fixed man page

[strongswan.git] / src / starter / ipsec.conf.5

.TH IPSEC.CONF 5 "20 Jan 2006"
.\" RCSID $Id: ipsec.conf.5,v 1.2 2006/01/22 15:33:46 as Exp $
.SH NAME
ipsec.conf \- IPsec configuration and connections
.SH DESCRIPTION
The optional
.I ipsec.conf
file
specifies most configuration and control information for the
strongSwan IPsec subsystem.
(The major exception is secrets for authentication;
see
.IR ipsec.secrets (5).)
Its contents are not security-sensitive.
.PP
The file is a text file, consisting of one or more
.IR sections .
White space followed by
.B #
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.
.PP
A line which contains
.B 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
.IR sh (1));
for example:
.PP
.B include
.B "ipsec.*.conf"
.PP
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
.B also
parameter (described below) which permits splitting a single logical
section (e.g. a connection description) into several actual sections.
.PP
A section
begins with a line of the form:
.PP
.I type
.I name
.PP
where
.I type
indicates what type of section follows, and
.I 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.
.PP
Lines within the section are generally of the form
.PP
\ \ \ \ \ \fIparameter\fB=\fIvalue\fR
.PP
(note the mandatory preceding white space).
There can be white space on either side of the
.BR = .
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.
.PP
An empty
.I 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
.I value
may contain white space only if the entire
.I value
is enclosed in double quotes (\fB"\fR);
a
.I value
cannot itself contain a double quote,
nor may it be continued across more than one line.
.PP
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).
.PP
There is currently one parameter which is available in any type of
section:
.TP
.B 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
.B also
in a single section,
although it is forbidden to append the same section more than once.)
.PP
A section with name
.B %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
.B %default
section.
There may be multiple
.B %default
sections of a given type,
but only one default may be supplied for any specific parameter name,
and all
.B %default
sections of a given type must precede all non-\c
.B %default
sections of that type.
.B %default
sections may not contain the
.B also
parameter.
.PP
Currently there are three types of sections:
a
.B config
section specifies general configuration information for IPsec, a
.B conn
section specifies an IPsec connection, while a
.B ca
section specifies special properties a certification authority.
.SH "CONN SECTIONS"
A
.B conn
section contains a
.IR "connection specification" ,
defining a network connection to be made using IPsec.
The name given is arbitrary, and is used to identify the connection.
Here's a simple example:
.PP
.ne 10
.nf
.ft B
.ta 1c
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
.ft
.fi
.PP
A note on terminology: 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 path to control the connection is called 'ISAKMP SA' in IKEv1 and
'IKE SA' in the IKEv2 protocol. That what is beeing negotiated, the kernel
level data path, is called 'IPsec SA'.
strongSwan currently uses two separate keying daemons. Pluto handles
all IKEv1 connections, Charon is the new daemon supporting the IKEv2 protocol.
Charon does not support all keywords yet.
.PP
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
.I left
and
.I right
participants,
rather than in terms of local and remote.
Which participant is considered
.I left
or
.I 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
.I left
for the local side and
.I right
for the remote side (the first letters are a good mnemonic).
.PP
Many of the parameters relate to one participant or the other;
only the ones for
.I left
are listed here, but every parameter whose name begins with
.B left
has a
.B right
counterpart,
whose description is the same but with
.B left
and
.B right
reversed.
.PP
Parameters are optional unless marked '(required)'.
.SS "CONN PARAMETERS"
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.
.TP 14
.B type
the type of the connection; currently the accepted values
are
.B tunnel
(the default)
signifying a host-to-host, host-to-subnet, or subnet-to-subnet tunnel;
.BR transport ,
signifying host-to-host transport mode;
.BR passthrough ,
signifying that no IPsec processing should be done at all;
.BR drop ,
signifying that packets should be discarded; and
.BR reject ,
signifying that packets should be discarded and a diagnostic ICMP returned.
Charon currently supports only 
.BR tunnel
and
.BR transport
connection types.
