Networking on Linux Platform - Week #1 Notes

Lesson Overview

• Network Services:
  • Understanding related files and settings.
  • Static and dynamic IP configuration.
  • Hostname resolution (both static and dynamic).
  • Overview of network management tools.
  • Device management and common network errors.

Service Management

• Network Service Management: Utilize systemctl for service management:
  • Commands include: status, start, stop, restart, reload, enable, disable.
• NetworkManager:
  • Manage individual interfaces with commands:
  • nmcli connection up (to activate a connection).
  • nmcli connection down (to deactivate a connection).
  • ip link set <interface> up (to set an interface up).
• Network Configuration: Source scripts setup networking from:
  • /etc/sysconfig/network-scripts/
  • /etc/NetworkManager/system-connections/

Interface Configuration

• Interface Configuration Files:
  • Each interface has its own configuration file at /etc/sysconfig/network-scripts/ifcfg-interface.
• Configuration Options:
  • Includes static and dynamic settings:
  • Static Configuration: Manually supplied IP parameters.
  • Dynamic Configuration: IP parameters supplied by DHCP.

Example: Dynamic IP Configuration

• Configuration file example for dynamic IP:

  DEVICE=ens160
  TYPE=Ethernet
  ONBOOT=yes
  BOOTPROTO=dhcp
  PEERDNS=yes
  DEFROUTE=yes

Example: Static IP Configuration

• Configuration file example for static IP:

  DEVICE=ens224
  TYPE=Ethernet
  ONBOOT=yes
  BOOTPROTO=none
  IPADDR=172.16.30.167
  NETMASK=255.255.0.0
  NETWORK=172.16.0.0
  #GATEWAY=172.16.30.1 #Optional Gateway

Assigned Hostname

• Hostnames:
  • Static Hostname: A hostname assigned manually.
  • Transient Hostname: Reflects the current network configuration (e.g., provided by DHCP).
• Hostname Management:
  • Set a static hostname:
  • Command: hostnamectl set-hostname moe000-srv.example167.lab
  • Recorded in /etc/hostname.
  • View the hostname with hostnamectl.

Hostname Resolution

• Definition of Hostname Resolution:
  • Process by which a Fully Qualified Domain Name (FQDN) resolves to an IP address.
• Static vs Dynamic Resolution:
  • Static resolution managed via /etc/hosts:
  • Contains localhost entry and server name entry.
  • Dynamic resolution managed via /etc/resolv.conf:
  • Contains a list of name servers.
• Configuration Example for Static and Dynamic Resolution:
  • Static /etc/hosts:
    127.0.0.1 localhost.localdomain localhost 172.16.30.167 moe000-srv.example167.lab
  • Dynamic /etc/resolv.conf:
    search <list of default domain names> nameserver <IP of DNS server> nameserver <IP of another DNS server>

Default Gateway

• Default Gateway:
  • Entry for all traffic not destined for the local network.
  • Can be configured via DHCP or statically.
  • To view routing table: ip route (displays default via <IP>, dev <interface>).

Verifying Network Setup

• Device Setup Commands:
  • Use ip link instead of ifconfig.
  • View hardware with lspci -v.
• IP Configuration Commands:
  • Use ip addr (replaces ifconfig).
  • Use ip route (replaces route).
  • Use ping <IP> to check connectivity.
• Hostname Setting/Resolution:
  • Check with hostnamectl, getent hosts, and ping <hostname>.

Common Causes of Network Issues

• Possible issues to check:
  • Network cables unplugged or faulty.
  • Interface disabled or not properly configured in VMware.
  • Wrong network service or DHCP client not started.
  • Incomplete routing table, multiple default gateways, or hostname resolutions issues (static/dynamic).