ipsec.conf - IPsec configuration and connections

The optional ipsec.conf file specifies most configuration and control information for the Openswan IPsec subsystem. (The major exception is secrets for authentication; see ipsec.secrets(5).) Its contents are not security-sensitive unless manual keying is being done for more than just testing, in which case the encryption/authentication keys in the descriptions for the manually-keyed connections are very sensitive (and those connection descriptions are probably best kept in a separate file, via the include facility described below).

The file is a text file, consisting of one or more sections. White space followed by # followed by anything to the end of the line is a comment and is ignored, as are empty lines which are not within a section.

A line which contains include and a file name, separated by white space, is replaced by the contents of that file, preceded and followed by empty lines. If the file name is not a full pathname, it is considered to be relative to the directory containing the including file. Such inclusions can be nested. Only a single filename may be supplied, and it may not contain white space, but it may include shell wildcards (see sh(1)); for example:

include ipsec.*.conf

The intention of the include facility is mostly to permit keeping information on connections, or sets of connections, separate from the main configuration file. This permits such connection descriptions to be changed, copied to the other security gateways involved, etc., without having to constantly extract them from the configuration file and then insert them back into it. Note also the also and alsoflip parameters (described below) which permit splitting a single logical section (e.g. a connection description) into several actual sections.

The first significant line of the file must specify the version of this specification that it conforms to:

version 2

A section begins with a line of the form:

type name

where type indicates what type of section follows, and name is an arbitrary name which distinguishes the section from others of the same type. (Names must start with a letter and may contain only letters, digits, periods, underscores, and hyphens.) All subsequent non-empty lines which begin with white space are part of the section; comments within a section must begin with white space too. There may be only one section of a given type with a given name.

Lines within the section are generally of the form

parameter=value

(note the mandatory preceding white space). There can be white space on either side of the =. Parameter names follow the same syntax as section names, and are specific to a section type. Unless otherwise explicitly specified, no parameter name may appear more than once in a section.

An empty value stands for the system default value (if any) of the parameter, i.e. it is roughly equivalent to omitting the parameter line entirely. A value may contain white space only if the entire value is enclosed in double quotes ("); a value cannot itself contain a double quote, nor may it be continued across more than one line.

Numeric values are specified to be either an ``integer'' (a sequence of digits) or a ``decimal number'' (sequence of digits optionally followed by `.' and another sequence of digits).

There is currently one parameter which is available in any type of section:

also

the value is a section name; the parameters of that section are appended to this section, as if they had been written as part of it. The specified section must exist, must follow the current one, and must have the same section type. (Nesting is permitted, and there may be more than one also in a single section, although it is forbidden to append the same section more than once.) This allows, for example, keeping the encryption keys for a connection in a separate file from the rest of the description, by using both an also parameter and an include line. (Caution, see BUGS below for some restrictions.)

alsoflip

can be used in a conn section. It acts like an also that flips the referenced section's entries left-for-right.

Parameter names beginning with x- (or X-, or x_, or X_) are reserved for user extensions and will never be assigned meanings by IPsec. Parameters with such names must still observe the syntax rules (limits on characters used in the name; no white space in a non-quoted value; no newlines or double quotes within the value). All other as-yet-unused parameter names are reserved for future IPsec improvements.

A section with name %default specifies defaults for sections of the same type. For each parameter in it, any section of that type which does not have a parameter of the same name gets a copy of the one from the %default section. There may be multiple %default sections of a given type, but only one default may be supplied for any specific parameter name, and all %default sections of a given type must precede all non-c %default sections of that type. %default sections may not contain also or alsoflip parameters.

Currently there are two types of section: a config section specifies general configuration information for IPsec, while a conn section specifies an IPsec connection.

