NAME¶

vnetbuild - an easy to use but powerful namespace setup tool

SYNOPSIS¶

sudo vnetbuild CONFIGFILE { start | stop | status }

vnetbuild CONFIGFILE graphviz OUTFILE.{gv|png|pdf|ps}

DESCRIPTION¶

VNetBuild is a program that helps you set up groups of interconnected network namespaces, to simulate networks of any complexity without resorting to using real or virtual machines.

This is ideal for testing complex multi-host configurations with a minimal amount of resources on a single machine:

•: Each namespace can have its own network setup, including firewall and QOS configuration.
•: Commands can be run in the namespace and will have that specific view of the network, including running standard network tools and daemons.

Run without any arguments, vnetbuild will present some help on usage.

COMMANDS¶

start: Sets up a series of network namespaces as defined in CONFIGFILE. vnetbuild creates interconnected network devices as specified in the configuration, sets up routing and runs any custom commands that are given within the namespace.

stop: Removes any devices from the namespaces defined in CONFIGFILE and kills any processes running with the namespaces, then removes the namespaces themselves.

status: For each namespace defined in CONFIGFILE, shows if it is active and if so its network devices and their configuration.

graphviz OUTFILE: Generates a graph of the network defined in CONFIGFILE. This does not need root access, nor does it require the namespaces to have been started.

OUTFILE can be png pdf or ps. If the extension gv is given the output is a graphviz(7) file which you can process separately.

RUNNING COMMANDS IN A NAMESPACE¶

Once you have created a set of network namespaces, you can easily run any commands you want within them. If for instance you defined three hosts (host_a with IP 10.0.0.1, host_b with IP 10.0.0.2 and host_c with IP 10.0.0.3) connected via a common switch sw0:

 # ping host_b and host_c from host_a
 sudo ip netns exec host_a ping 10.0.0.2
 sudo ip netns exec host_a ping 10.0.0.3
 # use netcat to listen on host_a and send data from host_b
 # (use two terminals to run the commands simultaneously)
 sudo ip netns exec host_a nc -l -p 23
 sudo ip netns exec host_b nc -q 0 10.0.0.1 23 < /etc/hosts
 # capture traffic passing through the switch, then view it
 sudo ip netns exec sw0 tcpdump -i switch -w capfile
 wireshark capfile
 # Use 'firehol panic' in host_b to block all traffic
 # (you could equally load a full config etc.)
 sudo ip netns exec host_b firehol panic
 # this is now blocked
 sudo ip netns exec host_a ping 10.0.0.2
 # not blocked (host_b not involved)
 sudo ip netns exec host_a ping 10.0.0.3
 # obtain a shell for your regular user, only "in" host_c
 sudo ip netns exec host_c sudo -i -u $USER
 ip a | grep 10.0.0.3

SEE ALSO¶

•: vnetbuild.conf(5) - VNetBuild configuration file
•: firehol(1) - FireHOL program
•: fireqos(1) - FireQOS program
•: FireHOL Website (http://firehol.org/)
•: VNetBuild Online PDF Manual (http://firehol.org/vnetbuild-manual.pdf)
•: VNetBuild Online Documentation (http://firehol.org/documentation/) 8 192.168.1.2/24 host b dev vppp0 a/veth0 10.0.0.2/8 192.168.1.3/24 ````

A dev may not specify an IP address if it is in a switch. Switches exist just to tie together multiple devices in hosts, just like a physical network switch.

bridgedev BRIDGE ...: Define an ethernet bridge, BRIDGE in a host. These are setup automatically using ip(8) and shown with bridge(8).

A bridge can specify network devices from its own namespace to be automatically added, as well as its own IP address(es).

host a
  dev veth0
  dev veth1 otherns/vdev0
  bridgedev vbr0 veth0 veth1 10.0.0.3/8

Devices included in a bridge generally do not need their own IP address (although that is permitted).

Bridges cannot have a pair themselves, but any devices added to a bridge need a pair as usual.

route ROUTECMD: Specify an additional network route for a host.

Most commonly to add a default route from hosts on a "LAN" to the machine that acts as a gateway, e.g.:

route default via 10.0.0.254

The syntax of ROUTECMD is anything that can fit this pattern:

ip route add ROUTECMD

See ip(8) and ip-route(8) for help adding routes. If you want to do anything more complex than simply adding routes, use the exec configuration statement.

pre_up DEVICE CUSTOMCMD: Execute custom commands in a host or switch just before bringing up the specified device. All of the pre_up statements for a device are combined and executed in the namespace.

