Ubuntu Manpage: libreswan - Internet Key Exchange (IKE) Manager for IPsec

Provided by: libreswan_5.2-2.2ubuntu1_amd64

NAME

       libreswan - Internet Key Exchange (IKE) Manager for IPsec

DESCRIPTION

Libreswan is an Internet Key Exchange (IKE) manager. It consists of the Internet Key Exchange Daemon
pluto (see ipsec-pluto(8)), the auxiliary command ipsec that provides a way to manipulate pluto (see
ipsec(8)), and the configuration file ipsec.conf (see ipsec.conf(5)). For authentication, Libreswan uses
an NSS trust store containing X.509 certificates and raw private keys, or a separate file containing
preshared secrets (see ipsec.secrets(5)).

Libreswan is used to negotiate and create shared Security Associations (SA) on a system that has IPsec,
the secure IP protocol using the IKE protocol. The actual transmission of IPsec packets is the
responsibility of the kernel. Libreswan can talk to various IPsec kernel implementations, such as the
Linux XFRM and BSD KAME IPsec stacks.

Libreswan implements IKE version 1 (RFC 2409) and IKE version 2 (RFC 7296). IKEv1 is considered
Deprecated (RFC 9395) and it is strongly recommended to migrate all existing IKEv1 configurations to
IKEv2. Currently, to enable IKEv1 at all, the ipsec.conf section config setup must contain the line
ikev1-policy=yes. The default is to not accept IKEv1 packets. Each connection configuration needs to
specify to use IKEv1 as well using the keyword keyexchange=ikev1. Finally, libreswan must have been
compiled with USE_IKEv1=true. While this is the currently the default, it is expected to change in the
near future. Unless the peer does not support IKEv2, IKEv1 SHOULD NOT be used. Peers that do not support
IKEv2 at this point are likely running on "end of life" software or hardware. The IKEv1 code is in
maintenance mode and no new features will be considered.

Internet Key Exchange Protocol version 2
A Security Association (SA) is an agreement between two network nodes on how to process certain traffic
between them. This processing may involve encapsulation, authentication, encryption, and compression. The
Internet Key Exchange Protocol (IKE) provides a standardized way to establish these associations
dynamically.

IKE can be deployed on a network node to negotiate Security Associations for that node. These IKE
implementations can only negotiate with other IKE implementations, so IKE must be on each node that is to
be an endpoint of an IKE-negotiated Security Association. No other nodes need to be running IKE.

An IKE instance (i.e. an IKE implementation on a particular network node) communicates with other IKE
instance using either UDP or TCP packets, so there must be a route between the nodes in each direction.

The negotiation of Security Associations requires a number of choices that involve tradeoffs between
security, convenience, trust, and efficiency. These are policy issues and are normally specified to the
IKE instance by the system administrator.

IKE deals with two kinds of Security Associations. The first part of a negotiation between IKE instances
is to build an IKE SA. An IKE SA is used to establish an authenticated and private communication channel
between the two IKE nodes. This communication channel is used to negotiate the actually Child SAs, which
are the actual IPsec SAs. The IPsec SAs carry protected IP traffic between the systems.

Negotiating an IKE SA (referred to as the The Initial Exchanges) consists of at least the IKE_SA_INIT
exchange to establish a private channel, and the IKE_AUTH exchange to authenticate the channel.
Extensions, such as EAP and INTERMEDIATE, may add further exchanges.

Negotiating a Child SA requires a single CREATE_CHILD_SA exchange. As an optimization, the first Child
SA's negotiation may be piggybacked on the IKE_AUTH exchange.

IKE negotiation can be initiated by any instance with any other instance. If both can find an agreeable
set of characteristics for a Security Association, and both recognize each others authenticity, they can
set up a Security Association. The standards do not specify what causes an IKE instance to initiate a
negotiation.

In summary, an IKE instance is prepared to automate the management of Security Associations in an IPsec
environment, but a number of issues are considered policy and are left in the system administrator's
hands.

Libreswan
Libreswan implements the Internet Key Exchange (both versions 1 and 2). It runs as a daemon (called
pluto) on a network node. Currently, this network node must be a Linux, NetBSD, FreeBSD, or OpenBSD
system.

The policy for acceptable characteristics for Security Associations are specified using the configuration
file ipsec.conf (see ipsec.conf(5)).

