1 - Managing the Network Configuration

The network service, which is enabled by default, starts when the system boots. You manage the network service by using systemd commands, such as systemd-networkd, systemd-resolvd, and networkctl.

You can check the status of the network service by running the following command:

systemctl status systemd-networkd

The following is a result of the command:

* systemd-networkd.service - Network Service
   Loaded: loaded (/usr/lib/systemd/system/systemd-networkd.service; enabled; vendor preset: enabled)
   Active: active (running) since Fri 2016-04-29 15:08:51 UTC; 6 days ago
     Docs: man:systemd-networkd.service(8)
 Main PID: 291 (systemd-network)
   Status: "Processing requests..."
   CGroup: /system.slice/systemd-networkd.service
           `-291 /lib/systemd/systemd-networkd

2 - Inspecting IP Addresses

VMware recommends that you use the ip or ss commands as the ifconfig and netstat commands are deprecated.

To display a list of network interfaces, run the ss command. Similarly, to display information for IP addresses, run the ip addr command.


ip addr 					ifconfig -a
ss 							netstat
ip route 					route
ip maddr 					netstat -g
ip link set eth0 up 		ifconfig eth0 up
ip -s neigh					arp -v
ip link set eth0 mtu 9000	ifconfig eth0 mtu 9000

Use the ip route version of a command instead of the net-tools to get accurate information:

ip neigh dev eth0 lladdr 00:50:56:e2:02:0f STALE dev eth0 lladdr 00:50:56:e7:13:d9 STALE dev eth0 lladdr 00:50:56:c0:00:08 DELAY

arp -a
? ( at 00:50:56:e2:02:0f [ether] on eth0
? ( at 00:50:56:e7:13:d9 [ether] on eth0
? ( at 00:50:56:c0:00:08 [ether] on eth0

Important: If you modify an IPv6 configuration or add an IPv6 interface, you must restart systemd-networkd. Traditional methods of using ifconfig commands will be inadequate to register the changes. Run the following command instead:

systemctl restart systemd-networkd

3 - Inspecting the Status of Network Links with 'networkctl'

The networkctl command displays information about network connections that helps you configure networking services and troubleshoot networking problems.

You can progressively add options and arguments to the networkctl command to move from general information about network connections to specific information about a network connection.

Running networkctl without options defaults to the list command:

IDX LINK             TYPE               OPERATIONAL SETUP
  1 lo               loopback           carrier     unmanaged
  2 eth0             ether              routable    configured
  3 docker0          ether              routable    unmanaged
 11 vethb0aa7a6      ether              degraded    unmanaged
 4 links listed.

Run the networkctl with the status command to display active network links with IP addresses for not only the Ethernet connection, but also the Docker container.

root@photon-rc [ ~ ]# networkctl status
*      State: routable
     Address: on eth0
     on docker0
              fe80::20c:29ff:fe55:3ca6 on eth0
              fe80::42:f0ff:fef7:bd81 on docker0
              fe80::4c84:caff:fe76:a23f on vethb0aa7a6
     Gateway: on eth0

You can add a network link, such as the Ethernet connection, as the argument of the status command to show specific information about the link:

root@photon-rc [ ~ ]# networkctl status eth0
* 2: eth0
       Link File: /usr/lib/systemd/network/99-default.link
    Network File: /etc/systemd/network/10-dhcp-en.network
            Type: ether
           State: routable (configured)
            Path: pci-0000:02:01.0
          Driver: e1000
      HW Address: 00:0c:29:55:3c:a6 (VMware, Inc.)
             MTU: 1500
        CLIENTID: ffb6220feb00020000ab116724f520a0a77337

You can add a Docker container as follows:

networkctl status docker0
* 3: docker0
       Link File: /usr/lib/systemd/network/99-default.link
    Network File: n/a
            Type: ether
           State: routable (unmanaged)
          Driver: bridge
      HW Address: 02:42:f0:f7:bd:81
             MTU: 1500

In the example above, the output indicates that state of the Docker container is unmanaged. Docker uses the bridge drive to handle managing the networking for the containers and not systemd-resolved or systemd-networkd.

For more information about networkctl commands and options, see https://www.freedesktop.org/software/systemd/man/networkctl.html.

4 - Network Debugging

You can set systemd-networkd to work in debug mode so that you can analyze log files with debugging information to help troubleshoot networking problems.

The following procedure turns on network debugging by adding a drop-in file in /etc/systemd to customize the default systemd configuration in /usr/lib/systemd.

  1. Run the following command as root to create a directory with this exact name, including the .d extension:

    mkdir -p /etc/systemd/system/systemd-networkd.service.d/


  2. Run the following command as root to establish a systemd drop-in unit with a debugging configuration for the network service:

    cat > /etc/systemd/system/systemd-networkd.service.d/10-loglevel-debug.conf << "EOF"
  3. Reload the systemctl daemon and restart the systemd-networkd service for the changes to take effect:

    systemctl daemon-reload
    systemctl restart systemd-networkd
  4. Verify that your changes took effect:

    systemd-delta --type=extended`


  5. View the log files by running this command:

    journalctl -u systemd-networkd`


  6. After debugging the network connections, turn debugging off by deleting the drop-in file:

    rm /etc/systemd/system/systemd-networkd.service.d/10-loglevel-debug.conf


5 - Checking Firewall Rules

The design of Photon OS emphasizes security. On the minimal and full versions of Photon OS, the default security policy turns on the firewall and drops packets from external interfaces and applications. As a result, you might need to add rules to iptables to permit forwarding, allow protocols like HTTP, and open ports. In other words, you must configure the firewall for your applications and requirements.

The default iptables settings on the full version look like this:

iptables --list
Chain INPUT (policy DROP)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere             ctstate RELATED,ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:ssh

Chain FORWARD (policy DROP)
target     prot opt source               destination

Chain OUTPUT (policy DROP)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere

To find out how to adjust the settings, see the man page for iptables.

Although the default iptables policy accepts SSH connections, the sshd configuration file on the full version of Photon OS is set to reject SSH connections. See Permitting Root Login with SSH.

If you are unable to ping a Photon OS machine, check the firewall rules. Verify if the rules allow connectivity for the port and protocol.

You can supplement the iptables commands by using lsof to, for instance, see the processes listening on ports:

	lsof -i -P -n

6 - Inspect Network Settings with 'netmgr'

If you are running a VMware appliance on Photon OS and the VAMI module has problems or if there are networking issues, you can use the Photon OS netmgr utility to inspect the networking settings. Make sure that the IP addresses for the DNS server and other infrastructure are correct. Use tcpdump to analyze the issues.

The error code that you get from netmgr is a standard Unix error code. Enter it into a search engine to obtain more information on the error.