L2CAP SMP通道创建时机咨询及BLE配对流程日志疑问

Your conjecture is exactly right—L2CAP channel 0x0006 for SMP is pre-established as part of the BLE connection setup, so you won’t see explicit L2CAP Connection Request/Response messages in your HCI logs.

Here’s why: #

• The Bluetooth Core Specification defines SMP’s Channel Identifier (CID) 0x0006 as a mandatory oriented channel that’s automatically created when a BLE link layer connection is formed. It’s part of the base connection handshake, not something negotiated via dynamic L2CAP signaling.
• L2CAP Connection Request/Response frames are only used for dynamic channels—like custom services that need extra oriented channels beyond the mandatory ones (ATT uses 0x0004, SMP uses 0x0006). These pre-defined channels don’t require explicit setup messages.
• Even when capturing initialization-phase logs, you won’t see these channel creation events because they’re handled internally by the BLE protocol stack below the HCI layer. Most commercial stacks don’t expose this low-level setup in standard HCI logging since it’s core to the connection process.

Quick Reference: #

Check Section 3.2.2 of the Bluetooth Core Specification (Vol 3, Part A) for explicit details on mandatory L2CAP channels for BLE, including SMP’s pre-allocated 0x0006 CID.

内容的提问来源于stack exchange，提问作者jiapeng.ye