[Udpcast] Info on UDPcast IGMP packets

Manon Lessard Manon.Lessard at sit.ulaval.ca
Thu Feb 9 17:36:07 CET 2006


I work for the telecom dept of a large university and we are currently
working with some UDPcast users on a very strange problem. 

It appears they are unable to start a cast on a given group of machines.
If they use Ghost, they are able send their image fine (using Ghost's
multicast). If they use UDPcast, the multicast will start randomly on a
couple of machines (when one's lucky) but for 99% of machines it just
won't work.
Since they are one of the very few if not the only ones having this
problem with multicasting, we went ahead and monitored their
transactions with ethereal (latest version). 

The access layer switches which connect our clients' machines and server
are Cisco 3500XL. These switches do not have advanced multicast features
and need our L3
switch (Cisco 6509 with sup 720) to tell them to open the multicast
session. It so appears that the IGMP packets sent by UDPcast differ from
Ghost on 2 points: in the header they are using ID field with a value of
0 (1 for Ghost) and the DF bit is set to 1 (0 for Ghost). The IGMP
packets sent by Ghost are recognized and the session established. The
ones sent by UDPcast are not, and the session is obviously dropped...

These clients are using a version of UDPcast dating from dec. 04.
Are you aware of anything in UDPcast or any incompatibilities with some
Cisco IOS versions that could cause this problem?



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