vpcs(1)

Usage

vpcs [options] [scriptfile]

Overview

VPCS provides a command line interface to nine simulated virtual PCs. You can ping/trace route from/to them, or ping/trace route other hosts/routers from the virtual PCs, making it an ideal study tool when you simulate Cisco or Juniper routers in a Dynamips or GNS3 environment.

Virtual PCs are able to generate and respond to ICMP (ping), TCP and UDP packets delivered to the application via a UDP pipe or Unix tap interface. If scriptfile is specified, then vpcs reads the file on start-up and executes the commands in the scriptfile. scriptfile must be in vpcs script file format.

vpcs listens for messages on nine consecutive UDP ports and sends messages on nine consecutive UDP ports. By the default, vpcs listens on UDP ports 20000 to 20008 and sends messages on UDP ports 30000 to 30008. Each UDP port pair (20000/30000, 20001/30001...20008/30008) represents a virtual PC. Virtual PCs are numbered 1 to 9.

Options

-h, --help: Print the command line options and exit

-v: Print the version information and exit

-i num: number of vpc instances to start (default is 9)

[-r] scriptfile: If scriptfile is specified, then vpcs reads the file on start-up and executes the commands in the scriptfile. scriptfile must be in vpcs script file format. By default, if a file named startup.vpc exists in the directory where the vpcs program was started, it will be read and executed when vpcs starts. The -r option is optional if scriptfile is the last parameter.

-p port: Run vpcs as a daemon process listening on TCP port specified by port. As a daemon process, vpcs does not present a command line interface to the user, but the command line interface can be accessed remotely using a TCP stream application such as telnet or netcat (nc). Once the daemon has been started, there is no internal mechanism for terminating the program, and the program must be terminated by sending a system signal 9, typically by using the command kill -9 PID (where PID is the process id of the vpcs instance)

-m num: vpcs uses 9 consecutive MAC addresses for the 9 vpcs stating at 00:50:79:66:68:00 by default. The -m option adds num to the last byte of the base MAC address. Should any increment cause the last byte exceed 0xFF during this process, it will increment to 0x00.

-e: On systems that support the /dev/tapx interface (Unix/Linux), run vpcs in tap mode rather than UDP mode. In tap mode, IP packets are sent and received via /dev/tapx interfaces rather than via UDP streams. Typically /dev/tapx interfaces are only available to the root user, meaning vpcs would also be required to be run by the root user (sudo vpcs -e) to use tap mode.

[-u]: This option is the default and not necessary, but included to contrast with the -e option. By default, vpcs sends and receives IP packets to and from specified UDP ports. vpcs listens on UDP port 20000 and sends to port 127.0.0.1:30000 by default. The listening and sending ports can be manipulated using the -s, -c and -t options.

UDP Mode Options

-s port: port specifies the base port number that vpcs uses to listen for messages. By default vpcs listens for messages on UDP ports 20000 to 20008. By changing the base port that vpcs listens to using the -s option causes nine consecutive UDP ports to be used starting at the port specified by port.

-t ip: vpcs streams packets to nine UDP ports commencing at 127.0.0.1:30000 by default. The -t option allows you to stream packets to a remote host as specified by IPv4 address ip. Typically the remote host will be running dynamips with a cloud connection configured to link to this host’s IP address.

-c port: vpcs streams packets to nine UDP ports commencing at 127.0.0.1:30000. The -c option allows you to stream packets to a different set of nine ports commencing at the base port number specified by port.

TAP Mode Options

-d device: Device name, works only when -i is set to 1

Hypervisor Mode Option

-H port: Run as a hypervisor, listening on TCP port specified by port. In the hypervisor mode, you can connect this control port with telnet, start or stop an instance of vpcs.

