Thomas Portmann
2015-Jun-26 13:30 UTC
[Q] TCP segment sent is larger than peers advertised MSS
On 06/26/2015 03:21 PM, Flavien Lebarbe wrote:> Thomas Portmann ecrivait : >> I am in the process of troubleshooting another problem and noticed a >> rather strange behavior with the openssh client. A client (OpenSSH >> 5.3) and a server (6.7p1) do the TCP handshake, the client announces >> a MSS of 1460 (its MTU is 1500), while the server announces a MSS of >> 1260 (its MTU is set to 1300). What troubles me is, that the client >> is sending the server a frame of 2034 bytes (TCP segment length of >> 1968, during the "Client: Key Exchange Init"). Why is it that the >> client seems to ignore the servers MSS? > From what you say, the client not only disregards the server MSS, but > also the client MSS itself : 2034 is larger than 1500. That's weird... > Do you have a pcap capture of it ? Where do you see the 2034 ? In a > strace by chance ?I have a tcpdump I made on the client. Since it is rather small (~7KB), I will just attach it to the mail. The 2034 is taken from the capture. tom