17. Internet Applications Module Documentation

The goal of this module is to hold all the Internet-specific applications, and most notably some very specific applications (e.g., ping) or daemons (e.g., radvd). Other non-Internet-specific applications such as packet generators are contained in other modules.

The source code for the new module lives in the directory src/internet-apps.

Each application has its own goals, limitations and scope, which are briefly explained in the following.

All the applications are extensively used in the top-level examples directories. The users are encouraged to check the scripts therein to have a clear overview of the various options and usage tricks.

17.1. Ping

The Ping application supports both IPv4 and IPv6 and replaces earlier ns-3 implementations called v4Ping and Ping6 that were address family dependent. Ping was introduced in the ns-3.38 release cycle.

17.1.1. Model Description

This application behaves similarly to the Unix ping application, although with fewer options supported. Ping sends ICMP Echo Request messages to a remote address, and collects statistics and reports on the ICMP Echo Reply responses that are received. The application can be used to send ICMP echo requests to unicast, broadcast, and multicast IPv4 and IPv6 addresses. The application can produce a verbose output similar to the real application, and can also export statistics and results via trace sources. The following can be controlled via attributes of this class:

  • Destination address

  • Local address (sender address)

  • Packet size (default 56 bytes)

  • Packet interval (default 1 second)

  • Timeout value (default 1 second)

  • The count, or maximum number of packets to send

  • Verbose mode

In practice, the real-world ping application behavior varies slightly depending on the operating system (Linux, macOS, Windows, etc.). Most implementations also support a very large number of options. The ns-3 model is intended to handle the most common use cases of testing for reachability. Design

The aim of ns-3 Ping application is to mimic the built-in application found in most operating systems. In practice, ping is usually used to check reachability of a destination, but additional options have been added over time and the tool can be used in different ways to gather statistics about reachability and round trip times (RTT). Since ns-3 is mainly used for performance studies and not for operational forensics, some options of real ping implementations may not be useful for simulations. However, the ns-3 application can deliver output and RTT samples similar to how the real application operates.

Ping is usually installed on a source node and does not require any ns-3 application installation on the destination node. Ping is an Application that can be started and stopped using the base class Application APIs. Behavior

The behavior of real ping applications varies across operating systems. For example, on Linux, the first ICMP sequence number sent is one, while on macOS, the first sequence number is zero. The behavior when pinging non-existent hosts also can differ (Linux is quiet while macOS is verbose). Windows and other operating systems like Cisco routers also can behave slightly differently.

This implementation tries to generally follow the Linux behavior, except that it will print out a verbose ‘request timed out’ message when an echo request is sent and no reply arrives in a timely manner. The timeout value (time that ping waits for a response to return) defaults to one second, but once there are RTT samples available, the timeout is set to twice the observed RTT. In contrast to Linux (but aligned with macOS), the first sequence number sent is zero. Scope and Limitations

ping implementations have a lot of command-line options. The ns-3 implementation only supports a few of the most commonly-used options; patches to add additional options would be welcome.

At the present time, fragmentation (sending an ICMP Echo Request larger than the path MTU) is not handled correctly during Echo Response reassembly.

17.1.2. Usage

Users may create and install Ping applications on nodes on a one-by-one basis using CreateObject or by using the PingHelper. For CreateObject, the following can be used:

Ptr<Node> n = ...;
Ptr<Ping> ping = CreateObject<Ping> ();
// Configure ping as needed...
n->AddApplication (ping);

Users should be aware of how this application stops. For most ns-3 applications, StopApplication() should be called before the simulation is stopped. If the Count attribute of this application is set to a positive integer, the application will stop (and a report will be printed) either when Count responses have been received or when StopApplication() is called, whichever comes first. If Count is zero, meaning infinite pings, then StopApplication() should be used to eventually stop the application and generate the report. If StopApplication() is called while a packet (echo request) is in-flight, the response cannot be received and the packet will be treated as lost in the report– real ping applications work this way as well. To avoid this, it is recommended to call StopApplication() at a time when an Echo Request or Echo Response packet is not expected to be in flight. Helpers

The PingHelper supports the typical Install usage pattern in ns-3. The following sample code is from the program examples/tcp/tcp-validation.cc.

PingHelper pingHelper(Ipv4Address(""));
pingHelper.SetAttribute("Interval", TimeValue(pingInterval));
pingHelper.SetAttribute("Size", UintegerValue(pingSize));
pingHelper.SetAttribute("VerboseMode", EnumValue(Ping::VerboseMode::SILENT));
ApplicationContainer pingContainer = pingHelper.Install(pingServer);
Ptr<Ping> ping = pingContainer.Get(0)->GetObject<Ping>();
ping->TraceConnectWithoutContext("Rtt", MakeBoundCallback(&TracePingRtt, &pingOfStream));
pingContainer.Stop(stopTime - Seconds(1));

The first statement sets the remote address (destination) for all application instances created with this helper. The second and third statements perform further configuration. The fourth statement configures the verbosity to be totally silent. The fifth statement is a typical Install() method that returns an ApplicationContainer (in this case, of size 1). The sixth and seventh statements fetch the application instance created and configure a trace sink (TracePingRtt) for the Rtt trace source. The eighth and ninth statements configure the start and stop time, respectively.

