Changes between Initial Version and Version 1 of FeddAbout

Timestamp:

Mar 14, 2014 10:35:42 AM (10 years ago)

Author:

faber

Comment:

Initial import

FeddAbout

@@ +1 @@
+= The DETER Federation Architecture (DFA) =
+
+This is a basic overview of the DETER federation system.  More details
+on this implementation and configuration are in later documents.  You
+can also [wiki:FeddPubs read these academic papers] that capture the evolution of the
+design to this point.
+
+DFA is a system that allows a researcher to construct experiments that
+span testbeds by dynamically acquiring resources from other testbeds and
+configuring them into a single experiment.  As closely as possible that
+experiment will mimic a single DETER/Emulab experiment.
+
+Though the experiment appears to be a cohesive whole, the testbeds that
+loan the resources retain control of those resources.  Because testbeds
+retain this control, each testbed may issue credential necessary for
+manipulating the federated resources.  For example, a testbed that has
+loaned nodes to an experiment may require the experimenter to present a
+credential issued by that testbed (e.g., an SSH key or SSL certificate)
+to reboot those nodes.  The system acquires those credentials on behalf
+of experimenters and distributes them on behalf of testbeds.
+
+Testbed administrators may use the system to establish regular policies
+between testbeds to share resources across many users of a testbed.
+Similarly, a single user with accounts on multiple testbeds can use the
+same interfaces to coordinate experiments that share his testbed
+resource, assuming sharing those resources does not violate the policy
+of any of the constituent testbeds.
+
+= Overview = 
+
+[[Image(Full-Fed-Arch-New-tvf-small.png)]]
+
+Fedd plays the role of the Federator in the diagram above.  It is divided into two parts:
+
+ '''Experiment controller'''::
+  Presents the abstraction of a federated experiment to the users.  Allows allocation, configuration, and release of resources to the federated experiment.
+ '''Access Controller'''::
+  Negotaties access and allocation of resources from federant testbeds.
+
+The access controller is depicted by the regular plug-in shapes in the federator.  These are standard plug-in interfaces that allow standard access to a variety of testbed types.  Currently emulab style testbeds and DRAGON style transit networks are supported.  The regular system interface to fedd allows new systems to be added easily.
+
+Depending on the nature of the access controller it may be implemented on the local testbed, on the same host as the experiment controller (even in the same process) or partially in both places.  This depends on the access mechanisms of the underlying testbed and the policies of the administrators.  We have implemented plugins for Emulab-style testbeds that run completely remotely and access the testbed through ssh and plug-ins that run on the Emulab testbed directly and communicate outside the testbed entirely through fedd interfaces.  Access controllers that run directly on the remote testbed have more discretion in executing privledged local commands than remote access controllers.
+
+The [FeddPluginArchitecture access controller/experiment controller interface] is documented.
+
+= Fedd: The DETER Federation Daemon =
+
+Fedd is the name for the codebase that supports both the access controller and experiment controller function.  Generally any instance of fedd will be acting as either an experiment controller or an access controller.  We continue to move toward reflecting the distinction in function in the codebase, but this is not complete.
+
+Generally fedd is configured by the testbed's administration to allow
+controlled sharing of the resources, though the same software and
+interfaces can be used by single users to coordinate federated
+resources.
+
+Creating a federated experiment consists of breaking an annotated
+experiment into sub-experiments, gaining access to testbeds that can
+host those experiments, and coordinating the creation and connection of
+those sub-experiments.  Fedd insulates the user from the various
+complexities of creating sub-experiments and dealing with cleanup and
+partial failures.  Once an experiment is created, fedd returns
+credentials necessary to administer the experiment.
+
+On termination, fedd cleans up the various sub-experiments and
+deallocates any dynamic resources or credentials.
+
+= Access Control =
+
+This section describes the basic model of access control that fedd
+implements.  We start by explaining how users are represented between
+fedds and then describe the process of acquiring and releasing access to
+a testbed's resources.
