
# Using the CORE GUI

* Table of Contents
{:toc}

The following image shows the CORE GUI:
![](static/core_screenshot.png)


## Overview

CORE can be used via the GUI or [Python_Scripting](scripting.md). Often the GUI is used to draw nodes and network devices on the canvas. A Python script could also be written, that imports the CORE Python module, to configure and instantiate nodes and networks. This chapter primarily covers usage of the CORE GUI.

The following image shows the various phases of a CORE session:
![](static/core-workflow.jpg)

After pressing the start button, CORE will proceed through these phases, staying in the **runtime** phase.  After the session is stopped, CORE will proceed to the **data collection** phase before tearing down the emulated state.

CORE can be customized to perform any action at each phase in the workflow above. See the *Hooks...* entry on the **Session Menu** for details about when these session states are reached.

__Note: The CORE GUI is currently in a state of transition.  The replacement candidate is currently in an alpha version, and can be found [here](https://github.com/coreemu/core/wiki/CORE-GUI-Update).__

## Prerequisites

Beyond installing CORE, you must have the CORE daemon running.  This is done on the command line with either Systemd or SysV
```shell
# systed
sudo systemctl daemon-reload
sudo systemctl start core-daemon

# sysv
sudo service core-daemon start
```

You can also invoke the daemon directly from the command line, which can be useful if you'd like to see the logging output directly.
```
# direct invocation
sudo core-daemon
```

## Modes of Operation

The CORE GUI has two primary modes of operation, **Edit** and **Execute** modes. Running the GUI, by typing **core-gui** with no options, starts in Edit mode.  Nodes are drawn on a blank canvas using the toolbar on the left and configured from right-click menus or by double-clicking them. The GUI does not need to be run as root.

Once editing is complete, pressing the green **Start** button (or choosing **Execute** from the **Session** menu) instantiates the topology within the Linux kernel and enters Execute mode. In execute mode, the user can interact with the running emulated machines by double-clicking or right-clicking on them. The editing toolbar disappears and is replaced by an execute toolbar, which provides tools while running the emulation. Pressing the red **Stop** button  (or choosing **Terminate** from the **Session** menu) will destroy the running emulation and return CORE to Edit mode.

CORE can be started directly in Execute mode by specifying **--start** and a topology file on the command line:

```shell
core-gui --start ~/.core/configs/myfile.imn
```

Once the emulation is running, the GUI can be closed, and a prompt will appear asking if the emulation should be terminated. The emulation may be left running and the GUI can reconnect to an existing session at a later time.

The GUI can be run as a normal user on Linux.

The GUI can be connected to a different address or TCP port using the **--address** and/or **--port** options. The defaults are shown below.

```shell
core-gui --address 127.0.0.1 --port 4038
```

## Toolbar

The toolbar is a row of buttons that runs vertically along the left side of the CORE GUI window. The toolbar changes depending on the mode of operation.

### Editing Toolbar

When CORE is in Edit mode (the default), the vertical Editing Toolbar exists on the left side of the CORE window. Below are brief descriptions for each toolbar item, starting from the top. Most of the tools are grouped into related sub-menus, which appear when you click on their group icon.

| Toolbar item | Functionality |
|---|---|
| ![alt text](../gui/icons/tiny/select.gif) *Selection Tool* | default tool for selecting, moving, configuring nodes. |
| ![alt text](../gui/icons/tiny/start.gif) *Start button* | starts Execute mode, instantiates the emulation. |
| ![alt text](../gui/icons/tiny/link.gif) *Link* | the Link Tool allows network links to be drawn between two nodes by clicking and dragging the mouse. |
### ![alt text](../gui/icons/tiny/router.gif) Network-layer virtual nodes

| Network-layer node | Description |
|---|---|
| ![alt text](../gui/icons/tiny/router.gif) *Router* | runs Quagga OSPFv2 and OSPFv3 routing to forward packets. |
| ![alt text](../gui/icons/tiny/host.gif) *Host* | emulated server machine having a default route, runs SSH server. |
| ![alt text](../gui/icons/tiny/pc.gif) *PC* | basic emulated machine having a default route, runs no processes by default. |
| ![alt text](../gui/icons/tiny/mdr.gif) *MDR* | runs Quagga OSPFv3 MDR routing for MANET-optimized routing. |
| ![alt text](../gui/icons/tiny/router_green.gif) *PRouter* | physical router represents a real testbed machine. |
| ![alt text](../gui/icons/tiny/document-properties.gif) *Edit* | edit node types button invokes the CORE Node Types dialog. New types of nodes may be created having different icons and names. The default services that are started with each node type can be changed here. |
### ![alt text](../gui/icons/tiny/hub.gif) Link-layer nodes

| Link-layer node | Description |
|---|---|
| ![alt text](../gui/icons/tiny/hub.gif)  *Hub* | the Ethernet hub forwards incoming packets to every connected node. |
| ![alt text](../gui/icons/tiny/lanswitch.gif) *Switch* | the Ethernet switch intelligently forwards incoming packets to attached hosts using an Ethernet address hash table. |
| ![alt text](../gui/icons/tiny/wlan.gif) *Wireless LAN* | when routers are connected to this WLAN node, they join a wireless network and an antenna is drawn instead of a connecting line; the WLAN node typically controls connectivity between attached wireless nodes based on the distance between them. |
| ![alt text](../gui/icons/tiny/rj45.gif) *RJ45* | with the RJ45 Physical Interface Tool, emulated nodes can be linked to real physical interfaces; using this tool, real networks and devices can be physically connected to the live-running emulation. |
| ![alt text](../gui/icons/tiny/tunnel.gif) *Tunnel* | the Tunnel Tool allows connecting together more than one CORE emulation using GRE tunnels. |

