HOSTAPD.CONF(5) OpenBSD Programmer's Manual HOSTAPD.CONF(5)NAMEhostapd.conf - configuration file for the Host Access Point daemon
DESCRIPTIONhostapd.conf is the configuration file for the hostapd(8) daemon.
SECTIONS
The hostapd.conf file is divided into four main sections.
Macros
User-defined variables may be defined and used later, simplifying
the configuration file.
Tables
Tables provide a mechanism to handle a large number of link layer
addresses easily, with increased performance and flexibility.
Global Configuration
Global runtime settings for hostapd(8).
Event Rules
Event rules provide a powerful mechanism to trigger certain actions
when receiving specified IEEE 802.11 frames.
IP Roaming
The concepts and details about the optional IP based roaming in
hostapd(8).
Comments can be put anywhere in the file using a hash mark (`#'), and
extend to the end of the current line.
Additional configuration files can be included with the include keyword,
for example:
include "/etc/hostapd.conf.local"
MACROS
Macros can be defined that will later be expanded in context. Macro
names must start with a letter, and may contain letters, digits and
underscores. Macro names may not be reserved words (for example, set,
interface, or hostap). Macros are not expanded inside quotes.
For example:
wlan="ath0"
set iapp handle subtype { ! add notify, radiotap }
set iapp interface $wlan
TABLES
Tables are named structures which can hold a collection of link layer
addresses, masked address ranges, and link layer to IP address
assignments. Lookups against tables in hostapd(8) are relatively fast,
making a single rule with tables much more efficient, in terms of
processor usage and memory consumption, than a large number of rules
which differ only in link layer addresses.
Tables are used for hostapd(8) event rules to match specified IEEE 802.11
link layer addresses and address ranges, and the capability to assign
link layer to IP addresses and an option netmask is a requirement for
advanced IAPP functionality.
Table options may be presented after the table name declaration. The
following options are supported:
const The table is constant and cannot be later changed from its
original definition.
For example:
cisco="00:40:06:ff:ff:ff & ff:ff:ff:00:00:00"
table <black> { $cisco, 00:0d:60:ff:f1:2a }
table <myess> const {
00:00:24:c3:40:18 -> 10.195.64.24,
00:00:24:c3:40:19 -> 10.195.64.25,
00:00:24:c3:40:1a -> 10.195.64.26
}
table <myclient> const {
00:05:4e:45:d4:b9 -> 172.23.5.1/30
}
GLOBAL CONFIGURATION
The following configuration settings are understood:
set hostap interface interface | {interface0, interface1, ... }
Specify the wireless interface running in Host AP mode. This
option could be omitted to use hostapd(8) to log received IAPP
messages. Multiple hostap interfaces may be specified as a
comma-separated list, surrounded by curly braces.
set hostap mode mode
Specify the Host AP capture mode. The supported modes are:
radiotap Capture IEEE 802.11 frames with additional
radiotap headers. They will provide optional but
useful information like received frame signal
levels.
pcap Capture plain IEEE 802.11 frames.
set hostap hopper interface interface | {interface0, interface1, ... }
Enable a channel hopper on the selected wireless interface.
Multiple hostap interfaces may be specified as a comma-separated
list, surrounded by curly braces.
set hostap hopper delay number
Set the delay in milliseconds for the channel hopper before
hopping to the next available channel. The default value is 800
milliseconds.
set iapp interface interface
Specify the mandatory Inter-Access-Point (IAPP) interface. It is
important that the IAPP interface is on a trusted network because
there is no authentication and an attacker could force
disassociation of selected stations on all listening access
points.
set iapp [address | route] roaming table <table>
Specify a table used for IP Roaming lookups of link layer address
to IP address or subnet assignments.
set iapp handle subtype subtype | {subtype0, subtype1, ... }
Specify the IAPP subtypes to use:
[not] add notify
Send and receive ADD.notify messages. This
option is enabled by default.
[not] radiotap
Receive radiotap messages. This option is
enabled by default.
