3Com PathBuilder S200 Series, Owner'S Manual

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Bridging 39
T0008-16F Release 5.2M
Configuring the PathBuilder S200 Series Switch for Bridging Operation
Bridge Frame Handling
Introduction
This section summarizes how PathBuilder S200 series switches handle frames
during Source Route Bridge operation.
How Frame
Handling Works
Once a PathBuilder S200 series switch station connected to a Token Ring and is
operating normally, non-MAC frames are copied from the ring as they pass through
the bridge station only if they satisfy these requirements:
• The Routing Information Present bit must be set in the source MAC Address
of the frame.
• If the frame is non-broadcast, the local ring number, bridge number, and
remote ring number must match the bridge's stored values for these numbers,
and the routing field must have less than 7 to 14 LAN/bridge couplets
(depending on the configured maximum allowed).
• If the frame is single route broadcast and forwarding of single route broadcast
is enabled, then the Routing Information field must not contain the remote
ring number since the frame has already been on the forward ring. If single
route broadcast is disabled, the frame is not copied.
• If the frame is All Route Broadcast, then the Routing Information field must
not contain the remote ring number.
These rules apply to frames with either locally or universally administered addresses
and for frames with either individual or group addresses.
Broadcast Frame
Handling When the All Route Broadcast frame is received from the LAN and initiated by
another device on the LAN, it is sent to all remote bridges on all SVCs.
The single route broadcast frame is sent only to the remote bridge that is part of the
spanning tree. The specific route frame is sent to the remote bridge via the single
SVC that connects the bridges.
When received from the WAN, broadcast frames are sent to the Token Ring. They
are sent to the other SVCs for general or spanning tree distribution, as appropriate,
after the LAN port removes the frame from the local ring.
Routed Frame
Handling When a specifically routed frame is received from the WAN, it is sent to the Token
Ring if the next bridge listed in the Routing Information field does not correspond to
a bridge formed by a local SVC. Otherwise, it is forwarded to the proper SVC for
additional bridging without being sent to the LAN. This keeps transit traffic off rings
where it can be avoided.