I am seeing a strange problem with my WS2008R2 server I believe is related to networking. The symptom is that 6% of all attempts to ping the server using tcp fails. For example, from another machine, I see:

$ nc -vz 172.25.79.12 11555
Connection to 172.25.79.12 11555 port [tcp/*] succeeded!
$ nc -vz 172.25.79.12 11555
Connection to 172.25.79.12 11555 port [tcp/*] succeeded!
$ nc -vz 172.25.79.12 11555
nc: connect to 172.25.79.12 port 11555 (tcp) failed: Connection timed out
$ nc -vz 172.25.79.12 11555
Connection to 172.25.79.12 11555 port [tcp/*] succeeded!

I see this regardless of port, and this problem was first reported as 6% of the users' attempts to connect to the SQL Server database timing out.

We started seeing this around the time we connected an external storage device from pogo linux to the server using iSCSI. Indeed, when we disconnect the device, the symptom disappears. The reason it was attached directly to the server was because it is being used by SQL Server to store an archive database, and we wanted the best performance possible. (We are a very resource limited department.)

I don't have network experience, and was wondering if there are any smoking guns in my routing table and config. Any tips or advice would be very much appreciated.

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\>route print
===========================================================================
Interface List
 16...00 21 9b 92 6b 91 ......Broadcom BCM5709C NetXtreme II GigE (NDIS VBD Clie
nt) #7
 15...00 21 9b 92 6b 93 ......Broadcom BCM5709C NetXtreme II GigE (NDIS VBD Clie
nt) #6
  1...........................Software Loopback Interface 1
===========================================================================

IPv4 Route Table
===========================================================================
Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0    172.25.79.100     172.25.79.12    266
          1.2.3.0    255.255.255.0         On-link           1.2.3.1    266
          1.2.3.1  255.255.255.255         On-link           1.2.3.1    266
        1.2.3.255  255.255.255.255         On-link           1.2.3.1    266
        127.0.0.0        255.0.0.0         On-link         127.0.0.1    306
        127.0.0.1  255.255.255.255         On-link         127.0.0.1    306
  127.255.255.255  255.255.255.255         On-link         127.0.0.1    306
      172.25.79.0    255.255.255.0         On-link      172.25.79.12    266
     172.25.79.12  255.255.255.255         On-link      172.25.79.12    266
    172.25.79.255  255.255.255.255         On-link      172.25.79.12    266
        224.0.0.0        240.0.0.0         On-link         127.0.0.1    306
        224.0.0.0        240.0.0.0         On-link           1.2.3.1    266
        224.0.0.0        240.0.0.0         On-link      172.25.79.12    266
  255.255.255.255  255.255.255.255         On-link         127.0.0.1    306
  255.255.255.255  255.255.255.255         On-link           1.2.3.1    266
  255.255.255.255  255.255.255.255         On-link      172.25.79.12    266
===========================================================================
Persistent Routes:
  Network Address          Netmask  Gateway Address  Metric
          0.0.0.0          0.0.0.0    172.25.79.100  Default
          0.0.0.0          0.0.0.0   172.25.100.100  Default
===========================================================================

IPv6 Route Table
===========================================================================
Active Routes:
 If Metric Network Destination      Gateway
  1    306 ::1/128                  On-link
  1    306 ff00::/8                 On-link
===========================================================================
Persistent Routes:
  None
C:\>ipconfig /all

Windows IP Configuration

   Host Name . . . . . . . . . . . . : embarrassing.hostname.redacted
   Primary Dns Suffix  . . . . . . . : department.domain1.redacted
   Node Type . . . . . . . . . . . . : Hybrid
   IP Routing Enabled. . . . . . . . : No
   WINS Proxy Enabled. . . . . . . . : No
   DNS Suffix Search List. . . . . . : department.domain1.redacted
                                        department.domain2.redacted

Ethernet adapter Local Area Connection 3:

   Connection-specific DNS Suffix  . :
   Description . . . . . . . . . . . : Broadcom BCM5709C NetXtreme II GigE (NDIS
 VBD Client) #7
   Physical Address. . . . . . . . . : 00-21-9B-92-6B-91
   DHCP Enabled. . . . . . . . . . . : No
   Autoconfiguration Enabled . . . . : Yes
   IPv4 Address. . . . . . . . . . . : 1.2.3.1(Preferred)
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . :
   NetBIOS over Tcpip. . . . . . . . : Enabled

Ethernet adapter Local Area Connection 2:

   Connection-specific DNS Suffix  . :
   Description . . . . . . . . . . . : Broadcom BCM5709C NetXtreme II GigE (NDIS
 VBD Client) #6
   Physical Address. . . . . . . . . : 00-21-9B-92-6B-93
   DHCP Enabled. . . . . . . . . . . : No
   Autoconfiguration Enabled . . . . : Yes
   IPv4 Address. . . . . . . . . . . : 172.25.79.12(Preferred)
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 172.25.79.100
   DNS Servers . . . . . . . . . . . : 128.95.112.1
                                       128.95.120.1
   NetBIOS over Tcpip. . . . . . . . : Enabled
  • There's a slight discrepancy in your question. You said you connected the server to the storage via iSCSI and then you said you connected it directly to the server. Can you clarify that? – joeqwerty Jun 23 '15 at 19:39
  • 1
    Things I notice that I find interesting: The persistent route to the 0 network through 172.25.100.100 seems odd. The network address of 1.2.3.0/24 for what I assume is the iSCSI network is not a private address range. It's not common to use public DNS servers on a Windows network, and shouldn't be done if the server is part of a Domain. Are your SQL clients on the 172.25.79.0/24 network or are they on a different subnet? Have you configured jumbo frames on the iSCSI interface? Are the interfaces two ports on the same card? – Todd Wilcox Jun 23 '15 at 19:39
  • 1
    Agreed. You probably shouldn't have those persistent routes. Also, did you try to configure a Default Gateway on both network cards? If so, you shouldn't. – joeqwerty Jun 23 '15 at 19:42
  • Thanks for taking a look. Regarding the discrepancy: The storage is physically connected to the server. (There is a cable connecting the card in the storage device to the card on the server.) We are running Microsoft iSCSI Initiator on the server. – TripleScience Jun 23 '15 at 20:30
  • The server is part of a Domain. The clients are on the same subnet, and the interfaces are indeed two ports on the same card. Also for full disclosure, consultants from pogo linux came out to set this up for us, so I don't fully understand what is going on. – TripleScience Jun 23 '15 at 20:32
up vote 0 down vote accepted

Try removing the persistent route to 172.25.100.100 for the 0 network. It doesn't seem to fit your configuration. Also your DNS servers for all domain joined servers and workstations should be AD integrated DNS servers that are at least hosting the forward lookup zone for the domain in question.

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