Networking, subnets, and Windows NIC's

I have a machine with 2 NIC's defined as follows: (Note:  no gateways are defined)

NIC_1:
   IP:       10.14.101.105
   Mask:     255.255.255.248
   Gateway:  N/A
   DNS:      10.14.10.10

NIC_2:
   IP:       10.14.101.113
   Mask:     255.255.255.248
   Gateway:  N/A
   DNS:      10.14.10.10

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They are part of the following 2 subnets.  (Notice that the first NIC is in the first subnet, and the second NIC of that same machine is in the second subnet)

Subnet 1

   Network:   10.14.101.104/29    
   Hosts:     10.14.101.105 - 10.14.101.110  
   Broadcast: 10.14.101.111 

   I assigned the following nodes to this subnet

      10.14.101.105  Windows
      10.14.101.108  Linux

Subnet 2

   Network:   10.14.101.112/29   
   Hosts:     10.14.101.113 - 10.14.101.118        
   Broadcast: 10.14.101.119  

   I assigned the following nodes to this subnet

      10.14.101.113  Windows
      10.14.101.114  Linux

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I then send packets to my servers as follows:

10.14.101.105    ---->  10.14.101.108
255.255.255.248         255.255.255.248


10.14.101.113    ---->  10.14.101.114
255.255.255.248         255.255.255.248

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This results in BOTH NIC's taking an equal amount of traffice

If I have 2 client processes sending to 108, the task mgr only reports traffice in the 10.14.101.105 NIC.  Same for sending to 114, only the 114 NIC shows traffice.

So I am happy with the results, so I try something else...

I change the subnets so that both the the servers now have 255.255.0.0 masks, so they are technically no longer part of the 2255.255.255.248 subnets

I then send as follows:

10.14.101.105    ---->  10.14.101.108
255.255.255.248         255.255.0.0


10.14.101.113    ---->  10.14.101.114
255.255.255.248         255.255.0.0

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All traffic from the 105 NIC goes to 108.  All traffic from the 113 goes to 114.

I then try 2 procedures sending to the .108 server.  This time I get twice as much traffice on the .105 NIC, and no traffice on the 113 NIC

So why is it doing this ?  How does it know that 105 should go to 108, since they are no longer in the same subnet

I reactivated the server NIC's after changing the mask to 255.255.0.0.

I saw nothing in the route table:

IPv4 Route Table
================================================================
Active Routes:
Network Destination        Netmask          Gateway       Interf
          0.0.0.0          0.0.0.0      10.14.10.10    10.14.101
    10.14.101.104  255.255.255.248         On-link     10.14.101
    10.14.101.105  255.255.255.255         On-link     10.14.101
    10.14.101.111  255.255.255.255         On-link     10.14.101
    10.14.101.112  255.255.255.248         On-link     10.14.101
    10.14.101.113  255.255.255.255         On-link     10.14.101
    10.14.101.119  255.255.255.255         On-link     10.14.101
        127.0.0.0        255.0.0.0         On-link         127.0
        127.0.0.1  255.255.255.255         On-link         127.0
  127.255.255.255  255.255.255.255         On-link         127.0
        224.0.0.0        240.0.0.0         On-link         127.0
        224.0.0.0        240.0.0.0         On-link     10.14.101
        224.0.0.0        240.0.0.0         On-link     10.14.101
  255.255.255.255  255.255.255.255         On-link         127.0
  255.255.255.255  255.255.255.255         On-link     10.14.101
  255.255.255.255  255.255.255.255         On-link     10.14.101
================================================================
Persistent Routes:
  Network Address          Netmask  Gateway Address  Metric
          0.0.0.0          0.0.0.0      10.14.10.10  Default
================================================================

IPv6 Route Table
================================================================
Active Routes:
 If Metric Network Destination      Gateway
 16     58 ::/0                     On-link
  1    306 ::1/128                  On-link
 16     58 2001::/32                On-link
 16    306 2001:0:9d38:953c:8d8:e7c:f5f1:9a96/128
                                    On-link
 12    266 fe80::/64                On-link
 16    306 fe80::/64                On-link
 16    306 fe80::8d8:e7c:f5f1:9a96/128
                                    On-link
 12    266 fe80::491e:90d0:c3b9:ca5f/128
                                    On-link
  1    306 ff00::/8                 On-link
 16    306 ff00::/8                 On-link
 12    266 ff00::/8                 On-link
================================================================

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Any ideas why it is acting this way ?
Los Angeles1Asked:
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Brian UtterbackConnect With a Mentor Principle Software EngineerCommented:
I am not sure that I see the problem. When you say you start two "procedures" do you mean processes? Are these processes binding the local address to one or the other of the local interface addresses or are they not specifying the local address? The route data appears to be truncated on the right, do you have the full data?
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