### Anotation Tools

| Tool | Functionality |
|---|---|
| ![alt text](../gui/icons/tiny/marker.gif) *Marker* | for drawing marks on the canvas. |
| ![alt text](../gui/icons/tiny/oval.gif) *Oval* | for drawing circles on the canvas that appear in the background. |
| ![alt text](../gui/icons/tiny/rectangle.gif) *Rectangle* | for drawing rectangles on the canvas that appear in the background. |
| ![alt text](../gui/icons/tiny/text.gif) *Text* | for placing text captions on the canvas. |

### Execution Toolbar

When the Start button is pressed, CORE switches to Execute mode, and the Edit toolbar on the left of the CORE window is replaced with the Execution toolbar Below are the items on this toolbar, starting from the top.

| Tool | Functionality |
|---|---|
| ![alt text](../gui/icons/tiny/select.gif) *Selection Tool* | in Execute mode, the Selection Tool can be used for moving nodes around the canvas, and double-clicking on a node will open a shell window for that node; right-clicking on a node invokes a pop-up menu of run-time options for that node. |
| ![alt text](../gui/icons/tiny/stop.gif) *Stop button* | stops Execute mode, terminates the emulation, returns CORE to edit mode. |
| ![alt text](../gui/icons/tiny/observe.gif) *Observer Widgets Tool* | clicking on this magnifying glass icon  invokes a menu for easily selecting an Observer Widget. The icon has a darker gray background when an Observer Widget is active, during which time moving the mouse over a node will pop up an information display for that node. |
| ![alt text](../gui/icons/tiny/plot.gif) *Plot Tool* | with this tool enabled, clicking on any link will activate the Throughput Widget and draw a small, scrolling throughput plot on the canvas. The plot shows the real-time kbps traffic for that link. The plots may be dragged around the canvas; right-click on a plot to remove it. |
| ![alt text](../gui/icons/tiny/marker.gif) *Marker* | for drawing freehand lines on the canvas, useful during demonstrations; markings are not saved. |
| ![alt text](../gui/icons/tiny/twonode.gif) *Two-node Tool* | click to choose a starting and ending node, and run a one-time *traceroute* between those nodes or a continuous *ping -R* between nodes. The output is displayed in real time in a results box, while the IP addresses are parsed and the complete network path is highlighted on the  CORE display. |
| ![alt text](../gui/icons/tiny/run.gif) *Run Tool* | this tool allows easily running a command on all or a subset of all nodes. A list box allows selecting any of the nodes. A text entry box allows entering any command. The command should return immediately, otherwise the display will block awaiting response. The *ping* command, for example, with no parameters, is not a good idea. The result of each command is displayed in a results box. The first occurrence of the special text "NODE" will be replaced with the node name. The command will not be attempted to run on nodes that are not routers, PCs, or hosts, even if they are selected. |

## Menubar

The menubar runs along the top of the CORE GUI window and provides access to a
variety of features. Some of the menus are detachable, such as the *Widgets*
menu, by clicking the dashed line at the top.

### File Menu

The File menu contains options for manipulating the **.imn** Configuration Files. Generally, these menu items should not be used in
Execute mode.

| Option | Functionality |
|---|---|
| *New* |this starts a new file with an empty canvas. |
| *Open* | invokes the File Open dialog box for selecting a new **.imn** or XML file to open. You can change the default path used for this dialog in the Preferences Dialog. |
| *Save* | saves the current topology. If you have not yet specified a file name, the Save As dialog box is invoked. |
| *Save As XML* | invokes the Save As dialog box for selecting a new **.xml** file for saving the current configuration in the XML file. |
| *Save As imn* | invokes the Save As dialog box for selecting a new **.imn** topology file for saving the current configuration. Files are saved in the *IMUNES network configuration* file. |
| *Export Python script* | prints Python snippets to the console, for inclusion in a CORE Python script. |
| *Execute XML or Python script* | invokes a File Open dialog box for selecting an XML file to run or a Python script to run and automatically connect to. If a Python script, the script must create a new CORE Session and add this session to the daemon's list of sessions in order for this to work. |
| *Execute Python script with options* | invokes a File Open dialog box for selecting a Python script to run and automatically connect to. After a selection is made, a Python Script Options dialog box is invoked to allow for command-line options to be added. The Python script must create a new CORE Session and add this session to the daemon's list of sessions in order for this to work. |
| *Open current file in editor* | this opens the current topology file in the **vim** text editor. First you need to save the file. Once the file has been edited with a text editor, you will need to reload the file to see your changes. The text editor can be changed from the Preferences Dialog. |
| *Print* | this uses the Tcl/Tk postscript command to print the current canvas to a printer. A dialog is invoked where you can specify a printing command, the default being **lpr**. The postscript output is piped to the print command. |
| *Save screenshot* | saves the current canvas as a postscript graphic file. |
| *Recently used files* | above the Quit menu command is a list of recently use files, if any have been opened. You can clear this list in the Preferences dialog box. You can specify the number of files to keep in this list from the Preferences dialog. Click on one of the file names listed to open that configuration file. |
| *Quit* | the Quit command should be used to exit the CORE GUI. CORE may prompt for termination if you are currently in Execute mode. Preferences and the recently-used files list are saved. |

