syn connection not replied with ack

[mpe <michele@unipex.it>]

Hi all,
I have very very strange behaviour with a virtual machine (centos 6 
up-to-date).
Then I try to connect to it with a linux ssh client, I see the syn, but 
not the syn-ack replied. On the same target when I connect with windows 
machine, it reply correctly and the communication starts.

tshark show me with linux:
386.134073 172.18.0.160 -> 172.18.0.254 TCP 45092 > ssh [SYN] Seq=0 
Win=4240 Len=0 MSS=1060 TSV=497047 TSER=0 WS=5
389.134556 172.18.0.160 -> 172.18.0.254 TCP 45092 > ssh [SYN] Seq=0 
Win=4240 Len=0 MSS=1060 TSV=497798 TSER=0 WS=5
395.134926 172.18.0.160 -> 172.18.0.254 TCP 45092 > ssh [SYN] Seq=0 
Win=4240 Len=0 MSS=1060 TSV=499298 TSER=0 WS=5

and windows:
1099.091686 172.18.0.141 -> 172.18.0.254 TCP 32906 > ssh [SYN] Seq=0 
Win=8192 Len=0 MSS=1260 WS=8
1099.092934 172.18.0.254 -> 172.18.0.141 TCP ssh > 32906 [SYN, ACK] 
Seq=0 Ack=1 Win=5840 Len=0 MSS=1380
1099.092960 172.18.0.141 -> 172.18.0.254 TCP 32906 > ssh [ACK] Seq=1 
Ack=1 Win=65520 Len=0
1099.102017 172.18.0.254 -> 172.18.0.141 SSH Server Protocol: 
SSH-2.0-OpenSSH_4.3

iptables are disabled, no modules active (lsmod | grep ip show nothing)
I tried also to remove the vmware vmxnet3 module, reloaded, network 
restart, but the same.

But... if I reboot, the communication start for the next 2/3 days and 
after it stops another time.

Hope that someone can help me.

Michele