A conn section contains a connection specification, defining a network connection to be made using IPsec. The name given is arbitrary, and is used to identify the connection to ipsec_auto(8) and ipsec_manual(8). Here's a simple example:

conn snt
	left=10.11.11.1
	leftsubnet=10.0.1.0/24
	leftnexthop=172.16.55.66
	right=192.168.22.1
	rightsubnet=10.0.2.0/24
	rightnexthop=172.16.88.99
	keyingtries=%forever

A note on terminology... In automatic keying, there are two kinds of communications going on: transmission of user IP packets, and gateway-to-gateway negotiations for keying, rekeying, and general control. The data path (a set of ``IPsec SAs'') used for user packets is herein referred to as the ``connection''; the path used for negotiations (built with ``ISAKMP SAs'') is referred to as the ``keying channel''.

To avoid trivial editing of the configuration file to suit it to each system involved in a connection, connection specifications are written in terms of left and right participants, rather than in terms of local and remote. Which participant is considered left or right is arbitrary; IPsec figures out which one it is being run on based on internal information. This permits using identical connection specifications on both ends. There are cases where there is no symmetry; a good convention is to use left for the local side and right for the remote side (the first letters are a good mnemonic).

Many of the parameters relate to one participant or the other; only the ones for left are listed here, but every parameter whose name begins with left has a right counterpart, whose description is the same but with left and right reversed.

Parameters are optional unless marked ``(required)''; a parameter required for manual keying need not be included for a connection which will use only automatic keying, and vice versa.

CONN PARAMETERS: GENERAL

CONN PARAMETERS: AUTOMATIC KEYING

CONN PARAMETERS: MANUAL KEYING

At present, the only config section known to the IPsec software is the one named setup, which contains information used when the software is being started (see ipsec_setup(8)). Here's an example:

config setup
	interfaces="ipsec0=eth1 ipsec1=ppp0"
	klipsdebug=none
	plutodebug=all
	manualstart=

Parameters are optional unless marked ``(required)''.

The currently-accepted parameter names in a config setup section are:

myid

the identity to be used for %myid. %myid is used in the implicit policy group conns and can be used as an identity in explicit conns. If unspecified, %myid is set to the IP address in %defaultroute (if that is supported by a TXT record in its reverse domain), or otherwise the system's hostname (if that is supported by a TXT record in its forward domain), or otherwise it is undefined. An explicit value generally starts with ``@''.

interfaces

virtual and physical interfaces for IPsec to use: a single virtual=physical pair, a (quoted!) list of pairs separated by white space, or %none. One of the pairs may be written as %defaultroute, which means: find the interface d that the default route points to, and then act as if the value was ``ipsec0=d''. %defaultroute is the default; %none must be used to denote no interfaces. If %defaultroute is used (implicitly or explicitly) information about the default route and its interface is noted for use by ipsec_manual(8) and ipsec_auto(8).)

forwardcontrol

whether setup should turn IP forwarding on (if it's not already on) as IPsec is started, and turn it off again (if it was off) as IPsec is stopped; acceptable values are yes and (the default) no. For this to have full effect, forwarding must be disabled before the hardware interfaces are brought up (e.g., net.ipv4.ip_forward = 0 in Red Hat 6.x /etc/sysctl.conf), because IPsec doesn't get control early enough to do that.

rp_filter

whether and how setup should adjust the reverse path filtering mechanism for the physical devices to be used. Values are %unchanged (to leave it alone) or 0, 1, 2 (values to set it to). /proc/sys/net/ipv4/conf/PHYS/rp_filter is badly documented; it must be 0 in many cases for ipsec to function. The default value for the parameter is 0.

syslog

the syslog(2) ``facility'' name and priority to use for startup/shutdown log messages, default daemon.error.

klipsdebug

how much KLIPS debugging output should be logged. An empty value, or the magic value none, means no debugging output (the default). The magic value all means full output. Otherwise only the specified types of output (a quoted list, names separated by white space) are enabled; for details on available debugging types, see ipsec_klipsdebug(8).

plutodebug

how much Pluto debugging output should be logged. An empty value, or the magic value none, means no debugging output (the default). The magic value all means full output. Otherwise only the specified types of output (a quoted list, names without the --debug- prefix, separated by white space) are enabled; for details on available debugging types, see ipsec_pluto(8).

