Digi Connect WAN Series User Manual page 74

Digi Connect WAN Family web interface
received by the DNS Proxy. The DNS Proxy does not cache the actual detailed client requests
nor the responses received from the DNS servers. Rather, it acts as a request/response relay
agent between the DNS clients and servers.
The DNS Proxy will cycle through the DNS servers that are configured in the Digi device. DNS
client requests are identified by the client's IP address and the unique Query ID in the DNS
request message. For each new DNS client request (new Query ID), the DNS Proxy uses the
first DNS server in its list of DNS servers. If the client retries the same request (same Query ID),
the DNS Proxy will recognize that retry message and will either send the retry request to the
same DNS server as the previous request for this client, or it will move to the next DNS server
in its list of DNS servers. The DNS Proxy feature determines when to retry the same DNS
server, or move to the next DNS server, according to the DNS Proxy: Request Retries Per
DNS Server configuration setting (see below). The DNS Proxy itself does not perform
unsolicited retries of DNS client requests.
Note The DHCP Server feature on the Digi device may be configured to use the DNS Proxy
feature. For more information, see
in its content. For example, when DNS server IP addresses are received from a mobile service
provider's network, they are added to the DNS server list of this Digi device. Those DNS server
IP addresses may or may not be configured when the DHCP Server offers a lease to a DHCP
client. As a result, the DHCP client may have no DNS servers provided to it in the lease, and
domain name resolution may fail for that client. A significant benefit of the DNS Proxy feature is
that the DHCP Server can offer its own IP address as a DNS server in the client lease, and the
DNS Proxy will forward DNS requests and responses as stated above. Since the DHCP protocol
does not allow a DHCP Server to force an unsolicited DNS server list update to its clients, the
DNS Proxy feature provides an indirect method by which such updates may be made effective
for the client.
Request Cache Size Maximum: Specifies the maximum number of DNS client request records
n
that the DNS Proxy will maintain concurrently in its cache. A large cache consumes more
system resources than does a small cache. However, if the maximum cache size is too small,
new DNS client requests may be quietly discarded until the cache has room to add new client
request records, or existing cache entries may be replaced by the new requests. If a large
number of concurrent DNS client lookups is anticipated, configuring a larger maximum cache
size is recommended. See also the setting For new client requests received when the
request cache is full below.
Request Idle Time-To-Live: Specifies the period of time, in seconds, that a DNS client request
n
will remain in the DNS Proxy cache, before it is deleted. This is a period of idle time, during
which neither a DNS client request retry is received by the DNS Proxy, nor a DNS server
response is received by the DNS Proxy, for a specific DNS client request. A shorter Idle TTL
results in the DNS Proxy using resources more efficiently, since the client request cache is
reduced in size and the request buffers are released more quickly for future use for other DNS
client requests.
Digi Connect WAN Family User Guide
Configuration through the web interface
DHCP server settings. The DNS server list may be dynamic
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