+
+This section documents the current access control system of fedd.  It is
+undergoing development.
+
+== Global Identifiers: Fedids ==
+
+In order to avoid collisions between local user names the DFA defines a
+global set of names called DETER federation IDs, or more concisely
+fedids.  A fedid has two properties:
+
+ * An entity claiming to be named by a fedid can prove it interactively
+ * Two entities referring to the same fedid can be sure that they are referring to the same entity
+
+An example implementation of a fedid is an RSA public key.  An entity
+claiming to be identified by a given public key can prove it by
+responding correctly to a challenge encrypted by that key.  For a large
+enough key size, collisions are rare enough that the second property
+holds probabilistically.
+
+We adopt public keys as the basis for DFA fedids, but rather than tie
+ourselves to one public key format, we use subject key identifiers as
+derived using method (1) in RFC3280.  That is, we use the 160 bit SHA-1
+hash of the public key.  While this allows a slightly higher chance of
+collisions than using the key itself, the advantage of a single
+representation in databases and configuration files outweighs the
+increase in risk for this application.
+
+== Global Identifiers: Three-level Names ==
+
+In Emulab, projects are created by users within projects and those
+attributes determine what resources can be accessed.  We generalized
+this idea into a testbed, project, user triple that is used for access
+control decisions.  A requester identified as ("DETER", "proj1",
+"faber") is a user from the DETER testbed, proj1 project, user faber.
+Testbeds contain projects and users, projects contain users, and users
+do not contain anything.
+
+Parts of the triple can be left blank: ( , ,"faber") is a user named faber
+without a testbed or project affiliation.
+
+Though the examples used above are simple strings, the outermost (i.e., leftmost) non-blank field
+of a name must be a fedid to be valid, and are treated as the entity
+asserting the name.  Contained fields can either be fedids or local
+names.  This allows a testbed to continue to manage its namespace
+locally.
+
+If DETER has fedid:1234 then the name (fedid:1234, "proj1", "faber")
+refers to the DETER user faber in proj1, if and only if the requester
+can prove they are identified by fedid:1234.  Note that by making
+decisions on the local names a testbed receiving a request is trusting
+the requesting testbed about the membership of those projects and names
+of users.
+
+Testbeds make decisions about access based on these three level names.
+For example, any user in the "emulab-ops" project of a trusted testbed may
+be granted access to federated resources.  It may also be the case that
+any user from a trusted testbed is granted some access, but that users
+from the emulab-ops project of that testbed are granted access to more
+kinds of resources.
+
+These three level names are used only for testbed access control.  All
+other entities in the system are identified by a single fedid.
+
+== Granting Access ==
+
+An access controller is responsible for mapping from the global identifier space into the local access control of the testbed
+This may mean mapping a request into a local Emulab project and user, a local DRAGON certificate, or a local [http://www.protogeni.net/trac/protogeni ProtoGENI] certificate.  As other plugins are added other mappings will appear
+
+=== Emulab Projects ===
+
+Once an access controller managing an Emulab has decided to grant a researcher access to resources, it
+implements that decision by granting the researcher access to an Emulab
+project with relevant permissions on the local testbed.  The terminology
+is somewhat unfortunate in that the access controller is configured to grant access
+based on the global three-level name that includes project and user
+components and implements that decision by granting access to a local
+Emulab project and Emulab user.
+
+The Emulab project to which the fedd grants access may exist and contain
+static users and resource rights, may exist but be dynamically
+configured by fedd with additional resource rights and access keys, or
+may be created completely by fedd.  Completely static projects are
+primarily used when a user wants to tie together his or her accounts on
+multiple testbeds that do not bar that behavior, but do not run fedd.
+
+Whether to dynamically modify or dynamically create files depends
+significantly on testbed administration policy and how widespread and
+often federation is conducted.  In Emulabs projects are intended as
+long-term entities, and creating and destroying them on a per-experiment
+basis may not appeal to some users.  However, static projects require
+some administrator investment per-project.
