 | 1 | initial version |
The pcap of the failing connection to the new server is showing an MTU issue. The MSS being received is 1440. I assume it is clamped somewhere in the path between the server and you. When you look at the sequence number of the first received data, it is missing 2896 bytes. This is two MSS of 1460 when you take into account that the TCP timestamps option takes 12 bytes. So per packet 1460 - 12 = 1448 bytes of TCP data, times two is 2896.
This means the MSS in the SYN packet is somehow not clamped and the server just uses the standard MSS of 1460 instead of the 1440. Which means the part of the network with the lower MTU/MSS will not be able to forward the packes due to the IP Don't Fragment flag being set.
Funny thing is that I see the same MSS in the SYN/ACK when I make a connection myself to the same site (on the same IP), but the data segments are now reduced the the MSS of 1440. So somehow the MSS in my SYN is indeed clamped. This means that either the problem has been solved or that there is a problem specificly on the path between you and this server.
Hope this helps!
