<s>
pfsync	B-Protocol
is	O
a	O
computer	O
protocol	O
used	O
to	O
synchronise	O
firewall	O
states	O
between	O
machines	O
running	O
Packet	B-Protocol
Filter	I-Protocol
(	O
PF	B-Protocol
)	O
for	O
high	O
availability	O
.	O
</s>
<s>
It	O
is	O
used	O
along	O
with	O
CARP	B-Application
to	O
make	O
sure	O
a	O
backup	O
firewall	O
has	O
the	O
same	O
information	O
as	O
the	O
main	O
firewall	O
.	O
</s>