### Edit Menu

| Option | Functionality |
|---|---|
| *Undo* | attempts to undo the last edit in edit mode. |
| *Redo* | attempts to redo an edit that has been undone. |
| *Cut*, *Copy*, *Paste* | used to cut, copy, and paste a selection. When nodes are pasted, their node numbers are automatically incremented, and existing links are preserved with new IP addresses assigned. Services and their customizations are copied to the new node, but care should be taken as node IP addresses have changed with possibly old addresses remaining in any custom service configurations. Annotations may also be copied and pasted.
| *Select All* | selects all items on the canvas. Selected items can be moved as a group. |
| *Select Adjacent* | select all nodes that are linked to the already selected node(s). For wireless nodes this simply selects the WLAN node(s) that the wireless node belongs to. You can use this by clicking on a node and pressing CTRL+N to select the adjacent nodes. |
| *Find...* | invokes the *Find* dialog box. The Find dialog can be used to search for nodes by name or number. Results are listed in a table that includes the node or link location and details such as IP addresses or link parameters. Clicking on a result will focus the canvas on that node or link, switching canvases if necessary. |
| *Clear marker* | clears any annotations drawn with the marker tool. Also clears any markings used to indicate a node's status. |
| *Preferences...* | invokes the Preferences dialog box. |

### Canvas Menu

The canvas menu provides commands for adding, removing, changing, and switching to different editing canvases.

| Option | Functionality |
|---|---|
| *New* | creates a new empty canvas at the right of all existing canvases. |
| *Manage...* | invokes the *Manage Canvases* dialog box, where canvases may be renamed and reordered, and you can easily switch to one of the canvases by selecting it. |
| *Delete* | deletes the current canvas and all items that it contains. |
| *Size/scale...* | invokes a Canvas Size and Scale dialog that allows configuring the canvas size, scale, and geographic reference point. The size controls allow changing the width and height of the current canvas, in pixels or meters. The scale allows specifying how many meters are equivalent to 100 pixels. The reference point controls specify the latitude, longitude, and altitude reference point used to convert between geographic and Cartesian coordinate systems. By clicking the *Save as default* option, all new canvases will be created with these properties. The default canvas size can also be changed in the Preferences dialog box.
| *Wallpaper...* | used for setting the canvas background image. |
| *Previous*, *Next*, *First*, *Last* | used for switching the active canvas to the first, last, or adjacent canvas. |

### View Menu

The View menu features items for controlling what is displayed on the drawing
canvas.

| Option | Functionality |
|---|---|
| *Show* | opens a submenu of items that can be displayed or hidden, such as interface names, addresses, and labels. Use these options to help declutter the display. These options are generally saved in the topology files, so scenarios have a more consistent look when copied from one computer to another. |
| *Show hidden nodes* | reveal nodes that have been hidden. Nodes are hidden by selecting one or more nodes, right-clicking one and choosing *hide*. |
| *Locked* | toggles locked view; when the view is locked, nodes cannot be moved around on the canvas with the mouse. This could be useful when sharing the topology with someone and you do not expect them to change things. |
| *3D GUI...* | launches a 3D GUI by running the command defined under Preferences, *3D GUI command*. This is typically a script that runs the SDT3D display. SDT is the Scripted Display Tool from NRL that is based on NASA's Java-based WorldWind virtual globe software. |
| *Zoom In* | magnifies the display. You can also zoom in by clicking *zoom 100%* label in the status bar, or by pressing the **+** (plus) key. |
| *Zoom Out* | reduces the size of the display. You can also zoom out by right-clicking *zoom 100%* label in the status bar or by pressing the **-** (minus) key. |

### Tools Menu

The tools menu lists different utility functions.

