--- name: "ipsec_set_policy" section: "3" platform: "linux" package: "racoon" version: "1:0.8.2+20140711-8+deb9u1" release: "Debian 9 (Stretch)" platforms: ["linux", "freebsd", "macos"] url: "https://new.carta.tech/ipsec_set_policy" --- # ipsec\_set\_policy(3) manipulate IPsec policy specification structure from human-readable policy string ## NAME **ipsec\_set\_policy**, **ipsec\_get\_policylen**, **ipsec\_dump\_policy** – manipulate IPsec policy specification structure from human-readable policy string ## LIBRARY library “libipsec” ## SYNOPSIS **#include \** *char \**\ **ipsec\_set\_policy**(*char \*policy*, *int len*); *int*\ **ipsec\_get\_policylen**(*char \*buf*); *char \**\ **ipsec\_dump\_policy**(*char \*buf*, *char \*delim*); ## DESCRIPTION **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)](/free/3.md)'d by the caller. You can get the length of the generated buffer with **ipsec\_get\_policylen**() (i.e. for calling [setsockopt(2)](/setsockopt/2.md)). **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)](/free/3.md) 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)](/setkey/8.md). - *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)](/sysctl/8.md), such as net.inet.ipsec.esp\_trans\_deflev. See [ipsec(4)](/ipsec/4.md) 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)](/setkey/8.md). In the specification of [setkey(8)](/setkey/8.md), both entrust and bypass are not used. Refer to [setkey(8)](/setkey/8.md) 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 ``` ## RETURN VALUES **ipsec\_set\_policy**() returns a pointer to the allocated buffer with the policy specification if successful; otherwise a NULL pointer is returned. **ipsec\_get\_policylen**() returns a positive value (meaning the buffer size) on success, and a negative value on errors. **ipsec\_dump\_policy**() returns a pointer to a dynamically allocated region on success, and NULL on errors. ## SEE ALSO [ipsec\_strerror(3)](/ipsec_strerror/3.md), [ipsec(4)](/ipsec/4.md), [setkey(8)](/setkey/8.md) ## HISTORY The functions first appeared in the WIDE/KAME IPv6 protocol stack kit.