pluto
is an IKE (``IPsec Key Exchange'') daemon.
whack
is an auxiliary program to allow requests to be made to a running
pluto.
pluto
is used to automatically build shared ``security associations'' on a
system that has IPsec, the secure IP protocol.
In other words,
pluto
can eliminate much of the work of manual keying.
The actual
secure transmission of packets is the responsibility of other parts of
the system (see
KLIPS,
the companion implementation of IPsec).
ipsec_auto(8) provides a more convenient interface to
pluto and whack.
IKE's Job
A Security Association (SA) is an agreement between two network nodes on
how to process certain traffic between them. This processing involves
encapsulation, authentication, encryption, or compression.
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 another IKE instance using UDP IP 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 ISAKMP SA. An
ISAKMP SA is used to protect communication between the two IKEs.
IPsec SAs can then be built by the IKEs - these are used to carry
protected IP traffic between the systems.
The negotiation of the ISAKMP SA is known as Phase 1. In theory,
Phase 1 can be accomplished by a couple of different exchange types,
but we only implement one called Main Mode (we don't implement
Aggressive Mode).
Any negotiation under the protection of an ISAKMP SA, including the
negotiation of IPsec SAs, is part of Phase 2. The exchange type
that we use to negotiate an IPsec SA is called Quick Mode.
IKE instances must be able to authenticate each other as part of their
negotiation of an ISAKMP SA. This can be done by several mechanisms
described in the draft standards.
IKE negotiation can be initiated by any instance with any other. 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.
Pluto
pluto is an implementation of IKE. It runs as a daemon on a network
node. Currently, this network node must be a LINUX system running the
KLIPS implementation of IPsec.
pluto only implements a subset of IKE. This is enough for it to
interoperate with other instances of pluto, and many other IKE
implementations. We are working on implementing more of IKE.
The policy for acceptable characteristics for Security Associations is
mostly hardwired into the code of pluto (spdb.c). Eventually
this will be moved into a security policy database with reasonable
expressive power and more convenience.
pluto uses shared secrets or RSA signatures to authenticate
peers with whom it is negotiating.
pluto initiates negotiation of a Security Association when it is
manually prodded: the program whack is run to trigger this.
It will also initiate a negotiation when KLIPS traps an outbound packet
for Opportunistic Encryption.
pluto implements ISAKMP SAs itself. After it has negotiated the
characteristics of an IPsec SA, it directs KLIPS to implement it.
It also invokes a script to adjust any firewall and issue route(8)
commands to direct IP packets through KLIPS.
When pluto shuts down, it closes all Security Associations.
Before Running Pluto
pluto runs as a daemon with userid root. Before running it, a few
things must be set up.
pluto requires KLIPS, the Open implementation of IPsec.
All of the components of KLIPS and pluto should be installed.
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. Each interface with a name of the form
ipsec[0-9] is taken as a KLIPS virtual public interface.
Another network interface with the same IP address (there should be only
one) is taken as the corresponding real public
interface. ifconfig(8) with the -a flag 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 KLIPS for pluto
The most basic network topology that pluto supports has two security
gateways negotiating on behalf of client subnets. The diagram of RGB's
testbed is a good example (see klips/doc/rgb_setup.txt).
The file INSTALL in the base directory of this distribution
explains how to start setting up the whole system, including KLIPS.
Make sure that the security gateways have routes to each other. This
is usually covered by the default route, but may require issuing
route(8)
commands. The route must go through a particular IP
interface (we will assume it is eth0, but it need not be). The
interface that connects the security gateway to its client must be a
different one.
It is necessary to issue a
ipsec_tncfg(8)
command on each gateway. The required command is:
A command to set up the ipsec0 virtual interface will also need to be
run. It will have the same parameters as the command used to set up
the physical interface to which it has just been connected using
ipsec_tncfg(8).
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/openswan/ipsec.secrets is used to keep preshared secret keys
and RSA private keys for
authentication with other IKE daemons. 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.
pluto attempts to create a lockfile with the name
/var/run/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.
All logging, including diagnostics, is sent to
syslog(3)
with facility=authpriv;
it decides where to put these messages (possibly in /var/log/secure).
Since this too can make debugging awkward, there is an option to
steer logging to stderr.