Libreswan can be configured to authenticate its peer using shared secrets or using public and private
keys (see ipsec.conf(5)). Shared secrets are stored in the file ipsec.secrets (see ipsec.secrets(5)).
Public keys (for instance, X.509 certificates) are stored in either Libreswan's NSS trust store, obtained
from the peer, or using DNS(SEC). Corresponding Private keys are always stored in the Libreswan's NSS
trust store.

Libreswan initiates negotiation of a Security Association when:

• it is manually prodded (see ipsec-up(8))

• it is configured to negotiate on-demand and traffic flow (see ipsec-route(8))

• it is configured to negotiate from startup (see auto=up in ipsec.conf(5))

Libreswan implements IKE SAs itself. After it has negotiated the characteristics for a Child SA (IPsec
SA), it directs the kernel to install the association. If necessary, it also invokes a script to adjust
any firewall or routing rules (see ipsec-updown(5)).

When Libreswan shuts down, it closes all Security Associations.

The updown command
Whenever libreswan brings a connection up or down, it invokes the updown command. This command is
specified either using ipsec.conf configuration file option leftupdown= or the ipsec whack option
--updown option. This allows for customized control over routing and firewall manipulation.

The updown script is invoked for five different operations. The operation name, with -host, -client and
-v6, appended is passed to the updown script using the environment variable PLUTO_VERB (see below) The
operations, in the order they are normally invoked, are as follows:

prepare
is run before bringing up a new connection if no other connection with the same clients is up.
Generally, this is useful for deleting a route that might have been set up before libreswan was
started or perhaps by some agent not known to libreswan.

route
is run when bringing up a connection for a new peer client subnet (even if prepare was run). The
command should install a suitable route. Routing decisions are based only on the destination (peer's
client) subnet address, unlike kernel policy (SPDs) which discriminate based on source too.

up
is run when first bringing up the IPsec tunnel for a pair of client subnets. This command should
install firewall rules as appropriate. It is generally a good idea to allow IKE messages (UDP port
500) travel between the hosts.

down
is run when bringing down the IPsec tunnel for a pair of client subnets. This command should delete
firewall rules as appropriate. Note that there may remain some inbound IPsec SAs with these client
subnets.

unroute
is run when bringing down the last connection for a particular peer client subnet. It should undo
what route did.

The script is passed a large number of environment variables to specify what needs to be done:

PLUTO_VERB
specifies the name of the operation to be performed (prepare-host, prepare-client, prepare-host-v6,
prepare-client-v6; route-host, route-client, route-host-v6, route-client-v6; up-host, up-client,
up-host-v6, up-client-v6; down-host, down-client, down-host-v6, down-client-v6; unroute-host,
unroute-client, unroute-host-v6, unroute-client-v6). If the address family for security gateway to
security gateway communications is IPv6, then a suffix of -v6 is added to the verb.

PLUTO_CONNECTION
is the name of the connection for which we are routing.

PLUTO_NEXT_HOP
is the next hop to which packets bound for the peer must be sent.

PLUTO_INTERFACE
is the name of the ipsec interface to be used.

PLUTO_ME
is the IP address of our host.

PLUTO_MY_CLIENT
is the IP address / count of our client subnet. If the client is just the host, this will be the
host's own IP address / max (where max is 32 for IPv4 and 128 for IPv6).

PLUTO_MY_CLIENT_NET
is the IP address of our client net. If the client is just the host, this will be the host's own IP
address.

PLUTO_MY_CLIENT_MASK
is the mask for our client net. If the client is just the host, this will be 255.255.255.255.

PLUTO_PEER
is the IP address of our peer.

PLUTO_PEER_CLIENT
is the IP address / count of the peer's client subnet. If the client is just the peer, this will be
the peer's own IP address / max (where max is 32 for IPv4 and 128 for IPv6).

PLUTO_PEER_CLIENT_NET
is the IP address of the peer's client net. If the client is just the peer, this will be the peer's
own IP address.

PLUTO_PEER_CLIENT_MASK
is the mask for the peer's client net. If the client is just the peer, this will be 255.255.255.255.

PLUTO_MY_PROTOCOL
lists the protocols allowed over this IPsec SA.

