XL Network Configuration

Syntax Overview

This document specifies the xl config file format vif configuration option. It has the following form:

    vif = [ '<vifspec>', '<vifspec>', ... ]

where each vifspec is in this form:

    [<key>=<value>|<flag>,]

For example:

    'mac=00:16:3E:74:3d:76,model=rtl8139,bridge=xenbr0'
    'mac=00:16:3E:74:34:32'
    '' # The empty string

These might be specified in the domain config file like this:

    vif = [ 'mac=00:16:3E:74:34:32', 'mac=00:16:3e:5f:48:e4,bridge=xenbr1' ]

More formally, the string is a series of comma-separated keyword/value pairs. All keywords are optional.

Each device has a DEVID which is its index within the vif list, starting from 0.

Keywords

mac

If specified then this option specifies the MAC address inside the guest of this VIF device. The value is a 48-bit number represented as six groups of two hexadecimal digits, separated by colons (:).

The default if this keyword is not specified is to be automatically generate a MAC address inside the space assigned to Xen's Organizationally Unique Identifier (00:16:3e).

If you are choosing a MAC address then it is strongly recommend to follow one of the following strategies:

• Generate a random sequence of 6 byte, set the locally administered bit (bit 2 of the first byte) and clear the multicast bit (bit 1 of the first byte). In other words the first byte should have the bit pattern xxxxxx10 (where x is a randomly generated bit) and the remaining 5 bytes are randomly generated See [http://en.wikipedia.org/wiki/MAC_address] for more details the structure of a MAC address.
• Allocate an address from within the space defined by your organization's OUI (if you have one) following your organization's procedures for doing so.
• Allocate an address from within the space defined by Xen's OUI (00:16:3e). Taking care not to clash with other users of the physical network segment where this VIF will reside.

If you have an OUI for your own use then that is the preferred strategy. Otherwise in general you should prefer to generate a random MAC and set the locally administered bit since this allows for more bits of randomness than using the Xen OUI.

bridge

Specifies the name of the network bridge which this VIF should be added to. The default is xenbr0. The bridge must be configured using your distribution's network configuration tools. See the wiki for guidance and examples.

type

This keyword is valid for HVM guests only.

Specifies the type of device to valid values are:

• ioemu (default) -- this device will be provided as an emulate device to the guest and also as a paravirtualised device which the guest may choose to use instead if it has suitable drivers available.
• vif -- this device will be provided as a paravirtualised device only.

model

This keyword is valid for HVM guest devices with type=ioemu only.

Specifies the type device to emulated for this guest. Valid values are:

• rtl8139 (default) -- Realtek RTL8139
• e1000 -- Intel E1000
• in principle any device supported by your device model

vifname

Specifies the backend device name for the virtual device.

If the domain is an HVM domain then the associated emulated (tap) device will have a "-emu" suffice added.

The default name for the virtual device is vifDOMID.DEVID where DOMID is the guest domain ID and DEVID is the device number. Likewise the default tap name is vifDOMID.DEVID-emu.

script

Specifies the hotplug script to run to configure this device (e.g. to add it to the relevant bridge). Defaults to XEN_SCRIPT_DIR/vif-bridge but can be set to any script. Some example scripts are installed in XEN_SCRIPT_DIR.

ip

Specifies the IP address for the device, the default is not to specify an IP address.

What, if any, effect this has depends on the hotplug script which is configured. A typically behaviour (exhibited by the example hotplug scripts) if set might be to configure firewall rules to allow only the specified IP address to be used by the guest (blocking all others).

backend

Specifies the backend domain which this device should attach to. This defaults to domain 0. This option does not work if run_hotplug_scripts is not disabled in xl.conf (see xl.conf(5) man page for more information on this option). Specifying another domain requires setting up a driver domain which is outside the scope of this document.

rate

Specifies the rate at which the outgoing traffic will be limited to. The default if this keyword is not specified is unlimited.

The rate may be specified as "/s" or optionally "/s@".

• RATE is in bytes and can accept suffixes:
  • GB, MB, KB, B for bytes.
  • Gb, Mb, Kb, b for bits.
• INTERVAL is in microseconds and can accept suffixes: ms, us, s. It determines the frequency at which the vif transmission credit is replenished. The default is 50ms.

Vif rate limiting is credit-based. It means that for "1MB/s@20ms", the available credit will be equivalent of the traffic you would have done at "1MB/s" during 20ms. This will results in a credit of 20,000 bytes replenished every 20,000 us.

For example:

    'rate=10Mb/s' -- meaning up to 10 megabits every second
    'rate=250KB/s' -- meaning up to 250 kilobytes every second
    'rate=1MB/s@20ms' -- meaning 20,000 bytes in every 20 millisecond period

NOTE: The actual underlying limits of rate limiting are dependent on the underlying netback implementation.