.TP
.B left
(required)
the IP address of the left participant's public-network interface,
in any form accepted by
.IR ipsec_ttoaddr (3)
or one of several magic values.
If it is
.BR %defaultroute ,
and
the
.B config
.B setup
section's,
.B interfaces
specification contains
.BR %defaultroute,
.B 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
.BR leftnexthop .
(Either
.B left
or
.B right
may be
.BR %defaultroute ,
but not both.)
The value
.B %any
signifies an address to be filled in (by automatic keying) during
negotiation.
.TP
.B leftsubnet
private subnet behind the left participant, expressed as
\fInetwork\fB/\fInetmask\fR
(actually, any form acceptable to
.IR ipsec_ttosubnet (3));
if omitted, essentially assumed to be \fIleft\fB/32\fR,
signifying that the left end of the connection goes to the left participant
only. When using IKEv2, the configured subnet of the peers may differ, the
protocol narrows it to the greates common subnet.
.TP
.B leftnexthop
next-hop gateway IP address for the left participant's connection
to the public network;
defaults to
.B %direct
(meaning
.IR right ).
If the value is to be overridden by the
.B left=%defaultroute
method (see above),
an explicit value must
.I not
be given.
If that method is not being used,
but
.B leftnexthop
is
.BR %defaultroute ,
and
.B interfaces=%defaultroute
is used in the
.B config
.B setup
section,
the next-hop gateway address of the default-route interface
will be used.
The magic value
.B %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. Currently not supported
in IKEv2.
.TP
.B leftupdown
what ``updown'' script to run to adjust routing and/or firewalling
when the status of the connection
changes (default
.BR "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
.IR ipsec_pluto (8)
for details.
Relevant only locally, other end need not agree on it. IKEv2 uses the updown
script to insert firewall rules only. Routing is not support and will be
implemented directly into Charon.
.TP
.B leftfirewall
whether the left participant is doing forwarding-firewalling
(including masquerading) for traffic from \fIleftsubnet\fR,
which should be turned off (for traffic to the other subnet)
once the connection is established;
acceptable values are
.B yes
and (the default)
.BR no .
May not be used in the same connection description with
.BR leftupdown .
Implemented as a parameter to the default
.I 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
.I updown
script (see
.IR ipsec_pluto (8)).

In situations calling for more control,
it may be preferable for the user to supply his own
.I updown
script,
which makes the appropriate adjustments for his system.
.TP
.B auto
what operation, if any, should be done automatically at IPsec startup;
currently-accepted values are
.B add
,
.B route
,
.B start
and
.B ignore
.
.B add
loads a connection without starting it.
.B route
loads a connection and installs kernel traps. If traffic is detected between
.B leftsubnet
and
.B rightsubnet
, a connection is established.
.B start
loads a connection and brings it up immediatly.
.B ignore
ignores the connection. This is equal to delete a connection from the config
file. 
Relevant only locally, other end need not agree on it
(but in general, for an intended-to-be-permanent connection,
both ends should use
.B auto=start
to ensure that any reboot causes immediate renegotiation).
.TP
.B auth
whether authentication should be done as part of
ESP encryption, or separately using the AH protocol;
acceptable values are
.B esp
(the default) and
.BR ah .
The IKEv2 daemon currently supports only ESP.
.TP
.B authby
how the two security gateways should authenticate each other;
acceptable values are
.B secret
for shared secrets,
.B rsasig
for RSA digital signatures (the default),
.B secret|rsasig
for either, and
.B never
if negotiation is never to be attempted or accepted (useful for shunt-only conns).
Digital signatures are superior in every way to shared secrets. In IKEv2, the
two ends must not agree on this parameter, it is relevant for the own
authentication method only. IKEv2 additionally supports the value
.B eap,
which indicates an initiator to request EAP authentication. The EAP method to 
use is selected by the server (see
.B eap).
.TP
.B compress
whether IPComp compression of content is proposed on the connection
(link-level compression does not work on encrypted data,
so to be effective, compression must be done \fIbefore\fR encryption);
acceptable values are
.B yes
and
.B no
(the default). A value of
.B yes
causes IPsec to propose both compressed and uncompressed,
and prefer compressed.
