Wireshark · Wireshark-users: Re: [Wireshark-users] wireshark shows: TCP Port numbers reused on PlanetLab nodes

[Sake Blok <sake@xxxxxxxxxx>]

A teamed physical interface is when you combine two network cards into one logical network card. Cisco calls it Etherchannel, other network vendors call it trunking and linux calls it bonding while in is called teaming in the windows world.

Of course the SYN/ACK could not have been on the network before the SYN to which it was a response, therefor for some reason the capture process saw the SYN/ACK earlier than the SYN. This can be caused by using two network interfaces for the same TCP session. As the timestamping is done in the OS and not on the network card.

Cheers,

Sake

On 22 mrt 2013, at 10:48, wen lui wrote:

what do you mean for this : " a teamed physical interface"
there are many virtual machines in one PlanetLab nodes, are there any implications?

but from the time, the second packet arrives at a minus time, it means it arrives earlier than the first?

I don't know why they are out order? any reasons?

2013/3/21 Martin Visser <martinvisser99@xxxxxxxxx>

Very simply, you have have captured the packets 1 and 2 out of order. Packet 2 it would seem is the SYN,  that initiated the SYN-ACK in packet 1. (At least it seems that way to me - a sane stack wouldn't reuse the same TCP source port at such a small interval). Are you running a teamed physical interface, and hence why you are capturing packets out of order?.

Regards, Martin

MartinVisser99@xxxxxxxxx

On 21 March 2013 00:18, wen lui <esolvepolito@xxxxxxxxx> wrote:

I run a simple TCP client on machine A and a simple TCP server on machine B (machine B is a Planetlab node while machine A is not).
Then the client establishes a tcp connection with machine B and send some data.
I capture packets on both A and B, on A the wireshark shows that it is a normal 3-Way handshaking, but on B, it shows as below:

1	0.000000	138.46.116.22	138.46.201.109	TCP	74	54000 > 57182 [SYN, ACK] Seq=0 Ack=0 Win=5792 Len=0 MSS=1460 SACK_PERM=1 TSval=1751648211 TSecr=1119925943 WS=128 0.000000



2	-0.000062	138.46.201.109	138.46.116.22	TCP	74	[TCP Port numbers reused] 57182 > 54000 [SYN] Seq=0 Win=14600 Len=0 MSS=1460 SACK_PERM=1 TSval=1119925943 TSecr=0 WS=128	-0.000062
3	0.000308	138.46.201.109	138.46.116.22	TCP	66	57181 > 54000 [ACK] Seq=1 Ack=1 Win=14720 Len=0 TSval=1119737278 TSecr=1751459556	0.000308




while I see on machine B, actually the tcp connection is established.
before the client sends the SYN and ACK, I checked machine B and found no TCP connection

netstat -tnp
(Not all processes could be identified, non-owned process info will not be shown, you would have to be root to see it all.)
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address               Foreign Address                State       PID/Program name   
tcp        0      0 138.46.116.22:54000         138.46.201.109:57181        ESTABLISHED 17879/tcp_server 



anyway, I can send data to the tcp server and it receives it correctly.



why wireshark shows TCP Port numbers reused? and the time is '-0.000062'? 

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