I was playing with ethereal by doing some tests on our network and I realised that when I read a big file from a NW6.5SP5 server I get a lot of "Duplicate Ack" and when I write the same file back to the server I get a lot of "Bad checksum/Detected New server session". When I disable the checksum verification in ethereal the error transforms in "Acked lost segment".

Is that something to worry about ?