PLUTO_PEER_PROTOCOL
lists the protocols the peer allows over this IPsec SA.

PLUTO_MY_PORT
lists the ports allowed over this IPsec SA.

PLUTO_PEER_PORT
lists the ports the peer allows over this IPsec SA.

PLUTO_MY_ID
lists our id.

PLUTO_PEER_ID
lists our peer's id.

PLUTO_PEER_CA
lists the peer's CA.

All output sent by the script to stderr or stdout is logged. The script should return an exit status of 0
if and only if it succeeds.

pluto waits for the script to finish and will not do any other processing while it is waiting. The script
may assume that pluto will not change anything while the script runs. The script should avoid doing
anything that takes much time and it should not issue any command that requires processing by pluto.
Either of these activities could be performed by a background subprocess of the script.

OLD DESCRIPTION

What follows is older documentation. Patches to overhaul it welcome.

Before Running Pluto
pluto runs as a daemon with userid root. Before running it, a few things must be set up.

pluto requires a working IPsec stack.

pluto supports multiple public networks (that is, networks that are considered insecure and thus need to
have their traffic encrypted or authenticated). It discovers the public interfaces to use by looking at
all interfaces that are configured (the --interface option can be used to limit the interfaces
considered). It does this only when whack tells it to --listen, so the interfaces must be configured by
then. The --listen can be used to limit listening on only 1 IP address of a certain interface. ip(8)
with the addr option will show the name and status of each network interface.

pluto requires a database of preshared secrets and RSA private keys. This is described in the
ipsec.secrets(5). pluto is told of RSA public keys via whack commands. If the connection is
Opportunistic, and no RSA public key is known, pluto will attempt to fetch RSA keys using the Domain Name
System.

Setting up XFRM for pluto
No special requirements are necessary to use XFRM - it ships with all modern versions of Linux 2.4 and
later.

ipsec.secrets file
A pluto daemon and another IKE daemon (for example, another instance of pluto) must convince each other
that they are who they are supposed to be before any negotiation can succeed. This authentication is
accomplished by using either secrets that have been shared beforehand (manually) or by using RSA
signatures. There are other techniques, but they have not been implemented in pluto.

The file /etc/ipsec.secrets is used to keep preshared secret keys and XAUTH passwords. RSA private keys,
X.509 certificates, CRLs, OCSP and smartcards are handled via NSS. For debugging, there is an argument to
the pluto command to use a different file. This file is described in ipsec.secrets(5).

Running Pluto
To fire up the daemon, just type pluto (be sure to be running as the superuser). The default IKE port
number is 500, the UDP port assigned by IANA for IKE Daemons. pluto must be run by the superuser to be
able to use the UDP 500 port. If pluto is told to enable NAT-Traversal, then UDP port 4500 is also taken
by pluto to listen on.

Pluto supports different IPstacks on different operating systems. This can be configured using one of the
options --use-netkey (Linux), --use-bsdkame (BSD). On startup, pluto might also read the protostack=
option to select the IPsec stack to use if --config /etc/ipsec.conf is given as argument to pluto. If
both --use-XXX and --config /etc/ipsec.conf are specified, the last command line argument specified takes
precedence.

Pluto supports RFC 3947 NAT-Traversal. The allowed range behind the NAT routers is submitted using the
--virtual-private option. See ipsec.conf(5) for the syntax. The option --force-keepalive forces the
sending of the keep-alive packets, which are send to prevent the NAT router from closing its port when
there is not enough traffic on the IPsec connection. The --keep-alive sets the delay (in seconds) of
these keep-alive packets. The newer NAT-T standards support port floating, and Libreswan enables this per
default.

Pluto supports the use of X.509 certificates and sends certificates when needed. Pluto uses NSS for all
X.509 related data, including CAcerts, certs, CRLs and private keys. The Certificate Revocation Lists can
also be retrieved from an URL. The option --crlcheckinterval sets the time between checking for CRL
expiration and issuing new fetch commands. Pluto logs a warning if no valid CRL was loaded or obtained
for a connection. If --crl-strict is given, the connection will be rejected until a valid CRL has been
loaded.

Pluto can also use helper children to off-load cryptographic operations. This behavior can be fine tuned
using the --nhelpers. Pluto will start (n-1) of them, where n is the number of CPU's you have (including
hypherthreaded CPU's). A value of 0 forces pluto to do all operations in the main process. A value of -1
tells pluto to perform the above calculation. Any other value forces the number to that amount.

