Fragmentation.

Donghyuk Woo shine21 at korea.com
Thu Sep 30 08:45:08 EDT 2004


I'd like to let my HostAP machine be connected to the ethernet, thus all its
associated nodes can enjoy the internet. And also, I'd like to use some
specific packets whose length is bigger than 1500 bytes and which is used
only in the WLAN BSS. Then what should I do? I guess bridging mode might not
be the solution for this purpose.

-----Original Message-----
From: hostap-bounces+shine21=korea.com at shmoo.com
[mailto:hostap-bounces+shine21=korea.com at shmoo.com] On Behalf Of Jouni
Malinen
Sent: Thursday, September 30, 2004 11:31 AM
To: hostap at shmoo.com
Subject: Re: Fragmentation.


On Tue, Sep 28, 2004 at 10:56:57AM -0700, nondito wrote:
> If the fragmentation is set to 512 (iwconfig wlan0
> frag 512) and mtu to be set to 1500 (ifconfig wlan0
> mtu 1500), what will be the layer 2 frame size between
> an accesspoint (master) and client (managed)?

512 in case of plaintext mode; possibly larger if encryption is used (and
less for packets that happen to be shorter than 512 bytes and for the final
fragments of the frames).

> How is fragmentation related to mtu on wireless
> layer-2?

Well, not really related much at all.. In practice, MTU is limit for the
MSDU size and each MSDU may be fragmented into number of MPDUs based on the
fragmentation threshold. Howeverm, this fragmentation does not change the
maximum "packet size" in the same way that, e.g., IP fragmentation does.

-- 
Jouni Malinen                                            PGP id EFC895FA
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