nwDecIVFwdIfCtrFilteredBytes is a read-only Counter tracking the total number of bytes contained in DECnet packets that have been administratively filtered (blocked by a configured access control policy), on this one specific router port, identified by the ifIndex value paired with this row, during the relevant OperationalTime measurement window. A climbing value here tells an admin their access-control list is actively blocking DECnet traffic, useful for confirming a filter is doing its job, or for investigating if it is wrongly blocking traffic that should pass. For example, if an admin just applied a new DECnet access control list and the filtered-bytes count immediately starts climbing on this one router port, that confirms the list is actively rejecting matching traffic through that single port.