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pfsync - packet filter state table logging interface
By default, all local changes to the state table are exposed via . However, state changes from packets received by over the network are not rebroadcast. States created by a rule marked with the no-sync keyword are omitted from the interface (see pf.conf5 for details).
The 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 Aq Pa net/if_pfsync.h as:
struct pfsync_header {
u_int8_t version;
u_int8_t af;
u_int8_t action;
u_int8_t count;
};
# 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 to start its operation automatically at the system boot time, pfsync_enable and pfsync_syncdev variables should be used in rc.conf5. It is not advisable to set up with common network interface configuration variables of rc.conf5 because must start after its syncdev which cannot be always ensured in the latter case.
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 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 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
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