A value of
.B no
prevents IPsec from proposing compression;
a proposal to compress will still be accepted.
IKEv2 does not support IP compression yet.
.TP
.B dpdaction
controls the use of the Dead Peer Detection protocol (DPD, RFC 3706) where
R_U_THERE notification messages (IKEv1) or empty INFORMATIONAL messages (IKEv2)
are periodically sent in order to check the
liveliness of the IPsec peer. The values
.B clear
and
.B hold
both activate DPD. If no activity is detected, all connections with a dead peer
are stopped and unrouted (
.B clear
) or put in the hold state (
.B hold
). For
.B IKEv1
, the default is
.B none
which disables the active sending of R_U_THERE notifications.
Nevertheless pluto will always send the DPD Vendor ID during connection set up
in order to signal the readiness to act passively as a responder if the peer
wants to use DPD. For
.B IKEv2, none
does't make sense, as all messages are used to detect dead peers. If specified,
it has the same meaning as the default (
.B clear
).
.TP
.B dpddelay
defines the period time interval with which R_U_THERE messages/INFORMATIONAL
exchanges are sent to the peer. These are only sent if no other traffic is
received. In IKEv2, a value of 0 sends no additional INFORMATIONAL
messages and uses only standard messages (such as those to rekey) to detect
dead peers.
.TP
.B dpdtimeout
defines the timeout interval, after which all connections to a peer are deleted
in case of inactivity. This only applies to IKEv1, in IKEv2 the default
retransmission timeout applies, as every exchange is used to detect dead peers.
.TP
.B failureshunt
what to do with packets when negotiation fails.
The default is
.BR none :
no shunt;
.BR passthrough ,
.BR drop ,
and
.B reject
have the obvious meanings. Has no effect in IKEv2 yet.
.TP
.B ikelifetime
how long the keying channel of a connection ('ISAKMP/IKE SA')
should last before being renegotiated.
.TP
.B keyexchange
method of key exchange;
which protocol should be used to initialize the connection. Connections marked with
.B ikev1
are initiated with pluto, those marked with
.B ikev2
with charon. An incoming request from the remote peer is handled by the correct 
daemon, unaffected from the 
.B keyexchange
setting. The default value
.B ike
currently behaves exactly as
.B ikev1.
.TP
.B keyingtries
how many attempts (a whole number or \fB%forever\fP) should be made to
negotiate a connection, or a replacement for one, before giving up
(default
.BR %forever ).
The value \fB%forever\fP
means 'never give up'.
Relevant only locally, other end need not agree on it.
.TP
.B 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
.BR s
(a time in seconds)
or a decimal number followed by
.BR m ,
.BR h ,
or
.B d
(a time
in minutes, hours, or days respectively)
(default
.BR 1h ,
maximum
.BR 24h ).
Normally, the connection is renegotiated (via the keying channel)
before it expires.
The two ends need not exactly agree on
.BR keylife ,
although if they do not,
there will be some clutter of superseded connections on the end
which thinks the lifetime is longer.
.TP
.B leftca
the distinguished name of a certificate authority which is required to
lie in the trust path going from the left participant's certificate up
to the root certification authority. 
.TP
.B leftcert
the path to the left participant's X.509 certificate. The file can be coded either in
PEM or DER format. OpenPGP certificates are supported as well.
Both absolute paths or paths relative to
.B /etc/ipsec.d/certs
are accepted. By default
.B leftcert
sets 
.B leftid
to the distinguished name of the certificate's subject and
.B leftca
to the distinguished name of the certificate's issuer.
The left participant's ID can be overriden by specifying a
.B leftid
value which must be certified by the certificate, though.
