Eurotech ZyWAN, User Manual

Page: 46 / 130

ZyWAN - User Manual
46 110150-1001F
Default Route
The ZyWAN will make one of its interfaces the default route based on the configuration and the availability of
each network. The order of preference for the default route is:
• Ethernet 0 (eth0)
• Ethernet 1 (eth1)
• WiFi (wlan0)
• Cellular (ppp0)
The first interface which has a Default Gateway (static configuration in Web page, or dynamically obtained
with DHCP) will be the one used for the ZyWAN’s default gateway. If the network cable is unplugged or the
WiFi becomes unavailable, the list of interfaces is checked again, and the first available interface will be
selected dynamically as the default route, in order of preference.
This means, for instance, that if an application requires the cellular network to be the default gateway for
network traffic, any static Default Gateway (in the ZyWAN Web configuration) or gateway obtained from
DHCP will interfere with the intended operation.
DHCP Server and NAT
If either the Ethernet or WiFi (master or ad-hoc mode) is running a DHCP server, then the ZyWAN will reply
to any device on the network that asks for an IP address using DHCP protocol. The ZyWAN will give the
device an address in accordance with the list of addresses specified in the ZyWAN Web configuration. The
device will be supplied the ZyWAN’s network address as its Default Gateway.
The ZyWAN is able to act as a gateway, but in order to route traffic from one interface to another, there must
also be a NAT entry configured on the Networking page to route from the source network to the destination
network. The “Open Ports” section on the
Networking
page must include UDP port 67 to allow DHCP traffic
to the ZyWAN.
DNS Server
As a DHCP Server, the ZyWAN may also be configured to pass DNS server addresses to other devices, so
they can resolve named addresses (URL or FQDN). When this happens, the ZyWAN will provide its own IP
address as the DNS server. The ZyWAN acts as a DNS proxy, so that any DNS requests from the client
device are passed to the one of the DNS servers known to the ZyWAN, and the resulting IP address is
returned to the client device.
In order to resolve DNS addresses, the ZyWAN needs to have a list of known DNS server(s). It obtains the
list of these servers in the same way as it obtains its default route. The ZyWAN checks its interfaces in the
preferred order: eth0, eth1, wlan0, and ppp0. The first active interface which contains one or more DNS
servers (static address configured via the Web page, or obtained by the ZyWAN using DHCP) is used. This
list of address(es) is used by the DNS proxy. If the Ethernet cable is unplugged or the WiFi becomes
unavailable, the list of interfaces is checked again, and the first available interface will be selected
dynamically as the location for DNS servers, in order of preference.
The “Open Ports” section on the Networking page must include UDP port 53, to allow DNS requests to the
ZyWAN.