[not] [address | route] roaming
Enable dynamic roaming of IP addresses or
routes. These options are disabled by default.
set iapp mode mode
Specify the IAPP mode. The supported modes are:
multicast [address ipv4addr] [port number] [ttl number]
Use multicast(4) frames. A multicast time-to-
live (TTL) of 2 or higher is required to allow
multicast forwarding, for example for use with
mrouted(8).
broadcast [port number]
Use broadcast frames.
The default is multicast using the multicast address 224.0.1.178
and port 3517 with a TTL limited to 1 hop. Some access point
vendors still use broadcast with the pre-standard IAPP port 2313.
EVENT RULES
Event rules provide a powerful way to trigger a certain action when
receiving specified IEEE 802.11 frames on the hostap interface. The
rules are handled in sequential order, from first to last. Rules are
handled without a state: each rule is processed independently from the
others and from any previous actions. This behaviour is somewhat
different to that of packet filter rules specified in pf.conf(5).
All hostapd(8) event rules are single line statements beginning with the
mandatory hostap handle keywords and optional rule options, interface,
frame matching, a specified action, a limit, and a minimal rate:
hostap handle [option] [interface] [frame] [action] [limit] [rate]
Some rule statements support the optional keyword not, also represented
by the ! operator, for inverse matching.
The optional parts are defined below.
Rule Option
The rule option will modify the behaviour of handling the statement.
There are two possible options, quick and skip. If either the keyword
quick or the keyword skip is specified, no further event rules will be
handled for this frame after processing this rule successfully. The
keyword skip additionally skips any further IAPP processing of the frame,
which is normally done after handling the event rules.
Rule Interface
The rule interface specifies the hostap interface the rule is matched on.
The available interface list is specified by the global set hostap
interface configuration setting.
on [not] interface
If not given, the event rule is matched on all available hostap
interfaces.
Rule Frame
The frame description specifies a mechanism to match IEEE 802.11 frames.
any Match all frames.
frame [type] [dir] [from] [to] [bssid] [radiotap]
Apply rules to frames matching the given parameters. The
parameters are explained below.
The type parameter specifies the frame type to match on. The
frame type may be specified in the following ways:
type any
Match all frame types.
type [not] data
Match data frames. Presence of the not keyword negates
the match and will match all non-data frames.
type [not] management [[not] subtype]
Match management frames. The subtype argument may be
specified to optionally match management frames of the
given subtype. The subtype match may be negated by
specifying the not keyword. See the Management Frame
Subtypes section below for available subtypes
specifications.
The dir parameter specifies the direction the frame is being
sent. The direction may be specified in the following ways:
dir any
Match all directions.
dir framedir
Match frames with the given direction framedir. See the
Frame Directions section below for available direction
specifications.
The radiotap rules allow parsing and matching of the extra
information reported by the radiotap header. Support for the
specified radiotap headers is optional and the specific
parameters depend on the radiotap elements reported by the
wireless interface. Support for the radiotap data link type can
be verified with the tcpdump(8) command. These rules require
hostap mode radiotap in the global configuration.
signal [operator] percentage %
Match the signal quality of the received frame.
freq [operator] value (GHz | MHz)
Match the transmit rate of the received frame.
txrate [operator] rate Mb
Match the frequency of the received frame.
The radiotap rules support the following operators. If omitted,
the specified value will be checked if it is equal or not.
= (equal)
!= (not equal)
< (less than)
<= (less than or equal)
> (greater than)
>= (greater than or equal)
The from, to, and bssid parameters specify the IEEE 802.11
address fields to match on. They can be specified in the
following ways:
(from | to | bssid) any
Allow all addresses for the specified address field.
(from | to | bssid) [not] <table>
Allow allow addresses from the given <table> (see Tables
above) for the specified address field.
(from | to | bssid) [not] lladdr
Allow the given address lladdr for the specified address
field.
Rule Action
An optional action is triggered if a received IEEE 802.11 frame matches
the frame description. The following actions are supported:
with frame type [dir] from to bssid
Send an arbitrary constructed frame to the wireless network. The
arguments are as follows.
The type describes the IEEE 802.11 frame type to send, specified
in the frame control header. The following frames types are
supported at present:
type data
Send a data frame. This is normally used to encapsulate
ordinary IEEE 802.3 frames into IEEE 802.11 wireless
frames.
type management subtype
Send a management frame with the specified subtype.