.TP
.B leftgroups
a comma separated list of group names. If the
.B leftgroups
parameter is present then the peer must be a member of at least one
of the groups defined by the parameter. Group membership must be certified
by a valid attribute certificate stored in \fI/etc/ipsec.d/acerts\fP thas has been
issued to the peer by a trusted Authorization Authority stored in
\fI/etc/ipsec.d/aacerts\fP. Attribute certificates are not supported in IKEv2 yet.
.TP
.B leftid
how
the left participant
should be identified for authentication;
defaults to
.BR left .
Can be an IP address (in any
.IR ipsec_ttoaddr (3)
syntax)
or a fully-qualified domain name preceded by
.B @
(which is used as a literal string and not resolved).
The magic value
.B %myid
stands for the current setting of \fImyid\fP.
This is set in \fBconfig setup\fP or by \fIipsec_whack\fP(8)), or, if not set,
it is the IP address in \fB%defaultroute\fP (if that is supported by a TXT record in its reverse domain), or otherwise
it is the system's hostname (if that is supported by a TXT record in its forward domain), or otherwise it is undefined.
.TP
.B leftsourceip
The internal source IP to use in a tunnel, also known as virtual IP. If the
value is
.B %modeconfig
or
.B %config,
an address is requested from the peer. In IKEv2, a defined address is requested,
but the server may change it. If the server does not support it, the address
is enforced. 
.TP
.B rightsourceip
The internal source IP to use in a tunnel for the remote peer. If the
value is
.B %config
on the responder side, the initiator must propose a address which is then echoed
back.
.TP
.B leftsubnetwithin
Not relevant for IKEv2, as subnets are narrowed.
.TP
.B 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
.B yes
(the default)
and
.BR no
. IKEv2 always uses PFS for IKE_SA rekeying. PFS for rekeying IPsec SAs is
currently not supported.
.TP
.B rekey
whether a connection should be renegotiated when it is about to expire;
acceptable values are
.B yes
(the default)
and
.BR no .
The two ends need not agree,
but while a value of
.B no
prevents Pluto/Charon from requesting renegotiation,
it does not prevent responding to renegotiation requested from the other end,
so
.B no
will be largely ineffective unless both ends agree on it.
.TP
.B reauth
whether rekeying of an IKE_SA should also reauthenticate the peer. In IKEv1,
reauthentication is always done. In IKEv2, a value of
.B no
rekeys without uninstalling the IPsec SAs, a value of
.B yes
(the default) creates a new IKE_SA from scratch and tries to recreate
all IPsec SAs.
.TP
.B rekeyfuzz
maximum percentage by which
.B 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
.IR ipsec_pluto (8),
currently
.BR 100% ).
The value of
.BR rekeymargin ,
after this random increase,
must not exceed
.BR keylife .
The value
.B 0%
will suppress time randomization.
Relevant only locally, other end need not agree on it.
.TP
.B rekeymargin
how long before connection expiry or keying-channel expiry
should attempts to
negotiate a replacement
begin; acceptable values as for
.B keylife
(default
.BR 9m ).
Relevant only locally, other end need not agree on it.
.TP
.B ike
IKE/ISAKMP SA encryption/authentication algorithm to be used, e.g.
.B aes128-sha1-modp2048
(encryption-integrity-dhgroup). In IKEv2, multiple algorithms and proposals
may be included, such as
.B aes128-aes256-sha1-modp1536-modp2048,3des-sha1-md5-modp1024.
.TP
.B esp
ESP encryption/authentication algorithm to be used
for the connection, e.g.
.B 3des-md5
(encryption-integrity-[dh-group]). If dh-group is specified, CHILD_SA setup
and rekeying include a separate diffe hellman exchange (IKEv2 only).
.TP
.B ah
AH authentication algorithm to be used
for the connection, e.g.
.B hmac-md5.
.SH "CA SECTIONS"
This are optional sections that can be used to assign special
parameters to a Certification Authority (CA). These parameters are not 
supported in IKEv2 yet.
.TP 10
.B auto
currently can have either the value
.B ignore
or
.B add
. 
.TP
.B cacert
defines a path to the CA certificate either relative to 
\fI/etc/ipsec.d/cacerts\fP or as an absolute path.