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.
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.
KLIPS hooks into the routing code in a LINUX kernel.
Traffic to be processed by an IPsec SA must be directed through
KLIPS by routing commands. Furthermore, the processing to be
done is specified by ipsec eroute(8) commands.
pluto takes the responsibility of managing both of these special
kinds of routes.
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).
Each eroute is associated with the state object for an IPsec SA
because it has the particular characteristics of the SA.
Two eroutes conflict if they specify the identical local
and remote clients (unlike for routes, the local clients are
taken into account).
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.
All of these routing characteristics are expected change when
KLIPS is modified to use the firewall hooks in the LINUX 2.4.x
kernel.
Using Whack
whack is used to command a running pluto.
whack uses a UNIX domain socket to speak to pluto
(by default, /var/pluto.ctl).
whack has an intricate argument syntax.
This syntax allows many different functions to be specified.
The help form shows the usage or version information.
The connection form gives pluto a description of a potential connection.
The public key form informs pluto of the RSA public key for a potential peer.
The delete form deletes a connection description and all SAs corresponding
to it.
The listen form tells pluto to start or stop listening on the public interfaces
for IKE requests from peers.
The route form tells pluto to set up routing for a connection;
the unroute form undoes this.
The initiate form tells pluto to negotiate an SA corresponding to a connection.
The terminate form tells pluto to remove all SAs corresponding to a connection,
including those being negotiated.
The status form displays the pluto's internal state.
The debug form tells pluto to change the selection of debugging output
``on the fly''. The shutdown form tells
pluto to shut down, deleting all SAs.
Most options are specific to one of the forms, and will be described
with that form. There are three options that apply to all forms.
--ctlbasepath
path.ctl is used as the UNIX domain socket for talking
to pluto.
This option facilitates debugging.
--optionsfromfilename
adds the contents of the file to the argument list.
--labelstring
adds the string to all error messages generated by whack.
The help form of whack is self-explanatory.
--help
display the usage message.
--version
display the version of whack.
The connection form describes a potential connection to pluto.
pluto needs to know what connections can and should be negotiated.
When pluto is the initiator, it needs to know what to propose.
When pluto is the responder, it needs to know enough to decide whether
is is willing to set up the proposed connection.
The description of a potential connection can specify a large number
of details. Each connection has a unique name. This name will appear
in a updown shell command, so it should not contain punctuation
that would make the command ill-formed.
--nameconnection-name
The topology of
circuit is symmetric, so to save space here is half a picture:
client_subnet<-->host:ikeport<-->nexthop<---
A similar trick is used in the flags. The same flag names are used for
both ends. Those before the --to flag describe the left side
and those afterwards describe the right side. When pluto attempts
to use the connection, it decides whether it is the left side or the right
side of the connection, based on the IP numbers of its interfaces.
--idid
the identity of the end. Currently, this can be an IP address (specified
as dotted quad or as a Fully Qualified Domain Name, which will be resolved
immediately) or as a Fully Qualified Domain Name itself (prefixed by ``@''
to signify that it should not be resolved), or as user@FQDN.
pluto only authenticates the identity, and does not use it for
addressing, so, for example, an IP address need not be the one to which
packets are to be sent. If the option is absent, the
identity defaults to the IP address specified by --host.
--hostip-address
--host%any
--host%opportunistic
the IP address of the end (generally the public interface).
If pluto is to act as a responder
for IKE negotiations initiated from unknown IP addresses (the
``Road Warrior'' case), the
IP address should be specified as %any (currently,
the obsolete notation 0.0.0.0 is also accepted for this).
If pluto is to opportunistically initiate the connection,
use %opportunistic
--ikeportport-number
the UDP port that IKE listens to on that host. The default is 500.
(pluto on this machine uses the port specified by its own command
line argument, so this only affects where pluto sends messages.)
--nexthopip-address
where to route packets for the peer's client (presumably for the peer too,
but it will not be used for this).
When pluto installs an IPsec SA, it issues a route command.
It uses the nexthop as the gateway.
The default is the peer's IP address (this can be explicitly written as
%direct; the obsolete notation 0.0.0.0 is accepted).
This option is necessary if pluto's host's interface used for sending
packets to the peer is neither point-to-point nor directly connected to the
peer.
--clientsubnet
the subnet for which the IPsec traffic will be destined. If not specified,
the host will be the client.
The subnet can be specified in any of the forms supported by ipsec_atosubnet(3).
The general form is address/mask. The address can be either
a domain name or four decimal numbers (specifying octets) separated by dots.
The most convenient form of the mask is a decimal integer, specifying
the number of leading one bits in the mask. So, for example, 10.0.0.0/8
would specify the class A network ``Net 10''.
--dnskeyondemand]
specifies that when an RSA public key is needed to authenticate this
host, and it isn't already known, fetch it from DNS.
--updownupdown
specifies an external shell command to be run whenever pluto
brings up or down a connection.
The script is used to build a shell command, so it may contain positional
parameters, but ought not to have punctuation that would cause the
resulting command to be ill-formed.
The default is ipsec _updown.
--to
separates the specification of the left and right ends of the connection.
The potential connection description also specifies characteristics of
rekeying and security.
--aggrmode
This tunnel is using aggressive mode ISAKMP negotiation. The default is
main mode. Aggressive mode is less secure than main mode as it reveals
your identity to an eavesdropper, but is needed to support road warriors
using PSK keys or to interoperate with other buggy implementations insisting
on using aggressive mode.
--psk
Propose and allow preshared secret authentication for IKE peers. This authentication
requires that each side use the same secret. May be combined with --rsasig;
at least one must be specified.
--rsasig
Propose and allow RSA signatures for authentication of IKE peers. This authentication
requires that each side have have a private key of its own and know the
public key of its peer. May be combined with --psk;
at least one must be specified.
--encrypt
All proposed or accepted IPsec SAs will include non-null ESP.
The actual choices of transforms are wired into pluto.
--authenticate
All proposed IPsec SAs will include AH.
All accepted IPsec SAs will include AH or ESP with authentication.
The actual choices of transforms are wired into pluto.
Note that this has nothing to do with IKE authentication.
--compress
All proposed IPsec SAs will include IPCOMP (compression).
This will be ignored if KLIPS is not configured with IPCOMP support.
--tunnel
the IPsec SA should use tunneling. Implicit if the SA is for clients.
Must only be used with --authenticate or --encrypt.
--ipv4
The host addresses will be interpreted as IPv4 addresses. This is the
default. Note that for a connection, all host addresses must be of
the same Address Family (IPv4 and IPv6 use different Address Families).
--ipv6
The host addresses (including nexthop) will be interpreted as IPv6 addresses.
Note that for a connection, all host addresses must be of
the same Address Family (IPv4 and IPv6 use different Address Families).
--tunnelipv4
The client addresses will be interpreted as IPv4 addresses. The default is
to match what the host will be. This does not imply --tunnel so the
flag can be safely used when no tunnel is actually specified.
Note that for a connection, all tunnel addresses must be of the same
Address Family.
--tunnelipv6
The client addresses will be interpreted as IPv6 addresses. The default is
to match what the host will be. This does not imply --tunnel so the
flag can be safely used when no tunnel is actually specified.
Note that for a connection, all tunnel addresses must be of the same
Address Family.
--pfs
There should be Perfect Forward Secrecy - new keying material will
be generated for each IPsec SA rather than being derived from the ISAKMP
SA keying material.
Since the group to be used cannot be negotiated (a dubious feature of the
standard), pluto will propose the same group that was used during Phase 1.
We don't implement a stronger form of PFS which would require that the
ISAKMP SA be deleted after the IPSEC SA is negotiated.
--disablearrivalcheck
If the connection is a tunnel, allow packets arriving through the tunnel
to have any source and destination addresses.
If none of the --encrypt, --authenticate, --compress,
or --pfs flags is given, the initiating the connection will
only build an ISAKMP SA. For such a connection, client subnets have
no meaning and must not be specified.
More work is needed to allow for flexible policies. Currently
policy is hardwired in the source file spdb.c. The ISAKMP SAs may use
Oakley groups MODP1024 and MODP1536; 3DES encryption; SHA1-96
and MD5-96 authentication. The IPsec SAs may use 3DES and
MD5-96 or SHA1-96 for ESP, or just MD5-96 or SHA1-96 for AH.
IPCOMP Compression is always Deflate.
--ikelifetimeseconds
how long pluto will propose that an ISAKMP SA be allowed to live.
The default is 3600 (one hour) and the maximum is 28800 (8 hours).
This option will not affect what is accepted.
pluto will reject proposals that exceed the maximum.
--ipseclifetimeseconds
how long pluto will propose that an IPsec SA be allowed to live.
The default is 28800 (eight hours) and the maximum is 86400 (one day).
This option will not affect what is accepted.
pluto will reject proposals that exceed the maximum.
--rekeymarginseconds
how long before an SA's expiration should pluto try to negotiate
a replacement SA. This will only happen if pluto was the initiator.
The default is 540 (nine minutes).
--rekeyfuzzpercentage
maximum size of random component to add to rekeymargin, expressed as
a percentage of rekeymargin. pluto will select a delay uniformly
distributed within this range. By default, the percentage will be 100.
If greater determinism is desired, specify 0. It may be appropriate
for the percentage to be much larger than 100.
--keyingtriescount
how many times pluto should try to negotiate an SA,
either for the first time or for rekeying.
A value of 0 is interpreted as a very large number: never give up.
The default is three.
--dontrekey
Do not initiate rekeying. This applies to Phase 1 and Phase 2.
This is currently the only automatic way for a connection to terminate.
It may be useful with Road Warrior or Opportunistic connections.
IPsec SA rekeying will still be done by the Respsonder if the connection
was specified to have a shorter lifetime than the Initiator proposed
(there is no good way to negotiate the lifetime).
--delete
when used in the connection form, it causes any previous connection
with this name to be deleted before this one is added. Unlike a
normal delete, no diagnostic is produced if there was no previous
connection to delete. Any routing in place for the connection is undone.
The delete form deletes a named connection description and any
SAs established or negotiations initiated using this connection.
Any routing in place for the connection is undone.
--delete
--nameconnection-name
The deletestate form deletes the state object with the specified serial number.
This is useful for selectively deleting instances of connections.
--deletestatestate-number
The route form of the whack command tells pluto to set up
routing for a connection.
Although like a traditional route, it uses an ipsec device as a
virtual interface.
Once routing is set up, no packets will be
sent ``in the clear'' to the peer's client specified in the connection.
A TRAP shunt eroute will be installed; if outbound traffic is caught,
Pluto will initiate the connection.
An explicit whack route is not always needed: if it hasn't been
done when an IPsec SA is being installed, one will be automatically attempted.
When a routing is attempted for a connection, there must not already
be a routing for a different connection with the same subnet but different
interface or destination, or if
there is, it must not be being used by an IPsec SA. Otherwise the
attempt will fail.
--route
--nameconnection-name
The unroute form of the whack command tells pluto to undo
a routing. pluto will refuse if an IPsec SA is using the connection.
If another connection is sharing the same routing, it will be left in place.
Without a routing, packets will be sent without encryption or authentication.
--unroute
--nameconnection-name
The initiate form tells pluto to initiate a negotiation with another
pluto (or other IKE daemon) according to the named connection.
Initiation requires a route that --route would provide;
if none is in place at the time an IPsec SA is being installed,
pluto attempts to set one up.
--initiate
--nameconnection-name
--asynchronous
The initiate form of the whack command will relay back from
pluto status information via the UNIX domain socket (unless
--asynchronous is specified). The status information is meant to
look a bit like that from FTP. Currently whack simply
copies this to stderr. When the request is finished (eg. the SAs are
established or pluto gives up), pluto closes the channel,
causing whack to terminate.
The terminate form tells pluto to delete any SAs that use the specified
connection and to stop any negotiations in process.
It does not prevent new negotiations from starting (the delete form
has this effect).
--terminate
--nameconnection-name
The public key for informs pluto of the RSA public key for a potential peer.
Private keys must be kept secret, so they are kept in
ipsec.secrets(5).
--keyid id
specififies the identity of the peer for which a public key should be used.
Its form is identical to the identity in the connection.
If no public key is specified, pluto attempts to find KEY records
from DNS for the id (if a FQDN) or through reverse lookup (if an IP address).
Note that there several interesting ways in which this is not secure.
--addkey
specifies that the new key is added to the collection; otherwise the
new key replaces any old ones.
--pubkeyrsa key
specifies the value of the RSA public key. It is a sequence of bytes
as described in RFC 2537 ``RSA/MD5 KEYs and SIGs in the Domain Name System (DNS)''.
It is denoted in a way suitable for ipsec_ttodata(3).
For example, a base 64 numeral starts with 0s.
The listen form tells pluto to start listening for IKE requests
on its public interfaces. To avoid race conditions, it is normal to
load the appropriate connections into pluto before allowing it
to listen. If pluto isn't listening, it is pointless to
initiate negotiations, so it will refuse requests to do so. Whenever
the listen form is used, pluto looks for public interfaces and
will notice when new ones have been added and when old ones have been
removed. This is also the trigger for pluto to read the
ipsec.secrets file. So listen may useful more than once.
--listen
start listening for IKE traffic on public interfaces.
--unlisten
stop listening for IKE traffic on public interfaces.
The status form will display information about the internal state of
pluto: information about each potential connection, about
each state object, and about each shunt that pluto is managing
without an associated connection.
--status
The shutdown form is the proper way to shut down pluto.
It will tear down the SAs on this machine that pluto has negotiated.
It does not inform its peers, so the SAs on their machines remain.
--shutdown
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:
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 secret
Finally, we are ready to get pluto to initiate negotiation
for an IPsec SA (and implicitly, an ISAKMP SA):
ipsec whack --initiate --name secret
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.
The updown command
Whenever pluto brings a connection up or down, it invokes
the updown command. This command is specified using the --updown
option. This allows for customized control over routing and firewall manipulation.
The updown is invoked for five different operations. Each of
these operations can be for our client subnet or for our host itself.
prepare-host or prepare-client
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 pluto was run or
perhaps by some agent not known to pluto.
route-host or route-client
is run when bringing up a connection for a new peer client subnet
(even if prepare-host or prepare-client was run). The
command should install a suitable route. Routing decisions are based
only on the destination (peer's client) subnet address, unlike eroutes
which discriminate based on source too.
unroute-host or unroute-client
is run when bringing down the last connection for a particular peer
client subnet. It should undo what the route-host or route-client
did.
up-host or up-client
is run when bringing up a tunnel eroute with a pair of client subnets
that does not already have a tunnel eroute.
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-host or down-client
is run when bringing down the eroute 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.
The script is passed a large number of environment variables to specify
what needs to be done.
PLUTO_VERSION
indicates what version of this interface is being used. This document
describes version 1.1. This is upwardly compatible with version 1.0.
PLUTO_VERB
specifies the name of the operation to be performed
(prepare-host,r prepare-client,
up-host, up-client,
down-host, or down-client). 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.
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.
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 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 be 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 but which would use the same keys so-far used for
authentication. If it finds one, it will switch to using this better
connection (or a temporary 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 authentications does not
require that the responder know 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.
--interfaceinterfacename
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.
--ikeportport-number
changes the UDP port that pluto will use
(default, specified by IANA: 500)
--ctlbasepath
basename for control files.
path.ctl is the socket through which whack communicates with
pluto.
path.pid is the lockfile to prevent multiple pluto instances.
The default is /var/run/pluto).
--secretsfilefile
specifies the file for authentication secrets
(default: /etc/openswan/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.
--adnspathname
specifies where to find pluto's helper program for asynchronous DNS lookup.
By default, this program will be called _pluto_adns and be in
$IPSEC_DIR (if that environment variable is defined) or, failing that,
in the same directory as pluto.
--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.
--noklips
don't actually implement negotiated IPsec SAs
--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.
--stderrlog
log goes to standard out {default is to use syslogd(8))
lets one test pluto without using the superuser account.
pluto is willing to produce a prodigious amount of debugging
information. To do so, it must be compiled with -DDEBUG. 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 error
messages.
When pluto is invoked, it may be given arguments to specify
which classes to output. The current options are:
--debug-raw
show the raw bytes of messages
--debug-crypt
show the encryption and decryption of messages
--debug-parsing
show the structure of input messages
--debug-emitting
show the structure of output messages
--debug-control
show pluto's decision making
--debug-lifecycle
[this option is temporary] log more detail of lifecycle of SAs
--debug-klips
show pluto's interaction with KLIPS
--debug-dns
show pluto's interaction with DNS for KEY and TXT records.
