This Counter64 counts reassembly failures detected by the virtual router's IP reassembly logic, for reasons ranging from timeouts to internal errors, and it is not a precise count of dropped fragments since some algorithms lose track of fragments as they combine them. A rising value on a specific virtual router means fragmented traffic destined for it is failing to reconstitute, often due to fragment loss earlier on the path. If this counter climbs on a virtual router serving a customer over a lossy satellite link, fragment loss on that link is the likely cause.