+
+=== Certificate Systems: DRAGON and ProtoGENI ===
+
+Access controllers on these systems map the request into a flat space of X.509 certificates and keys that provide the identity for these identity based systems.  Unlike the self-signed certificates representing [FeddAbout#GlobalIdentifiers:Fedids fedids], these are full X.509 certificates used to establish a chain of trust.  Different global users are mapped into certificates and keyes that match the access level intended.
+
+= Experiments =
+
+A federated experiment combines resources from multiple independently administered testbeds into a cohesive environment for experimentation.  Earlier versions of fedd enforced a !Master/Slave relationship with one emulab project exporting its environment to others.  While this model remains viable, current fedd implementations allow compositions of the services and views of the facilities as well as their resources.
+
+Currently experiments can be described in the same ns2 syntax that DETER
+and Emulab use, except that additional annotations for the testbed on
+which to place each node have been added.  (The extension is
+set-node-testbed, and described elsewhere.)  Most users will specify experiments in this format, initially. The testbed name here is a
+local string meaningful to the experimenter.  Each fedd knows some set
+of such strings, and experimenters can also inform fedd of the
+appropriate mapping between local testbed name and fedd address to
+contact.
+
+Fedd also understands experiments expressed in the [FeddPluginArchitecture#TopologyDescriptionLanguage topdl] language that it uses to communicate with facilities.
+
+An experimenter creates an experiment by presenting it to a fedd that
+knows him or her - usually the fedd on their local testbed - along with
+the master testbed name, local Emulab project to export and local
+mappings.  That fedd will map the local user into the global (testbed,
+project, user) namespace and acquire and configure resources to create
+the experiment.  A fedd may try different mappings of the experimenter
+into the global namespace in order to acquire all the resources.  For
+example a local experimenter may be a member of several local Emulab
+projects that map into different global testbed-scoped projects.
+
+Once created the user can gather information on the resources allocated to the experiment and where to access them.  (Experiments are identified by
+fedids).  The local name is mnemonic and can be used locally to access
+information about the experiment and to terminate it.  The experimenter
+can suggest a name when requesting experiment creation.
+
+In order to create a fedid, a key pair is created.  The public and
+private keys for the fedid representing the experiment are returned in
+an encrypted channel from fedd to the requesting experimenter.  The
+experimenter can use this key pair as a capability to grant access to the
+experiment to other users.
+
+While an experiment exists, experimenters can access the nodes directly
+using the credentials passed back and can acquire information about the
+experiment's topology from fedd.  Only the experimenter who created it
+or one given the capability to manipulate it can get this information.
+
+Finally, fedd will terminate an experiment on behalf of the experimenter
+who created it, or one who has been granted control of it.  Fedd is
+responsible for deallocating the running experiments and telling the
+testbeds that this experimenter is done with their access.
+
+The `fedd` installation includes a [FeddCommands#Fedd_client.py command line program] that allows users to create and delete federated experiments.  We are currently developing other interfaces, including a [http://seer.isi.deterlab.net SEER ] interface.
+
+=== Experiment Descriptions ===
+
+An experiment description is currently given in a slightly extended version of the [https://users.emulab.net/trac/emulab/wiki/nscommands ns2 dialect that is used for an Emulab experiment description.] Specifically, the `tb-set-node-testbed` command has been added.  Its syntax is:
+
+{{{
+tb-set-node-testbed node_reference testbed_name
+}}}
+
+The `node_reference` is the tcl variable containing the node and the `testbed_string` is a name meaningful to the `fedd` creating the experiment.  The experiment creation interface has a mechanism that a requester can use to supply translations from testbed names to the URIs needed to contact that testbed's `fedd` for access.
+
+Multiple segments of a federerated experiment can be embedded on the same testbed specifying the testbed_name as ''name''/''subname''.  In that syntax, ''name'' is the identifier of the testbed on which to embed the node and ''subname'' is a unique identifier within the federated experiment.  All the nodes assigned to '''deter/attack''' will be in the same sub-experiment and that will be a different sub-experiment from nodes in '''deter/defend'''.
