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:
net.inet.carp.preempt=1
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.