A while back I think I posted something asking about what to do about TSO (large send) and how it generated "IP bad-len 0" output when tracing on a TSO-enabled sender.
I've had acouple folks ask "What's TSO?" so...
TSO == TCP Segmentation Offload. AKA "large send." A feature of (at least) AIX, Windows, HP-UX and Linux starting with various versions.
With TSO enabled, TCP sends larger than MSS segments down the stack, and the NIC performs the segmentation to transmit MSSized packets on the network. It can be thought of as a "poor man's Jumbo Frame" in that it give the sender _most_ of the benefits of a larger MTU without the need for Jumbo Frame support in the infrastructure.
IIRC the "programming model" for most of this is such that the datagram length field of the IP header is set to zero, hence the "IP bad-len 0" messages with a stock tcpdump.
hth,
rick jones - This is the tcpdump-workers list. Visit https://lists.sandelman.ca/ to unsubscribe.
