# IPv6 TCP connection



## bv_arvind (Jan 20, 2012)

Hi,

I am having a problem with TCP connection establishment phase when I use an IPv6 adress. This is also observed only when I use the RealTek driver. The issue I see is that 


```
Device A                 Device B
(client on e100         (server running on realtek driver)
SYN sent
                          SYN RCVD
                          SYN+ACK sent
SYN+ACK rcvd
SYN sent
```

Was not sure why client doesn't recognize the SYN+ACK recieved. The parameters that identfy a connection viz., source IP, destination IP, source port number and destination port number seem to be correct. Any TCP debugging tip in FreeBSD is welcome. Is it possible for me to view the state machine transitions using any CLI or debug option?

Thanks


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## SirDice (Jan 20, 2012)

bv_arvind said:
			
		

> Was not sure why client doesn't recognize the SYN+ACK recieved.


The sequence number might be incorrect. In that case it'll be treated as a spurious packet and ignored.


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