Bridge for UDP tunnels, Ethernet, TAP and VMnet interfaces.
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uBridge is a simple application to create user-land bridges between various technologies. Currently bridging between UDP tunnels, Ethernet and TAP interfaces is supported. Packet capture is also supported.



  • pcap library (Winpcap on Windows).
  • pthread library.

For Ubuntu or other Debian based Linux you need to install this package:

  • libpcap-dev


In the source directory:

sudo make install


In the source directory:

sudo gmake install

Be sure to modify gns_server.conf to point to /usr/local/bin/ubridge.


Install the dependencies:

  • Install Winpcap:
  • Install Cygwin 32-bit (setup-x86.exe):
  • And run setup-x86.exe -X -q -O -s -P make -P gcc-core (install last package compatible with Windows XP)
  • Download and unzip Winpcap developer pack:
  • Copy the libraries WpdPack\Lib\libpacket.a and WpdPack\Lib\libwpcap.a to cygwin\lib\
  • Copy all headers from WpdPack\Include to cygwin\usr\include\

Open the Cygwin terminal:

git clone git://
cd ubridge

You should get ubridge.exe if everything goes well.

Hypervisor mode

The hypervisor mode of uBridge allows you to dynamically add and remove bridges.

You can connect directly to the TCP control port with telnet.

Usage: ubridge -H [<ip_address>:]<tcp_port>

The command syntax is simple: <module> <function> [arguments...] For example: "bridge create test" creates a bridge named "test".

The modules that are currently defined are given below:

  • hypervisor : General hypervisor management
  • bridge : bridges management
  • iol_bridge : IOL (IOS on Linux) bridges management
  • docker : Docker veth management
  • brctl : Linux bridge management

Hypervisor module ("hypervisor")

  • "hypervisor version" : Display the version of dynamips.
hypervisor version
  • "hypervisor module_list" : Display the module list.
101 brctl
101 iol_bridge
101 docker
101 bridge
101 hypervisor
  • "hypervisor cmd_list <module>" : Display commands recognized by the specified module.
hypervisor cmd_list bridge
101 list (min/max args: 0/0)
101 set_pcap_filter (min/max args: 1/2)
101 reset_packet_filters (min/max args: 1/1)
101 delete_packet_filter (min/max args: 2/2)
101 add_packet_filter (min/max args: 2/10)
101 stop_capture (min/max args: 1/1)
101 start_capture (min/max args: 2/3)
101 add_nio_linux_raw (min/max args: 2/2)
101 add_nio_ethernet (min/max args: 2/2)
101 add_nio_tap (min/max args: 2/2)
101 add_nio_unix (min/max args: 3/3)
101 delete_nio_udp (min/max args: 4/4)
101 remove_nio_udp (min/max args: 4/4)
101 add_nio_udp (min/max args: 4/4)
101 rename (min/max args: 2/2)
101 reset_stats (min/max args: 1/1)
101 get_stats (min/max args: 1/1)
101 show (min/max args: 1/1)
101 stop (min/max args: 1/1)
101 start (min/max args: 1/1)
101 delete (min/max args: 1/1)
101 create (min/max args: 1/1)
  • "hypervisor close" : Close the current session.
hypervisor close
Connection closed by foreign host.
  • "hypervisor stop" : Destroy all objects and stop hypervisor.
hypervisor stop
Connection closed by foreign host.
  • "hypervisor reset" : Destroy all objects. (used to get an empty configuration)
hypervisor reset

Bridge module ("bridge")

