Path MTU and beacon

[Jean-Jacques Pansiot <pansiot@crc.u-strasbg.fr>]

Hello,
I have been experiencing with the beacon v1.1-0 for darwin,
using the default group *233.4.200.19*
My beacon sees only a fraction of all other beacons listed in the 
central server
(say 6 or 10 among 80).
However, if I run ethereal, I observe that most, if not all, RTCP 
packets I receive
are fragmented at the IP level :  the UDP packets (including UDP header) 
are 1504 or 1508
bytes and are splitted in 2 IP fragments (the first one being of size 
1500 including IP header).
Since *233.4.200.19 *has many members, there is a tendancy to have RTCP 
reports of the maximum size.
*
*On the other hand the file rtp.h (obtained with the beacon) indicates :
#define RTP_MAX_PACKET_LEN 1500

which gives UDP packets of size 1500 + 8 , and IP packets of size 1500 + 
8 + 20
Ět appears that this is too big for the Path-MTU of many networks, this 
creates fragmentation
(and some firewalls filter IP fragments).

Is it a known problem ? Should we consider lowering RTP_MAX_PACKET_LEN  
to 1500 -28 ?
or even using Path MTU discovery ?


thanks

Jean-Jacques Pansiot