#1818: Fragmentation bug in adhoc/ahdemo mode when using WEP encryption -------------------------------------+-------------------------------------- Reporter: [EMAIL PROTECTED] | Type: defect Status: new | Priority: critical Component: madwifi: driver | Version: v0.9.3.3 Keywords: fragmentation adhoc WEP | Patch_attached: 0 -------------------------------------+-------------------------------------- Very simple scenario and very easy to reproduce the bug: 2 PCs with madwifi ( I tried 0.9.3.2 & 0.9.3.3 ) are in adhoc mode and using WEP encryption (keylength doesn't matter). One of the PC is pinging the other one, with a defined packetsize S (ping -s packetsize IPaddr). If I put the Fragmentation Threshold to 300 Bytes (for example), I will not get a ping reply for the following packetsizes: S = 509, 510, 511, 512 & S = 781, 782, 783, 784 & every S = S + 272, ... ! I sniffed in the air and saw what's wrong: let's take S = 508 , in the air you will see 2 WLAN-Fragments, both with the length of 300Bytes and both are complete.
when S = 509, in the air you will see again 2 WLAN-Fragmets, both with the length of 300Bytes ! So the last fragment lost the last Byte (509 - 508) of the initial packet. when S = 510 the last fragment is truncated by the 2 last Bytes and so on till S = 513, when a third fragment takes the last 5 Bytes of the initial packet and puts it on the air, so everything works again fine ! The general rule for the bug can be defined like this: When a packet (in the air) is 1 to 4 bytes longer then the multiple of the fragmentation threshold, the driver does NOT generate a new necessary fragment for this last 1 to 4 bytes ! The packet is delivered by madwifi truncated by this last 1 to 4 bytes !!! It begins to generate a new fragment, only with at least 5 bytes length ! I hope that somebody can solve this problem, after this detailed explanation ;-) CC -- Ticket URL: <http://madwifi.org/ticket/1818> madwifi.org <http://madwifi.org/> Multiband Atheros Driver for Wireless Fidelity ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Madwifi-tickets mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/madwifi-tickets