Pluto uses the NSS crypto library as its random source. Some government Three Letter Agency requires that
pluto reads 440 bits from /dev/random and feed this into the NSS RNG before drawing random from the NSS
library, despite the NSS library itself already seeding its internal state. As this process can block
pluto for an extended time, the default is to not perform this redundant seeding. The --seedbits option
can be used to specify the number of bits that will be pulled from /dev/random and seeded into the NSS
RNG. This can also be accomplished by specifying seedbits in the "config setup" section of ipsec.conf.
This option should not be used by most people.

pluto attempts to create a lockfile with the name /run/pluto/pluto.pid. If the lockfile cannot be
created, pluto exits - this prevents multiple plutos from competing Any "leftover" lockfile must be
removed before pluto will run. pluto writes its PID into this file so that scripts can find it. This
lock will not function properly if it is on an NFS volume (but sharing locks on multiple machines doesn't
make sense anyway).

pluto then forks and the parent exits. This is the conventional "daemon fork". It can make debugging
awkward, so there is an option to suppress this fork. In certain configurations, pluto might also launch
helper programs to assist with DNS queries or to offload cryptographic operations.

All logging, including diagnostics, is sent to syslog(3) with facility=authpriv; it decides where to put
these messages (possibly in /var/log/secure or /var/log/auth.log). Since this too can make debugging
awkward, the option --stderrlog is used to steer logging to stderr.

Alternatively, --logfile can be used to send all logging information to a specific file.

Once pluto is started, it waits for requests from whack.

Pluto's Internal State
To understand how to use pluto, it is helpful to understand a little about its internal state.
Furthermore, the terminology is needed to decipher some of the diagnostic messages.

Pluto supports food groups for Opportunistic IPsec. The policies for these are located in
/etc/ipsec.d/policies, or another directory as specified by --ipsecdir.

Pluto supports X.509 Certificates. All certificate handling is done using the NSS library and all
certificate material is stored in an NSS database in /var/lib/ipsec/nss or another directory as specified
by --nssdir.

Pluto may core dump. It will normally do so into the current working directory. You can specify the
--coredir option for pluto, or specify the dumpdir= option in ipsec.conf.

If you are investigating a potential memory leak in pluto, start pluto with the --leak-detective option.
Before the leak causes the system or pluto to die, shut down pluto in the regular way. pluto will display
a list of leaks it has detected.

If you are investigating a potential use-after-free or double-free in pluto, first build pluto with
USE_EFENCE=true and then start pluto with --efence-protect. See efence(2) and EF_PROTECT_BELOW and
EF_PROTECT_FREE.

The (potential) connection database describes attributes of a connection. These include the IP addresses
of the hosts and client subnets and the security characteristics desired. pluto requires this
information (simply called a connection) before it can respond to a request to build an SA. Each
connection is given a name when it is created, and all references are made using this name.

During the IKE exchange to build an SA, the information about the negotiation is represented in a state
object. Each state object reflects how far the negotiation has reached. Once the negotiation is complete
and the SA established, the state object remains to represent the SA. When the SA is terminated, the
state object is discarded. Each State object is given a serial number and this is used to refer to the
state objects in logged messages.

Each state object corresponds to a connection and can be thought of as an instantiation of that
connection. At any particular time, there may be any number of state objects corresponding to a
particular connection. Often there is one representing an ISAKMP SA and another representing an IPsec SA.

XFRM requires no special routing.

Each connection may be routed, and must be while it has an IPsec SA. The connection specifies the
characteristics of the route: the interface on this machine, the "gateway" (the nexthop), and the peer's
client subnet. Two connections may not be simultaneously routed if they are for the same peer's client
subnet but use different interfaces or gateways (pluto's logic does not reflect any advanced routing
capabilities).

When pluto needs to install a route for a connection, it must make sure that no conflicting route is in
use. If another connection has a conflicting route, that route will be taken down, as long as there is no
IPsec SA instantiating that connection. If there is such an IPsec SA, the attempt to install a route will
fail.