| Option | Functionality |
|---|---|
| *Autorearrange all* |automatically arranges all nodes on the canvas. Nodes having a greater number of links are moved to the center. This mode can continue to run while placing nodes. To turn off this autorearrange mode, click on a blank area of the canvas with the select tool, or choose this menu option again. |
| *Autorearrange selected* | automatically arranges the selected nodes on the canvas. |
| *Align to grid* | moves nodes into a grid formation, starting with the smallest-numbered node in the upper-left corner of the canvas, arranging nodes in vertical columns. |
| *Traffic...* | invokes the CORE Traffic Flows dialog box, which allows configuring, starting, and stopping MGEN traffic flows for the emulation. |
| *IP addresses...* | invokes the IP Addresses dialog box for configuring which IPv4/IPv6 prefixes are used when automatically addressing new interfaces. |
| *MAC addresses...* | invokes the MAC Addresses dialog box for configuring the starting number used as the lowest byte when generating each interface MAC address. This value should be changed when tunneling between CORE emulations to prevent MAC address conflicts. |
| *Build hosts file...* | invokes the Build hosts File dialog box for generating **/etc/hosts** file entries based on IP addresses used in the emulation. |
| *Renumber nodes...* | invokes the Renumber Nodes dialog box, which allows swapping one node number with another in a few clicks. |
| *Experimental...* |  menu of experimental options, such as a tool to convert ns-2 scripts to IMUNES imn topologies, supporting only basic ns-2 functionality, and a tool for automatically dividing up a topology into partitions. |
| *Topology generator* | opens a submenu of topologies to generate. You can first select the type of node that the topology should consist of, or routers will be chosen by default. Nodes may be randomly placed, aligned in grids, or various other topology patterns. All of the supported patterns are listed in the table below. |
| *Debugger...* | opens the CORE Debugger window for executing arbitrary Tcl/Tk commands. |

| Pattern | Description |
|---|---|
| *Random* | nodes are randomly placed about the canvas, but are not linked together. This can be used in conjunction with a WLAN node to quickly create a wireless network. |
| *Grid* | nodes are placed in horizontal rows starting in the upper-left corner, evenly spaced to the right; nodes are not linked to each other. |
| *Connected Grid* | nodes are placed in an N x M (width and height) rectangular grid, and each node is linked to the node above, below, left and right of itself. |
| *Chain* | nodes are linked together one after the other in a chain. |
| *Star* |  one node is placed in the center with N nodes surrounding it in a circular pattern, with each node linked to the center node. |
| *Cycle* | nodes are arranged in a circular pattern with every node connected to its neighbor to form a closed circular path. |
| *Wheel* | the wheel pattern links nodes in a combination of both Star and Cycle patterns. |
| *Cube* | generate a cube graph of nodes. |
| *Clique* | creates a clique graph of nodes, where every node is connected to every other node. |
| *Bipartite* | creates a bipartite graph of nodes, having two disjoint sets of vertices. |

### Widgets Menu

*Widgets* are GUI elements that allow interaction with a running emulation.
Widgets typically automate the running of commands on emulated nodes to report
status information of some type and display this on screen.

#### Periodic Widgets

These Widgets are those available from the main *Widgets* menu. More than one
of these Widgets may be run concurrently. An event loop fires once every second
that the emulation is running. If one of these Widgets is enabled, its periodic
routine will be invoked at this time. Each Widget may have a configuration
dialog box which is also accessible from the *Widgets* menu.

Here are some standard widgets:

* *Adjacency* - displays router adjacency states for Quagga's OSPFv2 and OSPFv3
  routing protocols. A line is drawn from each router halfway to the router ID
  of an adjacent router. The color of the line is based on the OSPF adjacency
  state such as Two-way or Full. To learn about the different colors, see the
  *Configure Adjacency...* menu item. The **vtysh** command is used to
  dump OSPF neighbor information.
  Only half of the line is drawn because each
  router may be in a different adjacency state with respect to the other.
* *Throughput* - displays the kilobits-per-second throughput above each link,
  using statistics gathered from the ng_pipe Netgraph node that implements each
  link. If the throughput exceeds a certain threshold, the link will become
  highlighted. For wireless nodes which broadcast data to all nodes in range,
  the throughput rate is displayed next to the node and the node will become
  circled if the threshold is exceeded.

#### Observer Widgets

These Widgets are available from the *Observer Widgets* submenu of the
*Widgets* menu, and from the Widgets Tool on the toolbar. Only one Observer Widget may
be used at a time. Mouse over a node while the session is running to pop up
an informational display about that node.

Available Observer Widgets include IPv4 and IPv6 routing tables, socket
information, list of running processes, and OSPFv2/v3 neighbor information.

Observer Widgets may be edited by the user and rearranged. Choosing *Edit...*
from the Observer Widget menu will invoke the Observer Widgets dialog. A list
of Observer Widgets is displayed along with up and down arrows for rearranging
the list. Controls are available for renaming each widget, for changing the
command that is run during mouse over, and for adding and deleting items from
the list. Note that specified commands should return immediately to avoid
delays in the GUI display. Changes are saved to a **widgets.conf** file in
the CORE configuration directory.

