R
Rajesh Gupta
Hi Everyone,
I am writting a IM driver, where i am modifing the Source Ip and Destonation
IP in the outgoing packets.
I am not sure what to do with the TCP checksum, if adapter supports TCP
checksum offloading.
I have tested my driver with adapter, which does not support TCP checksum
offloading. It works fine. My checksum calculations are fine. When i am
testing my IM driver on adapter which supports TCP checksum offloading, its
not working.
I am not sure, ho to handle TCp checksum offloading in IM driver. Here are
the strange things i have noticed.
1. If i do not change anything, then it does not work. Understood.
2. If i calculate the TCP checksum (using TCp psuedo header and TCP segment)
and insert this checksum in the TCP header. It works for the first TCp
packet. For rest of the packets, its incorrect. I have written simple server
and client socket application. So this checksum works for first packet i.e.
SYN packet. Thats strange to me, why it worked for SYN and after that its
incorrect for all other packets.
NOTE: I am checking my packets on another machine. So i am seeing the
correct data send on wire using etherreal.
3. I read somewhere, that sometimes TCP calculate the checksum of
psudoheader and fill this in the TCP header. So hardware only calculate the
TCP segment checksum and does not have to touch the IP header. I tried that.
Nothing works after that.
I am not sure, why SYN worked and how should i handle this in my IM driver?
Thanks a lot in advance.
Rajesh
I am writting a IM driver, where i am modifing the Source Ip and Destonation
IP in the outgoing packets.
I am not sure what to do with the TCP checksum, if adapter supports TCP
checksum offloading.
I have tested my driver with adapter, which does not support TCP checksum
offloading. It works fine. My checksum calculations are fine. When i am
testing my IM driver on adapter which supports TCP checksum offloading, its
not working.
I am not sure, ho to handle TCp checksum offloading in IM driver. Here are
the strange things i have noticed.
1. If i do not change anything, then it does not work. Understood.
2. If i calculate the TCP checksum (using TCp psuedo header and TCP segment)
and insert this checksum in the TCP header. It works for the first TCp
packet. For rest of the packets, its incorrect. I have written simple server
and client socket application. So this checksum works for first packet i.e.
SYN packet. Thats strange to me, why it worked for SYN and after that its
incorrect for all other packets.
NOTE: I am checking my packets on another machine. So i am seeing the
correct data send on wire using etherreal.
3. I read somewhere, that sometimes TCP calculate the checksum of
psudoheader and fill this in the TCP header. So hardware only calculate the
TCP segment checksum and does not have to touch the IP header. I tried that.
Nothing works after that.
I am not sure, why SYN worked and how should i handle this in my IM driver?
Thanks a lot in advance.
Rajesh