plutoopts

additional options to pass to pluto upon startup. See ipsec_pluto(8).

plutostderrlog

do not use syslog, but rather log to stderr, and direct stderr to the argument file.

dumpdir

in what directory should things started by setup (notably the Pluto daemon) be allowed to dump core? The empty value (the default) means they are not allowed to.

manualstart

which manually-keyed connections to set up at startup (empty, a name, or a quoted list of names separated by white space); see ipsec_manual(8). Default is none.

pluto

whether to start Pluto or not; Values are yes (the default) or no (useful only in special circumstances).

plutowait

should Pluto wait for each negotiation attempt that is part of startup to finish before proceeding with the next? Values are yes or no (the default).

prepluto

shell command to run before starting Pluto (e.g., to decrypt an encrypted copy of the ipsec.secrets file). It's run in a very simple way; complexities like I/O redirection are best hidden within a script. Any output is redirected for logging, so running interactive commands is difficult unless they use /dev/tty or equivalent for their interaction. Default is none.

postpluto

shell command to run after starting Pluto (e.g., to remove a decrypted copy of the ipsec.secrets file). It's run in a very simple way; complexities like I/O redirection are best hidden within a script. Any output is redirected for logging, so running interactive commands is difficult unless they use /dev/tty or equivalent for their interaction. Default is none.

fragicmp

whether a tunnel's need to fragment a packet should be reported back with an ICMP message, in an attempt to make the sender lower his PMTU estimate; acceptable values are yes (the default) and no.

hidetos

whether a tunnel packet's TOS field should be set to 0 rather than copied from the user packet inside; acceptable values are yes (the default) and no.

uniqueids

whether a particular participant ID should be kept unique, with any new (automatically keyed) connection using an ID from a different IP address deemed to replace all old ones using that ID; acceptable values are yes (the default) and no. Participant IDs normally are unique, so a new (automatically-keyed) connection using the same ID is almost invariably intended to replace an old one.

overridemtu

value that the MTU of the ipsecn interface(s) should be set to, overriding IPsec's (large) default. This parameter is needed only in special situations.

nat_traversal

whether to accept/offer to support NAT (NAPT, also known as "IP Masqurade") workaround for IPsec. Acceptable values are: yes and no (the default). This parameter may eventually become per-connection.

The system automatically defines several conns to implement default policy groups. Each can be overridden by explicitly defining a new conn with the same name. If the new conn has auto=ignore, the definition is suppressed.

Here are the automatically supplied definitions.

conn clear
	type=passthrough
	authby=never
	left=%defaultroute
	right=%group
	auto=route

conn clear-or-private type=passthrough left=%defaultroute leftid=%myid right=%opportunisticgroup failureshunt=passthrough keyingtries=3 ikelifetime=1h keylife=1h rekey=no auto=route

conn private-or-clear type=tunnel left=%defaultroute leftid=%myid right=%opportunisticgroup failureshunt=passthrough keyingtries=3 ikelifetime=1h keylife=1h rekey=no auto=route

conn private type=tunnel left=%defaultroute leftid=%myid right=%opportunisticgroup failureshunt=drop keyingtries=3 ikelifetime=1h keylife=1h rekey=no auto=route

conn block type=reject authby=never left=%defaultroute right=%group auto=route

# default policy conn packetdefault type=tunnel left=%defaultroute leftid=%myid left=0.0.0.0/0 right=%opportunistic failureshunt=passthrough keyingtries=3 ikelifetime=1h keylife=1h rekey=no auto=route

These conns are not affected by anything in conn %default. They will only work if %defaultroute works. The leftid will be the interfaces IP address; this requires that reverse DNS records be set up properly.

The implicit conns are defined after all others. It is appropriate and reasonable to use also=private-or-clear (for example) in any other opportunistic conn.

