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PFSYNC(4) Device Drivers Manual PFSYNC(4)
NAME
pfsync - packet filter state table logging interface
SYNOPSIS
pseudo-device pfsync
DESCRIPTION
The NetBSD version of PF is obsolete, and its use is strongly
discouraged. Use npf(7) instead.
The pfsync interface is a pseudo-device which exposes certain changes to
the state table used by pf(4). State changes can be viewed by invoking
tcpdump(8) on the pfsync interface. If configured with a physical
synchronisation interface, pfsync will also 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
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.
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) (it is not supported
at the moment on NetBSD due to the lack of any encapsulation pseudo-
device).
There is a one-to-one correspondence between packets seen by bpf(4) on
the pfsync interface, and packets sent out on the synchronisation
interface, i.e. a packet with 4 state deletion messages on pfsync means
that the same 4 deletions were sent out on the synchronisation interface.
However, the actual packet contents may differ as the messages sent over
the network are "compressed" where possible, containing only the
necessary information.
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):
/etc/ifconfig.sis0:
inet 10.0.0.254 255.255.255.0 NONE
/etc/ifconfig.sis1:
inet 192.168.0.254 255.255.255.0 NONE
/etc/ifconfig.sis2:
inet 192.168.254.254 255.255.255.0 NONE
/etc/ifconfig.carp0:
inet 10.0.0.1 255.255.255.0 10.0.0.255 vhid 1 pass foo
/etc/ifconfig.carp1:
inet 192.168.0.1 255.255.255.0 192.168.0.255 vhid 2 pass bar
/etc/ifconfig.pfsync0:
up 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
/etc/ifconfig.carp1 would look like this:
inet 192.168.0.1 255.255.255.0 192.168.0.255 vhid 2 pass bar \
advskew 100
The following must also be added to /etc/sysctl.conf:
net.inet.carp.preempt=1
SEE ALSO
bpf(4), carp(4), inet(4), inet6(4), ipsec(4), netintro(4), pf(4),
ifconfig.if(5), pf.conf(5), protocols(5), ifconfig(8), tcpdump(8)
HISTORY
The pfsync device first appeared in OpenBSD 3.3.
CAVEATS
pfsync is not available when using pf(4) as a kernel module.
NetBSD 10.99 August 17, 2018 NetBSD 10.99