SNMP Version Detection

Hello,

 

I need to write a irule SNMP traps that balances between different pools depending on the version used

 

Capturing with wireshark I see that byte 5 of package SNMP is an integer with the protocol version ( binary 0 = v1, v2c 1 = 3 = 3 )

 

How i can read this byte?.

 

Regards.