TechTalk: LAN Bridged Frames

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Q: We're having trouble configuring the connection between our two LANs. We're using a bridge to connect them. IBM has told us that we have "bridged framing size conflicts." What does this mean?

-Jeff Whitney

A: If a data frame is being transmitted to a station that resides on a different LAN, the frame is copied and retransmitted by a bridge/router. If the bridge/router isn't set up to support a frame size as large as that configured on the AS/400's communication line description, the frame will be discarded. The frame may also be discarded if the network does not support the frame size specified on the AS/400 communication line description used for a bridged frame relay configuration.

When running SNA in a token-ring environment, the system that originated the connection is informed of the frame size supported by the bridge/router and will automatically retry with that frame size. The CPF5908 message "Controller contacted..." sent to the QSYSOPR message queue will inform you of the effective maximum frame size for that connection.

If you are unable to configure the bridge/router to support larger frame sizes, you may need to adjust one of the following parameters to a value acceptable to the bridge/router in question.

* MAXFRAME?controller description parameter

* SSAP?line description parameter

* MAXFRAME?line description parameter (except Ethernet lines)

Keep in mind that larger values for these parameters may yield better performance.

-Kris Neely