User's Manual

30
Network Planning
3
the same segment (that is, the local network or remote network) as the source
address.
Routing
When Router Mode is selected, the Gateway forwards incoming IP packets and
uses RIP or RIP-2 for routing path management if enabled. The router supports both
static routing and dynamic routing.
• Static routing requires routing information to be stored in the router, either manually
or when a connection is set up, using the default gateway designated by your ISP.
• Dynamic routing uses a routing protocol to exchange routing information,
calculates routing tables, and responds to changes in the status or traffic on the
network.
Dynamic Routing Protocols - This router supports both RIP and RIP-2 dynamic
routing protocols. Routing Information Protocol (RIP) is the most widely used
method for dynamically maintaining routing tables in small to medium networks. RIP
uses a distance vector-based approach to routing. Routes are chosen to minimize
the distance vector, or hop count, which serves as a rough estimate of transmission
cost. Each router broadcasts an advertisement every 30 seconds, together with any
updates to its routing table. This allows all routers on the network to build consistent
tables of next hop links which lead to relevant subnets.
RIP-2 is a compatible upgrade to RIP. However, RIP-2 adds useful capabilities for
plain text authentication, multiple independent RIP domains, variable length subnet
masks, and multicast transmissions for route advertising (see RFC 1388).
Note: If the destination route is not found in the routing table, the router simply transmits
the packet to a default router for resolution.
Network Applications
The Gateway 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 Gateway can be configured to act as a transparent bridge between a local PC
or LAN attached to the Ethernet ports and a remote site across the WAN VDSL link.
Bridging can be used to make two separate networks appear as if they were part of
the same physical network. When data enters an Ethernet port on the Gateway, its
destination MAC address (physical address) is checked in the address database to
see if it is located in the local segment (that is, attached to one of the Gateway’s
Ethernet ports). If the destination address is not found, the frame is forwarded to the
VDSL port and queued for output. If the destination address is found to belong to
one of the local ports, the frame is dropped or “filtered.” However, note that
broadcast or multicast frames are always broadcast across the VDSL link.