ipsec_set_policy() generates an IPsec policy specification structure, namely
struct sadb_x_policy and/or
struct sadb_x_ipsecrequest from a human-readable policy specification. The policy specification must be given as a C string
policy and its length
len.
ipsec_set_policy() will return a buffer with the corresponding IPsec policy specification structure. The buffer is dynamically allocated, and must be
free(3)'d by the caller.
You can get the length of the generated buffer with
ipsec_get_policylen() (i.e. for calling
setsockopt(2)).
ipsec_dump_policy() converts an IPsec policy structure into human-readable form. Therefore,
ipsec_dump_policy() can be regarded as the inverse function to
ipsec_set_policy().
buf points to an IPsec policy structure,
struct sadb_x_policy.
delim is a delimiter string, which is usually a blank character. If you set
delim to
NULL, a single whitespace is assumed.
ipsec_dump_policy() returns a pointer to a dynamically allocated string. It is the caller's responsibility to
free(3) it.
policy is formatted as either of the following:
direction [priority specification] discard
direction must be
in,
out, or
fwd.
direction specifies in which direction the policy needs to be applied. The non-standard direction
fwd is substituted with
in on platforms which do not support forward policies.
priority specification is used to control the placement of the policy within the SPD. The policy position is determined by a signed integer where higher priorities indicate the policy is placed closer to the beginning of the list and lower priorities indicate the policy is placed closer to the end of the list. Policies with equal priorities are added at the end of the group of such policies.
Priority can only be specified when libipsec has been compiled against kernel headers that support policy priorities (Linux >= 2.6.6). It takes one of the following formats:
{priority,prio} offset
offset is an integer in the range -2147483647..214783648.
{priority,prio} base {+,-} offset
base is either
low (-1073741824),
def (0), or
high (1073741824).
offset is an unsigned integer. It can be up to 1073741824 for positive offsets, and up to 1073741823 for negative offsets.
The interpretation of policy priority in these functions and the kernel DOES differ. The relationship between the two can be described as p(kernel) = 0x80000000 - p(func)
With
discard policy, packets will be dropped if they match the policy.
direction [priority specification] entrust
entrust means to consult the SPD defined by
setkey(8).
direction [priority specification] bypass
bypass means to bypass the IPsec processing. (the packet will be transmitted in clear). This is for privileged sockets.
direction [priority specification] ipsec request ...
ipsec means that the matching packets are subject to IPsec processing.
ipsec can be followed by one or more
request strings, which are formatted as below:
protocol / mode / src - dst [/level]
protocol is either
ah,
esp, or
ipcomp.
mode is either
transport or
tunnel.
src and
dst specifies the IPsec endpoint.
src always means the “sending node” and
dst always means the “receiving node”. Therefore, when
direction is
in,
dst is this node and
src is the other node (peer). If
mode is
transport, Both
src and
dst can be omitted.
level must be set to one of the following:
default,
use,
require, or
unique.
default means that the kernel should consult the system default policy defined by
sysctl(8), such as
net.inet.ipsec.esp_trans_deflev. See
ipsec(4) regarding the system default.
use means that a relevant SA can be used when available, since the kernel may perform IPsec operation against packets when possible. In this case, packets can be transmitted in clear (when SA is not available), or encrypted (when SA is available).
require means that a relevant SA is required, since the kernel must perform IPsec operation against packets.
unique is the same as
require, but adds the restriction that the SA for outbound traffic is used only for this policy. You may need the identifier in order to relate the policy and the SA when you define the SA by manual keying. You can put the decimal number as the identifier after
unique like
unique:
number.
number must be between 1 and 32767 . If the
request string is kept unambiguous,
level and slash prior to
level can be omitted. However, it is encouraged to specify them explicitly to avoid unintended behavior. If
level is omitted, it will be interpreted as
default.
Note that there are slight differences to the specification of
setkey(8). In the specification of
setkey(8), both
entrust and
bypass are not used. Refer to
setkey(8) for details.
Here are several examples (long lines are wrapped for readability):
in discard
out ipsec esp/transport//require
in ipsec ah/transport//require
out ipsec esp/tunnel/10.1.1.2-10.1.1.1/use
in ipsec ipcomp/transport//use
esp/transport//use