+
+In addition, `fedd` understands the `tb-set-default-failure-action` command.  This sets the default failure action for nodes in the experiment to one of '''fatal''', '''nonfatal''', or '''ignore'''.  Those values have the same meaning as in standard Emulabs. Nodes that do not have their failure mode reset by the `tb-set-node-failure-action` command will user the explicit default.  If no default is set, '''fatal''' is used.
+
+=== Federated Experiment Creation ===
+
+TO give an intuition for how `fedd` works, we present a sample experiment description and show how it would be turned into a federated experiment.  The experiment description is:
+
+{{{
+# simple DETER topology for playing with SEER
+
+set ns [new Simulator]
+source tb_compat.tcl
+
+set a [$ns node]
+set b [$ns node]
+set c [$ns node]
+set d [$ns node]
+set e [$ns node]
+
+set deter_os "FC6-STD"
+set deter_hw "pc"
+set ucb_os "FC6-SMB"
+set ucb_hw "bvx2200"
+
+tb-set-node-os $a $deter_os
+tb-set-node-testbed $a "deter"
+tb-set-hardware $a $deter_hw
+
+
+tb-set-node-os $b $deter_os
+tb-set-node-testbed $b "deter"
+tb-set-hardware $b $deter_hw
+
+tb-set-node-os $c $ucb_os
+tb-set-node-testbed $c "ucb"
+tb-set-hardware $c $ucb_hw
+
+tb-set-node-os $d $ucb_os
+tb-set-node-testbed $d "ucb"
+tb-set-hardware $d $ucb_hw
+
+tb-set-node-os $e $ucb_os
+tb-set-node-testbed $e "ucb"
+tb-set-hardware $e $ucb_hw
+
+
+set link0 [ $ns duplex-link $a $b 100Mb 0ms DropTail]
+set link1 [ $ns duplex-link $c $b 100Mb 0ms DropTail]
+set lan0 [ $ns make-lan "$c $d $e" 100Mb 0ms ]
+
+$ns rtproto Static
+$ns run
+}}}
+
+That experiment file generates the following topology:
+
+[[Image(example_topology.png)]]
+
+Each of the boxes is a node and the circle is a shared network.  Considering the values of the `set-node-testbed` calls, the experiment will be split up like this:
+
+[[Image(testbeds.png)]]
+
+The assignment of nodes to testbeds implicitly creates links (or networks) that must be connected across the wide area, and one of the key jobs of `fedd` is to create these connections.  Fedd splits the experiment description into two descriptions (one for each testbed), adds extra nodes and startcmds to create the shared experiment, and swaps them in.  The sub-experiments look something like these:
+
+{{{
+set ns [new Simulator]
+source tb_compat.tcl
+
+set a [$ns node]
+tb-set-hardware $a pc
+tb-set-node-os $a FC6-STD
+tb-set-node-tarfiles $a /usr /proj/emulab-ops//tarfiles/bwfed/fedkit.tgz 
+# tb-set-node-testbed $a "deter"
+tb-set-node-startcmd $a "sudo -H /usr/local/federation/bin/make_hosts /proj/emulab-ops/exp/bwfed/tmp//hosts >& /tmp/federate \$USER"
+tb-set-node-failure-action $a "fatal"
+set b [$ns node]
+tb-set-hardware $b pc
+tb-set-node-os $b FC6-STD
+tb-set-node-tarfiles $b /usr /proj/emulab-ops//tarfiles/bwfed/fedkit.tgz 
+# tb-set-node-testbed $b "deter"
+tb-set-node-startcmd $b "sudo -H /usr/local/federation/bin/make_hosts /proj/emulab-ops/exp/bwfed/tmp//hosts >& /tmp/federate \$USER"
+set control [$ns node]
+tb-set-hardware $control pc
+tb-set-node-os $control FC6-STD
+tb-set-node-tarfiles $control /usr /proj/emulab-ops//tarfiles/bwfed/fedkit.tgz
+# tb-set-node-testbed $control "deter"
