Specifications

Chapter 1. Router Concepts 19
¥ Routing takes precedence over bridging; i.e., when routing is active, the router uses the packetÕs protocol
address information to route the packet.
¥ If the protocol is not supported, the router uses the MAC address information to forward the packet.
Routing and Bridging Controls
The router can be configured to perform general routing and bridging while allowing you to set specific controls.
¥ One remote router can be designated as the outbound default bridging destination. All outbound bridging
traffic with an unknown destination is sent to the default bridging destination.
¥ Bridging from specific remote routers can be controlled by enabling or disabling bridging from individual
remote routers.
¥ Routing is performed to all remote routers entered into the remote router database. All routing can be enabled
or disabled with a system-wide control.
Operation of the router is influenced by routing and bridging controls and filters set during router configuration as
well as automatic spoofing and filtering performed by the router. For example, general IP or IPX routing, and
routing or bridging from specific remote routers are controls set during the configuration process.
Spoofing and filtering, which minimize the number of packets that flow across the WAN, are performed
automatically by the router. For example, RIP routing packets and certain NetBEUI packets are spoofed even if
only bridging is enabled.
Bridge Filtering
You can control the flow of packets across the router using bridge filtering. Bridge filtering lets you ÒdenyÓ or
ÒallowÓ packets to cross the network based on position and hexadecimal content within the packet. This feature
lets you restrict or forward messages with a specified address, protocol, or data content. Common uses are to
prevent access to remote networks, control unauthorized access to the local network, and limit unnecessary traffic.
For example, it might be necessary to restrict remote access for specific users on the local network. In this case,
bridging filters are defined using the local MAC address for each user to be restricted. Each bridging filter is
specified as a ÒdenyÓ filter based on the MAC address and position of the address within the packet. Deny
filtering mode is then enabled to initiate bridge filtering. No packet with one of the MAC addresses can be bridged
across the router until the deny filtering mode is disabled.
Similarly, protocol filtering can be used to prevent a specific protocol from being bridged. In this case, the
protocol ID field in a packet is used to deny or allow a packet. You can also restrict, for example, the bridging of
specific broadcast packets.
For a further discussion of bridge filtering, see page 79.
Telephony Services
A Voice over DSL (VoDSL) router allows the delivery of both telephony (voice) and data services over a single
DSL line. It acts as an Integrated Access Device (IAD), residing on the customer premises and connecting to a
DSL circuit. As such, it serves as a circuit/packet gateway and provides standard telephone service as well as
Internet service via an Ethernet connection. Thus, the user has access to toll-quality telephone lines and
continuous, high-speed Internet and remote LAN services over a single copper loop.
Features provided in your VoDSL router may include: