Problem with MTU size and don't fragement switch (General questions)

by johnag, Thursday, November 16, 2006, 15:48 (6582 days ago)

My application has been working perfectly in a WAN and LAN environment, but we have now encountered a problem in a wireless broadband environment which requires a MTU size 1352. On transferring a file we always get error 30027 as a result of a timeout in sending the data. My network support has traced the packets and found 1) the sending PC appears to have ignored the target linux system MTU size and is using too large a MTU and 2) the Don't Fragment (DF) is on. The result is the wireless network throws away the packet. We believe the problem can be solved in two ways - A) use the correct MTU (I know this works since when both transmitter and receiver are on the same wireless network the correct MTU size is used), and B) do not set the (DF) flag. Has anyone any experience with these issues? Who sets the (DF) flag - wodsftp or is it forced by Windows (2K and XP)? How is the MTU size for the connection determined?