ADTRAN NetVanta 3000 User Manual

TECHNICAL SUPPORT NOTE
NetVanta 3000 Series Routers

Bridging (Point-to-Point & Multipoint)

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Introduction

Bridging is an OSI Model Layer 2 function. Bridges and switches are often talked about
interchangeably because both of these devices work at the Data Link Layer. Bridges are a step
above a network device called a hub. A hub operates at the Physical Layer, connecting one or
more network devices on the LAN, sharing bandwidth or acting as a termination point for multiple
network devices in a star topology. A bridge is a LAN (Local Bridge) or WAN (Remote Bridge)
device that interconnects network segments and uses the destination MAC address of each frame
of information to determine whether to pass the signal to the other network segment. Bridges can
be used to connect network segments of dissimilar media, extend the number of hosts allowed on
a single segment, or segment data traffic to reduce overall bandwidth usage.

A bridge keeps a forwarding table, which is a list of MAC (or Layer 2) addresses with their
associated interface. If the bridge does not have an entry for a destination address that comes
across, the packet is forwarded to all attached interfaces. All broadcast and multicast packets are
forwarded to all interfaces (flooded).

Care should be used in deciding when to use a bridge. In general, it is only wise to bridge data
that cannot be routed. The NetVanta 3000 Router can route IP while bridging all other protocols.

Local Bridge

Remote Bridge – Like the Net Vant as

☛

☛ Before You Begin

☛☛

Before configuring and testing a bridging application, verify that the point-to-point network
connection is installed and operational. All cables necessary for network connection installation

Bridging: NetVanta 3000 Series Routers

are provided with your NetVanta shipment. Obtain the correct IP Addresses for the Ethernet
interfaces from your network administrator before configuring this application. Generally, the
Ethernet interfaces on all units will need to be on the same subnet for bridging applications.
The first example details a simple point-to-point bridge configured using PPP as the WAN
protocol. The second example demonstrates the NetVanta router configuration for multipoint
bridging over frame relay.

Denver

T1

T1

Atlanta

TELCO

PPP Point-to-Point Bridging Example

Denver

T1

T1

Frame

T1

Frame Relay Multipoint Bridging example

Atlanta

Albany

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Bridging: NetVanta 3000 Series Routers

Configuring Point-to-Point Bridging

Log into the router via the craft port and enter the enable (privileged) mode by typing enable and
entering the password (if enable passwords are configured). Next, enter the global configuration
mode by typing config t . From the global configuration mode, enter the bridge command and
specify a bridge group number. (The valid range for a bridge group number is 1 through 255.)
Specify the protocol for the bridge group at the end of the command. The bridging protocol must
match the protocol used on the remote NetVanta or compatible router. In this example, the bridge
group 1 is being configured to use the IEEE bridging protocol.

Router(config)# bridge 1 protocol ieee

Bridge Command Example Syntax

Configuring Bridge Interfaces

1. All interfaces that are involved in the bridging process (WAN & LAN) must belong to the
appropriate bridge group. (Refer to the previous section, Configuring Point-to-Point Bridging,
for details on creating a bridge group.) Include an interface in the bridge group by using the
bridge command while in the interface configuration mode. To enter the interface
configuration mode, enter interface <interface type interface slot/port> from the global
configuration prompt. For example, interface eth 0/1.

Router(config-eth 0/1)# bridge-group 1
SPANNING TREE: Using default Address 00:A0:C8:08:CA:EE.
Please ensure this is unique.

Assigning Ethernet 0/1 Interface to Bridge Group 1

2. The bridge command must be used on the sub-interface to configure bridging interfaces on
WAN ports implementing Frame Relay signaling. Enter the sub-interface configuration mode
by typing interface frame relay X.Y from the global configuration mode prompt (where X is the
frame relay interface number and Y is the sub-interface – usually the DLCI – number). For
example, interface frame-relay 1.16. For PPP, the virtual interface must be included in the
bridge group (e.g., interface ppp 1).

Router(config-fr 1.16)# bridge-group 1
SPANNING TREE: Using default Address 00:A0:C8:08:CA:EE.
Please ensure this is unique.

Assigning a Frame Relay Sub-Interface to Bridge Group 1

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