Pluto internals

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The pluto daemon handles the IKE protocol layer and instructs the kernel about IPsec SA's.

  • pluto implements the IKEv1 and IKEv2 protocols
  • pluto communicates via the whack interface
  • pluto performs IKE packet processing

The pluto main binary can call pluto helpers:

pluto files

The filenames should be fairly self-explanatory. The important files are:

  • include/ietf_constants.h contains the names and values of the IKE and IPsec protocol IANA registries.
  • programs/pluto/ikev1* contains IKEv1 specific processing functions
  • programs/pluto/ikev2* contains IKEv2 specific processing functions
  • include/pluto_constants.h contains the names and values of our own options
  • programs/pluto/packet.c contains the structs representing the IKE/IPsec registries
  • lib/libswan/constants.c contains the enum_names of IETF and pluto constants
  • programs/pluto/connections.h contains struct connection
  • programs/pluto/state.h contains struct state


pluto concepts

Pluto is event driven. The design tries to avoid threads. Some of the scheduling currently done using select() will be replaced with a libevent structure.

Pluto has a concept of connections and states. A connection is what you define in a configuration file. There are a few types of connections, differentiated by c->kind:

  • CK_PERMANENT: static single connection which can be up or down
  • CK_TEMPLATE: a connection that can have multiple instantiations. The template itself is never "up"
  • CK_INSTANCE: An instance of a template

The reason for instantiating a template is that some parts of the connection are variable and the template connection should not be modified. For example:

  • right=%any Roadwarriors who have different right= IP addresses
  • rightprotoport=17/%any These connections can ask for any 1 port (usually depends on the NAT)
  • rightsubnet=vnet:%priv These connections allow various subnets from the RFC1918 (or virtual_network=) space to be used.
  • narrowing=yes (IKEv2) These connections can be dynamically narrowed on demand.

States represent the state of an connection or instance of of a connection. There can be multiple states per connection in various different states. States are described and defined in the state machines (in ikev1.c and ikev2.c) which list a state processing function that will be called. These functions return an stf_status code.

Pluto uses marshalling to convert the packet data to internal structs and back. The functions used for this are in_struct() and out_struct() which use the definitions from packet.h and packet.c


core structs

  • struct state - describes the state properties
  • struct connection - describes the connection properties
  • struct end - describes "this" and "that" end, which are filled in from "left" and "right" after orienting the connection
  • struct hostpair - describes the pair of IP addresses of gateways to look through in connection/state matching.



pluto contains an ipsec.conf and an ipsec.secrets parser

  • lib/libipsecconf/
  • lib/libswan/secrets.c


pluto consists several parts