Active scanning with enabled filter causes sending SCAN_REQ to every advertiser

[Kedlov]

Hi everybody,

I saw topics with similar naming like mine, but none of them actually describes my issue.

I develop some simple scanner and advertiser solution.

On advertiser side I've implemented ADV_SCAN_IND and SCAN_RSP packets. In ADV_SCAN_IND I've put some custom UUID to easy find my advertisers if there is many BLE devices around. In SCAN_RSP there is my custom data (0xFF - manufacture data).

On scanner side I've turned on active scanning with turned on filtering by UUID (same solution as it is in some sample code).

I've observed some strange behaviors:

1. Scanner side invokes "filter match" callback when ADV_SCAN_IND packet is received with correct UUID...and then "filter no match" callback when SCAN_RSP packet is received which contains my own custom data. To avoid this would I need to put UUID data also in SCAN_RSP packet? Or maybe some scanner configuration should be changed?

2. Even if in ADV_SCAN_IND there is no matching data (no UUID field), my scanner sends SCAN_REQ anyway...I think is pointless to waste time for sending SCAN_REQ for different advertisers.

- Can I configure my scanner in a way that it will send SCAN_REQ only to devices which contain correct data in first ADV_SCAN_IND?

- Can I avoid invoking "no filter match" callback for devices which have correct data only in ADV_SCAN_IND packets?

Best regards,

Adam

[Kedlov]

Hi,

Edvin said:

So if you plan to not bond the devices, how do you plan to transfer the IRK?

During post production process when I will have all around 32 or 64 peripherals on big PCB "matrix" and program it with UART/SPI through test pads and spring needles. Also bond information would need to be stored in central, but central should handle hundreds of peripherals so CONFIG_BT_KEYS_OVERWRITE_OLDEST would need to be enabled. If I would perform paring+bonding with every peripheral it will be time consuming, it's not only about the time to exchange data and create keys, but also to check every peripheral if the bond has been created. Another option would be to switch roles and advertise IRK key from central to all nodes in close area for few seconds, but there will be no confirmation from every node that it received IRK key.

Edvin said:

And why do you need to change addresses in the first place?

I think I was misunderstood - I don't need to change address, I've just observed on nRF sniffer that scanner address has changed few times. Maybe at happened only for scanner on mobile phone, but it would be also good for my scanner based on nRF528xx chip to change from time to time.

Edvin said:

To put you on track, you can use the configuration CONFIG_BT_PRIVACY=y to enable address switching.

I already have it turned on, anyway thanks for that hint

Edvin said:

Not between every advertising packet. If you are not connecting, I don't see what sort of security this adds.

Sure, I don't want to change address of peripherals, I didn't write anything like that :) I only wanted to send scan requests only to my peripherals (based on advertising data in first packet) and from peripherals side I want to send scan response only to my central. It's not about security, I just want to reduce cases when somebody will come with smartphone in range of central and peripherals, will try to act as central/peripheral and will disrupt my data flow. Of course if somebody will come with SDR, then only encrypted connection may help but storing keys for several hundreds of nodes may take a "little" of flash memory ;)

Edvin said:

int bt_id_create(bt_addr_le_t *addr, uint8_t *irk) from id.c. I think you can use this, and set the IRK to whatever you like (look at the declaration of bt_id_create() in bluetooth.h.

Great! Probably I will use it or something similar for central to get my own IRK key and distribute it to peripherals.

Anyway I think now everything is clear and I will somehow handle it in the code.

Thank you for help and I think I can close this case :)