ipsec(7P) Protocols ipsec(7P)NAMEipsec - Internet Protocol Security Architecture
DESCRIPTION
The IP Security Architecture (IPsec) provides protection for IP data‐
grams. The protection can include confidentiality, strong integrity of
the data, partial sequence integrity (replay protection), and data
authentication. IPsec is performed inside the IP processing, and it can
be applied with or without the knowledge of an Internet application.
IPsec applies to both IPv4 and IPv6. See ip(7P) and ip6(7P).
Protection Mechanisms
IPsec provides two mechanisms for protecting data. The Authentication
Header (AH) provides strong integrity, replay protection, and data
authentication. AH protects as much of the IP datagram as it can. AH
cannot protect fields that change nondeterministically between sender
and receiver.
The Encapsulating Security Payload (ESP) provides confidentiality over
what it encapsulates, as well as the services that AH provides, but
only over that which it encapsulates. ESP's authentication services are
optional, which allow ESP and AH to be used together on the same data‐
gram without redundancy.
Authentication and encryption algorithms are used for IPsec. Authenti‐
cation algorithms produce an integrity checksum value or "digest"based
on the data and a key. Encryption algorithms operate on data in units
of a "block size".
NAT Traversal
IPsec's ESP can also encapsulate itself in UDP if IKE (see in.iked(1M))
discovers a Network Address Translator (NAT) between two communicating
endpoints.
A UDP socket can be specified as a NAT-Traversal endpoint. See udp(7P)
for details.
Security Associations
AH and ESP use Security Associations (SA). SA's are entities that spec‐
ify security properties from one host to another. Two communicating
machines require two SAs (at a minimum) to communicate securely. How‐
ever, communicating machines that use multicast can share the same mul‐
ticast SA. SAs are managed through the pf_key(7P) interface. For IPv4,
automatic SA management is available through the Internet Key Exchange
(IKE), as implemented by in.iked(1M). A command-line front-end is
available by means of ipseckey(1M). An IPsec SA is identified by a
tuple of <AH or ESP, destination IP address, and SPI>. The Security
Parameters Index (SPI) is an arbitrary 32-bit value that is transmitted
on the wire with an AH or ESP packet. See ipsecah(7P) or ipsecesp(7P)
for an explanation about where the SPI falls in a protected packet.
Protection Policy and Enforcement Mechanisms
Mechanism and policy are separate. The policy for applying IPsec is
enforced on a system-wide or per-socket level. Configuring system-wide
policy and per-tunnel policy (see Transport Mode and Tunnel Mode sec‐
tions) is done via the ipsecconf(1M) command. Configuring per-socket
policy is discussed later in this section.
System-wide IPsec policy is applied to incoming and outgoing datagrams.
Some additional rules can be applied to outgoing datagrams because of
the additional data known by the system. Inbound datagrams can be
accepted or dropped. The decision to drop or accept an inbound datagram
is based on several criteria which sometimes overlap or conflict. Con‐
flict resolution is resolved by which rule is parsed first, with one
exception: if a policy entry states that traffic should bypass all
other policy, it is automatically be accepted. Outbound datagrams are
sent with or without protection. Protection may (or may not) indicate
specific algorithms. If policy normally would protect a datagram, it
can be bypassed either by an exception in system-wide policy or by
requesting a bypass in per-socket policy.
Intra-machine traffic policies are enforced, but actual security mecha‐
nisms are not applied. Instead, the outbound policy on an intra-machine
packet translates into an inbound packet with those mechanisms applied.
IPsec policy is enforced in the ip(7P) driver. Several ndd tunables for
/dev/ip affect policy enforcement, including:
icmp_accept_clear_messages If equal to 1 (the default), allow cer‐
tain cleartext icmp messages to bypass
policy. For ICMP echo requests
("ping"messages), protect the response
like the request. If zero, treat icmp
messages like other IP traffic.
igmp_accept_clear_messages If 1, allow inbound cleartext IGMP mes‐
sages to bypass IPsec policy.
pim_accept_clear_messages If 1, allow inbound cleartext PIM mes‐
sages to bypass IPsec policy.
ipsec_policy_log_interval IPsec logs policy failures and errors to
/var/adm/messages. To prevent syslog from
being overloaded, the IPsec kernel mod‐
ules limit the rate at which errors can
be logged. You can query/set ipsec_pol‐
icy_log_interval using ndd(1M). The value
is in milliseconds. Only one message can
be logged per interval.
