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How to Check IP Addresses in Ubuntu: Practical Commands for IPv4, IPv6, and Network Troubleshooting

Network Configuration
目次

1. What Is an IP Address?

An IP address is a unique number used to identify devices on a network. It is essential for sending and receiving data across the internet or a local network. There are two major types of IP addresses: IPv4 and IPv6. IPv4 uses a 32-bit address format, such as “192.168.0.1,” while IPv6 uses a 128-bit address format, such as “2001:0db8:85a3:0000:0000:8a2e:0370:7334.” IPv6 supports a significantly larger address space, allowing more devices to connect to the internet.

2. Basic Commands to Check IP Addresses in Ubuntu

Ubuntu provides various commands to check IP addresses. Using the following commands, you can easily identify the IP address assigned to your system.

2.1 ip addr show Command

The ip addr show command is a powerful and recommended tool in modern Linux distributions. It displays both IPv4 and IPv6 addresses assigned to network interfaces.

Example Usage:

$ sudo ip addr show

Example Output:

2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    inet 192.168.1.10/24 brd 192.168.1.255 scope global dynamic ens33
       valid_lft 86381sec preferred_lft 86381sec
    inet6 fe80::250:56ff:fe9a:de91/64 scope link 
       valid_lft forever preferred_lft forever
  • The value following inet, such as “192.168.1.10/24,” represents the IPv4 address. “/24” is CIDR notation, indicating the subnet mask (equivalent to 255.255.255.0). The first 24 bits represent the network portion, and the remaining 8 bits represent the host portion.
  • The value following inet6 is the IPv6 address—for example, “fe80::250:56ff:fe9a:de91.”

Additional Notes:

  • brd indicates the broadcast address.
  • scope specifies the address scope: global for internet-wide access, and link for link-local addresses within the same network segment.

2.2 hostname -I Command

The hostname -I command displays all IP addresses assigned to the system, separated by spaces. This is useful when you need only the IP addresses without additional details.

Example Usage:

$ hostname -I

Example Output:

192.168.1.10 fe80::250:56ff:fe9a:de91
  • The first value is the IPv4 address, and the next value is the IPv6 address. This command displays only assigned IP addresses without extra interface information.

Default Interface IP Address:

  • To display the IP address of the default network interface, run the following command:
$ ip route get 1.1.1.1

This command shows the route information to the specified address and identifies the default interface.

2.3 curl ifconfig.me Command

The curl ifconfig.me command retrieves your public IP address by accessing an external service. This is useful when you need to know how your system appears on the internet. However, note that this method communicates with an external server, so consider privacy implications.

Example Usage:

$ curl ifconfig.me

Example Output:

203.0.113.50

This output shows your global IP address as seen from the internet.

Privacy Considerations:

  • curl ifconfig.me sends IP-related information to an external server. If privacy is a concern, consider checking your public IP address via your router settings or another local method.

Public vs. Private IP Addresses:

  • ip addr show typically displays private IP addresses used within a local network. curl ifconfig.me reveals your global public IP address. Due to NAT (Network Address Translation), internal and external IP addresses often differ. NAT enables multiple devices to share a single public IP while accessing the internet.

3. The Deprecated ifconfig Command and Its Alternative

ifconfig was once the standard network management command in Linux but is now deprecated and not installed in most modern distributions. The more powerful ip command is recommended instead.

Installing ifconfig:

$ sudo apt install net-tools

Example Usage:

$ sudo ifconfig

Example Output:

inet 192.168.1.10  netmask 255.255.255.0  broadcast 192.168.1.255
  • The value after “inet,” such as “192.168.1.10,” represents the IPv4 address.

Limitations of ifconfig:

  • ifconfig may not display all interfaces, especially virtual ones, and might omit IPv6 details. The ip command provides more comprehensive and modern network information.

4. Using NetworkManager Tools

4.1 nmcli Command

nmcli is a command-line tool for managing NetworkManager. It allows you to view detailed information about network devices. If nmcli is not installed, use the following command:

Installation:

$ sudo apt install network-manager

Example Usage:

$ nmcli device show

Example Output:

IP4.ADDRESS[1]:                         192.168.1.10/24
  • The value following “IP4.ADDRESS[1]” indicates the IPv4 address.

Checking NetworkManager Status:

  • To verify whether NetworkManager is running, use:
$ systemctl status NetworkManager

5. Checking IP Addresses in Different Situations

Checking IP addresses is important for various networking tasks, including troubleshooting, server configuration, and preparing for remote access. Knowing multiple commands ensures you can choose the best method depending on the environment and context.

Troubleshooting Tips:

  • Network Issues: If an IP address is not assigned correctly, you may fail to connect to the network. Use ip addr show to verify the configuration and confirm that the correct interface has an IP address. Certain network configuration changes may require sudo privileges.
  • Remote Access: When configuring remote access to a server, you must know the correct public IP address. Use curl ifconfig.me to confirm the global IP address and ensure port forwarding on your router is properly configured.
  • Connection Tests: To verify network connectivity, use the ping command to confirm communication with a host. For example, run ping google.com to test internet access. Additionally, use traceroute to identify routing paths and pinpoint where delays or issues occur.
$ ping google.com
$ traceroute google.com
  • The ping results show response times and packet loss. Lack of response may indicate connection issues.
  • traceroute displays latency at each hop, helping you determine where delays occur.

6. Summary

There are multiple ways to check IP addresses in Ubuntu, and each method offers unique advantages. ip addr show provides detailed network information, while hostname -I offers a simple way to obtain IP addresses. curl ifconfig.me helps identify your public IP address but requires privacy awareness. Although ifconfig is deprecated, it may still be useful in specific situations.

By mastering these commands, you can manage networking tasks more efficiently on Ubuntu. Understanding IP address concepts and NAT (Network Address Translation) provides deeper insights into network configuration and security. Refer to official documentation and additional learning resources to enhance your network administration skills.

Reference Resources: