Token Ring Frame Copy Errors

3Com C36460T, 86-0621-000 Token Ring Frame Copy Errors, Frame Copy Errors under LAN Net Manager

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.

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.

Table 12 3Com Bridge/Routers and Supported Features

	Source Route		Source Route
	Transparent		Transparent
Platform	Bridging	Routing	Gateway	Source Routing

NETBuilder II	Yes	Yes	Yes	Yes
SuperStack II NETBuilder	No	Yes	No	Yes
Token Ring

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 If you have previously conﬁgured your LAN Network Manager to use the

with NETBuilder II NETBuilder II system as a virtual ring, and you want to use it as a physical ring, you Systems must set your virtual ring number back to None.