Transport Mode and Tunnel Mode
If IPsec is used on a tunnel (see tun(7M)) Tunnel Mode IPsec can be
used to protect distinct flows within a tunnel or to cause packets that
do not match per-tunnel policy to drop. System-wide policy is always
Transport Mode. A tunnel can use Transport Mode IPsec or Tunnel Mode
IPsec.
Per-Socket Policy
The IP_SEC_OPT or IPV6_SEC_OPT socket option is used to set per-socket
IPsec policy. The structure used for an IP_SEC_OPT request is:
typedef struct ipsec_req {
uint_t ipsr_ah_req; /* AH request */
uint_t ipsr_esp_req; /* ESP request */
uint_t ipsr_self_encap_req; /* Self-Encap request */
uint8_t ipsr_auth_alg; /* Auth algs for AH */
uint8_t ipsr_esp_alg; /* Encr algs for ESP */
uint8_t ipsr_esp_auth_alg; /* Auth algs for ESP */
} ipsec_req_t;
The IPsec request has fields for both AH and ESP. Algorithms may or may
not be specified. The actual request for AH or ESP services can take
one of the following values:
IPSEC_PREF_NEVER Bypass all policy. Only the superuser may
request this service.
IPSEC_PREF_REQUIRED Regardless of other policy, require the use of
the IPsec service.
The following value can be logically ORed to an IPSEC_PREF_REQUIRED
value:
IPSEC_PREF_UNIQUE Regardless of other policy, enforce a unique SA
for traffic originating from this socket.
In the event IP options not normally encapsulated by ESP need to be,
the ipsec_self_encap_req is used to add an additional IP header outside
the original one. Algorithm values from <net/pfkeyv2.h> are as follows:
SADB_AALG_MD5HMAC Uses the MD5-HMAC (RFC 2403) algorithm for
authentication.
SADB_AALG_SHA1HMAC Uses the SHA1-HMAC (RFC 2404) algorithm for
authentication.
SADB_EALG_DESCBC Uses the DES (RFC 2405) algorithm for encryption.
SADB_EALG_3DESCBC Uses the Triple DES (RFC 2451) algorithm for
encryption.
SADB_EALG_BLOWFISH Uses the Blowfish (RFC 2451) algorithm for
encryption.
SADB_EALG_AES Uses the Advanced Encryption Standard algo‐
rithm for encryption.
An application should use either the getsockopt(3SOCKET) or the set‐
sockopt(3SOCKET) call to manipulate IPsec requests. For example:
#include <sys/socket.h>
#include <netinet/in.h>
#include <net/pfkeyv2.h> /* For SADB_*ALG_* */
/* .... socket setup skipped */
rc = setsockopt(s, IPPROTO_IP, IP_SEC_OPT,
(const char *)&ipsec_req, sizeof (ipsec_req_t));
SECURITY
While IPsec is an effective tool in securing network traffic, it will
not make security problems disappear. Security issues beyond the mecha‐
nisms that IPsec offers may be discussed in similar "Security" or
"Security Consideration" sections within individual reference manual
pages.
While a non-root user cannot bypass IPsec, a non-root user can set pol‐
icy to be different from the system-wide policy. For ways to prevent
this, consult the ndd(1M) variables in /dev/ip.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Evolving │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOin.iked(1M), ipsecconf(1M), ipseckey(1M), ndd(1M), getsockopt(3SOCKET),
setsockopt(3SOCKET), attributes(5), tun(7M), inet(7P), ip(7P), ip6(7P),
ipsecah(7P), ipsecesp(7P), pf_key(7P), udp(7P)
Kent, S., and Atkinson, R., RFC 2401, Security Architecture for the
Internet Protocol, The Internet Society, 1998.
Kent, S. and Atkinson, R., RFC 2406, IP Encapsulating Security Payload
(ESP), The Internet Society, 1998.
Madson, C., and Doraswamy, N., RFC 2405, The ESP DES-CBC Cipher Algo‐
rithm with Explicit IV, The Internet Society, 1998.
Madsen, C. and Glenn, R., RFC 2403, The Use of HMAC-MD5-96 within ESP
and AH, The Internet Society, 1998.
Madsen, C. and Glenn, R., RFC 2404, The Use of HMAC-SHA-1-96 within ESP
and AH, The Internet Society, 1998.
Pereira, R. and Adams, R., RFC 2451, The ESP CBC-Mode Cipher Algo‐
rithms, The Internet Society, 1998.
Huttunen, A., Swander, B., Volpe, V., DiBurro, L., Stenberg, M., RFC
3948, UDP Encapsulation of IPsec ESP Packets, The Internet Society,
2005.
SunOS 5.10 17 May 2011 ipsec(7P)