Examples

No command line options

If you start the vpcs with no arguments, vpcs will start and look for the script startup.vpc in the current directory. If it exists, it will run the script. This is the normal way of running the vpcs. It is simply envoked from the command line like this:

vpcs

Starting vpcs with an alternative startup file

To start vpcs with a startup script file called say alternate.vpc, use the file name as an argument to the vpcs command:

vpcs alternate.vpc

Running more than nine Virtual PCs

Suppose you needed more than nine Virtual PCs, so you want to run a second instance of vpcs on your local host. You would have to consider:

1. The VPCs MAC addresses for the second instance would need to be different,

2. The "local" or listening UDP port numbers for the second instance would have to differ from the first instance.

3. The remote UDP port numbers for the second instance would have to differ from the first instance.

Since the default local listening port is 20000, and the default remote port is 30000, you would want to start vpcs with a local listening port of 20009 (or greater) and remote port of 30009 (or greater) . You would also want the base MAC address to be offset by at least nine to avoid any clashes. In this case you would use the command:

vpcs -s 20009 -c 30009 -m 9

Running two instances of vpcs that can communicate with each other on the one host

Suppose you wanted to run a second instance of vpcs on your local host that can communicate with the instance already running with a default configuration. You would have to consider:

1. The VPCs MAC addresses for the second instance would need to be different,

2. The "local" or listening UDP port numbers for the second instance would have to match the "remote" port numbers of the first instance

3. The remote UDP port numbers would have to match the "local" or listening UDP port numbers of the first instance

Since the default local listening port is 20000, and the default remote port is 30000, you would want to start vpcs with a local listening port of 30000 and remote port of 20000. You would also want the base MAC address to be offset by at least nine to avoid any clashes. In this case you would use the command:

vpcs -s 30000 -c 20000 -m 9

Base interface

vpcs presents the user with a command line interface (unless daemon mode has been invoked by the -p option). The interface prompt indicates which of the 9 virtual PCs currently has focus by indicating the VPC number in brackets. Eg.:
VPCS[1]
Here the digit 1 inside the brackets indcates that VPC 1 has focus, and any traffic generated will be sent from VPC 1, and basic show commands will relate to VPC 1.

Basic commands supported are:

?: Print help

<digit>: Switch to the VPC<digit>. <digit> range 1 to 9

arp: Shortcut for: show arp. Show arp table

clear [arguments]: Clear IPv4/IPv6, arp/neighbor cache, command history

dhcp [-options]: Shortcut for: ip dhcp. Get IPv4 address via DHCP

echo <text>: Display <text> in output

help: Print help

history: Shortcut for: show history. List the command history

ip [arguments]: Configure VPC's IP settings

load <filename>: Load the configuration/script from the file <filename>

ping <host> [-options]: Ping the network <host> with ICMP (default) or TCP/UDP

quit: Quit program

relay [arguments] <port>: Relay packets between two UDP port

rlogin [<ip>] <port>: Telnet to host relative to HOST PC

save <filename>: Save the configuration to the file <filename>

set [arguments]: Set VPC name, peer ports, dump options, echo on or off

show [arguments]: Print the information of VPCs (default). Try show ?

sleep <seconds> [text]: Print <text> and pause the running script for <seconds>

trace <host> [-options]: Print the path packets take to network <host>

version: Shortcut for: show version

vpcs script file format

Any text file consisting of valid vpcs commands can be used as a vpcs script file. Lines in the file beginning with the # character will be treated as comments and ignored. Command files can make use of the echo and sleep commands to create some form of interactive script.
Script file exececution can be aborted at any time by pressing Ctrl+c. This means that the ping <host> -t command (which must be terimated by Ctrl+c) is not useful in vpcs script files.

Hypervisor interface

commands supported are:

help | ?: Print help

vpcs [parameters]: Start vpcs daemon with parameters.

stop id: Stop vpcs process

list: List vpcs process

disconnect: Exit the telnet session

quit [-f]: Stop vpcs processes and hypervisor, -f force quit without prompting

telnet [<ip>] <port>: Telnet to <port> at <ip> (default 127.0.0.1)

rlogin [<ip>] <port>: Same as telnet

Releases

Unchanged in 6 releases since Debian 8 (Jessie).

8–13