.TP
.B crluri
defines a CRL distribution point (ldap, http, or file URI)
.TP
.B crluri2
defines an alternative CRL distribution point (ldap, http, or file URI)
.TP
.B ldaphost
defines an ldap host.
.TP
.B ocspuri
defines an OCSP URI.
.SH "CONFIG SECTIONS"
At present, the only
.B config
section known to the IPsec software is the one named
.BR setup ,
which contains information used when the software is being started
(see
.IR ipsec_setup (8)).
Here's an example:
.PP
.ne 8
.nf
.ft B
.ta 1c
config setup
        interfaces="ipsec0=eth1 ipsec1=ppp0"
        klipsdebug=none
        plutodebug=all
        manualstart=
.ft
.fi
.PP
Parameters are optional unless marked ``(required)''.
The currently-accepted
.I parameter
names in a
.B config
.B setup
section are:
.TP 14
.B myid
the identity to be used for
.BR %myid .
.B %myid
is used in the implicit policy group conns and can be used as
an identity in explicit conns.
If unspecified,
.B %myid
is set to the IP address in \fB%defaultroute\fP (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 ``\fB@\fP''.
.TP
.B interfaces
virtual and physical interfaces for IPsec to use:
a single
\fIvirtual\fB=\fIphysical\fR pair, a (quoted!) list of pairs separated
by white space, or
.BR %none .
One of the pairs may be written as
.BR %defaultroute ,
which means: find the interface \fId\fR that the default route points to,
and then act as if the value was ``\fBipsec0=\fId\fR''.
.B %defaultroute
is the default;
.B %none
must be used to denote no interfaces.
If
.B %defaultroute
is used (implicitly or explicitly)
information about the default route and its interface is noted for
use by
.IR ipsec_manual (8)
and
.IR ipsec_auto (8).)
.TP
.B forwardcontrol
whether
.I 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
.B yes
and (the default)
.BR no .
For this to have full effect, forwarding must be
disabled before the hardware interfaces are brought
up (e.g.,
.B "net.ipv4.ip_forward\ =\ 0"
in Red Hat 6.x
.IR /etc/sysctl.conf ),
because IPsec doesn't get control early enough to do that.
.TP
.B rp_filter
whether and how
.I setup
should adjust the reverse path filtering mechanism for the
physical devices to be used.
Values are \fB%unchanged\fP (to leave it alone)
or \fB0\fP, \fB1\fP, \fB2\fP (values to set it to).
\fI/proc/sys/net/ipv4/conf/PHYS/rp_filter\fP
is badly documented; it must be \fB0\fP in many cases
for ipsec to function.
The default value for the parameter is \fB0\fP.
.TP
.B syslog
the
.IR syslog (2)
``facility'' name and priority to use for
startup/shutdown log messages,
default
.BR daemon.error .
.TP
.B plutodebug
how much Pluto debugging output should be logged.
An empty value,
or the magic value
.BR none ,
means no debugging output (the default).
The magic value
.B all
means full output.
Otherwise only the specified types of output
(a quoted list, names without the
.B \-\-debug\-
prefix,
separated by white space) are enabled;
for details on available debugging types, see
.IR ipsec_pluto (8).
.TP
.B charondebug
how much Charon debugging output should be logged.
A comma separated list containing type level/pairs may
be specified, e.g:
.B dmn 3, ike 1, net -1.
Acceptable values for types are
.B dmn, mgr, ike, chd, job, cfg, knl, net, enc, lib
and the level is one of
.B -1, 0, 1, 2, 3, 4
(for silent, audit, control, controlmore, raw, private)
.TP
.B plutoopts
additional options to pass to pluto upon startup. See
.IR ipsec_pluto (8).
.TP
.B plutostderrlog
do not use syslog, but rather log to stderr, and direct stderr to the
argument file.
.TP
.B dumpdir
in what directory should things started by
.I setup
(notably the Pluto daemon) be allowed to
dump core?
The empty value (the default) means they are not
allowed to.
