Replaced an old unmanaged switch under a ControlLogix, 1756-L81E with a 1756-EN2T, for an IT-supplied Cisco IE3300 last week. Hanging off it are two 1794-AENT, three 1734-AENTR and four PowerFlex 525.
Every time that switch reboots, and IT rebooted it twice doing firmware, the I/O is fine for about five minutes and then every rack drops 16#0204 inside the same minute, drives included. Kepware on the same VLAN never drops, which is the bit I can't explain.
On a hunch I turned IGMP snooping off and the drops stopped, but IT put it straight back on because it's in their standard config. Swapped the EN2T for a spare and that changed nothing either. So it's a switch setting, I'm just not sure which one. Any ideas what to ask IT for?
Kepware is TCP, class 3, it doesn't care. Your I/O is multicast. Two things: is there an IGMP querier on that VLAN, and what's the snooping group timeout. Ask IT for the output of show ip igmp snooping, they'll have it.
> is there an IGMP querier on that VLAN
IT says "the router does that". The VLAN is layer 2 only, no SVI, nothing routes it. The show output says Querier: none. Group membership timeout 260 s, though I'm not sure that's the default.