Management frames are used to control states and to find
access points and IBSS nodes in IEEE 802.11 networks.
See the Management Frame Subtypes section below for
available subtypes specifications.
The dir describes the direction the IEEE 802.11 frame will be
sent. It has the following syntax:
dir framedir
See the Frame Directions section below for available direction
specifications.
The from, to, and bssid arguments specify the link layer address
fields used in IEEE 802.11 frames. All address fields are
mandatory in the frame action. The optional fourth address field
used by wireless distribution systems (WDS) is currently not
supported. Each argument is specified by a keyword of the same
name (from, to, or bssid) followed by one of the following
address specifications:
lladdr Specify the link layer addresses used in the IEEE
802.11 frame address field. The link layer address
`ff:ff:ff:ff:ff:ff' is the IEEE 802.11 broadcast
address.
&refaddr Fill in a link layer address from the previously
matched IEEE 802.11 frame. &from will use the source
link layer address; &to the destination link layer
address; and &bssid the BSSID link layer address of the
previously matched frame.
random Use a random link layer address in the specified IEEE
802.11 frame address field. Multicast and broadcast
link layer addresses will be skipped.
with iapp type iapp-type
Send a hostapd(8) specific IAPP frame with a raw IEEE 802.11
packet dump of the received frame to the wired network. The only
supported iapp-type is radiotap.
with log [verbose]
Write informational messages to the local system log (see
syslogd(8)) or standard error. If the Rule Rate has been
specified, log will print the actual rate.
node add | delete lladdr
Add or remove the specified node from the internal kernel node
table.
resend Resend the received IEEE 802.11 frame.
Rule Limit
It is possible to limit handling of specific rules with the limit
keyword:
limit number sec | usec
In some cases it is absolutely necessary to use limited matching to
protect hostapd(8) against excessive flooding with IEEE 802.11 frames.
For example, beacon frames will be normally received every 100 ms.
Rule Rate
It is possible to tell hostapd(8) to trigger the action only after a
specific rate of matched frames.
rate number / number sec
This will help to detect excessive flooding of IEEE 802.11 frames. For
example, de-auth flooding is a DoS (Denial of Service) attack against
IEEE 802.11 wireless networks.
Management Frame Subtypes
The subtype describes the IEEE 802.11 frame subtype, specified in the
frame control header. The choice of subtypes depends on the used frame
type. hostapd(8) currently only supports management frame subtypes.
Most frame subtypes require an additional subtype-specific header in the
frame body, but currently only the deauth and disassoc reason codes are
supported:
subtype beacon
A beacon frame. Wireless access points and devices running in ibss
master or hostap mode continuously send beacon frames to indicate
their presence, traffic load, and capabilities.
subtype deauth [reason]
A deauthentication frame with an optional reason code.
Deauthenticated stations will lose any IEEE 802.11 operational state.
subtype disassoc [reason]
A disassociation frame with an optional reason code.
subtype assoc request
An association request frame.
subtype assoc response
An association response frame.
subtype atim
An announcement traffic indication message (ATIM frame).
subtype auth [open request | response]
An authentication frame.
subtype probe request
A probe request frame. Probe requests are used to probe for access
points and IBSS nodes.
subtype probe response
A probe response frame.
subtype reassoc request
A re-association request frame.
subtype reassoc response
A re-association response frame.
The reason defines a descriptive reason for the actual deauthentication
or disassociation of a station:
reason assoc expire
Disassociated due to inactivity.
reason assoc leave
Disassociated because the sending station is leaving or has left the
wireless network.
reason assoc toomany
Disassociated because the access point has reached its limit of
associated stations.
reason auth expire
Previous authentication no longer valid.
reason auth leave
Deauthenticated because the sending station is leaving or has left the
wireless network.
reason ie invalid
IEEE 802.11i extension.
reason mic failure
IEEE 802.11i extension.
reason not authed
Frame received from unauthenticated station.
reason assoc not authed
Frame received from an associated but unauthenticated station.
reason not assoced
Frame received from unassociated station.
reason rsn required
IEEE 802.11i extension.
reason rsn inconsistent
IEEE 802.11i extension.
reason unspecified
Unspecified reason.
