Cabletron Systems 3T02-04 Manual De Usuario

Appendix B: Bridging Methods

Transparent or spanning tree bridging requires no initial programming. 
After being installed on the network, they “learn” and remember the 
location of the attached devices by reading the source addresses of 
incoming packets. Then they place the source address and port 
information in a lookup table.

When a packet comes into a port, the bridge reads the destination address 
and attempts to find the location of the destination node using its lookup 
table. If the address is in the table, the bridge simply re-transmits the 
packet out of the appropriate port. If the address is not found in the table 
the bridge re-transmits the packet out of all the ports except the source 
port.

Transparent or spanning tree bridges also usually provide some packet 
filtering capabilities. On some networks it is desirable to prevent certain 
stations from accessing other segments. The ATX uses this bridging 
method.

a. source address is not learned

SRT

0

spanning tree

block

spanning tree

1

source route

source route

spanning tree

a

SR

0

block

block

block

1

source route

block

block

TST

0

spanning tree

block

spanning tree

1

spanning tree

a

block

spanning tree

a