### Session Menu

The Session Menu has entries for starting, stopping, and managing sessions,
in addition to global options such as node types, comments, hooks, servers,
and options.

| Option | Functionality |
|---|---|
| *Start* or *Stop* | this starts or stops the emulation, performing the same function as the green Start or red Stop button. |
| *Change sessions...* | invokes the CORE Sessions dialog box containing a list of active CORE sessions in the daemon. Basic session information such as name, node count, start time, and a thumbnail are displayed. This dialog allows connecting to different sessions, shutting them down, or starting a new session. |
| *Node types...* | invokes the CORE Node Types dialog, performing the same function as the Edit button on the Network-Layer Nodes toolbar. |
| *Comments...* | invokes the CORE Session Comments window where optional text comments may be specified. These comments are saved at the top of the configuration file, and can be useful for describing the topology or how to use the network. |
| *Hooks...* | invokes the CORE Session Hooks window where scripts may be configured for a particular session state. The session states are defined in the table right below. The top of the window has a list of configured hooks, and buttons on the bottom left allow adding, editing, and removing hook scripts. The new or edit button will open a hook script editing window.  A hook script is a shell script invoked on the host (not within a virtual node). |
| *Reset node positions* | if you have moved nodes around using the mouse or by using a mobility module, choosing this item will reset all nodes to their original position on the canvas. The node locations are remembered when you first press the Start button. |
| *Emulation servers...* | invokes the CORE emulation servers dialog for configuring. |
| *Change Sessions...* | invokes the Sessions dialog for switching between different running sessions. This dialog is presented during startup when one or more sessions are already running. |
| *Options...* | presents per-session options, such as the IPv4 prefix to be used, if any, for a control network the ability to preserve the session directory; and an on/off switch for SDT3D support. |

| Session state | Description |
|---|---|
| *definition* | used by the GUI to tell the backend to clear any state. |
| *configuration* | when the user presses the *Start* button, node, link, and other configuration data is sent to the backend. This state is also reached when the user customizes a service. |
| *instantiation* | after configuration data has been sent, just before the nodes are created. |
| *runtime* | all nodes and networks have been built and are running. (This is the same state at which the previously-named *global experiment script* was run.)
| *datacollect* | the user has pressed the *Stop* button, but before services have been stopped and nodes have been shut down. This is a good time to collect log files and other data from the nodes. |
| *shutdown* | all nodes and networks have been shut down and destroyed. |

### Help Menu

* *Online manual (www)*, *CORE website (www)*, *Mailing list (www)* - these
  options attempt to open a web browser with the link to the specified web
  resource.
* *About* - invokes the About dialog box for viewing version information

## Connecting with Physical Networks

CORE's emulated networks run in real time, so they can be connected to live
physical networks. The RJ45 tool and the Tunnel tool help with connecting to
the real world. These tools are available from the *Link-layer nodes* menu.

When connecting two or more CORE emulations together, MAC address collisions
should be avoided. CORE automatically assigns MAC addresses to interfaces when
the emulation is started, starting with **00:00:00:aa:00:00** and incrementing
the bottom byte. The starting byte should be changed on the second CORE machine
using the *MAC addresses...* option from the *Tools* menu.

### RJ45 Tool

The RJ45 node in CORE represents a physical interface on the real CORE machine.
Any real-world network device can be connected to the interface and communicate
with the CORE nodes in real time.

The main drawback is that one physical interface is required for each
connection. When the physical interface is assigned to CORE, it may not be used
for anything else. Another consideration is that the computer or network that
you are connecting to must be co-located with the CORE machine.

To place an RJ45 connection, click on the *Link-layer nodes* toolbar and select
the *RJ45 Tool* from the submenu. Click on the canvas near the node you want to
connect to. This could be a router, hub, switch, or WLAN, for example. Now
click on the *Link Tool* and draw a link between the RJ45 and the other node.
The RJ45 node will display "UNASSIGNED". Double-click the RJ45 node to assign a
physical interface. A list of available interfaces will be shown, and one may
be selected by double-clicking its name in the list, or an interface name may
be entered into the text box.

**NOTE:**
   When you press the Start button to instantiate your topology, the
   interface assigned to the RJ45 will be connected to the CORE topology. The
   interface can no longer be used by the system. For example, if there was an
   IP address assigned to the physical interface before execution, the address
   will be removed and control given over to CORE. No IP address is needed; the
   interface is put into promiscuous mode so it will receive all packets and
   send them into the emulated world.

Multiple RJ45 nodes can be used within CORE and assigned to the same physical
interface if 802.1x VLANs are used. This allows for more RJ45 nodes than
physical ports are available, but the (e.g. switching) hardware connected to
the physical port must support the VLAN tagging, and the available bandwidth
will be shared.

You need to create separate VLAN virtual devices on the Linux host,
and then assign these devices to RJ45 nodes inside of CORE. The VLANning is
actually performed outside of CORE, so when the CORE emulated node receives a
packet, the VLAN tag will already be removed.

