What sort of network stats would be useful to diagnose the problem? Below is
the output of netstat -s
It looks like data is being transmitted fine up until the point that the
remote server sends a [TCP Window Update] (see packet 1750 below). At that
point my postfix server doesn't respond and the next packet is a timeout
from the remote server. All of the data is transferred in about a second
and there is no delay in the tcpdump until right before the timeout.
> No. Time Source Destination
> Protocol Length Info
> 1750 2016-11-08 17:32:23.323985 DDD.222.3.44 10.10.10.123
> TCP 66 [TCP Window Update] smtp > 47372 [ACK] Seq=264 Ack=6071217
> Win=28960 Len=0 TSval=989115902 TSecr=2863598
>
> Frame 1750: 66 bytes on wire (528 bits), 66 bytes captured (528 bits)
> Ethernet II, Src: Dell_53:eb:0c (00:13:72:53:eb:0c), Dst:
> RealtekU_bd:b1:11
> (52:54:00:bd:b1:11)
> Internet Protocol Version 4, Src: DDD.222.3.44 (DDD.222.3.44), Dst:
> 10.10.10.123 (10.10.10.123)
> Transmission Control Protocol, Src Port: smtp (25), Dst Port: 47372
> (47372),
> Seq: 264, Ack: 6071217, Len: 0
#netstat -s
Ip:
1573140 total packets received
3130 with invalid addresses
0 forwarded
0 incoming packets discarded
1276252 incoming packets delivered
649817 requests sent out
Icmp:
65 ICMP messages received
3 input ICMP message failed.
ICMP input histogram:
timeout in transit: 45
echo requests: 4
echo replies: 16
3522 ICMP messages sent
0 ICMP messages failed
ICMP output histogram:
destination unreachable: 3463
echo request: 55
echo replies: 4
IcmpMsg:
InType0: 16
InType8: 4
InType11: 45
OutType0: 4
OutType3: 3463
OutType8: 55
Tcp:
3867 active connections openings
20871 passive connection openings
3 failed connection attempts
1701 connection resets received
3 connections established
729373 segments received
981408 segments send out
2196 segments retransmited
0 bad segments received.
4880 resets sent
Udp:
103932 packets received
3463 packets to unknown port received.
4 packet receive errors
97291 packets sent
InCsumErrors: 4
UdpLite:
TcpExt:
75 invalid SYN cookies received
14488 TCP sockets finished time wait in fast timer
10723 delayed acks sent
3 delayed acks further delayed because of locked socket
67 packets directly queued to recvmsg prequeue.
2662149 bytes directly in process context from backlog
7208 bytes directly received in process context from prequeue
255804 packet headers predicted
1888 packets header predicted and directly queued to user
130231 acknowledgments not containing data payload received
225519 predicted acknowledgments
15 times recovered from packet loss by selective acknowledgements
133 congestion windows recovered without slow start after partial ack
32 fast retransmits
4 forward retransmits
267 other TCP timeouts
TCPLossProbes: 1547
TCPLossProbeRecovery: 360
1633 DSACKs received
1746 connections reset due to unexpected data
395 connections reset due to early user close
36 connections aborted due to timeout
TCPDSACKIgnoredNoUndo: 1456
TCPSackShifted: 237
TCPSackMerged: 69
TCPSackShiftFallback: 189
IPReversePathFilter: 7
TCPRcvCoalesce: 57204
TCPAutoCorking: 4
TCPSynRetrans: 196
TCPOrigDataSent: 731195
IpExt:
InBcastPkts: 447052
InOctets: 703894455
OutOctets: 858029660
InBcastOctets: 48518221
InNoECTPkts: 1573150
--
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