+tb-set-node-startcmd $control "sudo -H /usr/local/federation/bin/make_hosts /proj/emulab-ops/exp/bwfed/tmp//hosts >& /tmp/federate \$USER "
+tb-set-node-failure-action $control "fatal"
+# Link establishment and parameter setting
+set link0 [$ns duplex-link $a $b 100000kb 0.0ms DropTail]
+
+tb-set-ip-link $a $link0 10.1.1.2
+tb-set-ip-link $b $link0 10.1.1.3
+# federation gateway
+set ucbtunnel0 [$ns node ]
+tb-set-hardware $ucbtunnel0 pc3000_tunnel
+tb-set-node-os $ucbtunnel0 FBSD7-TVF
+tb-set-node-startcmd $ucbtunnel0 "sudo -H /usr/local/federation/bin/fed-tun.pl -f /proj/emulab-ops/exp/bwfed/tmp/`hostname`.gw.conf >& /tmp/bridge.log"
+tb-set-node-tarfiles $ucbtunnel0 /usr/ /proj/emulab-ops//tarfiles/bwfed/fedkit.tgz
+# Link establishment and parameter setting
+set link1 [$ns duplex-link $ucbtunnel0 $b 100000kb 0.0ms DropTail]
+
+tb-set-ip-link $ucbtunnel0 $link1 10.1.3.2
+tb-set-ip-link $b $link1 10.1.3.3
+
+$ns rtproto Session
+$ns run
+}}}
+
+{{{
+set ns [new Simulator]
+source tb_compat.tcl
+
+set c [$ns node]
+tb-set-hardware $c pc
+tb-set-node-os $c FC6-SMB
+tb-set-node-tarfiles $c /usr /proj/Deter//tarfiles/bwfed/fedkit.tgz
+# tb-set-node-testbed $c "ucb"
+tb-set-node-startcmd $c "sudo -H /bin/sh /usr/local/federation/bin/federate.sh >& /tmp/startup \$USER "
+tb-set-node-failure-action $c "fatal"
+set d [$ns node]
+tb-set-hardware $d pc
+tb-set-node-os $d FC6-SMB
+tb-set-node-tarfiles $d /usr /proj/Deter//tarfiles/bwfed/fedkit.tgz 
+# tb-set-node-testbed $d "ucb"
+tb-set-node-startcmd $d "sudo -H /bin/sh /usr/local/federation/bin/federate.sh >& /tmp/startup \$USER "
+tb-set-node-failure-action $d "fatal"
+set e [$ns node]
+tb-set-hardware $e pc
+tb-set-node-os $e FC6-SMB
+tb-set-node-tarfiles $e /usr /proj/Deter//tarfiles/bwfed/fedkit.tgz
+# tb-set-node-testbed $e "ucb"
+tb-set-node-startcmd $e "sudo -H /bin/sh /usr/local/federation/bin/federate.sh >& /tmp/startup \$USER"
+tb-set-node-failure-action $e "fatal"
+set f [$ns node]
+tb-set-hardware $f pc
+tb-set-node-os $f FC6-SMB
+tb-set-node-tarfiles $f /usr /proj/Deter//tarfiles/bwfed/fedkit.tgz
+# tb-set-node-testbed $f "ucb"
+tb-set-node-startcmd $f "sudo -H /bin/sh /usr/local/federation/bin/federate.sh >& /tmp/startup \$USER"
+tb-set-node-failure-action $f "fatal"
+# Create LAN
+set lan0 [$ns make-lan "$c $d $e " 100000kb 0.0ms ]
+
+# Set LAN/Node parameters
+tb-set-ip-lan $c $lan0 10.1.2.2
+tb-set-lan-simplex-params $lan0 $c 0.0ms 100000kb 0 0.0ms 100000kb 0
+
+
+# Set LAN/Node parameters
+tb-set-ip-lan $d $lan0 10.1.2.3
+tb-set-lan-simplex-params $lan0 $d 0.0ms 100000kb 0 0.0ms 100000kb 0
+
+
+# Set LAN/Node parameters
+tb-set-ip-lan $e $lan0 10.1.2.4
+tb-set-lan-simplex-params $lan0 $e 0.0ms 100000kb 0 0.0ms 100000kb 0
+
+
+# federation gateway
+set detertunnel0 [$ns node ]
+tb-set-hardware $detertunnel0 pc3000_tunnel
+tb-set-node-os $detertunnel0 FBSD7-TVF
+tb-set-node-startcmd $detertunnel0 "sudo -H /usr/local/federation/bin/fed-tun.pl -f /proj/Deter/exp/bwfed/tmp/`hostname`.gw.conf >& /tmp/bridge.log"
+tb-set-node-tarfiles $detertunnel0 /usr/ /proj/Deter//tarfiles/bwfed/fedkit.tgz
+# Link establishment and parameter setting
+set link1 [$ns duplex-link $c $detertunnel0 100000kb 0.0ms DropTail]
+
+tb-set-ip-link $c $link1 10.1.3.2
+tb-set-ip-link $detertunnel0 $link1 10.1.3.3
