The E.N.a.A. (Ed Needs an A)
Network Bridge
An ELE 408 / URI / Miller Brewing
Company Presentation
What is a network bridge?
• The key component of a multi - tiered
network architecture.
• Connects different Local Area
Networks (LANs ) together…..
…… while at the same time keeping
each LAN independent of the other
one.
Multi - Tier Architecture
Bridge
Hub
Hub
LAN 1 LAN 2
What does this mean?
• Overall, makes the LAN “better” by extending
the “Collision Domain”:
• Employs CSMA / CD
• Distance
• Number of Users
• LAN can use its full bandwidth
• Less Collisions
• All of this is accomplished because the bridge
isolates each LAN and is smart enough to tell
where to route a packet.
The Bridge Table
• Table held in RAM that is dynamically
updated.
• Holds all LAN addresses that have used the
bridge, along with which interface they used.
Interface 1 Interface 2
12-34-56-78-9A-BC
1 12-34-56-78-9A-BC
The Program
• Initialize both Boards in Receive Mode
• When a packet is received through the
ethernet port, the data is stored in memory.
• If the source address is not in the table, it is
added.
• If the destination address is not in the table,
the packet is sent to the UART transmit
buffer, and the transmitter is enabled.
More of the program….
• The packet is stored in memory, if the
source address is not in the bridge table, it is
added.
• The packet is then transferred to the
ethernet transmit buffer and passed to the
connected LAN.
One problem….
• The $%##%#%#$#%%^^-freakin-
$#%^&#@$%%- son of a - $%^#@$% ^
ETHERNET CONTROLLER!
• Possibly over 2 million registers to program
• Difficult to strip away headers from different
network layers
The (temporary) solution
• Packets will enter the bridge through the
terminal.
• Data will be typed in, header information
will be stored in memory and then
combined with the data to form a simulated
packet.
Other problems…...
• Scalability
• Bandwidth Bottleneck
Future implementations...
• Security features
• LAN address filtering
• Interface firewall
• Trusts
• Implement Spanning Tree Protocol to
facilitate expansion
Conclusion
• Effective way to bridge to LANs
• Cheap to build, easy (in theory) to
implement
• Mass production easy due to the fact that its
highly software driven
• Ed definitely deserves an A