What are the default ports used for dhcp, ssh, smtp, dns, ftp, and squid?

DHCP (Dynamic Host Configuration Protocol):

1. • Server Port: 67 (UDP)
   • Client Port: 68 (UDP)
   • Application Case: DHCP enables automatic assignment of IP addresses to devices by the network server. For example, when you connect to Wi-Fi, it is typically the DHCP server that assigns an IP address to your device.
2. SSH (Secure Shell Protocol):
   • Default Port: 22 (TCP)
   • Application Case: SSH is used for securely accessing and managing remote servers. For example, system administrators often use SSH to connect to remote Linux servers for system maintenance and configuration updates.
3. SMTP (Simple Mail Transfer Protocol):
   • Default Port: 25 (TCP)
   • Application Case: SMTP is primarily used for sending emails. For example, when you send an email from Outlook, the Outlook client communicates with the mail server via SMTP to send the email.
4. DNS (Domain Name System):
   • Default Port: 53 (UDP/TCP)
   • Application Case: DNS converts domain names (such as www.example.com) to IP addresses. Every time you enter a URL in your browser, your computer uses DNS to find the actual IP address of the website.
5. FTP (File Transfer Protocol):
   • Default Port:
     • Data Transfer Port: 20 (TCP)
     • Command Control Port: 21 (TCP)
   • Application Case: FTP is used for transferring files between clients and servers. For example, website administrators may use FTP to upload new web pages to their server.
6. Squid (Proxy Server):
   • Default Port: 3128 (TCP)
   • Application Case: Squid is typically used as a caching proxy server, helping to reduce bandwidth consumption and improve response speed. For example, large enterprises may use Squid to cache frequently accessed website content, thereby speeding up access for internal users.