[ask]centos guest iptables.why like this?

[El_makong]

i want to ask about the iptables on centos guest.
why every time i create new CT, it always contain this line?

# Generated by iptables-save v1.4.7 on Mon Jan 20 00:13:28 2014*nat
:PREROUTING ACCEPT [3:405]
:POSTROUTING ACCEPT [1:84]
:OUTPUT ACCEPT [1:84]
COMMIT
# Completed on Mon Jan 20 00:13:28 2014
# Generated by iptables-save v1.4.7 on Mon Jan 20 00:13:28 2014
*mangle
:PREROUTING ACCEPT [8:805]
:INPUT ACCEPT [8:805]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [7:672]
:POSTROUTING ACCEPT [7:672]
COMMIT

then after that, its the iptables i set.
how to hide it?
if its cleared(so iptables only have the *filter one), what will happen?
if its cleared,and nothing happen or causing any error, how to disable it from adding automatically when creating CT?
configuration:
eth0(centos) bridged with vmbr0 on the host