There is an exception. If pluto, as Responder, needs to install a route to a fixed client subnet for a
connection, and there is already a conflicting route, then the SAs using the route are deleted to make
room for the new SAs. The rationale is that the new connection is probably more current. The need for
this usually is a product of Road Warrior connections (these are explained later; they cannot be used to
initiate).

When pluto needs to install an eroute for an IPsec SA (for a state object), first the state object's
connection must be routed (if this cannot be done, the eroute and SA will not be installed). If a
conflicting eroute is already in place for another connection, the eroute and SA will not be installed
(but note that the routing exception mentioned above may have already deleted potentially conflicting
SAs). If another IPsec SA for the same connection already has an eroute, all its outgoing traffic is
taken over by the new eroute. The incoming traffic will still be processed. This characteristic is
exploited during rekeying.

Old Examples
It would be normal to start pluto in one of the system initialization scripts. It needs to be run by the
superuser. Generally, no arguments are needed. To run in manually, the superuser can simply type

ipsec pluto

The command will immediately return, but a pluto process will be left running, waiting for requests from
whack or a peer.

Using whack, several potential connections would be described:

ipsec whack --name silly --host 127.0.0.1 --to --host 127.0.0.2 --ikelifetime 900 --ipseclifetime 800
--keyingtries 3

Since this silly connection description specifies neither encryption, authentication, nor tunneling, it
could only be used to establish an ISAKMP SA.

ipsec whack --name conn_name --host 10.0.0.1 --client 10.0.1.0/24 --to --host 10.0.0.2 --client
10.0.2.0/24 --encrypt

This is something that must be done on both sides. If the other side is pluto, the same whack command
could be used on it (the command syntax is designed to not distinguish which end is ours).

Now that the connections are specified, pluto is ready to handle requests and replies via the public
interfaces. We must tell it to discover those interfaces and start accepting messages from peers:

ipsec whack --listen

If we don't immediately wish to bring up a secure connection between the two clients, we might wish to
prevent insecure traffic. The routing form asks pluto to cause the packets sent from our client to the
peer's client to be routed through the ipsec0 device; if there is no SA, they will be discarded:

ipsec whack --route conn_name

Finally, we are ready to get pluto to initiate negotiation for an IPsec SA (and implicitly, an ISAKMP
SA):

ipsec whack --initiate --name conn_name

A small log of interesting events will appear on standard output (other logging is sent to syslog).

whack can also be used to terminate pluto cleanly, tearing down all SAs that it has negotiated.

ipsec whack --shutdown

Notification of any IPSEC SA deletion, but not ISAKMP SA deletion is sent to the peer. Unfortunately,
such Notification is not reliable. Furthermore, pluto itself ignores Notifications.

XAUTH
If pluto needs additional authentication, such as defined by the XAUTH specifications, then it may ask
whack to prompt the operator for username or passwords. Typically, these will be entered interactively. A
GUI that wraps around whack may look for the 041 (username) or 040 (password) prompts, and display them
to the user.

For testing purposes, the options --xauthuser user --xauthpass pass may be be given prior to the
--initiate to provide responses to the username and password prompts.

Rekeying
When an SA that was initiated by pluto has only a bit of lifetime left, pluto will initiate the creation
of a new SA. This applies to ISAKMP and IPsec SAs. The rekeying will be initiated when the SA's remaining
lifetime is less than the rekeymargin plus a random percentage, between 0 and rekeyfuzz, of the
rekeymargin.

Similarly, when an SA that was initiated by the peer has only a bit of lifetime left, pluto will try to
initiate the creation of a replacement. To give preference to the initiator, this rekeying will only be
initiated when the SA's remaining lifetime is half of rekeymargin. If rekeying is done by the responder,
the roles will be reversed: the responder for the old SA will be the initiator for the replacement. The
former initiator might also initiate rekeying, so there may be redundant SAs created. To avoid these
complications, make sure that rekeymargin is generous.

One risk of having the former responder initiate is that perhaps none of its proposals is acceptable to
the former initiator (they have not been used in a successful negotiation). To reduce the chances of this
happening, and to prevent loss of security, the policy settings are taken from the old SA (this is the
case even if the former initiator is initiating). These may be stricter than those of the connection.

pluto will not rekey an SA if that SA is not the most recent of its type (IPsec or ISAKMP) for its
potential connection. This avoids creating redundant SAs.