.TP
.B pluto
whether to start Pluto or not;
Values are
.B yes
(the default)
or
.B no
(useful only in special circumstances).
.TP
.B plutowait
should Pluto wait for each
negotiation attempt that is part of startup to
finish before proceeding with the next?
Values are
.B yes
or
.BR no
(the default).
.TP
.B prepluto
shell command to run before starting Pluto
(e.g., to decrypt an encrypted copy of the
.I 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
.I /dev/tty
or equivalent for their interaction.
Default is none.
.TP
.B postpluto
shell command to run after starting Pluto
(e.g., to remove a decrypted copy of the
.I 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
.I /dev/tty
or equivalent for their interaction.
Default is none.
.TP
.B 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
.B yes
(the default)
and
.BR no .
.TP
.B hidetos
whether a tunnel packet's TOS field should be set to
.B 0
rather than copied from the user packet inside;
acceptable values are
.B yes
(the default)
and
.BR no .
.TP
.B 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
.B yes
(the default)
and
.BR no .
Participant IDs normally \fIare\fR unique,
so a new (automatically-keyed) connection using the same ID is
almost invariably intended to replace an old one.
.TP
.B overridemtu
value that the MTU of the ipsec\fIn\fR interface(s) should be set to,
overriding IPsec's (large) default.
This parameter is needed only in special situations.
.TP
.B nat_traversal
.TP
.B crlcheckinterval
.TP
.B strictcrlpolicy
.TP
.B pkcs11module
.TP
.B pkcs11keepstate

.SH CHOOSING A CONNECTION
.PP
When choosing a connection to apply to an outbound packet caught with a 
.BR %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.
.PP
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.
.SH FILES
.nf
/etc/ipsec.conf
/etc/ipsec.d/cacerts
/etc/ipsec.d/certs
/etc/ipsec.d/crls
/etc/ipsec.d/aacerts
/etc/ipsec.d/acerts

.SH SEE ALSO
ipsec(8), ipsec_ttoaddr(8), ipsec_auto(8), ipsec_manual(8), ipsec_rsasigkey(8)
.SH HISTORY
Written  for  the  FreeS/WAN project
<http://www.freeswan.org>
by Henry Spencer.  Extended for the strongSwan project
<http://www.strongswan.org>
by Andreas Steffen. Updated to respect IKEv2 specific configuration
by Martin Willi.
.SH BUGS
.PP
When
.B type
or 
.B failureshunt
is set to
.B drop
or
.BR reject,
strongSwan blocks outbound packets using eroutes, but assumes inbound
blocking is handled by the firewall. strongSwan offers firewall hooks 
via an ``updown'' script.  However, the default 
.B ipsec _updown
provides no help in controlling a modern firewall.
.PP
Including attributes of the keying channel
(authentication methods,
.BR ikelifetime ,
etc.)
as an attribute of a connection,
rather than of a participant pair, is dubious and incurs limitations.
.PP
.IR Ipsec_manual
is not nearly as generous about the syntax of subnets,
addresses, etc. as the usual strongSwan user interfaces.
Four-component dotted-decimal must be used for all addresses.
It
.I is
smart enough to translate bit-count netmasks to dotted-decimal form.
.PP
It would be good to have a line-continuation syntax,
especially for the very long lines involved in
RSA signature keys.
.PP
The ability to specify different identities,
.BR 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
.BR 0.0.0.0 ,
and that is considered to be the ``participant'' for such connections.
.PP
In principle it might be necessary to control MTU on an
interface-by-interface basis,
rather than with the single global override that
.B overridemtu
provides.
.PP
A number of features which \fIcould\fR 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.
.PP
If conns are to be added before DNS is available,
\fBleft=\fP\fIFQDN\fP,
\fBleftnextop=\fP\fIFQDN\fP,
and
.B leftrsasigkey=%dnsonload
will fail.
.IR 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).
.PP
The \fBmyid\fP option does not affect explicit \fB ipsec auto \-\-add\fP or \fBipsec auto \-\-replace\fP commands for implicit conns.