Windows Server 2016 sends trafic to wrong network interface when connected to two different networks

[Rui Paz]

Running Windows Server 2016 Standard with Desktop Experience on a server with two network cards.

- the 1st network card is connected to the internet and receives the configuration via DHCP server on the network 193.136.***.***/24
- the 2nd card is manually configured as a private network with a fixed IP 192.168.1.254 and netmask 255.255.255.0 without gateway or DNS, this card is connected only to a network switch that is isolated not connected to anything else.

Configured another machine with a fixed IP 192.168.1.1 that is connected to the switch, the server and client can ping each other just fine.

On the server a tracert 192.168.1.1 works fine but if I do a tracert to a non-existing machine like 192.168.1.10 instead of getting "reports: Destination host unreachable." or something like that tracert shows that packages are sent to the gateway of the first network interface!!!

The exact same setup on older Windows servers didn't to that, I did several searches and coudn't find anything saying that this is a new behavior so i think this is a BUG!


C:\Users\Administrator>tracert 192.168.1.10

Tracing route to 192.168.1.10 over a maximum of 30 hops

1 1 ms <1 ms 1 ms router.domain.com [193.136.***.***]
2 <1 ms <1 ms <1 ms router-world.domain.com [193.1**.***.**]
3 3 ms 3 ms 3 ms Router13.ispdomain.domain2.com [193.***.*.*]


Using Powershell and Test-NetConnection its possible to notice the strange result!


PS C:\Users\Administrator> Test-NetConnection 192.168.1.12 -DiagnoseRouting

ComputerName : 192.168.1.12
RemoteAddress : 192.168.1.12
SelectedSourceAddress : 192.168.1.254
OutgoingInterfaceIndex : 2
SelectedNetRoute : DestinationPrefix: 192.168.1.0/24
NextHop: 0.0.0.0
RouteDiagnosticsSucceeded : True


PS C:\Users\Administrator> tracert -d 192.168.1.12

Tracing route to 192.168.1.12 over a maximum of 30 hops

1 192.168.1.254 reports: Destination host unreachable.

Trace complete.
PS C:\Users\Administrator> tracert -d 192.168.1.12

Tracing route to 192.168.1.12 over a maximum of 30 hops

1 <1 ms <1 ms <1 ms 193.136.***.**
2 <1 ms <1 ms <1 ms 193.***.**.**


PS C:\Users\Administrator> Test-NetConnection 192.168.1.12 -DiagnoseRouting

ComputerName : 192.168.1.12
RemoteAddress : 192.168.1.12
SelectedSourceAddress : 193.136.***.**
OutgoingInterfaceIndex : 6
SelectedNetRoute : DestinationPrefix: 0.0.0.0/0
NextHop: 193.136.***.***
RouteDiagnosticsSucceeded : True

PS C:\Users\Administrator>


Note: There is nothing using the IP 192.168.1.12

The network interfaces configuration:

Ethernet adapter Lab:
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Intel(R) 82566DM-2 Gigabit Network Connection
Physical Address. . . . . . . . . : 00-XX-17-9D-XX-XX
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes
IPv4 Address. . . . . . . . . . . : 192.168.1.254(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . :
NetBIOS over Tcpip. . . . . . . . : Enabled

Ethernet adapter Ethernet:

Connection-specific DNS Suffix . : domain.com
Description . . . . . . . . . . . : Intel(R) PRO/1000 MT Network Connection
Physical Address. . . . . . . . . : 00-XX-17-9D-XX-XX
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IPv4 Address. . . . . . . . . . . : 193.136.***.**(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.255.128
Lease Obtained. . . . . . . . . . : 12 de fevereiro de 2020 09:30:13
Lease Expires . . . . . . . . . . : 12 de fevereiro de 2020 10:40:13
Default Gateway . . . . . . . . . : 193.136.***.126
DHCP Server . . . . . . . . . . . : 193.136.***.125
DNS Servers . . . . . . . . . . . : 193.136.***.125
NetBIOS over Tcpip. . . . . . . . : Enabled

Continue reading...