The random component in the rekeying time (rekeyfuzz) is intended to make certain pathological patterns
of rekeying unstable. If both sides decide to rekey at the same time, twice as many SAs as necessary are
created. This could become a stable pattern without the randomness.

Another more important case occurs when a security gateway has SAs with many other security gateways.
Each of these connections might need to be rekeyed at the same time. This would cause a high peek
requirement for resources (network bandwidth, CPU time, entropy for random numbers). The rekeyfuzz can be
used to stagger the rekeying times.

Once a new set of SAs has been negotiated, pluto will never send traffic on a superseded one. Traffic
will be accepted on an old SA until it expires.

Selecting a Connection When Responding: Road Warrior Support
When pluto receives an initial Main Mode message, it needs to decide which connection this message is
for. It picks based solely on the source and destination IP addresses of the message. There might be
several connections with suitable IP addresses, in which case one of them is arbitrarily chosen. (The
ISAKMP SA proposal contained in the message could be taken into account, but it is not.)

The ISAKMP SA is negotiated before the parties pass further identifying information, so all ISAKMP SA
characteristics specified in the connection description should be the same for every connection with the
same two host IP addresses. At the moment, the only characteristic that might differ is authentication
method.

Up to this point, all configuring has presumed that the IP addresses are known to all parties ahead of
time. This will not work when either end is mobile (or assigned a dynamic IP address for other reasons).
We call this situation "Road Warrior". It is fairly tricky and has some important limitations, most of
which are features of the IKE protocol.

Only the initiator may be mobile: the initiator may have an IP number unknown to the responder. When the
responder doesn't recognize the IP address on the first Main Mode packet, it looks for a connection with
itself as one end and %any as the other. If it cannot find one, it refuses to negotiate. If it does find
one, it creates a temporary connection that is a duplicate except with the %any replaced by the source IP
address from the packet; if there was no identity specified for the peer, the new IP address will be
used.

When pluto is using one of these temporary connections and needs to find the preshared secret or RSA
private key in ipsec.secrets, and the connection specified no identity for the peer, %any is used as its
identity. After all, the real IP address was apparently unknown to the configuration, so it is
unreasonable to require that it be used in this table.

Part way into the Phase 1 (Main Mode) negotiation using one of these temporary connection descriptions,
pluto will receive an Identity Payload. At this point, pluto checks for a more appropriate connection,
one with an identity for the peer that matches the payload and would use the same keys as so far used for
authentication. If it finds one, it will switch to using this better connection (or a temporary one
derived from this, if it has %any for the peer's IP address). It may even turn out that no connection
matches the newly discovered identity, including the current connection; if so, pluto terminates
negotiation.

Unfortunately, if preshared secret authentication is being used, the Identity Payload is encrypted using
this secret, so the secret must be selected by the responder without knowing this payload. This limits
there to being at most one preshared secret for all Road Warrior systems connecting to a host. RSA
Signature authentication does not require that the responder knows how to select the initiator's public
key until after the initiator's Identity Payload is decoded (using the responder's private key, so that
must be preselected).

When pluto is responding to a Quick Mode negotiation via one of these temporary connection descriptions,
it may well find that the subnets specified by the initiator don't match those in the temporary
connection description. If so, it will look for a connection with matching subnets, its own host address,
a peer address of %any and matching identities. If it finds one, a new temporary connection is derived
from this one and used for the Quick Mode negotiation of IPsec SAs. If it does not find one, pluto
terminates negotiation.

Be sure to specify an appropriate nexthop for the responder to send a message to the initiator: pluto has
no way of guessing it (if forwarding isn't required, use an explicit %direct as the nexthop and the IP
address of the initiator will be filled in; the obsolete notation 0.0.0.0 is still accepted).

pluto has no special provision for the initiator side. The current (possibly dynamic) IP address and
nexthop must be used in defining connections. These must be properly configured each time the initiator's
IP address changes. pluto has no mechanism to do this automatically.

Although we call this Road Warrior Support, it could also be used to support encrypted connections with
anonymous initiators. The responder's organization could announce the preshared secret that would be used
with unrecognized initiators and let anyone connect. Of course the initiator's identity would not be
authenticated.

