Fragmentation.

Jouni Malinen jkmaline at cc.hut.fi
Wed Sep 29 22:31:28 EDT 2004


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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