Missing Gateway on Windows
packet was coming as
Incoming packet:
src: 10.8.8.10
dst: 10.4.0.2
The Windows VM receives the packet on nic2. IIS, which is listening on all
interfaces, handles the connection and sends the response to 10.8.8.10.
The Windows IP stack looks at its routes:
C:\> route print
IPv4 Route Table
===========================================================================
Active Routes:
Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 10.132.0.1 10.132.0.13 5
0.0.0.0 0.0.0.0 10.4.0.1 10.4.0.2 261
10.4.0.0 255.255.240.0 On-link 10.4.0.2 261
10.4.0.2 255.255.255.255 On-link 10.4.0.2 261
10.4.15.255 255.255.255.255 On-link 10.4.0.2 261
10.132.0.0 255.255.240.0 10.132.0.1 10.132.0.13 6
10.132.0.1 255.255.255.255 On-link 10.132.0.13 6
10.132.0.13 255.255.255.255 On-link 10.132.0.13 261
===========================================================================
Persistent Routes:
Network Address Netmask Gateway Address Metric
169.254.169.254 255.255.255.255 On-link 1
0.0.0.0 0.0.0.0 10.4.0.1 Default
===========================================================================
The response IP headers:
src: 10.4.0.2
dst: 10.8.8.10
Since the address 10.8.8.10 is
When the nic 2 has an empty gateway:
C:\> route print
IPv4 Route Table
===========================================================================
Active Routes:
Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 10.132.0.1 10.132.0.13 5
10.4.0.0 255.255.240.0 On-link 10.4.0.2 261
10.4.0.2 255.255.255.255 On-link 10.4.0.2 261
10.4.15.255 255.255.255.255 On-link 10.4.0.2 261
10.132.0.0 255.255.240.0 10.132.0.1 10.132.0.13 6
10.132.0.1 255.255.255.255 On-link 10.132.0.13 6
10.132.0.13 255.255.255.255 On-link 10.132.0.13 261
127.0.0.0 255.0.0.0 On-link 127.0.0.1 331
127.0.0.1 255.255.255.255 On-link 127.0.0.1 331
127.255.255.255 255.255.255.255 On-link 127.0.0.1 331
169.254.169.254 255.255.255.255 On-link 10.132.0.13 6
169.254.169.254 255.255.255.255 On-link 10.4.0.2 261
224.0.0.0 240.0.0.0 On-link 127.0.0.1 331
224.0.0.0 240.0.0.0 On-link 10.4.0.2 261
224.0.0.0 240.0.0.0 On-link 10.132.0.13 261
255.255.255.255 255.255.255.255 On-link 127.0.0.1 331
255.255.255.255 255.255.255.255 On-link 10.4.0.2 261
255.255.255.255 255.255.255.255 On-link 10.132.0.13 261
===========================================================================
Persistent Routes:
Network Address Netmask Gateway Address Metric
169.254.169.254 255.255.255.255 On-link 1
===========================================================================
Hypotheses:
- The packet arrives into the VM but the TCP connection cannot be initiated.
- The reason the TCP connection cannot be initiated is that Windows fails sending an ACK packet because it does not have a gateway IP set for this network card.
- The ACK cannot be sent because Windows does not find an entry for 10.8.8.10 in its ARP table, and since no gateway is set, it cannot figure out to which MAC address the ACK packet should be addressed.
Is it the same on Linux?