Frame Directions
The direction a frame is being transmitted (framedir) can be specified in
the following ways:
dir no ds
No distribution system direction is used for management frames.
dir to ds
A frame sent from a station to the distribution system, the access
point.
dir from ds
A frame from the distribution system, the access point, to a station.
dir ds to ds
A frame direction used by wireless distribution systems (WDS) for
wireless access point to access point communication.
EVENT RULE EXAMPLES
# Log probe requests locally
hostap handle type management subtype probe request \
with log
# Detect flooding of management frames except beacons.
# This will detect some possible Denial of Service attacks
# against the IEEE 802.11 protocol.
hostap handle skip type management subtype ! beacon \
with log \
rate 100 / 10 sec
# Log rogue access points via IAPP, limited to every second,
# and skip further IAPP processing.
hostap handle skip type management subtype beacon bssid !<myess> \
with iapp type radiotap limit 1 sec
# Send deauthentication frames to stations associated to rogue APs
hostap handle type data bssid !<myess> with frame type management \
subtype deauth reason auth expire \
from &bssid to &from bssid &bssid
# Send authentication requests from random station addresses to
# rogue access points. This is a common way to test the quality of
# various hostap implementations.
hostap handle skip type management subtype beacon bssid <pentest> \
with frame type management subtype auth \
from random to &bssid bssid &bssid
# Re-inject a received IEEE 802.11 frame on the interface ath0
hostap handle on ath0 type management subtype auth with resend
# Remove a blacklisted node from the kernel node tree
hostap handle type management subtype auth from <blacklist> \
with node delete &from
# Log rogue access points with a strong signal quality on
# channel 3 (2.422GHz) transmitting frames with 1Mb.
hostap handle type management subtype beacon bssid !<myess> \
signal >= 50% txrate 1Mb freq 2.422GHz \
with log
IP ROAMING
In a traditional wireless network, multiple access points are members of
a single layer 3 broadcast domain. The traffic is bridged between
physical collision domains, as with the bridge(4) interface in OpenBSD.
This may cause problems in large wireless networks with a heavy load of
broadcast traffic, like broadcasted ARP, DHCP or ICMP requests.
hostapd(8) implements IP based roaming to build wireless networks without
the requirement of a single broadcast domain. This works as follows:
1. Every access point running hostapd(8) is a router to an individual
internal broadcast domain, without using the bridge(4) interface.
2. An increased multicast TTL is used for IAPP communication between
access points in multiple network segments. Multicast routing is
required in the network infrastructure, like an OpenBSD router
running mrouted(8).
3. The configuration file hostapd.conf is used to assign IP subnets to
link layer addresses. If a station with the specified link layer
address successfully associates to the access point, hostapd(8) will
configure the specified IP address and subnet on the wireless
interface.
4. The IAPP ADD.notify message is used to notify other access points
running hostapd(8) to remove the station and any assigned IP
addresses or subnets from the wireless interface.
5. A dynamic routing daemon like ospfd(8) or bgpd(8) running on the
access point will be used to announce the new IP route to the
internal network and routers.
For example:
# Assign IP addresses to layer 2 addresses
table <clients> {
00:02:6f:42:d0:01 -> 172.23.5.1/30
00:05:4e:45:d3:b8 -> 172.23.5.4/30
00:04:2e:12:03:e0 -> 172.23.5.8/30
}
# Global options
set hostap interface ath0
set hostap mode radiotap
set iapp interface sis0
set iapp address roaming table <clients>
set iapp handle subtype address roaming
set iapp mode multicast ttl 2
FILES
/etc/hostapd.conf Default location of the configuration file.
SEE ALSOhostapd(8)AUTHORS
The hostapd(8) program was written by Reyk Floeter <reyk@openbsd.org>.
CAVEATS
IP Roaming requires statically assigned IP addresses of stations and does
not support DHCP at present.
OpenBSD 4.9 April 16, 2009 OpenBSD 4.9
