Conditional sentence of the first two bits

Hello, maybe anyone know, how to compare first two/three bits of IP address in conditional sentence?
for e.g
I have an ip A:

A=`192.23.43.132`
#know i need to check if it is an ip starting by 192.23, so how to determine it by first bits?

#if [$A= '192.23....'] ???
then
echo "true"
else
echo "false"
fi