[LEDE-DEV] [RFC] Disable 802.11b rates by default and set supported/basic rates appropriately for 2.4 GHz BSSes based on require_mode

[Nick Lowe]

Disable 802.11b rates by default and set supported/basic rates
appropriately for 2.4 GHz BSSes based on require_mode.

The require_mode option can currently be configured to a value of g or
n for 2.4 GHz BSSes or n or ac for 5 GHz BSSes to set the minimum mode
that connecting clients need to support to be able to connect.

This patch introduces a new require_mode of b and defaults to a
require_mode of g where this is unspecified.

The rationale for this, which is stronger now than in 2014, can be found in:

https://mentor.ieee.org/802.11/dcn/14/11-14-0099-00-000m-renewing-2-4ghz-band.pptx

The balance of equities between compatibility with b clients and the
detriment to the 2.4 GHz ecosystem as a whole in 2017 strongly favors
disabling b support by default.

Issues previously in the hostapd.sh shell script for 2.4 GHz BSSes for
the require_mode were:

1) Where a require_mode of g was configured, the supported rates still
included b rates yet the basic rates would not include b rates.

2) Where a require_mode of g was configured, the basic rates would be
set to 60 120 240 that would override the configuration of the
basic_rate option rather than filtering to exclude b rates.

3) Where a require_mode of n was configured, the b rates were still
used as basic rates which is not airtime efficient. The g require_mode
achieved better airtime efficiency for broadcast/multicast traffic.
Only where the require_mode was set to g would the basic rates be set
to not include b rates.

Now:

1) Where a require_mode is not configured to b and the supported_rates
option has not been configured, this will be changed to OFDM rates
only:

60 90 120 180 240 360 480 540

2) Where a require_mode is not configured to b and the supported_rates
option has been configured, this will be filtered to include OFDM
rates only.

3) Where a require_mode is not configured to b and the basic_rate
option has not been configured, this will be changed to OFDM rates
only:

60 120 240

4) Where a require_mode is not configured to b and the basic_rate
option has been configured, this will now be filtered to include OFDM
rates only.

Signed-off-by: Nick Lowe <nick.lowe at gmail.com>
---
 package/network/services/hostapd/files/hostapd.sh | 79 +++++++++++++++++++----
 1 file changed, 68 insertions(+), 11 deletions(-)

diff --git a/package/network/services/hostapd/files/hostapd.sh
b/package/network/services/hostapd/files/hostapd.sh
index 988ebc7..654d64e 100644
--- a/package/network/services/hostapd/files/hostapd.sh
+++ b/package/network/services/hostapd/files/hostapd.sh
@@ -90,23 +90,80 @@ hostapd_prepare_device_config() {
    }
    [ -n "$hwmode" ] && append base_cfg "hw_mode=$hwmode" "$N"

-   local brlist= br
-   json_get_values basic_rate_list basic_rate
-   for br in $basic_rate_list; do
-       hostapd_add_rate brlist "$br"
-   done
-   case "$require_mode" in
-       g) brlist="60 120 240" ;;
-       n) append base_cfg "require_ht=1" "$N";;
-       ac) append base_cfg "require_vht=1" "$N";;
-   esac
-
    local rlist= r
    json_get_values rate_list supported_rates
    for r in $rate_list; do
+       if [ "$require_mode" != "b" ]; then
+           case "$r" in
+               1000)
+                   continue
+               ;;
+               2000)
+                   continue
+               ;;
+               5500)
+                   continue
+               ;;
+               11000)
+                   continue
+               ;;
+           esac
+       fi
+
        hostapd_add_rate rlist "$r"
    done

+   local brlist= br
+   json_get_values basic_rate_list basic_rate
+   for br in $basic_rate_list; do
+       if [ "$require_mode" != "b" ]; then
+           case "$br" in
+               1000)
+                   continue
+               ;;
+               2000)
+                   continue
+               ;;
+               5500)
+                   continue
+               ;;
+               11000)
+                   continue
+               ;;
+           esac
+       fi
+
+       if [ -z $rate_list ]; then
+           hostapd_add_rate brlist "$br"
+       else
+           for r in $rate_list; do
+               if [ "$br" = "$r" ]; then
+                   hostapd_add_rate brlist "$br"
+                   break
+               fi
+           done
+       fi
+   done
+
+   if [ "$require_mode" != "b" ]; then
+       if [ -z "$rlist" ]; then
+           rlist="60 90 120 180 240 360 480 540"
+       fi
+
+       if [ -z "$brlist" ]; then
+           brlist="60 120 240"
+       fi
+
+       case "$require_mode" in
+           n)
+               append base_cfg "require_ht=1" "$N"
+           ;;
+           ac)
+               append base_cfg "require_vht=1" "$N"
+           ;;
+       esac
+   fi
+
    [ -n "$rlist" ] && append base_cfg "supported_rates=$rlist" "$N"
    [ -n "$brlist" ] && append base_cfg "basic_rates=$brlist" "$N"
    [ -n "$beacon_int" ] && append base_cfg "beacon_int=$beacon_int" "$N"
--
2.10.2
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