Content-type: text/html Manpage of IPSEC.CONF

IPSEC.CONF

Section: File Formats (5)
Updated: 26 Nov 2001
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NAME

ipsec.conf - IPsec configuration and connections

DESCRIPTION

The ipsec.conf file specifies most configuration and control information for the FreeS/WAN 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 parameter (described below) which permits splitting a single logical section (e.g. a connection description) into several actual sections.

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.)

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-%default sections of that type. %default sections may not contain also 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.

CONN SECTIONS

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=0                # be very persistent

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.

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

The following parameters are relevant to both automatic and manual keying. Unless otherwise noted, for a connection to work, in general it is necessary for the two ends to agree exactly on the values of these parameters.

type: the type of the connection; currently the accepted values are tunnel (the default) signifying a host-to-host, host-to-subnet, or subnet-to-subnet tunnel; transport, signifying host-to-host transport mode; and passthrough (supported only for manual keying), signifying that no IPsec processing should be done at all
left: (required) the IP address of the left participant's public-network interface, in any form accepted by ipsec_ttoaddr(3). If it is the magic value %defaultroute, and interfaces=%defaultroute is used in the config setup section, left will be filled in automatically with the local address of the default-route interface (as determined at IPsec startup time); this also overrides any value supplied for leftnexthop. (Either left or right may be %defaultroute, but not both.) The magic value %any signifies an address to be filled in (by automatic keying) during negotiation; the magic value %opportunistic signifies that both left and leftnexthop are to be filled in (by automatic keying) from DNS data for left's client.
leftsubnet: private subnet behind the left participant, expressed as network/netmask (actually, any form acceptable to ipsec_ttosubnet(3)); if omitted, essentially assumed to be left/32, signifying that the left end of the connection goes to the left participant only
leftnexthop: next-hop gateway IP address for the left participant's connection to the public network; defaults to %direct (meaning right). If the value is to be overridden by the left=%defaultroute method (see above), an explicit value must not be given. If that method is not being used, but leftnexthop is %defaultroute, and interfaces=%defaultroute is used in the config setup section, the next-hop gateway address of the default-route interface will be used. The magic value %direct signifies a value to be filled in (by automatic keying) with the peer's address. Relevant only locally, other end need not agree on it.
leftupdown: what ``updown'' script to run to adjust routing and/or firewalling when the status of the connection changes (default ipsec _updown). May include positional parameters separated by white space (although this requires enclosing the whole string in quotes); including shell metacharacters is unwise. See ipsec_pluto(8) for details. Relevant only locally, other end need not agree on it.
leftfirewall: whether the left participant is doing forwarding-firewalling (including masquerading) for traffic from leftsubnet, which should be turned off (for traffic to the other subnet) once the connection is established; acceptable values are yes and (the default) no. May not be used in the same connection description with leftupdown. Implemented as a parameter to the default updown script. See notes below. Relevant only locally, other end need not agree on it.

If one or both security gateways are doing forwarding firewalling (possibly including masquerading), and this is specified using the firewall parameters, tunnels established with IPsec are exempted from it so that packets can flow unchanged through the tunnels. (This means that all subnets connected in this manner must have distinct, non-overlapping subnet address blocks.) This is done by the default updown script (see ipsec_pluto(8)).

The implementation of this makes certain assumptions about firewall setup, notably the use of the old ipfwadm interface to the firewall. In situations calling for more control, it may be preferable for the user to supply his own updown script, which makes the appropriate adjustments for his system.

CONN PARAMETERS: AUTOMATIC KEYING

The following parameters are relevant only to automatic keying, and are ignored in manual keying. Unless otherwise noted, for a connection to work, in general it is necessary for the two ends to agree exactly on the values of these parameters.

