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16.2 Demand Dial
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Technical Peculiarities and Limitations
Demand dialing has its peculiarities and limitations. The limitations should be consid-
ered especially within designing and configuration of the network that will use WinRoute
for connection and of the dial-up connected to the Internet.
1. Demand dial cannot be performed directly from the host where WinRoute is installed
because it is initiated by WinRoute low-lever driver. This driver holds packets and
decides whether the line should be dialed or not. If the line is disconnected and
a packet is sent from the local host to the Internet, the packet will be dropped by
the operating system before the WinRoute driver is able to capture it.
2. Typically the server is represented by the DNS name within traffic between clients
and an Internet server. Therefore, the first packet sent by a client is represented by
the DNS query that is intended to resolve a host name to an IP address.
In this example, the DNS server is the WinRoute host (this is very common) and the
line to the Internet is disconnected. A client’s request on this DNS server is traffic
within the local network and, therefore, it will not result in dialing the line. If the
DNS server does not have the appropriate entry in the cache , it must forward the
request to another server on the Internet. The packet is forwarded to the Internet by
the local DNS client that is run at the WinRoute host. This packet cannot be held and
it will not cause dialing of the line. Therefore, the DNS request cannot be answered
and the traffic cannot continue.
For these reasons, WinRoute DNS Forwarder enables automatic dialing (if the DNS
server cannot respond to the request itself). This function is dependent on demand
dial — if the demand dial function is disabled, the DNS Forwarder will not dial the
line.
Note: If the DNS server is located on another host within the local network or clients
within the local network use an Internet DNS server, then the limitation is irrelevant
and the dialing will be available. If clients’ DNS server is located on the Internet, the
line will be dialed upon a client’s DNS query. If a local DNS server is used, the line
will be dialed upon a query sent by this server to the Internet (the default gateway
of the host where the DNS server is running must be set to the IP address of the
WinRoute host).
3. It can be easily understood through the last point that if the DNS server is to be
running at the WinRoute host, it must be represented by DNS Forwarder because it
can dial the line if necessary.
If there is a domain that is based on Active Directory in the Windows 2000 local net-
work, Microsoft DNS server must be used as communication with Active Directory