+
+$ns rtproto Session
+$ns run
+}}}
+
+The resulting topology across two testbeds looks like this:
+
+[[Image(federated_testbeds.png)]]
+
+The red nodes are the connector nodes inserted by `fedd`.  They both transfer experimental traffic verbatim and tunnel services, like a shared filesystem.  Exactly what gets tunneled and how the connections are made is a function of the federation kit, the topic of the next section.
+
+= Experiment Services =
+
+An important part of the cohesive experiment framework created by the DFA is the web of services interconnecting the sub experiments.  A service, in this context, is fairly liberally defined; it is any one of several pre-defined ways of sharing information statically or dynamically between sub-experiments.  Static information includes the accounts to create on various machines or the hostnames to export to sub-experiments.  Dynamic information includes mounting filesystems or connecting user experiment tools, like [http://seer.isi.deterlab.net SEER].
+
+Each service has an ''exporter'' the testbed that provides the service, and zero or more ''importers'', testbeds that use the information.  In addition, services can have attribute/value pairs as parameters.
+
+The specific services currently supported by fedd are:
+
+ '''hide_hosts'''::
+ By default, all hosts in the topology are visible across the experiment.  This allows some hosts to be completely local.  The hosts chosen are given by the hosts attribute.
+ '''local_seer_control'''::
+ Adds a local seer control node to sub-experiments in the exporting testbed.
+ '''project_export'''::
+ Exports the user configuration and filesystem named by the project attribute to the importing testbeds
+ '''seer_master'''::
+  Adds a second seer controller to the exporting testbed that is capable of aggregating the inputs from several local seer masters.  To create a seer instance that sees several sub experiments, create a local_seer_control in each and export a seer_master to all.
+ '''SMB'''::
+  Export a set of SMB/CIFS filesystems.
+ '''userconfig'''::
+  Export the account information from a given project or group.  Currently accepts the project attribute for that purpose.
+
+Service advertisement, provision, and specification is an ongoing area of research in federation, and we expect these specifications to become more detailed and useful as that research progresses.
+
+= The Federation Kit =
+
+The federation kit is the software used by `fedd` to connect testbeds and tunnel services from the master to the other testbeds. Currently we have a single fedkit (available from the [FeddDownload download section]) that provides SSH tunnels to connect experimental testbeds at the ethernet layer, and that tunnels the emulab event system and provides shared file service via [http://en.wikipedia.org/wiki/Server_Message_Block SMB].  That fedkit runs on any FreeBSD or Linux image that provides the SMB file system.
+
+By splitting this function out, we intend to allow different installations of `fedd` to provide different interconnection and service tunneling function.  Currently the [FeddDownload DETER fedkit] is the only federation kit in use, and `fedd` defaults its startcmd options for use with it.