  • "bridge create <bridge_name>" : Create a new bridge.
bridge create br0
100-bridge 'br0' created
  • "bridge list" : List all exiting Bridges.
bridge list
101 br0 (NIOs = 0)
  • "bridge delete <bridge_name>" : Delete a bridge.
bridge delete br0
100-bridge 'br0' deleted
  • "bridge start <bridge_name>" : Start a bridge. A bridge must have 2 NIOs added in order to start.
bridge start br0
100-bridge 'br0' started
  • "bridge stop <bridge_name>" : Stop a bridge.
bridge stop br0
100-bridge 'br0' stopped
  • "bridge rename <old_bridge_name> <new_bridge_name>" : Rename a bridge.
bridge rename br0 br1
100-bridge 'br0' renamed to 'br1'
  • "bridge add_nio_udp <bridge_name> <local_port> <remote_host> <remote_port>" : Add an UDP NIO with the specified parameters to a bridge.
bridge add_nio_udp br0 20000 30000
100-NIO UDP added to bridge 'br0'
  • "bridge delete_nio_udp <bridge_name> <local_port> <remote_host> <remote_port>" : Remove an UDP NIO with the specified parameters to a bridge.
bridge delete_nio_udp br0 20000 30000
100-NIO UDP deleted from bridge 'br0'
  • "bridge add_nio_unix <local> <remote>" : Add an UNIX NIO with 'local' the UNIX domain socket to receive and 'remote' to send
bridge add_nio_unix br0 "/tmp/local" "/tmp/remote"
100-NIO UNIX added to bridge 'br0'
  • "bridge add_nio_tap <bridge_name> <tap_device>" : Add an TAP NIO to a bridge. TAP devices are supported only on Linux and FreeBSD and require root access.
bridge add_nio_tap br0 tap0
100-NIO TAP added to bridge 'br0'
  • "bridge add_nio_ethernet <bridge_name> <eth_device>" : Add a generic Ethernet NIO to a bridge, using PCAP (0.9.4 and greater). It requires root access.
bridge add_nio_ethernet br0 eth0
100-NIO Ethernet added to bridge 'br0'
  • "bridge add_nio_linux_raw <bridge_name> <eth_device>" : Add a Linux RAW Ethernet NIO. It requires root access and is supported only on Linux platforms.
bridge add_nio_linux_raw br0 eth0
100-NIO Linux raw added to bridge 'br0'
  • "bridge add_nio_fusion_vmnet <bridge_name> <vmnet_device>" : Add a Fusion VMnet NIO. It requires root access and is supported only on Mac OS X.
bridge add_nio_fusion_vmnet br0 vmnet1
100-NIO Fusion VMnet added to bridge 'br0'
  • "bridge show <bridge_name>": Show the NIOs on a bridge.
bridge show bridge0
101 bridge 'br0' is running
101 Source NIO:     20000:
101 Destination NIO: eth0
  • "bridge start_capture <bridge_name> <pcap_file> [pcap_linktype]" : Start a PCAP packet capture on a bridge. PCAP link type default is Ethernet "EN10MB".
bridge start_capture br0 "/tmp/my_capture.pcap"
100-packet capture started on bridge 'br0'
  • "bridge stop_capture <bridge_name>" : Stop a PCAP packet capture on a bridge.
bridge stop_capture br0
100-packet capture stopped on bridge 'br0'
  • "bridge set_pcap_filter <bridge_name> [filter]" : Set a PCAP filter on a bridge. There must be a least one NIO Ethernet attached to the bridge. To reset any applied filter, same command without a filter.
bridge set_pcap_filter br0 "not ether src 00:50:56:c0:00:0a"
100-filter 'not ether src 00:50:56:c0:00:0a' applied on bridge 'br0'
bridge set_pcap_filter br0
100-filter reset on bridge 'br0'
  • "bridge stats <bridge_name>": Show statistics about a bridge input/output.
bridge get_stats bridge0
101 Source NIO:      IN: 5 packets (90 bytes) OUT: 15 packets (410 bytes)
101 Destination NIO: IN: 15 packets (410 bytes) OUT: 5 packets (90 bytes)
  • "bridge reset_stats <bridge_name>": Reset the statistics of a bridge.
bridge reset_stats bridge0
  • "bridge add_packet_filter <bridge_name> <filter_name> <filter_type> [<a4> [...*<a10>*]]": Add a packet filter to a bridge.

Filter types


"frequency_drop" has 1 argument "<frequency>". It will drop everything with a -1 frequency, drop every Nth packet with a positive frequency, or drop nothing.


"packet_loss" has 1 argument "<percentage>" (0 to 100%). The percentage represents the chance for a packet to be lost.


"delay" has 1 argument "<latency>" to delay packets in milliseconds and 1 optional argument <jitter> to add jitter in milliseconds (+/-) of the delay


"corrupt" has 1 argument "<percentage>" (0 to 100%). The percentage represents the chance for a packet to be corrupted.


"bpf" has 1 argument "<filter_expression>", a string written with the Berkeley Packet Filter (BPF) syntax. This filter will drop any packet matching the expression. It also has 1 optional argument <pcap_linktype> which is the PCAP link type, the default is Ethernet "EN10MB".

bridge add_packet_filter br0 "my_filter1" "delay" 50 10
bridge add_packet_filter br0 "my_filter2" "frequency_drop" 5
bridge add_packet_filter br0 "my_filter3" "packet_loss" 20
bridge add_packet_filter br0 "my_filter4" "corrupt" 30
bridge add_packet_filter br0 "my_filter5" "bpf" "icmp[icmptype] == 8"
bridge add_packet_filter br0 "my_filter6" "bpf" "ether host 11:22:33:44:55:66"
bridge add_packet_filter br0 "my_filter7" "bpf" "tcp src port 53"
bridge show br0
101 bridge 'br0' is not running
101 Filter 'my_filter1' configured in position 1
101 Filter 'my_filter2' configured in position 2
101 Filter 'my_filter3' configured in position 3
101 Filter 'my_filter4' configured in position 4
101 Filter 'my_filter5' configured in position 5
101 Filter 'my_filter6' configured in position 6
101 Filter 'my_filter7' configured in position 7
101 Source NIO: 20000:
101 Destination NIO: 20001:
  • "bridge delete_packet_filter <bridge_name> <filter_name>": Delete a packet filter configured on a bridge.
bridge delete_packet_filter br0 "my_filter1"
100-Filter 'my_filter1' delete from bridge 'br0'
  • "bridge reset_packet_filters <bridge_name>": Delete all packet filters configured on a bridge.
bridge reset_packet_filters br0

