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	Although netjail_exec.sh can execute an arbitrary command in the ng testing framework a special command is used: gnunet-cmds-helper This commands itself is of a special kind named helper processes which communicates via GNUNET_MessageHeaders on stdin/stdout with the process that started the helper. The gnunet-cmds-helper is used to load testcase plugins. Those plugins are implementations of an api which is used to start different test cases. Those plugins are dynamically loaded by gnunet-cmds-helper. Each plugin defines the commands which are running in a local interpreter loop started by the helper on that specific network namespace node. The plugins are also responsible for the communication via the helper with the master interpreter loop.
	Command Pattern
	The testing framework borrowed from the <a href="https://docs.taler.net/developers-manual.html#testing-library">GNU Taler testing library</a> was extended to handle asychronous commands. Therefore a struct GNUNET_TESTING_AsyncContext was added to struct GNUNET_TESTING_Command. By default the continuation function of GNUNET_TESTING_AsyncContext is the interpreter_next function of the interpreter loop (blocking asynchronous command) which will be executed calling GNUNET_TESTING_async_finish, when the asynchronous task finished, but also can be any other function to be executed when the asynchronous task is non blocking.
	Topology Configuration	Konfiguration
	The topology of the netjail setup can be configured via a configuration file, or with a configuration string handed over to the generic binary for starting netjail based tests.</br></br> Both method can be examined in two example test scripts</br></br> test_transport_send_simple.sh</br></br> and</br></br> test_transport_send_simple_string.sh</br></br> The Syntax of the configuration is as follows.</br></br> The configuration string is structured by lines and the delimiter ':' used for seperating key/value(s) pairs and the chars '{' and '}' for grouping several key/value pairs as value and '\|' to separate a group of values from the key/value(s) pair identifying a line. Below you find the EBNF of the configuration syntax.</br></br> config = line, {line} ;<br/><br/> line = ( "M:", NumberOfNodesPerSubnet ) \| ( "N:", NumberOfSubnets ) \| ( "X:", NumberOfGlobalNodes ) \| NumberOfAdditionalConnections \| ( "T:", GlobalPluginName ) \| ( GlobalPeer, "\|", KValue ) \| ( "R:", IndexOfSubnetRouter, "\|", RValue ) \| ( SubnetPeer, "\|", PValue ) ;<br/><br/> NumberOfNodesPerSubnet = Zero \| NaturalNumber ;<br/><br/> NumberOfSubnets = NaturalNumber ;<br/><br/> NumberOfGlobalNodes = NaturalNumber ;<br/><br/> NumberOfAdditionalConnections = "AC:", NaturalNumber GlobalPluginName = "libgnunet_test_transport_plugin_cmd_", PluginName ;<br/><br/> GlobalPeer = "K", ":", IndexOfGlobalNode ;<br/><br/> KValue = EstablishConnectionToPeerViaProtocol ;<br/><br/> IndexOfSubnetRouter = Zero \| NaturalNumber ;<br/><br/> RValue = OpenTCP, "\|", OpenUDP ;<br/><br/> SubnetPeer = "P:", SubnetIndex, ":", NodeIndexInSubnet ;<br/><br/> PValue = EstablishConnectionToPeerViaProtocol, { "\|", "{", NumberOfAdditionalConnections, "}" } ;<br/><br/> Zero = "0" ;<br/><br/> NaturalNumber = NumeralWithoutZero, { Numeral } ;<br/><br/> PluginName = Letter , { ( Letter \| "_" ) } ;<br/><br/> IndexOfGlobalNode = Zero \| NaturalNumber ;<br/><br/> EstablishConnectionToPeerViaProtocol = "{" "connect", ":" EstablishConnectionToPeerViaProtocolValues "}" ;<br/><br/> OpenTCP = OpenTCPNoSource \| OpenTCPWithSource ;<br/><br/> OpenUDP = OpenUDPNoSource \| OpenUDPWithSource ;<br/><br/> SubnetIndex = NaturalNumber ;<br/><br/> NodeIndexInSubnet = NaturalNumber ;<br/><br/> NumeralWithoutZero = "0" \| Numeral ;<br/><br/> Numeral = "1" \| "2" \| "3" \| "4" \| "5" \| "6" \| "7" \| "8" \| "9" ;<br/><br/> Letter = "A" \| "B" \| ... \| "Z" \| "a" \| ... \| "z";<br/><br/> EstablishConnectionToPeerViaProtocolValues = EstablishConnectionToPeerViaProtocolValue { "\|", EstablishConnectionToPeerViaProtocolValue } OpenTCPNoSource = "{tcp_port:", switch, "}" ;<br/><br/> OpenUDPNoSource = "{udp_port:", switch, "}" ;<br/><br/> OpenTCPWithSource = "{tcp_port:", SubnetPeer, { "tcp_port", SubnetPeer } ;<br/><br/> OpenTUDWithSource = "{udp_port:", SubnetPeer, { "udp_port", SubnetPeer } ;<br/><br/> EstablishConnectionToPeerViaProtocolValue = "{", ( GlobalPeer \| SubnetPeer ), ":", Protocol, "}" ;<br/><br/> switch = On \| Off ;<br/><br/> Protocol = "tcp" \| "udp" ;<br/><br/> On = 1 ;<br/><br/> Off = 0 ;<br/><br/>
	News archives:	Nachrichten-Archive
	NGI Assure project: Probabilistic NAT Traversal
	This project was funded through the NGI Assure Fund, a fund established by <a href="https://nlnet.nl/project/ProbabilisticNAT">NLnet</a>.</br>
	For establishing a peer to peer (p2p) network among regular internet users, unhindered connectivity is anything but self-evident. Today consumer devices are often not directly reachable via the internet but quite often are behind a so called NAT delivering only indirect internet connectivity.
	There are several methods to reach peers who are behind a NAT, but there are as many reasons those existing methods might fail. Manual configuration for example, as it is possible for example with home routers, often does not work for mobile devices like mobile phones. A further category of methods is subsumed under the term NAT hole punching. This exploits a behavior of the gateway that keeps the port of an outgoing packet open for a potential response. To make this port known to another peer a third peer is needed who is not behind a NAT. Using this method for a privacy preserving network like GNUnet, this could facilitate eclipse attacks (isolating a peer) which then can be used for deanonymization attacks and cencorship. Also any additional infrastructure needed to provide some kind of functionality has to be maintained by someone, becoming a target and/or point of failure. Therefore this method is not suitable. More sophisticated methods like "Autonomous NAT Traversal (pwnat)" using ICMP fake message, which do not need a third party for the initiation of the connection, are not successful in all circumstances, because this method depend on the behavior of the NAT firewall. All methods have in common that the external IP address of the peer behind the NAT must be known.
	Two peers trying to connect to each other will send out a burst of connection attempts to the other peer on different ports. The sheer vast amount of connections attempts from both side will lead to a high probability that two connection attempts from both peers onto the same port will be at the same time leading to a successful connection between those peers. If two natted peers are using the method to start a burst of connection attempts, this method still needs the global IP of the other peer and a “start signal” to coordinate. In the NGI Assure project <a href="../l2o">L2O</a> we are establishing a backchannel with neighbourhood routing over an ad-hoc distance vector protocol to solve the problem of not directly connected peers. The peers serving as hops to a distant peer which are a direct neighbour of the start or end peer on that path do know the global IP address of the start or end peer. If those two peers like to use the burst method for hole punching the global IP address is known. Via the distance vector protocol we are also able to communicate the "start signal".

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