User's Manual

31
Network Applications
3
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
512 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.
Figure 3-1 Transparent Bridged Network
Accessing the Internet
To access the Internet, which uses the TCP/IP protocol exclusively, the Gateway
should be configured to function as a router. One side of the connection is formed by
the ports attached to a local 10/100Mbps Ethernet LAN (or directly to a host PC with
an Ethernet adapter), while the other is the Layer 3 transport service running on the
VDSL port. When the Gateway receives an IP packet over the WAN interface, the
destination address is checked in the routing table. If the address is found, the
packet is forwarded to the associated interface/port. Otherwise, the packet is
dropped. When it receives an IP packet over the LAN interface, it also checks the
routing table. If the source and destination address are in the same subnet, no
action is required because the packet can be passed on at Layer 2. If the address is
found to be in a remote subnet, the packet is forwarded to the next hop router.
Otherwise, if not found in the address table, it is sent to the default gateway
designated by the ISP.
The routing table contains information on which networks are accessible through
each interface. It can be dynamically updated using the Routing Information Protocol
(RIP), or statically configured through the web management interface. If you use
RIP, the router will exchange information with neighboring routers to learn the best
routes to remote networks, and advertise the networks for which it can provide the
best route.
When the system is powered on, the Gateway builds its own routing
database
according to previous static routing entries, and/or collects
routing information from
adjacent routers through RIP or RIP-2
protocol. RIP (that is, RIP-1) is generally
supported by all routers, but RIP-2 carries
more information which allows the router to
10/100Mbps Ethernet LAN
ECG9210-04
ECG9210-04
VDSL
10/100Mbps Ethernet LAN