File Sharing Protocols Overview

Overview

• What you’ll learn: The major file sharing protocols used in Linux environments — NFS, SMB/CIFS, and FTP — including their architectures, strengths, limitations, and the network ports they require.
• Prerequisites: Basic Linux command-line skills, understanding of TCP/IP networking fundamentals
• Estimated reading time: 15 minutes

Introduction

File sharing is one of the most fundamental services provided by networked servers. Whether you are distributing configuration files to a fleet of Linux machines, providing shared storage to Windows desktops in an office, or allowing remote users to upload content, you need a protocol that matches your requirements for performance, security, and compatibility.

Linux supports several file sharing protocols natively, each designed for different scenarios. Network File System (NFS) is the traditional choice for Unix-to-Unix sharing, Server Message Block (SMB/CIFS) enables interoperability with Windows clients, and File Transfer Protocol (FTP) provides a simple mechanism for transferring files over the network. Understanding when and why to use each protocol is essential before diving into their individual configurations.

In this lesson, we will examine the architecture of each protocol, compare their features side by side, review the network ports they use, and discuss real-world use cases to help you choose the right protocol for any given scenario.

NFS — Network File System

NFS was developed by Sun Microsystems in the 1980s and has become the standard file sharing protocol in Unix and Linux environments. The current production version is NFSv4, which introduced significant improvements over NFSv3 including stateful operation, integrated security through Kerberos, and a single TCP port for firewall-friendly deployments.

NFS operates on a client-server model. The server exports directories by listing them in its configuration, and clients mount those exported directories as if they were local file systems. This transparency is one of NFS’s greatest strengths — applications on the client do not need to know they are accessing remote files.

# NFS uses the following ports:
# NFSv3: portmapper (111/tcp,udp), nfsd (2049/tcp,udp),
#         mountd (dynamic), statd (dynamic), lockd (dynamic)
# NFSv4: nfsd (2049/tcp) — single port only

# Check NFS server status
$ rpcinfo -p localhost
   program vers proto   port  service
    100000    4   tcp    111  portmapper
    100003    4   tcp   2049  nfs
    100005    3   tcp  20048  mountd

# View exports from a server
$ showmount -e 192.168.1.10
Export list for 192.168.1.10:
/srv/shared  192.168.1.0/24
/srv/home    *.example.com

NFS is best suited for homogeneous Linux/Unix environments where you need transparent file system access with POSIX permission support. Typical use cases include shared home directories across multiple servers, centralized application data, and NFS-backed storage for containers and virtual machines.

NFS Versions Compared

• NFSv3: Stateless protocol, uses multiple ports (requires RPC portmapper), supports UDP and TCP, relies on external locking via NLM (Network Lock Manager). Still widely used but harder to firewall.
• NFSv4: Stateful protocol, single port (2049/tcp), built-in locking and delegation, mandatory security with Kerberos support (via RPCSEC_GSS), compound operations for better performance over WAN. Recommended for all new deployments.
• NFSv4.1/4.2: Adds parallel NFS (pNFS) for clustered storage, server-side copy, sparse file support, and improved session management.

SMB/CIFS — Server Message Block

SMB is the native file sharing protocol of the Windows ecosystem. Originally developed by IBM and later extended by Microsoft, it is now an open standard. On Linux, the Samba project provides both server and client implementations of the SMB protocol, enabling seamless file sharing between Linux and Windows systems.

SMB is a more complex protocol than NFS because it was designed for environments that include user-level authentication, access control lists (ACLs), printer sharing, and service discovery. Modern SMB versions (SMB2 and SMB3) offer significant performance improvements, encryption, and multi-channel support.

# SMB uses the following ports:
# NetBIOS Name Service:   137/udp
# NetBIOS Datagram:       138/udp
# NetBIOS Session / SMB:  139/tcp
# SMB over TCP (Direct):  445/tcp
# SMB2/SMB3 use port 445/tcp exclusively

# Test connectivity to an SMB server
$ smbclient -L //192.168.1.10 -U guest
Sharename       Type      Comment
---------       ----      -------
shared          Disk      Public Files
printers        Printer   All Printers
IPC$            IPC       IPC Service

# Mount an SMB share on Linux
$ sudo mount -t cifs //192.168.1.10/shared /mnt/shared 
    -o username=admin,password=secret,vers=3.0

SMB is the right choice when your environment includes Windows clients, when you need integrated printer sharing, or when you need Active Directory-based authentication. Samba on Linux can even serve as a full Active Directory domain controller.

SMB Versions

• SMB1/CIFS: Legacy protocol, significant security vulnerabilities (WannaCry exploited SMBv1). Should be disabled on all systems.
• SMB2: Introduced with Windows Vista/2008. Reduced protocol chattiness, larger reads/writes, improved caching.
• SMB3: Introduced with Windows 8/2012. Adds encryption, multi-channel, transparent failover, and RDMA support. Recommended for all deployments.

