User`s guide

1-16
Introduction
1.7.1 Transparent Bridging
Transparent or spanning tree bridging requires no initial
programming. After being installed on the network, bridges
“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.
1.7.2 Source Route Translational Bridging
Source Route Translational Bridging (SRTB) allows the ATX to strip
and cache routing information for source route frames. Routing
information (RIF) is used in source route networks to indicate the
path a frame has taken through the network. This feature will
enable the ATX to switch between source route only networks like
Token Ring and transparent networks like Ethernet and FDDI. RIF
is not supported on Ethernet networks and is seldom used on
FDDI networks. In order to merge source routed Token Ring
networks with transparent Ethernet and FDDI networks the ATX
must strip the RIF when communicating to Ethernet or FDDI and
insert the RIF when communicating back to Token Ring. SRTB on
the ATX contains the following features:
• A redundant/load sharing source route network is NOT
supported when SRTB (RIF caching) is enabled. A
redundant/load sharing source route network could have
multiple paths to the transparent network and cause the