Hi,
I recently experienced a wired case:
Our software team is testing an new app. from network prospective, it will trigger a tcp connection between two IPs, and this tcp has two process.(it means this tcp connection engages two ports and this two ports are high-number ports randomized)
The source and destination IPs are two windows servers. when placed in a normal LAN environment, everything is fine.
when this test goes over a WAN, we have an issue. We are using Q-in-Q for Wan connection.
General speaking: the TCP becomes unstable.
In detail: the 3 way-hand-shake works and one of the tcp processes is forwarding and receiving packets as normal, but the other process is losing packets. TCP retransmission seems to be useless here as the sender is definitely sending out the packet and for authority issue, I cannot access to the receiver to check whether it receive the packet. But from the sender I cannot capture the ack for the second tcp process.
According to our softward team, if one of the two tcp process begin to loss packets, this tcp connection will be terminated. This explain why the tcp connection is unstable.
I tested mtu size along the path:1488. I know Q-in-Q will add extra 4 bytes in the header so I inform the ISP to increase MTU to 1504. Honestly I just gave it a try as I found all lost packets are small sized around 100-200 bytes. they wont be drop as a result of the mtu limitation.
However, after ISP changed the MTU size to 1504, it works perfectly. though i am happy to have this case resolved, I am confused.
I need an explanation for this! would anyone give me any advises.
any advises are welcomed
Will MTU
