When observium monitor device like router and you replace it with different model (leaving IP address same) it keep re-detecting interfaces with every poll. Here is example.
2011-06-21 12:00:34 dot11radio1 ifName: Do1 -> Nu0 2011-06-21 12:00:34 dot11radio1 ifDescr: Dot11Radio1 -> Null0 2011-06-21 12:00:34 dot11radio1 ifAdminStatus: down -> up 2011-06-21 12:00:34 dot11radio1 ifOperStatus: down -> up 2011-06-21 12:00:34 dot11radio1 ifSpeed: 54000000 -> 10000000000 2011-06-21 12:00:34 dot11radio1 ifHighSpeed: 54 -> 10000 2011-06-21 12:00:34 dot11radio1 ifType: ethernetCsmacd -> other 2011-06-21 12:00:34 dot11radio1 ifPhysAddress: 001bd50d0fb0 -> 2011-06-21 12:00:34 dot11radio1 ifConnectorPresent: true -> false 2011-06-21 12:00:34 dot11radio1 ifDuplex: unknown -> NULL 2011-06-21 12:00:34 FastEthernet3 ifName: Fa3 -> NV0 2011-06-21 12:00:34 FastEthernet3 ifDescr: FastEthernet3 -> NVI0 2011-06-21 12:00:34 FastEthernet3 ifMtu: 1500 -> 1514 2011-06-21 12:00:34 FastEthernet3 ifSpeed: 100000000 -> 56000 2011-06-21 12:00:34 FastEthernet3 ifHighSpeed: 100 -> 0 2011-06-21 12:00:34 FastEthernet3 ifType: ethernetCsmacd -> other 2011-06-21 12:00:34 FastEthernet3 ifPhysAddress: 001c58566065 -> 2011-06-21 12:00:34 FastEthernet3 ifConnectorPresent: true -> false 2011-06-21 12:00:34 FastEthernet3 ifDuplex: unknown -> NULL