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IBM Protocols and Services Notes 51
and route discovery are configured, bridge numbers must be unique for each
bridge/router on the same ring, and LLC2 is enabled on token ring ports.
Token Ring Frame Copy Errors
For transparent bridge or source route transparent configurations, token ring end
systems may generate a small number of MAC frame copy error reports when the
NETBuilder II bridge/router token ring interface is initializing or when the
bridge/router ages out a MAC address from its bridge table.
For the bridge/router to learn the MAC addresses of transparent end systems on
the token ring, it copies a packet with an unknown source address and sets the
address-recognized (A) and frame-copied (C) bits in the Frame Status (FS) field. A
problem occurs when the FS (A) and (C) bits have been set and the destination of
the frame is an end system on the local ring. The destination end system expects
the (A) and (C) bits to be zeros. When it receives a frame with these values already
set, it reports an error. The end system counts these errors and accumulates them
until the MAC layer Soft Error Report Timer period is reached; the default is two
seconds. A MAC Report Error packet is then sent to the Ring Error Monitor (REM)
Network Management entity.
A source route only configuration eliminates frame copy errors. Frame copy errors
do not occur in source route only environments when the NETBuilder
bridge/routers are configured properly. This is because the NETBuilder
bridge/router hardware filters source-routed packets based on the route
information field, not the MAC address. If the bridge/router is configured for
source route only, it never copies frames destined for a station on the local ring.
Frame copy errors can be eliminated by running in source-route-only mode.
Table 12 shows the features supported on the NETBuilder II and NETBuilder
SuperStack II token ring bridge/routers.
Frame Copy Errors under LAN Net Manager
Whenever LAN Net Manager is enabled, the token ring driver is set to N-way
bridging mode, which means the bridge/router copies all frames that match the
bridge number specified on the receiving port. If two NETBuilder bridge/routers
are connected to the same ring with the same bridge number, frame copy errors
will occur. To prevent this problem, do not configure two NETBuilder
bridge/routers with the same bridge number on the same ring.
LAN Network Manager
with NETBuilder II
Systems
If you have previously configured your LAN Network Manager to use the
NETBuilder II system as a virtual ring, and you want to use it as a physical ring, you
must set your virtual ring number back to None.
Table 12 3Com Bridge/Routers and Supported Features
Platform
Source Route
Transparent
Bridging
Routing
Source Route
Transparent
Gateway
Source Routing
NETBuilder II Yes Yes Yes Yes
SuperStack II NETBuilder
Token Ring
No Yes No Yes