f_cnt : what does it go up to?

[Anna Black]

It's 'frame count' right?

It starts at 1, but how big can it get? And what happens when it reaches that max?

[Mengting]

Hi, Anna,

Great questions! Here’s a simple explanation:

1. What is f_cnt?

It’s the Frame Counter in LoRaWAN messages.

Purpose: Prevents security risks (like replay attacks) by counting every data frame sent from your device.

2. Maximum value?

The length of the f_cnt field is 2 bytes (16 bits), so its value range is from 0 to 65535 (that is, from 0x0000 to 0xFFFF).

3. At maximum: What happens?

Resets to 0: The counter restarts from 0 (called "rollover").

Network handling: Servers automatically accept this reset.

No data loss: Your device keeps working normally.

Best Regards
Ting
Technical Support Engineer

 

Dragino Technology Co., Limited

Room 202, Block B, BCT Incubation Bases (BaoChengTai),  No.8 CaiYunRoad

LongCheng Street, LongGang District ; Shenzhen 518101,China

Direct: +86 755 86610829 |Fax: +86 755 86647123

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发件人：Anna Black <annabl...@gmail.com>

发送时间：2025年6月3日(周二) 10:10

收件人："Dragino-user"<dragin...@googlegroups.com>

主　题：f_cnt : what does it go up to?

It's 'frame count' right?

It starts at 1, but how big can it get? And what happens when it reaches that max?

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