Greetings, Simon, I have rerun our tests and cannot reproduce the situation I saw - where the SYN and SYN ACK specified MSS options of 536. I can only assume that we had a build problem and the updated TCP_MSS value did not get used until I did a complete rebuild. I have set TCP_MSS to 1460 and that is what I am now seeing in the MSS options going both ways. (The test runs 2 instances of the lwIP stack 'back-to-back' - one lwIP talks to another.)
Thank you for your reply - I'm sorry to have wasted time on what appears to be just our build problem. Art R. [EMAIL PROTECTED] wrote: > > Hi Art, > > Can you tell us which version of lwIP you are using? There has been a > change in the MSS handling in 1.3.0. > > Apart from that, TCP_MSS is the mss advertised to the remote host (the > remote host will use this to calculate the mss used to send to lwIP), > while pcb->mss contains the mss as advertised by the remote host. lwIP > will use this for sending. > > So if you see lwIP sending with 536, it might be the other side > advertises this. > > In my tests, I'm sure to have seen mss's of 1460, so your problem might > probably have another reason. The value of 536 is a historical value as > described in on of the TCP RFCs and has probably nothing to do with PPP. > > Simon > > > Art R. schrieb: >> The lwIP code seems to enforce an absolute maximum value for MSS of 536. >> If >> you set the TCP_MSS tag larger, the lwIP code limits the actual mss to >> 536. >> This value is hard-coded in tcp.c. I do not see any way for pcb->mss to >> become larger than 536, implying that the largest MSS that can be >> advertised >> by lwIP to be larger than 536. >> >> The result is that a tcp write of more than 536 bytes creates multiple >> outbound TCP packets. >> >> I would like to send 'full size' packets of 1460 bytes. Is there a way to >> do >> so using lwIP? >> >> (I realize that the 536 value is probably in place to limit packets >> destined >> for PPP or etc. I assume there is nothng in lwIP currently to discover >> packet delivery failures and reduce MSS in response? Is this the reason >> why >> lwIP clamps MSS to 536? Or ...?) >> >> Thanks, >> Art R. >> >> >> >> > > > > _______________________________________________ > lwip-users mailing list > [email protected] > http://lists.nongnu.org/mailman/listinfo/lwip-users > > -- View this message in context: http://www.nabble.com/MSS-maximum-tp16288107p16291047.html Sent from the lwip-users mailing list archive at Nabble.com. _______________________________________________ lwip-users mailing list [email protected] http://lists.nongnu.org/mailman/listinfo/lwip-users