The helper is most useful when there are many similarly configured applications to install on a collection of nodes (a NodeContainer). When there is only one Ping application to configure in a program, or when the configuration between different instances is different, it may be more straightforward to directly create the Ping applications without the PingHelper. Attributes

The following attributes can be configured:

  • Destination: The IPv4 or IPv6 address of the machine we want to ping

  • VerboseMode: Configure verbose, quiet, or silent output

  • Interval: Time interval between sending each packet

  • Size: The number of data bytes to be sent, before ICMP and IP headers are added

  • Count: The maximum number of packets the application will send

  • InterfaceAddress: Local address of the sender

  • Timeout: Time to wait for response if no RTT samples are available Output

If VerboseMode mode is set to VERBOSE, ping will output the results of ICMP Echo Reply responses to std::cout output stream. If the mode is set to QUIET, only the initial statement and summary are printed. If the mode is set to SILENT, no output will be printed to std::cout. These behavioral differences can be seen with the ping-example.cc as follows:

$ ./ns3 run --no-build 'ping-example --ns3::Ping::VerboseMode=Verbose'
$ ./ns3 run --no-build 'ping-example --ns3::Ping::VerboseMode=Quiet'
$ ./ns3 run --no-build 'ping-example --ns3::Ping::VerboseMode=Silent'

Additional output can be gathered by using the four trace sources provided by Ping:

  • Tx: This trace executes when a new packet is sent, and returns the sequence number and full packet (including ICMP header).

  • Rtt: Each time an ICMP echo reply is received, this trace is called and reports the sequence number and RTT.

  • Drop: If an ICMP error is returned instead of an echo reply, the sequence number and reason for reported drop are returned.

  • Report: When ping completes and exits, it prints output statistics to the terminal. These values are copied to a struct PingReport and returned in this trace source. Example

A basic ping-example.cc program is provided to highlight the following usage. The topology has three nodes interconnected by two point-to-point links. Each link has 5 ms one-way delay, for a round-trip propagation delay of 20 ms. The transmission rate on each link is 100 Mbps. The routing between links is enabled by ns-3’s NixVector routing.

By default, this program will send 5 pings from node A to node C. When using the default IPv6, the output will look like this:

The example program will also produce four pcap traces (one for each NetDevice in the scenario) that can be viewed using tcpdump or Wireshark.

Other program options include options to change the destination and source addresses, number of packets (count), packet size, interval, and whether to enable logging (if logging is enabled in the build). These program options will override any corresponding attribute settings.

Finally, the program has some code that can be enabled to selectively force packet drops to check such behavior.

17.1.3. Validation

The following test cases have been added for regression testing:

  1. Unlimited pings, no losses, StopApplication () with no packets in flight

  2. Unlimited pings, no losses, StopApplication () with one packet in flight

  3. Test for operation of count attribute and exit time after all pings are received, for IPv4”

  4. Test the operation of interval attribute, for IPv4

  5. Test for behavior of pinging an unreachable host when the network does not send an ICMP unreachable message

  6. Test pinging to IPv4 broadcast address and IPv6 all nodes multicast address

  7. Test behavior of first reply lost in a count-limited configuration

  8. Test behavior of second reply lost in a count-limited configuration

  9. Test behavior of last reply lost in a count-limited configuration.

17.2. Radvd

This app mimics a “RADVD” daemon. I.e., the daemon responsible for IPv6 routers advertisements. All the IPv6 routers should have a RADVD daemon installed.

The configuration of the Radvd application mimics the one of the radvd Linux program.

17.3. DHCPv4

The ns-3 implementation of Dynamic Host Configuration Protocol (DHCP) follows the specifications of RFC 2131 and RFC 2132.

The source code for DHCP is located in src/internet-apps/model and consists of the following 6 files:

  • dhcp-server.h,

  • dhcp-server.cc,

  • dhcp-client.h,

  • dhcp-client.cc,

  • dhcp-header.h and

  • dhcp-header.cc

17.3.1. Helpers

The following two files have been added to src/internet-apps/helper for DHCP:

  • dhcp-helper.h and

  • dhcp-helper.cc

17.3.2. Tests

The tests for DHCP can be found at src/internet-apps/test/dhcp-test.cc

17.3.3. Examples

The examples for DHCP can be found at src/internet-apps/examples/dhcp-example.cc

17.3.4. Scope and Limitations

The server should be provided with a network address, mask and a range of address for the pool. One client application can be installed on only one netdevice in a node, and can configure address for only that netdevice.

The following five basic DHCP messages are supported:






Also, the following eight options of BootP are supported:

  • 1 (Mask)

  • 50 (Requested Address)

  • 51 (Address Lease Time)

  • 53 (DHCP message type)

  • 54 (DHCP server identifier)

  • 58 (Address renew time)

  • 59 (Address rebind time)

  • 255 (end)

The client identifier option (61) can be implemented in near future.

In the current implementation, a DHCP client can obtain IPv4 address dynamically from the DHCP server, and can renew it within a lease time period.

Multiple DHCP servers can be configured, but the implementation does not support the use of a DHCP Relay yet.

17.4. V4TraceRoute

Documentation is missing for this application.