--debug-all
all of the above
--debug-private
allow debugging output with private keys.
--debug-none
none of the above
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 a pluto with a display of the structure of input
and output:
pluto --debug-emitting --debug-parsing
To later change this pluto to only display raw bytes:
Hint: ISAKMP SAs are often kept alive by IKEs even after the IPsec SA
is established. This allows future IPsec SA's to be negotiated
directly. If one of the IKEs is restarted, the other may try to use
the ISAKMP SA but the new IKE won't know about it. This can lead to
much confusion. pluto is not yet smart enough to get out of such a
mess.
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 which 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
If pluto is compiled without -DKLIPS, it negotiates Security
Associations but never ask the kernel to put them in place and never
makes routing changes. This allows pluto to be tested on systems
without KLIPS, but makes it rather useless.
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 Groups MODP 1024 and MODP 1536 (2 and 5)
are supported.
Group MODP768 (1) is not supported because it is too weak.
*
Host authetication can be done by RSA Signatures or Pre-Shared
Secrets.
*
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 and only
if KLIPS is configured with IPCOMP support.
*
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 recieves 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.
The rest of the Openswan distribution, in particular ipsec(8).
ipsec_auto(8) is designed to make using pluto more pleasant.
Use it!
ipsec.secrets(5)
describes the format of the secrets file.
ipsec_atoaddr(3), part of the Openswan distribution, describes the
forms that IP addresses may take.
ipsec_atosubnet(3), part of the Openswan distribution, describes the
forms that subnet specifications.
For more information on IPsec, the mailing list, and the relevant
documents, see:
This code is released under the GPL terms.
See the accompanying file COPYING for more details.
The GPL does NOT apply to those pieces of code written by others
which are included in this distribution, except as noted by the
individual authors.
This software was originally written
for the FreeS/WAN project
<http://www.freeswan.org>
by Angelos D. Keromytis
(angelos@dsl.cis.upenn.edu), in May/June 1997, in Athens, Greece.
Thanks go to John Ioannidis for his help.
It was then maintained until 2000 by
D. Hugh Redelmeier
(hugh@mimosa.com), in Canada. The regulations of Greece and Canada
allow us to make the code freely redistributable.
We gratefully acknowledge that we use parts of Eric Young's libdes
package; see ../libdes/COPYRIGHT.
BUGS
pluto
is a work-in-progress. It currently has many limitations.
For example, it ignores notification messages that it receives, and
it generates only Delete Notifications and those only for IPSEC SAs.
pluto does not support the Commit Flag.
The Commit Flag is a bad feature of the IKE protocol.
It isn't protected -- neither encrypted nor authenticated.
A man in the middle could turn it on, leading to DoS.
We just ignore it, with a warning.
This should let us interoperate with
implementations that insist on it, with minor damage.
pluto does not check that the SA returned by the Responder
is actually one that was proposed. It only checks that the SA is
acceptable. The difference is not large, but can show up in attributes
such as SA lifetime.
There is no good way for a connection to be automatically terminated.
This is a problem for Road Warrior and Opportunistic connections.
The --dontrekey option does prevent the SAs from
being rekeyed on expiry.
Additonally, if a Road Warrior connection has a client subnet with a fixed IP
address, a negotiation with that subnet will cause any other
connection instantiations with that same subnet to be unoriented
(deleted, in effect).
See also the --uniqueids option for an extension of this.
When pluto sends a message to a peer that has disappeared,
pluto receives incomplete information from the kernel, so it
logs the unsatisfactory message ``some IKE message we sent has been
rejected with ECONNREFUSED (kernel supplied no details)''. John
Denker suggests that this command is useful for tracking down the
source of these problems:
tcpdump -i eth0 icmp[0] != 8 and icmp[0] != 0
Substitute your public interface for eth0 if it is different.
The word ``authenticate'' is used for two different features. We must
authenticate each IKE peer to the other. This is an important task of
Phase 1. Each packet must be authenticated, both in IKE and in IPsec,
and the method for IPsec is negotiated as an AH SA or part of an ESP SA.
Unfortunately, the protocol has no mechanism for authenticating the Phase 2
identities.
