S/N/K-Series DVMRP routed Multicast Stream Loses Packets at Mroute Creation


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Article ID: 16193

Products
S-Series, all firmware
Matrix N-Series DFE, all firmware
K-Series, all firmware

Changes
Configured DVMRP for multicast routing.
Attempting to use it for a non-standard multicast application which requires lossless operation during communication setup.

Symptoms
Application failure upon the first communication attempt.

Cause
By design, multicast stream delivery is not expected to be 100%. During multicast route setup any associated multicast frames are dropped until the mroute has been established. Generally this is not problematic since UDP is not a guaranteed delivery protocol.

Solution/Workaround
Functions as Designed (FAD).

Workaround:
  • Assuming the first few packets of the data stream will be dropped, configure the problematic application to automatically re-send its initial traffic burst; -or-
  • Use a blind packet generation device to refresh the network path by sending a keep-alive packet more often than the expected route timeout of "query interval x 2"; -or-
  • Flatten the network in terms of the problematic application, by configuring policy to tunnel a single VLAN throughout the network. This would eliminate the need to multicast route the application's traffic, leaving it to IGMP to properly scope it - and IGMP floods traffic while learning.

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