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Intel Wireless 7260 as an access point

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source link: https://vincent.bernat.ch/en/blog/2014-intel-7260-access-point
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Intel Wireless 7260 as an access point

Vincent Bernat November 16, 2014

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My home router acts as an access point with an Intel Dual-Band Wireless-AC 7260 wireless card. This card supports 802.11ac (on the 5 GHz band) and 802.11n (on both the 5 GHz and 2.4 GHz band). While this seems a very decent card to use in managed mode, this is not really a great choice for an access point.

$ lspci -k -nn -d 8086:08b1
03:00.0 Network controller [0280]: Intel Corporation Wireless 7260 [8086:08b1] (rev 73)
        Subsystem: Intel Corporation Dual Band Wireless-AC 7260 [8086:4070]
        Kernel driver in use: iwlwifi

TL;DR

Use an Atheros card instead.

Limitations#

First, the card is said “dual-band” but you can only uses one band at a time because there is only one radio. Almost all wireless cards have this limitation. If you want to use both the 2.4 GHz band and the less crowded 5 GHz band, two cards are usually needed.

5 GHz band#

There is no support to set an access point on the 5 GHz band. The firmware doesn’t allow it. This can be checked with iw:

$ iw reg get
country CH: DFS-ETSI
  (2402 - 2482 @ 40), (N/A, 20), (N/A)
  (5170 - 5250 @ 80), (N/A, 20), (N/A)
  (5250 - 5330 @ 80), (N/A, 20), (0 ms), DFS
  (5490 - 5710 @ 80), (N/A, 27), (0 ms), DFS
  (57240 - 65880 @ 2160), (N/A, 40), (N/A), NO-OUTDOOR
$ iw list
Wiphy phy0
[…]
Band 2:
  Capabilities: 0x11e2
    HT20/HT40
    Static SM Power Save
    RX HT20 SGI
    RX HT40 SGI
    TX STBC
    RX STBC 1-stream
    Max AMSDU length: 3839 bytes
    DSSS/CCK HT40
  Frequencies:
    * 5180 MHz [36] (20.0 dBm) (no IR)
    * 5200 MHz [40] (20.0 dBm) (no IR)
    * 5220 MHz [44] (20.0 dBm) (no IR)
    * 5240 MHz [48] (20.0 dBm) (no IR)
    * 5260 MHz [52] (20.0 dBm) (no IR, radar detection)
      DFS state: usable (for 192 sec)
      DFS CAC time: 60000 ms
    * 5280 MHz [56] (20.0 dBm) (no IR, radar detection)
      DFS state: usable (for 192 sec)
      DFS CAC time: 60000 ms
[…]

While the 5 GHz band is allowed by the CRDA, all frequencies are marked with no IR. Here is the explanation for this flag:

The no-ir flag exists to allow regulatory domain definitions to disallow a device from initiating radiation of any kind and that includes using beacons, so for example AP/IBSS/Mesh/GO interfaces would not be able to initiate communication on these channels unless the channel does not have this flag.

Multiple SSID#

This card can only advertise one SSID. Managing several of them is useful to setup distinct wireless networks, like a public access (routed to Tor), a guest access and a private access. iw can confirm this:

$ iw list
[…]
valid interface combinations:
   * #{ managed } <= 1, #{ AP, P2P-client, P2P-GO } <= 1, #{ P2P-device } <= 1,
     total <= 3, #channels <= 1

Here is the output of an Atheros card able to manage 8 SSID:

$ iw list
[…]
valid interface combinations:
   * #{ managed, WDS, P2P-client } <= 2048, #{ IBSS, AP, mesh point, P2P-GO } <= 8,
     total <= 2048, #channels <= 1

Configuration as an access point#

Except for these two limitations, the card works fine as an access point. Here is the configuration that I use for hostapd:

interface=wlan-guest
driver=nl80211

# Radio
ssid=XXXXXXXXX
hw_mode=g
channel=11

# 802.11n
wmm_enabled=1
ieee80211n=1
ht_capab=[HT40-][SHORT-GI-20][SHORT-GI-40][DSSS_CCK-40][DSSS_CCK-40][DSSS_CCK-40]

# WPA
auth_algs=1
wpa=2
wpa_passphrase=XXXXXXXXXXXXXXX
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP

Because of the use of channel 11, only 802.11n HT40- rate can be enabled. Look at the Wikipedia page for 802.11n to check if you can use either HT40-, HT40+ or both.


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