Default value of CONNTRACK_MAX
On i386 architecture, CONNTRACK_MAX = RAMSIZE (in bytes) / 16384 = RAMSIZE (in MegaBytes) * 64. So for example, a 32 bits PC with 512MB of RAM can handle 512*1024^2/16384 = 512*64 = 32768 simultaneous netfilter connections by default.
But the real formula is:
CONNTRACK_MAX = RAMSIZE (in bytes) / 16384 / (x / 32) where x is the number of bits in a pointer (for example, 32 or 64 bits)
Please note that:
default CONNTRACK_MAX value will not be inferior to 128
for systems with more than 1GB of RAM, default CONNTRACK_MAX value is limited to 65536 (but can of course be set to more manually).