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There are two Windows10 PCs.
Both PCs are connected VPN even being connected phisical LAN.
I'm trying to have RDP connection between PC-A and PC-B for each direction as VPN connection is estblished.
However,RDP is allowed only one direction.
PC-A >>> PC-B is OK
PC-A <<< PC-B isn't OK
I captured packet each PC and each direction for the VPN interface.
The packet at PC-B in succeeded case shows client Hello after TCP's SYN and SYN+ACK.
However,the packet at PC-A in failure case doesn't show client Hello and even doesn't respond SYN+ACK.
So TCP Retransmission is sent three times from PC-B.
Does anyone know why PC-A doesn't respond SYN+ACK ?
PC-A can respond SYN+ACK When they are disconnected from VPN ,the phisical LAN alternatively works.
It't doesn't seem it is coused by VPN itself.I can have one direction of RDP even VPN is estblished.
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If the source fails to receive the ACK signal, it either repeats the block of data or else ceases transmission, depending on the protocol.
Client requests connection by sending SYN (synchronize) message to the server. Server acknowledges by sending SYN-ACK (synchronize-acknowledge) message back to the client. Client responds with an ACK (acknowledge) message, and the connection is established.
This means that if the sender does not receive the acknowledgement after three seconds (or RTT > 3 seconds), it will resend the packet. At this point the sender will wait for six seconds to get the acknowledgement.
After receiving SYN packet, server sends the syn ack packet to the client. Not to mention that this is a single tcp packet with syn and ack bit set to 1. The syn sequence number is the initial sequence number of server accepting the connection.
Include public peer IP to the ACLs. Due to the natting, the return leg of the handshake was being sent using the public peer IP, hence after adding the public peer IP to the ACLs it should work.
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