Network Router User Manual

N ETWORK A PPLICATIONS
1-7
Network Applications
The Barricade can be configured as a bridge for making a transparent
connection to a remote site, or as a router for accessing the Internet. These
applications are briefly described in the following sections.
Accessing a Remote Site
The Barricade can be configured to act as a transparent bridge between a
local PC or LAN attached to the Ethernet port and a remote site across
the ADSL link. Bridging can be used to make two separate networks
appear as if they were part of the same physical network. When data enters
the Ethernet port, its destination MAC address (physical address) is
checked in the address database to see if it is located in the local segment
(i.e., attached to the Barricade’s Ethernet port). If the destination address is
not found, the frame is forwarded to the ADSL port and queued for
output. If the destination address is found to belong to the local port, the
frame is dropped or “filtered.” However, broadcast or multicast frames are
always broadcast across the ADSL link.
The source MAC address of each frame is recorded into the address
database only if it belongs to the local LAN segment. This information is
then used to make subsequent decisions on frame forwarding. The address
database can hold up to 128 unique MAC addresses. An entry in the
address database will be discarded only if it has not been accessed for a
period of time called the aging time. This is to ensure that correct
forwarding decisions can still be made when a node is moved to another
port, and to keep the table clean. The aging time has a default value of 10
minutes.
Note: Compared to routing, bridging generates more traffic for each network
protocol, and uses more CPU time and system memory. Therefore, you
should only bridge if you need to use protocols other than TCP/IP.