If any Road Warrior connections are supported, pluto cannot reject an exchange initiated by an unknown
host until it has determined that the secret is not shared or the signature is invalid. This must await
the third Main Mode message from the initiator. If no Road Warrior connection is supported, the first
message from an unknown source would be rejected. This has implications for ease of debugging
configurations and for denial of service attacks.

Although a Road Warrior connection must be initiated by the mobile side, the other side can and will
rekey using the temporary connection it has created. If the Road Warrior wishes to be able to disconnect,
it is probably wise to set --keyingtries to 1 in the connection on the non-mobile side to prevent it
trying to rekey the connection. Unfortunately, there is no mechanism to unroute the connection
automatically.

Debugging
pluto accepts several optional arguments, useful mostly for debugging. Except for --interface, each
should appear at most once.

--interface interfacename
Specifies that the named real public network interface should be considered. The interface name
specified should not be ipsecN. If the option doesn't appear, all interfaces are considered. To
specify several interfaces, use the option once for each. One use of this option is to specify which
interface should be used when two or more share the same IP address.

--ikeport port-number
Changes the UDP port that pluto will use (default, specified by IANA: 500).

--rundir /run/pluto
Directory to store control socket, pluto.ctl, the socket through which whack communicates with pluto.
pluto.pid is the lockfile to prevent multiple pluto instances. The default is /run/pluto).

--secretsfile file
Specifies the file for authentication secrets (default: /etc/ipsec.secrets). This name is subject to
"globbing" as in sh(1), so every file with a matching name is processed. Quoting is generally needed
to prevent the shell from doing the globbing.

--nofork
Disable "daemon fork" (default is to fork). In addition, after the lock file and control socket are
created, print the line "Pluto initialized" to standard out.

--uniqueids
If this option has been selected, whenever a new ISAKMP SA is established, any connection with the
same Peer ID but a different Peer IP address is unoriented (causing all its SAs to be deleted). This
helps clean up dangling SAs when a connection is lost and then regained at another IP address.

--force-busy
If this option has been selected, pluto will be forced to be "busy". In this state, which happens
when there is a Denial of Service attack, will force pluto to use cookies before accepting new
incoming IKE packets. Cookies are send and required in ikev1 Aggressive Mode and in ikev2. This
option is mostly used for testing purposes, but can be selected by paranoid administrators as well.

--stderrlog
Log goes to standard out (default is to use syslogd(8)).

pluto is willing to produce a prodigious amount of debugging information. There are several classes of
debugging output, and pluto may be directed to produce a selection of them. All lines of debugging output
are prefixed with "|" to distinguish them from normal diagnostic messages.

When pluto is invoked, it may be given arguments to specify which debug classes to output. The current
options are:

--debug help (whack only)
List the debugging classes recognised by pluto.

--debug none
Disable logging for all debugging classes.

--debug base
Enable debug-logging.

--debug cpu-usage
Enable cpu-usage logging.

--debug class, --no-debug class, --debug no-class
Enable (disable) logging of the specified debugging class (--debug help lists debugging classes
supported by this version of pluto).

The debug form of the whack command will change the selection in a running pluto. If a connection name is
specified, the flags are added whenever pluto has identified that it is dealing with that connection.
Unfortunately, this is often part way into the operation being observed.

For example, to start pluto with both base and cpu-usage debug-logging enabled:

ipsec pluto --debug base --debug cpu-usage

To later change this pluto to disable base debug-logging use either:

ipsec whack --no-debug base

or:

ipsec whack --debug none --debug cpu-usage

Impairing
pluto and whack accept several optional arguments that alter (impair) correct behaviour.

These options are solely intended for use by developers when testing pluto.

--impair help (whack only)
List all the behaviours that can be altered (impaired).

--impair list (whack only)
List all the behaviours that are currently altered (impaired).

--impair none
Disable all altered (impaired) behaviours.

--impair behaviour, --impair behaviour:how, --no-impair behaviour
Alter (impair) pluto inducing the (possibly erroneous) behaviour.

Pluto's Behaviour When Things Go Wrong
When pluto doesn't understand or accept a message, it just ignores the message. It is not yet capable of
communicating the problem to the other IKE daemon (in the future it might use Notifications to accomplish
this in many cases). It does log a diagnostic.

When pluto gets no response from a message, it resends the same message (a message will be sent at most
three times). This is appropriate: UDP is unreliable.