Here are example commands for creating VLAN devices under Linux:

```shell
ip link add link eth0 name eth0.1 type vlan id 1
ip link add link eth0 name eth0.2 type vlan id 2
ip link add link eth0 name eth0.3 type vlan id 3
```

### Tunnel Tool

The tunnel tool builds GRE tunnels between CORE emulations or other hosts.
Tunneling can be helpful when the number of physical interfaces is limited or
when the peer is located on a different network. Also a physical interface does
not need to be dedicated to CORE as with the RJ45 tool.

The peer GRE tunnel endpoint may be another CORE machine or another
host that supports GRE tunneling. When placing a Tunnel node, initially
the node will display "UNASSIGNED". This text should be replaced with the IP
address of the tunnel peer. This is the IP address of the other CORE machine or
physical machine, not an IP address of another virtual node.

**NOTE:**
   Be aware of possible MTU (Maximum Transmission Unit) issues with GRE devices. The *gretap* device
   has an interface MTU of 1,458 bytes; when joined to a Linux bridge, the
   bridge's MTU
   becomes 1,458 bytes. The Linux bridge will not perform fragmentation for
   large packets if other bridge ports have a higher MTU such as 1,500 bytes.

The GRE key is used to identify flows with GRE tunneling. This allows multiple
GRE tunnels to exist between that same pair of tunnel peers. A unique number
should be used when multiple tunnels are used with the same peer. When
configuring the peer side of the tunnel, ensure that the matching keys are
used.

Here are example commands for building the other end of a tunnel on a Linux
machine. In this example, a router in CORE has the virtual address
**10.0.0.1/24** and the CORE host machine has the (real) address
**198.51.100.34/24**.  The Linux box
that will connect with the CORE machine is reachable over the (real) network
at **198.51.100.76/24**.
The emulated router is linked with the Tunnel Node. In the
Tunnel Node configuration dialog, the address **198.51.100.76** is entered, with
the key set to **1**. The gretap interface on the Linux box will be assigned
an address from the subnet of the virtual router node,
**10.0.0.2/24**.
```shell
# these commands are run on the tunnel peer
sudo ip link add gt0 type gretap remote 198.51.100.34 local 198.51.100.76 key 1
sudo ip addr add 10.0.0.2/24 dev gt0
sudo ip link set dev gt0 up
```


Now the virtual router should be able to ping the Linux machine:

```shell
# from the CORE router node
ping 10.0.0.2
```

And the Linux machine should be able to ping inside the CORE emulation:

```shell
# from the tunnel peer
ping 10.0.0.1
```

To debug this configuration, **tcpdump** can be run on the gretap devices, or
on the physical interfaces on the CORE or Linux machines. Make sure that a
firewall is not blocking the GRE traffic.

### Communicating with the Host Machine

The host machine that runs the CORE GUI and/or daemon is not necessarily
accessible from a node. Running an X11 application on a node, for example,
requires some channel of communication for the application to connect with
the X server for graphical display. There are several different ways to
connect from the node to the host and vice versa.


#### Control Network

The quickest way to connect with the host machine through the primary control network.

With a control network, the host can launch an X11 application on a node.
To run an X11 application on the node, the **SSH** service can be enabled on
the node, and SSH with X11 forwarding can be used from the host to the node:

```shell
# SSH from host to node n5 to run an X11 app
ssh -X 172.16.0.5 xclock
```

Note that the **coresendmsg** utility can be used for a node to send
messages to the CORE daemon running on the host (if the **listenaddr = 0.0.0.0**
is set in the **/etc/core/core.conf** file) to interact with the running
emulation. For example, a node may move itself or other nodes, or change
its icon based on some node state.

#### Other Methods

There are still other ways to connect a host with a node. The RJ45 Tool
can be used in conjunction with a dummy interface to access a node:

```shell
sudo modprobe dummy numdummies=1
```

A **dummy0** interface should appear on the host. Use the RJ45 tool assigned
to **dummy0**, and link this to a node in your scenario. After starting the
session, configure an address on the host.

```shell
sudo ip link show type bridge
# determine bridge name from the above command
# assign an IP address on the same network as the linked node
sudo ip addr add 10.0.1.2/24 dev b.48304.34658
```

In the example shown above, the host will have the address **10.0.1.2** and
the node linked to the RJ45 may have the address **10.0.1.1**.

## Building Sample Networks

### Wired Networks

Wired networks are created using the *Link Tool* to draw a link between two
nodes. This automatically draws a red line representing an Ethernet link and
creates new interfaces on network-layer nodes.

Double-click on the link to invoke the *link configuration* dialog box. Here
you can change the Bandwidth, Delay, Loss, and Duplicate
rate parameters for that link. You can also modify the color and width of the
link, affecting its display.

Link-layer nodes are provided for modeling wired networks. These do not create
a separate network stack when instantiated, but are implemented using Linux bridging.
These are the hub, switch, and wireless LAN nodes. The hub copies each packet from
the incoming link to every connected link, while the switch behaves more like an
Ethernet switch and keeps track of the Ethernet address of the connected peer,
forwarding unicast traffic only to the appropriate ports.

The wireless LAN (WLAN) is covered in the next section.

