Documentation/cImages/baseline-8.3.ndz: patch-01-ibss-fix.diff

File patch-01-ibss-fix.diff, 3.0 KB (added by mcgrof, 16 years ago)

A Solution to Ad-Hoc BSSID Partitioning Problems

  • net80211/ieee80211_node.c 

    A Solution to Ad-Hoc BSSID Partitioning Problems

http://orbit-lab.org/wiki/HowTo/bssidFix

When wifi network cards are placed in ad-hoc mode (iwconfig ath0 mode 'ad-hoc')
they will automatically search for networks with the same essid (iwconfig ath0
essid 'blah'). They will adopt the bssid of the first node to turn on that has
the specified essid.

Unfortunately, this algorithm and/or implementation is not very good and even
in relatively small networks, nodes that have the same 'essid' will end up
with different a 'bssid'. Since the wifi card drivers filter incoming packets
by bsssid, nodes that should be in the same ad-hoc network can't exchange
packets.

The solution to this problem can be found by modifying the madwifi drivers
(for Atheros wifi cards only), so that the bssid a node generates is a hash
of the essid instead of its MAC address. This ensures that nodes with identical
essid's end up with identical bssid's.

Although it has not been extensively tested with non-modified nodes, this
modification to the madwifi drivers should be fully backwards compatible with
non-modified nodes.

Signed-Off by: Luis Rodriguez <mcgrof@winlab.rutgers.edu>

diff -Naurp madwifi-3366.orig/net80211/ieee80211_node.c madwifi-3366/net80211/ieee80211_node.c
    old new  
    5353#include <net80211/ieee80211_var.h>
    5454#include <net80211/if_athproto.h>
    5555
     56static int ibss_grid = 1;
     57#if (LINUX_VERSION_CODE < KERNEL_VERSION(2,5,52))
     58MODULE_PARM(ibss_grid, "i");
     59#else
     60#include <linux/moduleparam.h>
     61module_param(ibss_grid, int, 0600);
     62#endif
     63MODULE_PARM_DESC(ibss_grid, "IBSS hack based on SSID for large networks");
     64
     65
    5666/*
    5767 * Association IDs are managed with a bit vector.
    5868 */
    … … ieee80211_create_ibss(struct ieee80211va  
    345355        if (vap->iv_flags & IEEE80211_F_DESBSSID) {
    346356            IEEE80211_ADDR_COPY(ni->ni_bssid, vap->iv_des_bssid);
    347357            IEEE80211_ADDR_COPY(vap->iv_bssid, vap->iv_des_bssid);
    348         } else {
    349             ni->ni_bssid[0] |= 0x02;    /* local bit for IBSS */
    350             vap->iv_bssid[0] |= 0x02;
    351         }
     358               } else {
     359            /* XXX: If we're on a large network then hash the SSID
     360            * instead of the MAC address to generate the BSSID.
     361            * This ensures that nodes with identical SSIDs end
     362            * up with identical BSSIDs, regardless of any
     363            * timing bugs. We might be able to fix this for good
     364            * elsewhere */
     365            if(ibss_grid) {
     366                int i;
     367                printk(KERN_INFO "net80211: IBSS BSSID "
     368                    "generation based on hash of SSID - "
     369                    "temporary fix for large networks\n");
     370                for(i=0; i<IEEE80211_ADDR_LEN;i++)
     371                    ni->ni_bssid[i] = ni->ni_essid[i %
     372                        ni->ni_esslen];
     373            }
     374                       else {
     375                ni->ni_bssid[0] |= 0x02;/* local bit for IBSS */
     376                    vap->iv_bssid[0] |= 0x02;
     377            }
     378               }
     379
    352380    } else if (vap->iv_opmode == IEEE80211_M_AHDEMO) {
    353381        if (vap->iv_flags & IEEE80211_F_DESBSSID) {
    354382            IEEE80211_ADDR_COPY(ni->ni_bssid, vap->iv_des_bssid);