In addition to any explicitly defined interfaces, switches have an implicit bridge device called switch which can also be used in pre_up commands.

Bridges always start after other devices, so to run a command after all everything has been created but before any interfaces are up, you can make use of pre_up on the first defined dev.

See below for some common uses for custom pre_up and exec commands.

exec CUSTOMCMD: Execute a custom command in a host or switch once the rest of the namespace setup is complete.

Once all the namespaces are created, the final step in setting each one up is to have its exec statements combined and executed.

It is roughly the equivalent to writing your own script and executing it after vnetbuild start has finished:

sudo ip netns exec myns ./myscript.sh

See below for some common uses for custom pre_up and exec commands.

COMMON CUSTOM COMMANDS¶

For the most part it doesn't matter whether these commands are used in pre_up or exec operations - the only difference is when they will execute, so e.g. if you want a firewall in place before any interfaces come up then start it from the pre_up of the first device. If you only want the firewall after all devices are up, put it in exec, e.g.:

host myfirewall
    ...
    exec firehol myfirewall.conf start

Forwarding is not enabled by the Linux kernel when a namespace is first created. This can be easily done for any hosts that need to forward traffic:

host mygateway
    ...
    exec echo 1 > /proc/sys/net/ipv4/ip_forward

The exec operates in the mygateway namespace so your host is not affected.

Bridges are created without STP being enabled. To enable STP to ensure loops are not created, the following can be done:

host myhost
    bridgedev vbr0 ...
    ...
    pre_up vbr0 echo 2 > /sys/class/net/vbr0/bridge/stp_state
switch myswitch
    ...
    pre_up switch echo 2 > /sys/class/net/vbr0/bridge/stp_state

You could also use brctl stp vbr0 on and brctl stp switch on instead of setting the values directly. To disable multicast snooping you can use exactly the same method e.g.:

switch myswitch
    ...
    pre_up switch echo 0 > /sys/class/net/switch/bridge/multicast_snooping

It is possible to run firehol within a namespace to set up custom

Logs from network namespaces are not included in the normal system logs. To enable iptables logging you must start an instance of ulogd(8) in the namespace and use ULOG or NFLOG logging. For FireHOL, that means set FIREHOL_LOG_MODE=ULOG or FIREHOL_LOG_MODE=NFLOG. Note that NFLOG only works with ulogd version 2.

The default configuration for ulogd(8) is /etc/ulogd.conf. Assuming the default place it will write iptables logs to is /var/log/ulog/syslogemu.log (otherwise change the sed command as required), it is simple to set up per-namespace logging:

host mygateway
  ...
  exec sed 's:/var/log/ulog/syslogemu.log:/var/log/ulog/mygateway.log:' /etc/ulogd.conf > $NSTMP/ulogd.conf
  exec /usr/sbin/ulogd -d -c $NSTMP/ulogd.conf

The -d flag to ulogd(8) makes it become a daemon; when vnetbuild stop executes it will automatically kill any programs running in the namespaces is is stopping, which includes the logging daemon.

The configuration file will get cleaned as soon as vnetbuild start is finished. To be able to access such files you need to write them to a location not under $NSTMP or create them outside the vnetbuild configuration altogether.

EXAMPLE¶

A simple LAN arrangement with two hosts, one of which is a gateway to third host:

host host01
  dev veth0 10.0.0.1/8
  dev vppp0 192.168.0.1/24
  exec echo 1 > /proc/sys/net/ipv4/ip_forward
  route default via 192.168.0.1
host host02
  dev veth0 10.0.0.2/8
  route default via 10.0.0.1
switch lan
  dev d01 host01/veth0
  dev d02 host02/veth0
host extern01
  dev veth0 host01/vppp0 192.168.0.254/24
  route default via 192.168.0.1
  exec echo 1 > /proc/sys/net/ipv4/ip_forward

LIMITATIONS¶

When created, the namespaces setup by vnetbuild are completely disconnected from any real network. There is no way of defining such a connection in the vnetbuild configuration as allowing it would lead to conflicts with the normal network setup tools and configuration files in most distributions.

It is possible to arrange your network so you can connect real devices into one or more network namespaces. For the general approach see this mailing list post (http://lists.firehol.org/pipermail/firehol-support/2015-April/003043.html).

AUTHORS¶

FireHOL Team.

Source file:	vnetbuild-route.5.en.gz (from firehol-doc 3.1.7-3.2)
Source last updated:	2024-02-26T08:21:39Z
Converted to HTML:	2024-05-02T01:09:12Z