FTP — File Transfer Protocol

FTP is one of the oldest Internet protocols, dating back to 1971. It provides a straightforward mechanism for uploading and downloading files. Unlike NFS and SMB, FTP does not provide transparent file system access — clients explicitly connect, browse, and transfer files using dedicated FTP commands.

FTP operates using two channels: a control channel (port 21) for commands and a data channel for actual file transfers. The data channel can operate in active mode (server connects back to client) or passive mode (client connects to server), which has significant implications for firewall configuration.

# FTP uses the following ports:
# Control channel:  21/tcp
# Active mode data: 20/tcp (server → client)
# Passive mode data: high ports (server → client connects to server)

# Connect to an FTP server
$ ftp 192.168.1.10
Connected to 192.168.1.10.
220 Welcome to the FTP server.
Name (192.168.1.10:user): admin
331 Please specify the password.
Password:
230 Login successful.
ftp> ls
drwxr-xr-x  2 admin admin  4096 Jan 15 10:30 documents
-rw-r--r--  1 admin admin  2048 Jan 15 09:15 readme.txt
ftp> get readme.txt
200 PORT command successful.
150 Opening ASCII mode data connection.
226 Transfer complete.

# Active mode vs. Passive mode
# Active:  Client sends PORT command, server connects back to client
# Passive: Client sends PASV command, server opens high port, client connects

FTP is suitable for scenarios where you need to provide file upload/download access to external users who may not have operating system-level accounts, such as web hosting file uploads, anonymous public file distribution, or batch file transfers between systems. For security, always use FTPS (FTP over TLS) or consider SFTP (SSH File Transfer Protocol) as a modern alternative.

Protocol Comparison and Port Summary

Choosing the right file sharing protocol depends on your specific requirements. The following comparison highlights the key differences:

# Protocol Comparison Table
#
# Feature           NFS              SMB/CIFS          FTP
# ─────────────────────────────────────────────────────────────
# Primary OS        Linux/Unix       Windows/Linux     Any
# Transparency      Mount as local   Mount or client   Client only
# Authentication    Kerberos/host    User/AD/Kerberos  User/anonymous
# Encryption        Kerberos/TLS     SMB3 built-in     FTPS (TLS)
# Printer sharing   No               Yes               No
# Port(s)           2049/tcp (v4)    445/tcp            21/tcp + data
# Firewall ease     Easy (v4)        Easy               Complex (active)
# Performance       Excellent        Very good          Good
# Use case          Unix-to-Unix     Cross-platform     File transfer

# Firewall rules example (UFW on Ubuntu)
$ sudo ufw allow from 192.168.1.0/24 to any port 2049 proto tcp  # NFS
$ sudo ufw allow from 192.168.1.0/24 to any port 445 proto tcp   # SMB
$ sudo ufw allow 21/tcp                                           # FTP control
$ sudo ufw allow 30000:31000/tcp                                  # FTP passive

• Choose NFS when: All clients are Linux/Unix, you need POSIX permissions, and you want transparent file system mounting with minimal overhead.
• Choose SMB when: You have Windows clients, need Active Directory integration, or want combined file and printer sharing.
• Choose FTP when: You need to provide file upload/download to external users, anonymous access to public files, or simple batch transfers.
• Consider SFTP/SCP when: You already have SSH access and need secure file transfers without deploying additional services.

Key Takeaways

• NFS is the native Linux file sharing protocol; NFSv4 uses a single port (2049/tcp) and supports Kerberos authentication for secure, transparent file system access.
• SMB/CIFS is essential for Windows interoperability; Samba on Linux implements the full SMB stack including file sharing, printer sharing, and Active Directory services.
• FTP provides simple file transfer capabilities but requires careful firewall configuration for active/passive modes; always use TLS encryption in production.
• Protocol choice depends on your client ecosystem, security requirements, and whether you need transparent mounting or explicit file transfers.
• Modern best practices favor NFSv4 for Linux-to-Linux sharing, SMB3 for cross-platform environments, and SFTP over traditional FTP for secure transfers.

What’s Next

In the next lesson, you will learn how to set up and configure an NFS server and client on Ubuntu, including exports configuration, mount options, and automounting with autofs.

