NAME¶
pfsync —
packet filter state table
logging interface
SYNOPSIS¶
device pfsync
DESCRIPTION¶
The
pfsync interface is a pseudo-device which exposes certain
changes to the state table used by
pf(4). If configured with
a physical synchronisation interface,
pfsync will send state
changes out on that interface using IP multicast, and insert state changes
received on that interface from other systems into the state table.
By default, all local changes to the state table are exposed via
pfsync. However, state changes from packets received by
pfsync over the network are not rebroadcast. States created
by a rule marked with the
no-sync keyword are omitted
from the
pfsync interface (see
pf.conf(5)
for details).
The
pfsync interface will attempt to collapse multiple updates
of the same state into one message where possible. The maximum number of times
this can be done before the update is sent out is controlled by the
maxupd parameter to ifconfig (see
ifconfig(8) and the example below for more details).
Each packet retrieved on this interface has a header associated with it of
length
PFSYNC_HDRLEN
. The header indicates the version
of the protocol, address family, action taken on the following states, and the
number of state table entries attached in this packet. This structure is
defined in ⟨
net/if_pfsync.h⟩ as:
struct pfsync_header {
u_int8_t version;
u_int8_t af;
u_int8_t action;
u_int8_t count;
};
NETWORK SYNCHRONISATION¶
States can be synchronised between two or more firewalls using this interface,
by specifying a synchronisation interface using
ifconfig(8).
For example, the following command sets fxp0 as the synchronisation interface:
# ifconfig pfsync0 syncdev fxp0
It is important that the underlying synchronisation interface is up and has an
IP address assigned.
By default, state change messages are sent out on the synchronisation interface
using IP multicast packets. The protocol is IP protocol 240, PFSYNC, and the
multicast group used is 224.0.0.240. When a peer address is specified using
the
syncpeer keyword, the peer address is used as a
destination for the pfsync traffic, and the traffic can then be protected
using
ipsec(4). In such a configuration, the syncdev should
be set to the
enc(4) interface, as this is where the traffic
arrives when it is decapsulated, e.g.:
# ifconfig pfsync0 syncpeer 10.0.0.2 syncdev enc0
It is important that the pfsync traffic be well secured as there is no
authentication on the protocol and it would be trivial to spoof packets which
create states, bypassing the pf ruleset. Either run the pfsync protocol on a
trusted network - ideally a network dedicated to pfsync messages such as a
crossover cable between two firewalls, or specify a peer address and protect
the traffic with
ipsec(4).
For
pfsync to start its operation automatically at the system
boot time,
pfsync_enable and
pfsync_syncdev variables should be used in
rc.conf(5). It is not advisable to set up
pfsync with common network interface configuration variables
of
rc.conf(5) because
pfsync must start
after its
syncdev, which cannot be always ensured in the
latter case.
EXAMPLES¶
pfsync and
carp(4) can be used together to
provide automatic failover of a pair of firewalls configured in parallel. One
firewall handles all traffic - if it dies or is shut down, the second firewall
takes over automatically.
Both firewalls in this example have three
sis(4) interfaces.
sis0 is the external interface, on the 10.0.0.0/24 subnet; sis1 is the
internal interface, on the 192.168.0.0/24 subnet; and sis2 is the
pfsync interface, using the 192.168.254.0/24 subnet. A
crossover cable connects the two firewalls via their sis2 interfaces. On all
three interfaces, firewall A uses the .254 address, while firewall B uses
.253. The interfaces are configured as follows (firewall A unless otherwise
indicated):
Interfaces configuration in
/etc/rc.conf:
network_interfaces="lo0 sis0 sis1 sis2"
cloned_interfaces="carp0 carp1"
ifconfig_sis0="10.0.0.254/24"
ifconfig_sis1="192.168.0.254/24"
ifconfig_sis2="192.168.254.254/24"
ifconfig_carp0="vhid 1 pass foo 10.0.0.1/24"
ifconfig_carp1="vhid 2 pass bar 192.168.0.1/24"
pfsync_enable="YES"
pfsync_syncdev="sis2"
pf(4) must also be configured to allow
pfsync and
carp(4) traffic through. The
following should be added to the top of
/etc/pf.conf:
pass quick on { sis2 } proto pfsync
pass on { sis0 sis1 } proto carp
If it is preferable that one firewall handle the traffic, the
advskew on the backup firewall's
carp(4) interfaces should be set to something higher than
the primary's. For example, if firewall B is the backup, its carp1
configuration would look like this:
ifconfig_carp1="vhid 2 pass bar advskew 100 192.168.0.1/24"
The following must also be added to
/etc/sysctl.conf:
BUGS¶
Possibility to view state changes using
tcpdump(1) has not
been ported from
OpenBSD yet.
SEE ALSO¶
bpf(4),
carp(4),
ifconfig(8),
inet(4),
inet6(4),
ipsec(4),
netintro(4),
pf(4),
pf.conf(5),
protocols(5),
rc.conf(5) ifconfig(8),
ifstated(8),
tcpdump(8)
HISTORY¶
The
pfsync device first appeared in
OpenBSD
3.3. The
pfsync device was imported to
FreeBSD 5.3.