10. Developer’s Guide

This section contains advanced usage information, intended for developers and others who are comfortable with the command line.

10.1. Coding Standard

The coding standard and style guide for the CORE project are maintained online. Please refer to the coding standard posted on the CORE Wiki.

10.2. Source Code Guide

The CORE source consists of several different programming languages for historical reasons. Current development focuses on the Python modules and daemon. Here is a brief description of the source directories.

These are being actively developed as of CORE 4.8:

  • gui - Tcl/Tk GUI. This uses Tcl/Tk because of its roots with the IMUNES project.
  • daemon - Python modules are found in the daemon/core directory, the daemon under daemon/sbin/core-daemon, and Python extension modules for Linux Network Namespace support are in daemon/src.
  • doc - Documentation for the manual lives here in reStructuredText format.
  • packaging - Control files and script for building CORE packages are here.

These directories are not so actively developed:

  • kernel - patches and modules mostly related to FreeBSD.

10.3. The CORE API

The CORE API is used between different components of CORE for communication. The GUI communicates with the CORE daemon using the API. One emulation server communicates with another using the API. The API also allows other systems to interact with the CORE emulation. The API allows another system to add, remove, or modify nodes and links, and enables executing commands on the emulated systems. On FreeBSD, the API is used for enhancing the wireless LAN calculations. Wireless link parameters are updated on-the-fly based on node positions.

CORE listens on a local TCP port for API messages. The other system could be software running locally or another machine accessible across the network.

The CORE API is currently specified in a separate document, available from the CORE website.

10.4. Linux network namespace Commands

Linux network namespace containers are often managed using the Linux Container Tools or lxc-tools package. The lxc-tools website is available here http://lxc.sourceforge.net/ for more information. CORE does not use these management utilities, but includes its own set of tools for instantiating and configuring network namespace containers. This section describes these tools.

The vnoded daemon is the program used to create a new namespace, and listen on a control channel for commands that may instantiate other processes. This daemon runs as PID 1 in the container. It is launched automatically by the CORE daemon. The control channel is a UNIX domain socket usually named /tmp/pycore.23098/n3, for node 3 running on CORE session 23098, for example. Root privileges are required for creating a new namespace.

The vcmd program is used to connect to the vnoded daemon in a Linux network namespace, for running commands in the namespace. The CORE daemon uses the same channel for setting up a node and running processes within it. This program has two required arguments, the control channel name, and the command line to be run within the namespace. This command does not need to run with root privileges.

When you double-click on a node in a running emulation, CORE will open a shell window for that node using a command such as:

gnome-terminal -e vcmd -c /tmp/pycore.50160/n1 -- bash

Similarly, the IPv4 routes Observer Widget will run a command to display the routing table using a command such as:

vcmd -c /tmp/pycore.50160/n1 -- /sbin/ip -4 ro

A script named core-cleanup is provided to clean up any running CORE emulations. It will attempt to kill any remaining vnoded processes, kill any EMANE processes, remove the /tmp/pycore.* session directories, and remove any bridges or ebtables rules. With a -d option, it will also kill any running CORE daemon.

The netns command is not used by CORE directly. This utility can be used to run a command in a new network namespace for testing purposes. It does not open a control channel for receiving further commands.

Here are some other Linux commands that are useful for managing the Linux network namespace emulation.

# view the Linux bridging setup
brctl show
# view the netem rules used for applying link effects
tc qdisc show
# view the rules that make the wireless LAN work
ebtables -L

Below is a transcript of creating two emulated nodes and connecting them together with a wired link:

# create node 1 namespace container
vnoded -c /tmp/n1.ctl -l /tmp/n1.log -p /tmp/n1.pid
# create a virtual Ethernet (veth) pair, installing one end into node 1
ip link add name n1.0.1 type veth peer name n1.0
ip link set n1.0 netns `cat /tmp/n1.pid`
vcmd -c /tmp/n1.ctl -- ip link set lo up
vcmd -c /tmp/n1.ctl -- ip link set n1.0 name eth0 up
vcmd -c /tmp/n1.ctl -- ip addr add dev eth0

# create node 2 namespace container
vnoded -c /tmp/n2.ctl -l /tmp/n2.log -p /tmp/n2.pid
# create a virtual Ethernet (veth) pair, installing one end into node 2
ip link add name n2.0.1 type veth peer name n2.0
ip link set n2.0 netns `cat /tmp/n2.pid`
vcmd -c /tmp/n2.ctl -- ip link set lo up
vcmd -c /tmp/n2.ctl -- ip link set n2.0 name eth0 up
vcmd -c /tmp/n2.ctl -- ip addr add eth0

# bridge together nodes 1 and 2 using the other end of each veth pair
brctl addbr b.1.1
brctl setfd b.1.1 0
brctl addif b.1.1 n1.0.1
brctl addif b.1.1 n2.0.1
ip link set n1.0.1 up
ip link set n2.0.1 up
ip link set b.1.1 up

# display connectivity and ping from node 1 to node 2
brctl show
vcmd -c /tmp/n1.ctl -- ping

The above example script can be found as twonodes.sh in the examples/netns directory. Use core-cleanup to clean up after the script.

