Kerio Tech KERIO WINROUTE FIREWALL 6 - Manual (Page 347)

25.5 Internet links dialed on demand
347
If WinRoute receives a packet from the local network, it will compare it with the system routing
table. If the packets goes out to the Internet, no record will be found, since there is no default
route in the routing table. Under usual circumstances, the packet would be dropped and
a control message informing about unavailability of the target would be sent to the sender. If
no default route is available, WinRoute holds the packet in the cache and dials the appropriate
line if the demand dial function is enabled. This creates an outgoing route in the routing table
via which the packet will be sent.
To avoid undesired dialing of the line, line dialing is allowed by certain packet types only.
The line can be dialed only by UDP or TCP packets with the SYN flag (connection attempts).
Demand dialing is disabled for Microsoft Networks services (sharing of files and printers, etc.).
Since this moment, the default route exists and other packets directed to the Internet will be
routed via a corresponding line. The line may be either disconnected manually or automati-
cally if idle for a certain time period. When the line is hung-up, the default route is removed
from the routing table. Any other packet directed to the Internet redials the line.
Note:
1. To ensure correct functionality of demand dialing there must be no default gateway set
at network adapters. If there is a default gateway at any interface, packets to the Inter-
net would be routed via this interface (no matter where it is actually connected to) and
WinRoute would not dial the line.
2. Only one link can be set for on-demand dialing in WinRoute. WinRoute does not enable
automatic selection of a line to be dialed.
3. Lines can be also dialed if this is defined by a static route in the routing table (refer to
chapter 18.1 ). If a static route via the dial-up is defined, the packet matching this route
will dial the line. This line will not be used as the default route — the Use default gateway
on remote network option in the dial-up definition will be ignored.
4. According to the factors that affect total time since receiving the request until the line
is dialed (i.e. line speed, time needed to dial the line, etc.) the client might consider
the destination server unavailable (if the timeout expires) before a successful connection
attempt. However, WinRoute always finishes dial attempts. In such cases, simply repeat
the request, i.e. with the Refresh button in your browser.
Technical Peculiarities and Limitations
Demand dialing has its peculiarities and limitations. The limitations should be considered
especially within designing and configuration of the network that will use WinRoute for con-
nection 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