keyexchange: method of key exchange; the default and currently the only accepted value is ike
auto: what operation, if any, should be done automatically at IPsec startup; currently-accepted values are add (signifying an ipsec auto --add), route (signifying that plus an ipsec auto --route), start (signifying that plus an ipsec auto --up), and ignore (also the default) (signifying no automatic startup operation). This parameter is ignored unless the plutoload or plutostart configuration parameter is set suitably; see the config setup discussion below. Relevant only locally, other end need not agree on it (but in general, for an intended-to-be-permanent connection, both ends should use auto=start to ensure that any reboot causes immediate renegotiation).
auth: whether authentication should be done as part of ESP encryption, or separately using the AH protocol; acceptable values are esp (the default) and ah.
authby: how the two security gateways should authenticate each other; acceptable values are secret for shared secrets (the default) and rsasig for RSA digital signatures
leftid: how the left participant should be identified for authentication; defaults to left. Can be an IP address (in any ipsec_ttoaddr(3) syntax) or a fully-qualified domain name preceded by @ (which is used as a literal string and not resolved).
leftrsasigkey: the left participant's public key for RSA signature authentication, in RFC 2537 format using ipsec_ttodata(3) encoding; the magic value %dns means to fetch it from DNS (at the time the connection description is read from ipsec.conf) instead. The identity used for the left participant must be a specific host, not %any or another magic value. Caution: if two connection descriptions specify different public keys for the same leftid, confusion and madness will ensue.
pfs: whether Perfect Forward Secrecy of keys is desired on the connection's keying channel (with PFS, penetration of the key-exchange protocol does not compromise keys negotiated earlier); acceptable values are yes (the default) and no.
keylife: how long a particular instance of a connection (a set of encryption/authentication keys for user packets) should last, from successful negotiation to expiry; acceptable values are an integer optionally followed by s (a time in seconds) or a decimal number followed by m, h, or d (a time in minutes, hours, or days respectively) (default 8.0h, maximum 24h). Normally, the connection is renegotiated (via the keying channel) before it expires. The two ends need not exactly agree on keylife, although if they do not, there will be some clutter of superseded connections on the end which thinks the lifetime is longer.
rekey: whether a connection should be renegotiated when it is about to expire; acceptable values are yes (the default) and no. The two ends need not agree, but while a value of no prevents Pluto from requesting renegotiation, it does not prevent responding to renegotiation requested from the other end, so no will be largely ineffective unless both ends agree on it.
rekeymargin: how long before connection expiry or keying-channel expiry should attempts to negotiate a replacement begin; acceptable values as for keylife (default 9m). Relevant only locally, other end need not agree on it.
rekeyfuzz: maximum percentage by which rekeymargin should be randomly increased to randomize rekeying intervals (important for hosts with many connections); acceptable values are an integer, which may exceed 100, followed by a `%' (default set by ipsec_pluto(8), currently 100%). The value of rekeymargin, after this random increase, must not exceed keylife. The value 0% will suppress time randomization. Relevant only locally, other end need not agree on it.
keyingtries: how many attempts (an integer) should be made to negotiate a connection, or a replacement for one, before giving up (default 3); the value 0 means ``never give up'' Relevant only locally, other end need not agree on it.
ikelifetime: how long the keying channel of a connection (buzzphrase: ``ISAKMP SA'') should last before being renegotiated; acceptable values as for keylife (default set by ipsec_pluto(8), currently 1h, maximum 8h). The two-ends-disagree case is similar to that of keylife.
compress: whether IPComp compression of content is desired on the connection (link-level compression does not work on encrypted data, so to be effective, compression must be done before encryption); acceptable values are yes and no (the default). The two ends need not agree. A value of no is absolute: IPsec will neither propose nor accept compression. A value of yes causes IPsec to propose both compressed and uncompressed, and prefer compressed.
disablearrivalcheck: whether KLIPS's normal tunnel-exit check (that a packet emerging from a tunnel has plausible addresses in its header) should be disabled; acceptable values are yes (the backward-compatible default) and no. Relevant only locally, other end need not agree on it.

CONN PARAMETERS: MANUAL KEYING

The following parameters are relevant only to manual keying, and are ignored in automatic keying. Unless otherwise noted, for a connection to work, in general it is necessary for the two ends to agree exactly on the values of these parameters. A manually-keyed connection must specify at least one of AH or ESP.

spi: (this or spibase required for manual keying) the SPI number to be used for the connection (see ipsec_manual(8)); must be of the form 0xhex, where hex is one or more hexadecimal digits (note, it will generally be necessary to make spi at least 0x100 to be acceptable to KLIPS, and use of SPIs in the range 0x100-0xfff is recommended)
spibase: (this or spi required for manual keying) the base number for the SPIs to be used for the connection (see ipsec_manual(8)); must be of the form 0xhex0, where hex is one or more hexadecimal digits (note, it will generally be necessary to make spibase at least 0x100 for the resulting SPIs to be acceptable to KLIPS, and use of numbers in the range 0x100-0xff0 is recommended)
esp: ESP encryption/authentication algorithm to be used for the connection, e.g. 3des-md5-96 (must be suitable as a value of ipsec_spi(8)'s --esp option); default is not to use ESP
espenckey: ESP encryption key (must be suitable as a value of ipsec_spi(8)'s --enckey option) (may be specified separately for each direction using leftespenckey (leftward SA) and rightespenckey parameters)
espauthkey: ESP authentication key (must be suitable as a value of ipsec_spi(8)'s --authkey option) (may be specified separately for each direction using leftespauthkey (leftward SA) and rightespauthkey parameters)
espreplay_window: ESP replay-window setting, an integer from 0 (the ipsec_manual default, which turns off replay protection) to 64; relevant only if ESP authentication is being used
leftespspi: SPI to be used for the leftward ESP SA, overriding automatic assignment using spi or spibase; typically a hexadecimal number beginning with 0x
ah: AH authentication algorithm to be used for the connection, e.g. hmac-md5-96 (must be suitable as a value of ipsec_spi(8)'s --ah option); default is not to use AH
ahkey: (required if ah is present) AH authentication key (must be suitable as a value of ipsec_spi(8)'s --authkey option) (may be specified separately for each direction using leftahkey (leftward SA) and rightahkey parameters)
ahreplay_window: AH replay-window setting, an integer from 0 (the ipsec_manual default, which turns off replay protection) to 64
leftahspi: SPI to be used for the leftward AH SA, overriding automatic assignment using spi or spibase; typically a hexadecimal number beginning with 0x

