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Checking Network Configuration (ip, ifconfig, ping)

1. Viewing Network Configuration​

1.1 Using the ip Command (Modern Tool)​

The ip command is part of the iproute2 package, which is the default network management tool in modern Linux systems. It replaces older commands like ifconfig.

Key Features of ip:

  • Shows detailed interface information.
  • Displays IP addresses, routes, and link status.
  • Allows configuration of IP addresses and routes (covered in later lessons).

Examples:​

1. View All Network Interfaces and Their Details:​

ip addr show

2. Show Only Active Interfaces:​

ip link show up
  • Displays only interfaces that are enabled and active.

3. Display Routing Table:​

ip route show

1.2 Using the ifconfig Command (Deprecated but Still Used)​

The ifconfig command is deprecated but may still be available on older systems. It’s simple to use and often preferred by beginners.

Examples:​

1. Display Network Interfaces and IP Information:​

ifconfig
  • Lists IP addresses, MAC addresses, and status of all network interfaces.

2. Check a Specific Interface (e.g., eth0)​

ifconfig eth0
  • Displays details only for the specified interface.

Note: For modern systems, the ip command should be used instead of ifconfig as it’s more robust and feature-rich.

2. Testing Network Connectivity​

2.1 Using the ping Command​

The ping command checks connectivity between your system and another host by sending ICMP Echo Requests.

Examples:​

1. Test Connectivity to an IP Address:​

ping 8.8.8.8
  • Tests if Google’s DNS server (8.8.8.8) is reachable.

2. Test Connectivity to a Domain Name:​

ping google.com
  • Verifies DNS resolution by checking if the domain resolves to an IP address and is reachable.

3. Limit the Number of Packets Sent (e.g., 4 packets):​

ping -c 4 google.com
  • Sends only 4 packets and stops, instead of pinging indefinitely.

4. Adjust Packet Size and Interval:​

ping -s 128 -i 0.5 google.com
  • Sends packets of 128 bytes every 0.5 seconds.

3. Checking DNS Resolution​

Sometimes, network connectivity may fail due to DNS issues rather than physical connectivity problems.

Examples:​

1. Test DNS Resolution with ping:​

ping example.com
  • Confirms whether the hostname resolves to an IP address.

2. Using the host Command (Optional):​

host example.com
  • Displays detailed DNS information, including IP addresses.

4. Troubleshooting Tips​

1. Interface Down Issue:​

ip link set eth0 up
  • Brings the interface up if it’s down.

2. No IP Address Assigned:​

dhclient eth0
  • Requests an IP address from the DHCP server.

3. Gateway Issues:​

ip route add default via 192.168.1.1 dev eth0
  • Manually sets the default gateway.

4. DNS Issues:​

Edit /etc/resolv.conf:

nameserver 8.8.8.8
  • Adds Google’s public DNS server as a resolver.

5. Quick Recap: Key Commands​

CommandPurpose
ip addr showDisplay IP address and interface details.
ip link show upShow only active network interfaces.
ip route showDisplay routing table.
ifconfigLegacy command for viewing interface information.
ping <ip>Test network connectivity with an IP address.
ping <hostname>Test DNS resolution and connectivity with a hostname.
ping -c 4 <ip>Send 4 packets to test connectivity.
ping -s 128 -i 0.5 <ip>Customize packet size and interval for ping.
host <domain>Check DNS information for a hostname.

Key Takeaways​

  • Use ip for modern systems as it is feature-rich and actively maintained.
  • Use ping to verify connectivity and isolate network issues quickly.
  • Transition from ifconfig to ip where possible, as ifconfig is deprecated.
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