Need help ionterpreting Cacti speed value

[Rno]

Hello,
I'm trying to undesrtand exactly what are the correct value given by cacti on a interface speed.

For my example I take a port channel à o Cisco device.
It's made of 4 10Gbits link, so it's 40Gigabit, like ti's display on the interface sh int :
BW 40000000 Kbit/sec

On Cacti on my device the ifSpeed is done as: 4'294'967'295, so 4.2 Gigabit
The if HisghSpeed is 40'000, so i suggest something like 40'000 KiloBits

Why is that ?

why the if speed is only 4.29Giga ?

Thanks for your help