When pluto gets a message that it has already seen, there are many cases when it notices and discards it.
This too is appropriate for UDP.

Combine these three rules, and you can explain many apparently mysterious behaviours. In a pluto log,
retrying isn't usually the interesting event. The critical thing is either earlier (pluto got a message
that it didn't like and so ignored, so it was still awaiting an acceptable message and got impatient) or
on the other system (pluto didn't send a reply because it wasn't happy with the previous message).

Notes
Each IPsec SA is assigned an SPI, a 32-bit number used to refer to the SA. The IKE protocol lets the
destination of the SA choose the SPI. The range 0 to 0xFF is reserved for IANA. Pluto also avoids
choosing an SPI in the range 0x100 to 0xFFF, leaving these SPIs free for manual keying. Remember that the
peer, if not pluto, may well chose SPIs in this range.

Policies
This catalogue of policies may be of use when trying to configure pluto and another IKE implementation to
interoperate.

In Phase 1, only Main Mode is supported. We are not sure that Aggressive Mode is secure. For one thing,
it does not support identity protection. It may allow more severe Denial Of Service attacks.

No Informational Exchanges are supported. These are optional and since their delivery is not assured,
they must not matter. It is the case that some IKE implementations won't interoperate without
Informational Exchanges, but we feel they are broken.

No Informational Payloads are supported. These are optional, but useful. It is of concern that these
payloads are not authenticated in Phase 1, nor in those Phase 2 messages authenticated with HASH(3).

•
Diffie Hellman Group MODP 1536 (5) is supported. Groups MODP768 and MODP 1024 (1 and 2) are not
supported because those are too weak.

•
Host authentication can be done by RSA Signatures or Pre-Shared Secrets.

•
TODO! This information is outdated. 3DES CBC (Cypher Block Chaining mode) is the only encryption
supported, both for ISAKMP SAs and IPSEC SAs.

•
MD5 and SHA1 hashing are supported for packet authentication in both kinds of SAs.

•
The ESP, AH, or AH plus ESP are supported. If, and only if, AH and ESP are combined, the ESP need not
have its own authentication component. The selection is controlled by the --encrypt and
--authenticate flags.

•
Each of these may be combined with IPCOMP Deflate compression, but only if the potential connection
specifies compression.

•
The IPSEC SAs may be tunnel or transport mode, where appropriate. The --tunnel flag controls this
when pluto is initiating.

•
When responding to an ISAKMP SA proposal, the maximum acceptable lifetime is eight hours. The default
is one hour. There is no minimum. The --ikelifetime flag controls this when pluto is initiating.

•
When responding to an IPSEC SA proposal, the maximum acceptable lifetime is one day. The default is
eight hours. There is no minimum. The --ipseclifetime flag controls this when pluto is initiating.

•
PFS is acceptable, and will be proposed if the --pfs flag was specified. The DH group proposed will
be the same as negotiated for Phase 1.

SIGNALS

       pluto responds to SIGHUP by issuing a suggestion that ``whack --listen'' might have been intended.

       pluto exits when it receives SIGTERM.

EXIT STATUS

       pluto normally forks a daemon process, so the exit status is normally a very preliminary result.

       0
           means that all is OK so far.

       1
           means that something was wrong.

       10
           means that the lock file already exists.

       If whack detects a problem, it will return an exit status of 1. If it received progress messages from
       pluto, it returns as status the value of the numeric prefix from the last such message that was not a
       message sent to syslog or a comment (but the prefix for success is treated as 0). Otherwise, the exit
       status is 0.

FILES

       /run/pluto/pluto.pid /run/pluto/pluto.ctl /etc/ipsec.secrets /dev/urandom

ENVIRONMENT

       pluto does not use any environment variables

HISTORY

       This code is released under the GPL terms. See the accompanying files CHANGES COPYING and CREDITS.* for
       more details.

       Detailed history (including FreeS/WAN and Openswan) can be found in the docs/ directory.

BUGS

       Please see <https://github.com/libreswan/libreswan/issues> for a list of currently known bugs and missing
       features.

       Bugs should be reported to the <swan-dev@lists.libreswan.org> mailing list.

AUTHOR

       Paul Wouters, Andrew Cagney

Libreswan 5.2                                      07/30/2025                                       LIBRESWAN(7)