System information

Troubleshooting Transparent Bridging Environments 20-425
Troubleshooting Transparent Bridging
• Flag—A one-byte field, of which only the first 2 bits are used. The topology change (TC) bit
signals a topology change. The topology change acknowledgment (TCA) bit is set to
acknowledge receipt of a configuration message with the TC bit set.
• Root ID—Identifies the root bridge by listing its 2-byte priority followed by its 6-byte ID.
• Root path cost—Contains the cost of the path from the bridge sending the configuration message
to the root bridge.
• Bridge ID—Identifies the priority and ID of the bridge sending the message.
• Port ID—Identifies the port from which the configuration message was sent. This field allows
loops created by multiply attached bridges to be detected and dealt with.
• Message age—Specifies the amount of time since the root sent the configuration message on
which the current configuration message is based.
• Maximum age—Indicates when the current configuration message should be deleted.
• Hello time—Provides the time period between root bridge configuration messages.
• Forward delay—Provides the length of time bridges should wait before transitioning to a new
state after a topology change. If a bridge transitions too soon, not all network links may be ready
to change their state, and loops can result.
Topological change messages consist of only 4 bytes. They include a protocol identifier field, which
contains the value 0; a version field, which contains the value 0; and a message type field, which
contains the value 128.
Troubleshooting Transparent Bridging
This section presents troubleshooting information for connectivity problems in transparent bridging
internetworks. It describes specific transparent bridging symptoms, the problems that are likely to
cause each symptom, and the solutions to those problems.
Note Problems associated with source-route bridging (SRB), translational bridging, and
source-route transparent (SRT) bridging are addressed in Chapter 10, “Troubleshooting IBM.”
The following sections describe the most common network problems in transparent bridged
networks:
• Transparent Bridging: No Connectivity
• Transparent Bridging: Sessions Terminate Unexpectedly
• Transparent Bridging: Looping and Broadcast Storms Occur
Transparent Bridging: No Connectivity
Symptom: Client cannot connect to hosts across a transparently bridged network.
Table 20-1 outlines the problems that might cause this symptom and describes solutions to those
problems.
Table 20-1 Transparent Bridging: No Connectivity