CONFIG SECTIONS

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=
 plutoload="snta sntb sntc sntd"
 plutostart=

Parameters are optional unless marked ``(required)''. The currently-accepted parameter names in a config setup section are:

interfaces: (required) virtual and physical interfaces for IPsec to use: a single virtual=physical pair, a (quoted!) list of pairs separated by white space, or %defaultroute, which means to find the interface d that the default route points to, and then act as if the value was ``ipsec0=d''. (Also, in the %defaultroute case, 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.
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).
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.
dump: obsolete variant of dumpdir. dump=no is synonymous with dumpdir= and dump=yes is synonymous with dump=/var/tmp.
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).
plutoload: which connections (by name) to load into Pluto's internal database at startup (empty, a name, or a quoted list of names separated by white space); see ipsec_auto(8) for details. Default is none. If the special value %search is used, all connections with auto=add, auto=route, or auto=start are loaded.
plutostart: which connections (by name) to attempt to negotiate at startup (empty, a name, or a quoted list of names separated by white space); any such names which do not appear in plutoload are implicitly added to it. Default is none. If the special value %search is used, all connections with auto=route or auto=start are routed, and all connections with auto=start are started.
plutowait: should Pluto wait for each plutostart negotiation attempt to finish before proceeding with the next? Values are yes (the default) or no.
plutobackgroundload: obsolete parameter, ignored, nominally specifying whether loading and starting of connections should be spun off as a background process to avoid startup delays. This is now always done. Values were 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.
packetdefault: what should be done with a packet which reaches KLIPS (via a route into a virtual interface) but does not match any eroute; acceptable values are pass (insecure unless you really know what you're doing!!!), drop (the default), and reject (currently same as drop, but eventually it will send an ICMP notification back to the sender).
no_eroute_pass: obsolete parameter similar to packetdefault but with more limited functionality; ignored if packetdefault is set; acceptable values are yes (synonymous with packetdefault=pass) and no (synonymous with packetdefault=drop) (the default).
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 and no (the default).
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.

RECOMMENDED CONFIGURATION

Certain parameters are now strongly-recommended defaults, but cannot (yet) be made system defaults due to backward compatibility. They are supplied as ``boilerplate'' in the sample ipsec.conf file which is put in place as part of a new FreeS/WAN install.

Recommended config setup parameters are:

plutoload=%search
plutostart=%search: In practice, it is preferable to use the auto parameter to control whether a particular connection is added or started automatically.
uniqueids=yes: Participant IDs normally are unique, so a new (automatically-keyed) connection using the same ID is almost invariably intended to replace an old one.

Recommended conn parameters (mostly for automatic keying, as manual keying seldom sees much use) are:

keyingtries=0: Unlimited retries are normally appropriate for VPN connections. Finite values may be needed for Road Warrior and other more-ephemeral applications, but the fixed small default is pretty much useless.
disablearrivalcheck=no: Tunnel-exit checks improve security and do not break any normal configuration.
authby=rsasig: Digital signatures are superior in every way to shared secrets.
leftrsasigkey=%dns
rightrsasigkey=%dns: Fetching public keys from DNS is generally more convenient than having to preconfigure them in configuration files.

FILES

/etc/ipsec.conf

HISTORY

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

BUGS

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.

In general, the defaults often were chosen for backward compatibility and are less than ideal. Notably, the keyingtries default should be 0.

Ipsec_manual is not nearly as generous about the syntax of subnets, addresses, etc. as the usual FreeS/WAN 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.

Index

NAME

DESCRIPTION

CONN SECTIONS

CONN PARAMETERS: GENERAL
CONN PARAMETERS: AUTOMATIC KEYING
CONN PARAMETERS: MANUAL KEYING

CONFIG SECTIONS

RECOMMENDED CONFIGURATION

This document was created by man2html, using the manual pages.
Time: 16:08:33 GMT, April 12, 2002