# NFS 使用以下連接埠：
# NFSv3: portmapper (111/tcp,udp), nfsd (2049/tcp,udp),
#         mountd (動態), statd (動態), lockd (動態)
# NFSv4: nfsd (2049/tcp) — 僅單一連接埠

# 檢查 NFS 伺服器狀態
$ rpcinfo -p localhost
   program vers proto   port  service
    100000    4   tcp    111  portmapper
    100003    4   tcp   2049  nfs
    100005    3   tcp  20048  mountd

# 檢視伺服器的匯出清單
$ showmount -e 192.168.1.10
Export list for 192.168.1.10:
/srv/shared  192.168.1.0/24
/srv/home    *.example.com

# SMB 使用以下連接埠：
# NetBIOS 名稱服務：   137/udp
# NetBIOS 資料報：     138/udp
# NetBIOS 工作階段 / SMB：139/tcp
# SMB over TCP（直接）：445/tcp
# SMB2/SMB3 專用連接埠 445/tcp

# 測試與 SMB 伺服器的連線
$ smbclient -L //192.168.1.10 -U guest
Sharename       Type      Comment
---------       ----      -------
shared          Disk      Public Files
printers        Printer   All Printers
IPC$            IPC       IPC Service

# 在 Linux 上掛載 SMB 共享
$ sudo mount -t cifs //192.168.1.10/shared /mnt/shared 
    -o username=admin,password=secret,vers=3.0

# FTP 使用以下連接埠：
# 控制通道：  21/tcp
# 主動模式資料：20/tcp（伺服器 → 客戶端）
# 被動模式資料：高連接埠（客戶端連線到伺服器）

# 連線到 FTP 伺服器
$ ftp 192.168.1.10
Connected to 192.168.1.10.
220 Welcome to the FTP server.
Name (192.168.1.10:user): admin
331 Please specify the password.
Password:
230 Login successful.
ftp> ls
drwxr-xr-x  2 admin admin  4096 Jan 15 10:30 documents
-rw-r--r--  1 admin admin  2048 Jan 15 09:15 readme.txt

# 協定比較表
#
# 功能             NFS              SMB/CIFS          FTP
# ─────────────────────────────────────────────────────────────
# 主要作業系統     Linux/Unix       Windows/Linux     任何
# 透明性           掛載為本地       掛載或客戶端       僅客戶端
# 認證             Kerberos/主機    使用者/AD/Kerberos 使用者/匿名
# 加密             Kerberos/TLS     SMB3 內建         FTPS (TLS)
# 印表機共享       否               是                 否
# 連接埠           2049/tcp (v4)    445/tcp            21/tcp + 資料
# 防火牆易用性     容易 (v4)        容易               複雜（主動）
# 效能             優秀             非常好             良好
# 使用案例         Unix 對 Unix     跨平台             檔案傳輸

# 防火牆規則範例（Ubuntu 上的 UFW）
$ sudo ufw allow from 192.168.1.0/24 to any port 2049 proto tcp  # NFS
$ sudo ufw allow from 192.168.1.0/24 to any port 445 proto tcp   # SMB
$ sudo ufw allow 21/tcp                                           # FTP 控制
$ sudo ufw allow 30000:31000/tcp                                  # FTP 被動

# NFS が使用するポート：
# NFSv3: portmapper (111/tcp,udp), nfsd (2049/tcp,udp),
#         mountd (動的), statd (動的), lockd (動的)
# NFSv4: nfsd (2049/tcp) — 単一ポートのみ

# NFS サーバーの状態を確認
$ rpcinfo -p localhost
   program vers proto   port  service
    100000    4   tcp    111  portmapper
    100003    4   tcp   2049  nfs
    100005    3   tcp  20048  mountd

# SMB が使用するポート：
# NetBIOS 名前サービス：   137/udp
# NetBIOS データグラム：   138/udp
# NetBIOS セッション / SMB：139/tcp
# SMB over TCP（ダイレクト）：445/tcp

# SMB サーバーへの接続テスト
$ smbclient -L //192.168.1.10 -U guest
Sharename       Type      Comment
---------       ----      -------
shared          Disk      Public Files
printers        Printer   All Printers
IPC$            IPC       IPC Service

# FTP が使用するポート：
# 制御チャネル：  21/tcp
# アクティブモードデータ：20/tcp（サーバー → クライアント）
# パッシブモードデータ：高ポート（クライアントがサーバーに接続）

# FTP サーバーに接続
$ ftp 192.168.1.10
Connected to 192.168.1.10.
220 Welcome to the FTP server.
Name (192.168.1.10:user): admin
331 Please specify the password.
Password:
230 Login successful.

# プロトコル比較表
#
# 機能             NFS              SMB/CIFS          FTP
# ─────────────────────────────────────────────────────────────
# 主要 OS          Linux/Unix       Windows/Linux     すべて
# 透過性           ローカルマウント マウントまたは     クライアントのみ
#                                   クライアント
# 認証             Kerberos/ホスト  ユーザー/AD       ユーザー/匿名
# 暗号化           Kerberos/TLS     SMB3 内蔵         FTPS (TLS)
# プリンター共有   なし             あり               なし
# ポート           2049/tcp (v4)    445/tcp            21/tcp + データ