10.5. FreeBSD Commands

10.5.1. FreeBSD Kernel Commands

The FreeBSD kernel emulation controlled by CORE is realized through several userspace commands. The CORE GUI itself could be thought of as a glorified script that dispatches these commands to build and manage the kernel emulation.

  • vimage - the vimage command, short for “virtual image”, is used to create lightweight virtual machines and execute commands within the virtual image context. On a FreeBSD CORE machine, see the vimage(8) man page for complete details. The vimage command comes from the VirtNet project which virtualizes the FreeBSD network stack.
  • ngctl - the ngctl command, short for “netgraph control”, creates Netgraph nodes and hooks, connects them together, and allows for various interactions with the Netgraph nodes. See the ngctl(8) man page for complete details. The ngctl command is built-in to FreeBSD because the Netgraph system is part of the kernel.

Both commands must be run as root. Some example usage of the vimage command follows below.

vimage                        # displays the current virtual image
vimage -l                     # lists running virtual images
vimage e0_n0 ps aux   # list the processes running on node 0
for i in 1 2 3 4 5
do                            # execute a command on all nodes
  vimage e0_n$i sysctl -w net.inet.ip.redirect=0

The ngctl command is more complex, due to the variety of Netgraph nodes available and each of their options.

ngctl l                       # list active Netgraph nodes
ngctl show e0_n8:             # display node hook information
ngctl msg e0_n0-n1: getstats # get pkt count statistics from a pipe node
ngctl shutdown \\[0x0da3\\]: # shut down unnamed node using hex node ID

There are many other combinations of commands not shown here. See the online manual (man) pages for complete details.

Below is a transcript of creating two emulated nodes, router0 and router1, and connecting them together with a link:

# create node 0
vimage -c e0_n0
vimage e0_n0 hostname router0
ngctl mkpeer eiface ether ether
vimage -i e0_n0 ngeth0 eth0
vimage e0_n0 ifconfig eth0 link 40:00:aa:aa:00:00
vimage e0_n0 ifconfig lo0 inet localhost
vimage e0_n0 sysctl net.inet.ip.forwarding=1
vimage e0_n0 sysctl net.inet6.ip6.forwarding=1
vimage e0_n0 ifconfig eth0 mtu 1500

# create node 1
vimage -c e0_n1
vimage e0_n1 hostname router1
ngctl mkpeer eiface ether ether
vimage -i e0_n1 ngeth1 eth0
vimage e0_n1 ifconfig eth0 link 40:00:aa:aa:0:1
vimage e0_n1 ifconfig lo0 inet localhost
vimage e0_n1 sysctl net.inet.ip.forwarding=1
vimage e0_n1 sysctl net.inet6.ip6.forwarding=1
vimage e0_n1 ifconfig eth0 mtu 1500

# create a link between n0 and n1
ngctl mkpeer eth0@e0_n0: pipe ether upper
ngctl name eth0@e0_n0:ether e0_n0-n1
ngctl connect e0_n0-n1: eth0@e0_n1: lower ether
ngctl msg e0_n0-n1: setcfg \\
  {{ bandwidth=100000000 delay=0  upstream={ BER=0 dupl
icate=0 }  downstream={ BER=0 duplicate=0 } }}
ngctl msg e0_n0-n1: setcfg {{ downstream={ fifo=1 } }}
ngctl msg e0_n0-n1: setcfg {{ downstream={ droptail=1 } }}
ngctl msg e0_n0-n1: setcfg {{ downstream={ queuelen=50 } }}
ngctl msg e0_n0-n1: setcfg {{ upstream={ fifo=1 } }}
ngctl msg e0_n0-n1: setcfg {{ upstream={ droptail=1 } }}
ngctl msg e0_n0-n1: setcfg {{ upstream={ queuelen=50 } }}

Other FreeBSD commands that may be of interest: .. index:: FreeBSD commands

  • kldstat, kldload, kldunload - list, load, and unload FreeBSD kernel modules
  • sysctl - display and modify various pieces of kernel state
  • pkg_info, pkg_add, pkg_delete - list, add, or remove FreeBSD software packages.
  • vtysh - start a Quagga CLI for router configuration

10.5.2. Netgraph Nodes

Each Netgraph node implements a protocol or processes data in some well-defined manner (see the netgraph(4) man page). The netgraph source code is located in /usr/src/sys/netgraph. There you might discover additional nodes that implement some desired functionality, that have not yet been included in CORE. Using certain kernel commands, you can likely include these types of nodes into your CORE emulation.

The following Netgraph nodes are used by CORE:

  • ng_bridge - switch node performs Ethernet bridging
  • ng_cisco - Cisco HDLC serial links
  • ng_eiface - virtual Ethernet interface that is assigned to each virtual machine
  • ng_ether - physical Ethernet devices, used by the RJ45 tool
  • ng_hub - hub node
  • ng_pipe - used for wired Ethernet links, imposes packet delay, bandwidth restrictions, and other link characteristics
  • ng_socket - socket used by ngctl utility
  • ng_wlan - wireless LAN node