Some system tries to access the 10.0.30.30 through the router.
So the router tries to find the MAC address for this system ==> ARP requests.
It has nothing to do with the DHCP as such.
Is there a port forwarding on the SG300-52P? any other special thing configured? around ip address 10.0.30.30?
If someone tries to reach (or ping) 10.0.30.30, the gateway's job is to find a way to that address.
So it sends broadcasts (ARP requests) to get the MAC address for 10.0.30.30.
As log as no one use this address, nobody can make an entry to his arp-table.
@Dirk that is only if the traffic goes through the router. Not if it another system on the LAN.
The ARP table should show an unresolved ARP entry... (hw address mentioning incomplete ..)
@ShawnGray
No ALG active? no proxies? Is the running config the same as the stored config?...
If there is a DHCP request from a system it may try to do a reachability check.. for the proposed address. That involves a least ARP.
Then there should be a system receiving that address shortly after it.
You may need a better picture by sampling a copy of all traffic to your SG300-52P
I'm not quite sure what that might be. Could you expand on the specifics of the situation?