UDP multicast - CISCO gigabit switch flooding

Unanswered Question
Nov 1st, 2008


1. I experience flooding of UDP packets and machine freeze when put rate is high. Using java MulticastSocket and Datagrams. Tried with iperf simulation same problem.

2. Tested with 2 machines to be in same multicast group, observerd that packets go to all other machines also which are not in multicast group.

3. Experience packet loss when put rate is high.

Enabled IGMP snooping on CISCO switch but same problem. Looks like IGMP forwarding table is not correct.

CISCO switch - 3560G (gigabit L3 switch)


I have this problem too.
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satish.setty Thu, 11/06/2008 - 06:49

Hi Jon,

1.Yes it is PIM running with IGMP snooping.

2.We created VLAN group so port traffic is restricted only to 2 machines. (does not come to deskstops). But when I run sender and recevier on same machine (M1) I see traffic also on M2. (Is it because both are in same VLAN group?

3. With java api's MulticastSocket and datagram I am able to send only 3000 udp packets/sec. How do I scale this up to 20,000 packets/sec?

4.Is there any way I can see udp packet loss?


Jon Marshall Thu, 11/06/2008 - 08:07


"We created VLAN group" - do you mean you put the 2 machines into a separate vlan ?

If so

1) Does this vlan have a L3 vlan interface

2) Is PIM enabled on this vlan interface

Apologies if i seem to be asking the same questions but i just wanted to clarify.

One other thing- what is the multicast address you are using and what ttl have you set on the multicast stream.


satish.setty Fri, 11/07/2008 - 05:28


1) VLAN is enabled-We have used CISCO Network Assistant, Under switching-IGMP snooping-multicast router ports, select create button, added 3 ports (which participate in multicast). Please see attached file (figures 1, 2 and 3)

2)PIM is enabled under igmp-snooping option. Please see figure4

switching->igmp snooping->settings

status enabled

immediate-leave disabled

multicast pim-dvmrp

3)Please see figure3. Actually port 10(machine1) and 11(machine2) show utilization even when sender and receiver are on same machine. For above figure I just disconnected machine2 from switch so u see utilization only on machine1.

4)Regarding ttl initially I made ttl=32 for ports 7,10,11 through switch commands. Also in java datagram I have set MultiSocket timeToLive=32 makes no difference.


mcast-port 10999


Jon Marshall Mon, 11/10/2008 - 03:58


Apologies for the delay in getting back. Couple of things if you could

1) Can you post the running-config from the 3560 switch

2) To rule out problems with your application have you tried using VLC which would allow you to setup a client and server situation.



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