+
+The federation kit has 2 roles
+
+ * Configuring experiment nodes to use [FeddAbout#ExperimentServices services], such as shared file systems.
+ * Configuring portal nodes to connect experiments
+
+== Fedkit on Experiment Nodes ==
+
+On experiment nodes, the fedkit starts dynamic routing, and optionally configures user accounts and samba filesystems if they are in use.  The system expects the following software to be available:
+
+ * quagga routing system (an old gated installation will also work)
+ * samba-client
+ * smbfs
+ 
+Those are the linux package names; equivalent FreeBSD packages will also work.  For software to be available is for it to be either installed or accessible using {{{yum}}} or {{{apt-get}}}.  DETER nodes have a local repository for that purpose.
+
+The fedkit is installed in {{{/usr/local/federation}}} and when run places a log in {{{/tmp/federate}}}.
+
+Services are initialized based on the contents of {{{/usr/local/federation/etc/client.conf}}}.  Possible values include:
+
+ '''!ControlGateway'''::
+  The DNS name (or IP address) of the node that will forward services
+ '''Hide''':
+  Do nat add this node to the node's view of the experiment.  Used for [FeddMulti multi-party experiments].
+ '''!PortalAlias'''::
+  A name that will be mapped to the same IP address as the control gateway.  SEER in particular expects nodes with certain functions to have certain names.
+ '''!ProjectUser'''::
+  The local user under which to mount shared project directories
+ '''!ProjectName'''::
+  Project name to derive shared project directories from
+ '''Service'''::
+  a string naming the [FeddAbout#ExperimentServices services] to initialize.
+ '''SMBShare'''::
+  The name of the share to mount
+
+
+
+== Fedkit on Portal Nodes ==
+
+On portal nodes the fedkit uses ssh to interconnect the segments and bridges traffic at layer 2.  If the portal node is a Linux image it needs to have the {{{bridge-tools}}} package available.  Like the fedkit on experiment nodes, it will attempt to load that software from repositories if it is not present.
+
+The fedkit configures the portal based on the contents of a configuration file containing the following parameters:
+
+ '''active'''::
+  a boolean.  If true this portal will initiate ssh connections to its peer.
+ '''nat_partner'''::
+  a boolean.  If true the fedkit's peer is behind a network address translator.  Not used yet.
+ '''tunnelip'''::
+  a boolean.  If true use the DETER system for binding external addresses.
+ '''peer'''::
+  a string.  A list of DNS names or IP addresses.  Usually this is one value, the DNS name of the peer, but passive ends of NATted portals may use a list of addresses to establish routing.
+ '''ssh_pubkey'''::
+  a string.  A file in which the access controller has placed the ssh key shared by this portal and its peer.  These are nonce keys discarded after the experiment ends.
+ '''ssh_privkey'''::
+  a string.  A file in which the access controller has placed the ssh key shared by this portal and its peer.  These are nonce keys discarded after the experiment ends.
+
+The passive portal node establishes routing connectivity to the active end, reconfigures the local sshd to allow link layer forwarding and to allow the active end to remotely configure it, and waits.  The active end connects through ssh, establishes a link layer forwarding tunnel and bridges that to the experimental interface.  It also forwards ports to connect experiment services.
+
+= Interfaces to fedd =
+
+The fedd interfaces are completely specified in WDSL and SOAP bindings.
+For simplicity and backward compatibility, fedd can export the same
+interfaces over XMLRPC, where the message formats are trivial
+translations.
+
+All fedd accesses are through HTTP over SSL.  Fedd can support
+traditional SSL CA chaining for access control, but the intention is to
+use self-signed certificates representing fedids.  The fedid semantics
+are always enforced.
+
+There are also several internal interfaces also specified in WSDL/SOAP
+and accessible through XMLRPC used to simplify the distributed
+implementation of fedd.  You can read about those in the [FeddDevelop development section].