate synchronization. | chronyc sources |
| TLS/SSL | Encryption layer for all secure traffic. | openssl s_client -connect host:443 |
| DHCP | Dynamic IP allocation & management. | ip addr show |
| ARP | IP to MAC resolution (Layer 2). | ip neighbor |
| NFS | Network file sharing (Linux/Unix). | showmount -e host |
| SMB | Network file sharing (Windows/Azure Files). | smbclient -L //host |
| SFTP | Secure file transfer over SSH. | sftp user@host |
| SMTP | Outbound mail & alert notifications. | swaks --to user@domain.com |
| SNMP | Monitoring hardware & network devices. | snmpwalk -v2c -c public host |
| LDAP | Centralized user authentication. | ldapsearch -x -h host |
| RDP | Remote desktop access (Windows/VDI). | telnet host 3389 |
| iSCSI | Storage over IP (SAN connectivity). | iscsiadm -m discovery |
| gRPC | High-performance microservices. | grpcurl host:port list |
| Redis | Fast caching & session management. | redis-cli -h host ping |
| SQL | Database connectivity (MySQL/PostgreSQL). | mysql -h host -P 3306 |
| MQTT | IoT & event-driven messaging. | mosquitto_pub -h host -t test |
| VXLAN | Overlay networks (CNIs like Flannel/Calico). | ip -d link show type vxlan |
| HTTP/2 | Modern web performance (Multiplexing). | curl -I --http2 https://google.com |
