Network Configuration

To configure the gateway network interfaces using the ESF Gateway Administration Console, select the Network option located in the System area. With this option selected, the Network display appears with a list of available interfaces. Configuration tabs for the selected interface appear on the right side of the screen. By default, the loopback (lo) interface is selected when the network interfaces are displayed. Choose the desired network interface (e.g., eth0, eth1, wlan0, ppp0) and apply the necessary configuration changes using the tabs on the right. Submit the modified configuration by clicking the Apply button.
In case of typing errors, the Reset button can be used to reload the prior configuration on the screen.
Since the network configuration shown on the screen may not be synchronized with the current state of the system, it can be updated pressing the Refresh button. This can be used also to force the reload of specific parameters like the RSSI or dynamic IP addresses. The refresh procedure reads all the needed parameters from the system and can take several seconds before updating.

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Configure TCP/IP First
It is recommended that the TCP/IP tab is configured first since it defines how the interface is going to be used.

TCP/IP Configuration

The TCP/IP tab contains the following configuration parameters:- Status

Disabled - disables the selected interface (i.e., administratively down).
Enabled for LAN - designates the interface for a local network. It can be set as a DHCP server for hosts on the local network and can serve as a default gateway for those hosts; however, it cannot be set as an actual gateway interface for this device. That is, packets must be routed from this interface to another interface that is configured as WAN. The interface is automatically brought up at boot.
Enabled for WAN - designates the interface as a gateway to an external network. The interface is automatically brought up at boot.
Not Managed - the interface will be ignored by ESF.
Layer 2 Only - only the Layer 2 portion of the interface will be configured. The interface is automatically brought up at boot.
Configure
- Manually - allows manual entry of the IP Address and Netmask fields, if the interface is configured as LAN; allows manual entry of the IP Address, Netmask, Gateway, and DNS Servers fields, if the interface is designated as WAN.
- Using DHCP - configures the interface as a DHCP client obtaining the IP address from a network DHCP server.
IP Address - defines the IP address of the interface, if manually configured.
Subnet Mask - defines the subnet mask of the interface, if manually configured.
Gateway - specifies the default gateway for the unit. (Required field if the interface is designated as WAN and manually configured.)
DNS Servers - provides a list of DNS servers, if the interface is designated as WAN and is manually configured.
Search Domains - Not implemented.

If the network interface is Enabled for LAN and manually configured (i.e., not a DHCP client), the DHCP & NAT tab allows the DHCP server to be configured and/or NAT (IP forwarding with masquerading) to be enabled.

More details about the Not Managed interface Status

When a network interface is configured as Not Managed, ESF will ignore it and the configuration will not be touched. The user can configure the interface with the network tools provided by the OS, allowing unusual network setups.

Regarding DNS, both ESF and the external tools store the DNS addresses in the /etc/resolv.conf file. So, if multiple interfaces are configured to get the DNS information and store it in the same file, the device can be misconfigured. To avoid that, the following table presents who is responsible to update the DNS file depending on the network interfaces configurations.

ESF WAN interface	ESF NotManaged interface	Does ESF manage resolv.conf?
NO	NO	YES
NO	YES	NO
YES	NO	YES
YES	YES	YES

So, the only way to configure the DNS addresses with external tools, is to configure at least one interface as Not Managed and not to set any interface as Enabled For Wan using ESF. If at least one WAN interface is configured by ESF, it will take the control of the /etc/resolv.conf/ file. Finally, if any interface is configured in Enabled For Wan or Not Managed mode, ESF will empty the file.

To avoid device misconfigurations when Not Managed interfaces are used, don't use the dns-nameservers directive in the /etc/network/interfaces file. Please add the DNS addresses directly to the /etc/resolv.conf file.

DHCP & NAT Configuration

The DHCP & NAT tab contains the following configuration parameters:

Router Mode
- DHCP and NAT - indicates that both DHCP server and NAT are enabled.
- DHCP Only - indicates that DHCP server is enabled and NAT is disabled.
- NAT Only - indicates that NAT is enabled and DHCP server is disabled.
- Off - indicates that both DHCP server and NAT are disabled.
DHCP Beginning Address - specifies the first address of DHCP pool (i.e., first available client IP address).
DHCP Ending Address - specifies the last address of DHCP pool (i.e., last IP address that can be assigned to a client).
DHCP Subnet Mask - defines the subnet mask that is assigned to a client.
DHCP Default Lease Time - sets the default time (in minutes) that the client retains the provided IP address. It must be greater than 0.
DHCP Max Lease Time - sets the maximum time (in minutes) that the client retains the provided IP address. It must be greater than 0.
Pass DNS Servers through DHCP - enables DNS Proxy (i.e., passing DNS servers through DHCP).

If NAT is enabled and there is another interface designated as WAN (e.g., ppp0), the following iptables rules are added to the custom automatic NAT service rules section of the /etc/init.d/firewall script:

# custom automatic NAT service rules (if NAT option is enabled for LAN interface)
iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
iptables -A FORWARD -i ppp0 -o eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i eth0 -o ppp0 -j ACCEPT

Also, IP forwarding is enabled in the kernel as follows:

# allow fowarding if any masquerade is defined
echo 1 > /proc/sys/net/ipv4/ip_forward

The rules shown above create an Overloaded (i.e., many-to-one) NAT. This type of network address translation maps multiple IP addresses on the LAN side to a single IP address on the WAN side, allowing internet access from hosts on a local network via a gateway (WAN) interface. Note that for NAT rules to be added, it is insufficient to enable NATing through the DHCP & NAT tab of the LAN interface; there must also be another interface designated as WAN.

Network Linux Configuration

When applying a new network configuration, ESF changes the configuration files of the Linux networking subsystem. Please read the following note before proceeding with manual changes of the Linux networking configuration.

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Avoid Conflicting Configuration Changes
Eurotech does NOT recommend performing manual editing of the Linux networking configuration files when the gateway configuration is being managed through ESF. While Linux may correctly accept manual changes, ESF may not be able to interpret the new configuration resulting in an inconsistent state.