### Wireless Networks

The wireless LAN node allows you to build wireless networks where moving nodes
around affects the connectivity between them. Connection between a pair of nodes is stronger
when the nodes are closer while connection is weaker when the nodes are further away.
The wireless LAN, or WLAN, node appears as a small cloud. The WLAN offers
several levels of wireless emulation fidelity, depending on your modeling needs.

The WLAN tool can be extended with plug-ins for different levels of wireless
fidelity. The basic on/off range is the default setting available on all
platforms. Other plug-ins offer higher fidelity at the expense of greater
complexity and CPU usage. The availability of certain plug-ins varies depending
on platform. See the table below for a brief overview of wireless model types.


|Model|Type|Supported Platform(s)|Fidelity|Description|
|-----|----|---------------------|--------|-----------|
|Basic|on/off|Linux|Low|Ethernet bridging with ebtables|
|EMANE|Plug-in|Linux|High|TAP device connected to EMANE emulator with pluggable MAC and PHY radio types|

To quickly build a wireless network, you can first place several router nodes
onto the canvas. If you have the
Quagga MDR software installed, it is
recommended that you use the *mdr* node type for reduced routing overhead. Next
choose the *wireless LAN* from the *Link-layer nodes* submenu. First set the
desired WLAN parameters by double-clicking the cloud icon. Then you can link
all of the routers by right-clicking on the WLAN and choosing *Link to all
routers*.

Linking a router to the WLAN causes a small antenna to appear, but no red link
line is drawn. Routers can have multiple wireless links and both wireless and
wired links (however, you will need to manually configure route
redistribution.) The mdr node type will generate a routing configuration that
enables OSPFv3 with MANET extensions. This is a Boeing-developed extension to
Quagga's OSPFv3 that reduces flooding overhead and optimizes the flooding
procedure for mobile ad-hoc (MANET) networks.

The default configuration of the WLAN is set to use the basic range model,
using the *Basic* tab in the WLAN configuration dialog.  Having this model
selected causes **core-daemon** to calculate the distance between nodes based
on screen pixels. A numeric range in screen pixels is set for the wireless
network using the *Range* slider. When two wireless nodes are within range of
each other, a green line is drawn between them and they are linked.  Two
wireless nodes that are farther than the range pixels apart are not linked.
During Execute mode, users may move wireless nodes around by clicking and
dragging them, and wireless links will be dynamically made or broken.

The *EMANE* tab lists available EMANE models to use for wireless networking.
See the [EMANE](emane.md) chapter for details on using EMANE.

### Mobility Scripting

CORE has a few ways to script mobility.

| Option | Description |
|---|---|
| ns-2 script | the script specifies either absolute positions or waypoints with a velocity. Locations are given with Cartesian coordinates. |
| CORE API | an external entity can move nodes by sending CORE API Node messages with updated X,Y coordinates; the **coresendmsg** utility allows a shell script to generate these messages. |
| EMANE events | see [EMANE](emane.md) for details on using EMANE scripts to move nodes around. Location information is typically given as latitude, longitude, and altitude. |

For the first method, you can create a mobility script using a text
editor, or using a tool such as [BonnMotion](http://net.cs.uni-bonn.de/wg/cs/applications/bonnmotion/),  and associate the script with one of the wireless
using the WLAN configuration dialog box. Click the *ns-2 mobility script...*
button, and set the *mobility script file* field in the resulting *ns2script*
configuration dialog.

Here is an example for creating a BonnMotion script for 10 nodes:

```shell
bm -f sample RandomWaypoint -n 10 -d 60 -x 1000 -y 750
bm NSFile -f sample
# use the resulting 'sample.ns_movements' file in CORE
```

When the Execute mode is started and one of the WLAN nodes has a mobility
script, a mobility script window will appear. This window contains controls for
starting, stopping, and resetting the running time for the mobility script. The
*loop* checkbox causes the script to play continuously. The *resolution* text
box contains the number of milliseconds between each timer event; lower values
cause the mobility to appear smoother but consumes greater CPU time.

The format of an ns-2 mobility script looks like:

```shell
# nodes: 3, max time: 35.000000, max x: 600.00, max y: 600.00
$node_(2) set X_ 144.0
$node_(2) set Y_ 240.0
$node_(2) set Z_ 0.00
$ns_ at 1.00 "$node_(2) setdest 130.0 280.0 15.0"
```

The first three lines set an initial position for node 2. The last line in the
above example causes node 2 to move towards the destination **(130, 280)** at
speed **15**. All units are screen coordinates, with speed in units per second.
The total script time is learned after all nodes have reached their waypoints.
Initially, the time slider in the mobility script dialog will not be
accurate.

Examples mobility scripts (and their associated topology files) can be found in the **configs/** directory.

## Multiple Canvases

CORE supports multiple canvases for organizing emulated nodes. Nodes running on
different canvases may be linked together.

To create a new canvas, choose *New* from the *Canvas* menu. A new canvas tab
appears in the bottom left corner. Clicking on a canvas tab switches to that
canvas. Double-click on one of the tabs to invoke the *Manage Canvases* dialog
box. Here, canvases may be renamed and reordered, and you can easily switch to
one of the canvases by selecting it.