The optional files under /etc/ipsec.d/policy, including

/etc/ipsec.d/policies/clear /etc/ipsec.d/policies/clear-or-private /etc/ipsec.d/policies/private-or-clear /etc/ipsec.d/policies/private /etc/ipsec.d/policies/block

may contain policy group configuration information to supplement ipsec.conf. Their contents are not security-sensitive.

These files are text files. Each consists of a list of CIDR blocks, one per line. White space followed by # followed by anything to the end of the line is a comment and is ignored, as are empty lines.

A connection in /etc/ipsec.conf which has right=%group or right=%opportunisticgroup is a policy group connection. When a policy group file of the same name is loaded, with

ipsec auto --rereadgroups

or at system start, the connection is instantiated such that each CIDR block serves as an instance's right value. The system treats the resulting instances as normal connections.

For example, given a suitable connection definition private, and the file /etc/ipsec.d/policy/private with an entry 192.0.2.3, the system creates a connection instance private#192.0.2.3. This connection inherits all details from private, except that its right client is 192.0.2.3.

The standard Openswan install includes several policy groups which provide a way of classifying possible peers into IPsec security classes: private (talk encrypted only), private-or-clear (prefer encryption), clear-or-private (respond to requests for encryption), clear and block. Implicit policy groups apply to the local host only, and are implemented by the IMPLICIT CONNECTIONS described above.

When choosing a connection to apply to an outbound packet caught with a %trap, the system prefers the one with the most specific eroute that includes the packet's source and destination IP addresses. Source subnets are examined before destination subnets. For initiating, only routed connections are considered. For responding, unrouted but added connections are considered.

When choosing a connection to use to respond to a negotiation which doesn't match an ordinary conn, an opportunistic connection may be instantiated. Eventually, its instance will be /32 -> /32, but for earlier stages of the negotiation, there will not be enough information about the client subnets to complete the instantiation.

/etc/ipsec.conf
/etc/ipsec.d/policies/clear
/etc/ipsec.d/policies/clear-or-private
/etc/ipsec.d/policies/private-or-clear
/etc/ipsec.d/policies/private
/etc/ipsec.d/policies/block

ipsec(8), ipsec_ttoaddr(8), ipsec_auto(8), ipsec_manual(8), ipsec_rsasigkey(8)

Designed for the FreeS/WAN project <http://www.freeswan.org> by Henry Spencer.

When type or failureshunt is set to drop or reject, Openswan blocks outbound packets using eroutes, but assumes inbound blocking is handled by the firewall. Openswan offers firewall hooks via an ``updown'' script. However, the default ipsec _updown provides no help in controlling a modern firewall.

Including attributes of the keying channel (authentication methods, ikelifetime, etc.) as an attribute of a connection, rather than of a participant pair, is dubious and incurs limitations.

Ipsec_manual is not nearly as generous about the syntax of subnets, addresses, etc. as the usual Openswan user interfaces. Four-component dotted-decimal must be used for all addresses. It is smart enough to translate bit-count netmasks to dotted-decimal form.

It would be good to have a line-continuation syntax, especially for the very long lines involved in RSA signature keys.

The ability to specify different identities, authby, and public keys for different automatic-keyed connections between the same participants is misleading; this doesn't work dependably because the identity of the participants is not known early enough. This is especially awkward for the ``Road Warrior'' case, where the remote IP address is specified as 0.0.0.0, and that is considered to be the ``participant'' for such connections.

In principle it might be necessary to control MTU on an interface-by-interface basis, rather than with the single global override that overridemtu provides.

A number of features which could be implemented in both manual and automatic keying actually are not yet implemented for manual keying. This is unlikely to be fixed any time soon.

If conns are to be added before DNS is available, left=FQDN, leftnextop=FQDN, and leftrsasigkey=%dnsonload will fail. ipsec_pluto(8) does not actually use the public key for our side of a conn but it isn't generally known at a add-time which side is ours (Road Warrior and Opportunistic conns are currently exceptions).

The myid option does not affect explicit ipsec auto --add or ipsec auto --replace commands for implicit conns.