[6lowpan] Question about RA packets

Damien Roth <d42roth@gmail.com> Fri, 09 March 2012 14:51 UTC

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From: Damien Roth <d42roth@gmail.com>
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Date: Fri, 9 Mar 2012 15:51:25 +0100
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Subject: [6lowpan] Question about RA packets
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Hello,

I have a question about the Router Advertisement (RA) packets described in draft-ietf-6lowpan-nd-18.

As I figure out, the RA packets are built like this : 
RA header + SLLAO + ABRO + ( PIO + 6CO ) * number_of_prefixes

With one prefix, the sum of the header / options length is equal to 104 bytes.
Here is the detail :

RA          : 16 bytes
SLLAO	: 16 bytes
ABRO 	: 24 bytes
PIO	        : 32 bytes
6CO 	: 16 bytes
               --------------
                  104 bytes

However, in 802.15.4 the maximum length of the payload is 102 bytes (127 bytes - 25 bytes for the MAC header). Which means that every RA packet have to be fragmented before being sent to the MAC layer.

Is my reasoning correct ?

Regards,

-- 
Damien ROTH - PhD student
Strasbourg University, France