Each canvas maintains its own set of nodes and annotations. To link between
canvases, select a node and right-click on it, choose *Create link to*, choose
the target canvas from the list, and from that submenu the desired node. A
pseudo-link will be drawn, representing the link between the two nodes on
different canvases. Double-clicking on the label at the end of the arrow will
jump to the canvas that it links.

## Check Emulation Light

The |cel| Check Emulation Light, or CEL, is located in the bottom right-hand corner
of the status bar in the CORE GUI. This is a yellow icon that indicates one or
more problems with the running emulation. Clicking on the CEL will invoke the
CEL dialog.

The Check Emulation Light dialog contains a list of exceptions received from
the CORE daemon. An exception has a time, severity level, optional node number,
and source. When the CEL is blinking, this indicates one or more fatal
exceptions. An exception with a fatal severity level indicates that one or more
of the basic pieces of emulation could not be created, such as failure to
create a bridge or namespace, or the failure to launch EMANE processes for an
EMANE-based network.

Clicking on an exception displays details for that
exception. If a node number is specified, that node is highlighted on the
canvas when the exception is selected. The exception source is a text string
to help trace where the exception occurred; "service:UserDefined" for example,
would appear for a failed validation command with the UserDefined service.

Buttons are available at the bottom of the dialog for clearing the exception
list and for viewing the CORE daemon and node log files.

**NOTE:**
   In batch mode, exceptions received from the CORE daemon are displayed on
   the console.

## Configuration Files

Configurations are saved to **xml** or **.imn** topology files using
the *File* menu. You
can easily edit these files with a text editor.
Any time you edit the topology
file, you will need to stop the emulation if it were running and reload the
file.

The **.xml** [file schema is specified by NRL](https://github.com/USNavalResearchLaboratory/NCS-Downloads/blob/master/mnmtools/EmulationScriptSchemaDescription.pdf) and there are two versions to date:
version 0.0  and version 1.0,
with 1.0 as the current default. CORE can open either XML version. However, the
xmlfilever line in **/etc/core/core.conf** controls the version of the XML file
that CORE will create.

In version 1.0, the XML file is also referred to as the Scenario Plan. The Scenario Plan will be logically
made up of the following:

| Plan | Description |
|---|---|
| **Network Plan** | describes nodes. hosts, interfaces, and the networks to which they belong. |
| **Motion Plan** | describes position and motion patterns for nodes in an emulation. |
| **Services Plan** | describes services (protocols, applications) and traffic flows that are associated with certain nodes. |
| **Visualization Plan** | meta-data that is not part of the NRL XML schema but used only by CORE. For example, GUI options, canvas and annotation info, etc. are contained here. |
| **Test Bed Mappings** | describes mappings of nodes, interfaces and EMANE modules in the scenario to test bed hardware. CORE includes Test Bed Mappings in XML files that are saved while the scenario is running. |

The **.imn** file format comes from IMUNES, and is
basically Tcl lists of nodes, links, etc.
Tabs and spacing in the topology files are important. The file starts by
listing every node, then links, annotations, canvases, and options. Each entity
has a block contained in braces. The first block is indented by four spaces.
Within the **network-config** block (and any *custom-*-config* block), the
indentation is one tab character.

**TIP:**
   There are several topology examples included with CORE in
   the **configs/** directory.
   This directory can be found in **~/.core/configs**, or
   installed to the filesystem
   under **/usr[/local]/share/examples/configs**.

**TIP:**
   When using the **.imn** file format, file paths for things like custom
   icons may contain the special variables **$CORE_DATA_DIR** or **$CONFDIR** which
   will be substituted with **/usr/share/core** or **~/.core/configs**.

**TIP:**
   Feel free to edit the files directly using your favorite text editor.

## Customizing your Topology's Look

Several annotation tools are provided for changing the way your topology is
presented. Captions may be added with the Text tool. Ovals and rectangles may
be drawn in the background, helpful for visually grouping nodes together.

During live demonstrations the marker tool may be helpful for drawing temporary
annotations on the canvas that may be quickly erased. A size and color palette
appears at the bottom of the toolbar when the marker tool is selected. Markings
are only temporary and are not saved in the topology file.

The basic node icons can be replaced with a custom image of your choice. Icons
appear best when they use the GIF or PNG format with a transparent background.
To change a node's icon, double-click the node to invoke its configuration
dialog and click on the button to the right of the node name that shows the
node's current icon.

A background image for the canvas may be set using the *Wallpaper...* option
from the *Canvas* menu. The image may be centered, tiled, or scaled to fit the
canvas size. An existing terrain, map, or network diagram could be used as a
background, for example, with CORE nodes drawn on top.

## Preferences

The *Preferences* Dialog can be accessed from the **Edit_Menu**. There are
numerous defaults that can be set with this dialog, which are stored in the
**~/.core/prefs.conf** preferences file.



