
ET100 LAN-WAN Bridge
7
Theory of Operation
A bridge is used to connect networks locally or remotely such that they
appear to the user to be the same network. An Ethernet LAN bridge will
connect two LAN segments at the Data Link Layer (ISO Layer 2). At
this layer, the MAC (Media Access Control) addresses, are used for low
level addressing to send information to devices. The bridge builds
tables of MAC addresses for each network segment based on the source
and destination addresses of the packets it receives and forwards, then
filters the traffic not destined for the remote network.
The Ethernet-WAN bridge will connect two remote Ethernet networks
over bit stream interfaces such as that of modems or DSU/CSUs. One
method to do this is to use HDLC, an international standard set by the
ISO, a set of protocols for carrying data over a link with error and flow
control.
The ET100 utilizes both Ethernet Bridging and HDLC encapsulation
to provide a connection between LANs over bit stream architectures.
The LAN side of the ET100 receives an Ethernet packet and examines
its destination MAC address. If it knows the MAC is on the local
network then it simply drops the packet. Otherwise, if it knows the
packet destination is on the remote side, or if it cannot be determined
because its MAC cannot be found in the table, then it forwards it.
During forwarding, the packet is processed for transmission across the
WAN link. Here is where the Ethernet packet in encapsulated in HDLC.
Comentarios a estos manuales