Docker module ("docker")

  • "docker create_veth <interface_name_1> <interface_name_2>" : Create virtual Ethernet interface pair.
docker create_veth hostif guestif
100-veth pair created: hostif and guestif
  • "docker move_to_ns <interface> <namespace_id> <dst_interface>" : Move Ethernet interface to network namespace. And rename it after the move.
docker move_to_ns guestif 6367 eth0
100-guestif moved to namespace 6367
  • "docker delete_veth <interface_name>" : Delete virtual Ethernet interface.
docker delete_veth hostif
100-veth interface hostif has been deleted

Linux bridge ("brctl")

IOL Bridge module ("iol_bridge")

  • iol_bridge create <name> <id>
iol_bridge create IOL-BRIDGE-513 513
100-IOL bridge 'IOL-BRIDGE-513' created
  • iol_bridge add_nio_udp <name> <iol_id> <bay> <unit> <lport> <rhost> <rport>
  • iol_bridge add_packet_filter <name> <bay> <unit> <filter_name> <filter_type>
  • iol_bridge reset_packet_filters <name> <bay> <unit>
  • iol_bridge start_capture <name> "<output_file>" <data_link_type>
  • iol_bridge delete <name>

Session example

This will bridge a tap0 interface to an UDP tunnel.

Start the hypervisor:

user@host# ./ubridge -H 2232
Hypervisor TCP control server started (port 2232).

Connect via telnet:

user@host# telnet localhost 2232
bridge create br0
100-bridge 'br0' created

bridge start br0
209-bridge 'br0' must have 2 NIOs to be started

bridge add_nio_tap br0 tap0
100-NIO TAP added to bridge 'br0'

bridge add_nio_udp br0 20000 30000
100-NIO UDP added to bridge 'br0'

bridge show br0
101 Source NIO:     tap0
101 Destination NIO: 20000:

bridge start br0
100-bridge 'br0' started

Config file mode

Usage: create a file named ubridge.ini in the same directory as uBridge and then start the executable.

Signal SIGHUP (not available on Windows) can be used to reload the config file.

Example of content:

; bridge Ethernet interface eth0 with an UDP tunnel
source_ethernet = eth0
destination_udp = 10000: ; syntax is local_port:remote_host:remote_port

; bridge TAP interface tap0 with an UDP tunnel
; and capture packets to /tmp/bridge1.pcap
source_tap = tap0
destination_udp = 11000:
pcap_file = /tmp/bridge1.pcap
pcap_protocol = EN10MB ; PCAP data link type, default is EN10MB

; it is even possible to bridge two UDP tunnels and capture!
source_udp = 40000:
destination_udp = 50000:
pcap_file = /tmp/bridge2.pcap

; or to bridge 2 interfaces
source_tap = tap0
destination_ethernet = vmnet2

On Linux you can use a RAW socket to bridge an Ethernet interface (a bit faster than with the default PCAP method).

; bridge Ethernet interface eth0 with an UDP tunnel
; using the RAW socket method (Linux rocks!)
source_linux_raw = eth0
destination_udp = 42000:

There is also the option to use a UNIX domain socket

; bridge UNIX domain socket with an UDP tunnel
source_unix = /tmp/local_file:/tmp/remote_file
destination_udp = 42002:

On Mac OS X you can use the proprietary vmnet ktext module to bridge an VMware Fusion vmnet interface.

; bridge VMware FUsion interface vmnet1 with an UDP tunnel
source_fusion_vmnet = vmnet1
destination_udp = 12000:

On Windows, interfaces must be specified with the NPF notation. You can display all available network devices using ubridge.exe -e on a command line.

; using a Windows NPF interface
source_ethernet = "\Device\NPF_{BC46623A-D65B-4498-9073-96B9DC4C8CBA}"
destination_udp = 10000:
; this will filter out frames with source MAC address 00:50:56:c0:00:0a
pcap_filter = "not ether src 00:50:56:c0:00:0a"


  • A Bridge name (e.g. bridge4) can be anything as long it is unique in the same file or inside the hypervisor.
  • Capabitilies must be set on the executable (Linux only) or you must have administrator rights to bridge Ethernet or TAP interfaces.
  • It is only possible to bridge two interfaces or tunnels together. uBridge is not a hub or a switch!