IP/Network

 

 

 

Directing IP packet to a specific NIC (Network Interface Card)

 

When we have multiple Network Card on the PC, there would be some cases where we want to flow to a specific network card that you want. The surest way would be to remove the whole routing table on your PC and add only one specific Network Card to the table, but this would be the most risky thing as well unless you know for sure on how to recover the original table. Otherwise, you would lose all the critical connection (like internet etc).

 

 

 

Directing Packets by Metric value

 

So, in this tutorial I would show you how to direct a data flow to a specific network card by changing Metric value of the network card.

 

Step 1 : Figure out and remember the ip address and interface ID of each of your network Card

 

C:\>ipconfig

     

    Windows IP Configuration

     

     

    Tunnel adapter Local Area Connection 3:

     

       Connection-specific DNS Suffix  . :

       IPv6 Address. . . . . . . . . . . : fd3a:255f:a321:6985:63b1:16f9:7569:a608

       Link-local IPv6 Address . . . . . : fe80::751a:739b:86c3:f2c8%24

       Autoconfiguration IPv4 Address. . : 169.254.242.200

       Subnet Mask . . . . . . . . . . . : 255.255.0.0

       Default Gateway . . . . . . . . . :

     

    Wireless LAN adapter Wireless Network Connection:

     

       Connection-specific DNS Suffix  . : us.anritsu.com

       Link-local IPv6 Address . . . . . : fe80::2c3e:aabf:6ffa:8145%12 <-- Interface ID

       IPv4 Address. . . . . . . . . . . : 172.25.228.101

       Subnet Mask . . . . . . . . . . . : 255.255.254.0

       Default Gateway . . . . . . . . . :

     

    Ethernet adapter Local Area Connection:

     

       Connection-specific DNS Suffix  . : us.anritsu.com

       Link-local IPv6 Address . . . . . : fe80::206c:68b4:2d2a:2f00%11 <-- Interface ID

       IPv4 Address. . . . . . . . . . . : 172.25.228.103

       Subnet Mask . . . . . . . . . . . : 255.255.254.0

       Default Gateway . . . . . . . . . : 172.25.228.1

 

 

Step 2 : Check current route table and check metrics for each network card (lower Metric value means higher priority to be used).

 

C:\>route -4 PRINT  // I used option '-4' to check only IPv4 info. But depending on your network,

                   // you may need to get all the network info. In that case, just remove '-4'

    ===========================================================================

    Interface List

     24...02 f0 95 b2 10 01 ......BlackBerry Virtual Private Network

     12...3c a9 f4 45 dd 58 ......Intel(R) Centrino(R) Ultimate-N 6300 AGN

     11...f0 1f af 28 8d 92 ......Intel(R) 82579LM Gigabit Network Connection

      1...........................Software Loopback Interface 1

     23...00 00 00 00 00 00 00 e0 Microsoft 6to4 Adapter

     35...00 00 00 00 00 00 00 e0 Microsoft ISATAP Adapter #2

     25...00 00 00 00 00 00 00 e0 Microsoft ISATAP Adapter #3

     34...00 00 00 00 00 00 00 e0 Teredo Tunneling Pseudo-Interface

    ===========================================================================

     

    // You would notice that Wired Lan Card has higher priority than WiFi in this PC

    IPv4 Route Table

    ===========================================================================

    Active Routes:

    Network Destination        Netmask          Gateway       Interface  Metric

              0.0.0.0          0.0.0.0     172.25.228.1   172.25.228.101    125 <-- WiFi

              0.0.0.0          0.0.0.0     172.25.228.1   172.25.228.103     21 <-- Wired

            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

          169.254.0.0      255.255.0.0         On-link    169.254.84.211    261

       169.254.84.211  255.255.255.255         On-link    169.254.84.211    261

      169.254.255.255  255.255.255.255         On-link    169.254.84.211    261

         172.25.228.0    255.255.254.0         On-link    172.25.228.103    276

         172.25.228.0    255.255.254.0         On-link    172.25.228.101    281

       172.25.228.103  255.255.255.255         On-link    172.25.228.103    276

       172.25.229.255  255.255.255.255         On-link    172.25.228.103    276

       172.25.229.255  255.255.255.255         On-link    172.25.228.101    281

            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    172.25.228.103    276

            224.0.0.0        240.0.0.0         On-link    169.254.84.211    261

            224.0.0.0        240.0.0.0         On-link    172.25.228.101    281

      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    172.25.228.103    276

      255.255.255.255  255.255.255.255         On-link    169.254.84.211   9999

      255.255.255.255  255.255.255.255         On-link    172.25.228.101    281

    ===========================================================================

    Persistent Routes:

      None

 

Step 3 : Verify data flows as shown in the routing table shown above. Run Windows Task Manager and select 'Network' tab. And then browser or download file or youTube.. check the data flows via the network card with lowest Matric would flow the most data.

 

 

 

Step 4 : Change the Metric of WLAN Card and Wired Card. In this example, I allocate large metric value to Wired Card and lower metric value to WLAN Card.

 

// '11' is interface ID for Wired Card in this PC. You may have different number in your PC. Confirm it with ipconfig

C:\>route change 0.0.0.0 MASK 0.0.0.0 172.25.228.1 metric 100 if 11  

 OK!

 

// '12' is interface ID for WLAN Card in this PC. You may have different number in your PC. Confirm it with ipconfig

C:\>route change 0.0.0.0 MASK 0.0.0.0 172.25.228.1 metric 1 if 12

 OK!

 

// Confirm that Metric Value of the interface card has been changed. It seems that in Windows 7, the value '20' is added to the metric value you specified

C:\>route -4 PRINT

    ===========================================================================

    Interface List

     24...02 f0 95 b2 10 01 ......BlackBerry Virtual Private Network

     12...3c a9 f4 45 dd 58 ......Intel(R) Centrino(R) Ultimate-N 6300 AGN

     11...f0 1f af 28 8d 92 ......Intel(R) 82579LM Gigabit Network Connection

      1...........................Software Loopback Interface 1

     23...00 00 00 00 00 00 00 e0 Microsoft 6to4 Adapter

     35...00 00 00 00 00 00 00 e0 Microsoft ISATAP Adapter #2

     25...00 00 00 00 00 00 00 e0 Microsoft ISATAP Adapter #3

     34...00 00 00 00 00 00 00 e0 Teredo Tunneling Pseudo-Interface

    ===========================================================================

     

    IPv4 Route Table

    ===========================================================================

    Active Routes:

    Network Destination        Netmask          Gateway       Interface  Metric

              0.0.0.0          0.0.0.0     172.25.228.1   172.25.228.103    120 <-- Wired

              0.0.0.0          0.0.0.0     172.25.228.1   172.25.228.101     21 <-- WiFi

            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

          169.254.0.0      255.255.0.0         On-link    169.254.84.211    261

       169.254.84.211  255.255.255.255         On-link    169.254.84.211    261

      169.254.255.255  255.255.255.255         On-link    169.254.84.211    261

         172.25.228.0    255.255.254.0         On-link    172.25.228.103    276

         172.25.228.0    255.255.254.0         On-link    172.25.228.101    276

       172.25.228.103  255.255.255.255         On-link    172.25.228.103    276

       172.25.229.255  255.255.255.255         On-link    172.25.228.103    276

       172.25.229.255  255.255.255.255         On-link    172.25.228.101    276

            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    172.25.228.103    276

            224.0.0.0        240.0.0.0         On-link    169.254.84.211    261

            224.0.0.0        240.0.0.0         On-link    172.25.228.101    276

      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    172.25.228.103    276

      255.255.255.255  255.255.255.255         On-link    169.254.84.211   9999

      255.255.255.255  255.255.255.255         On-link    172.25.228.101    276

    ===========================================================================

    Persistent Routes:

      None

 

 

Step 5 : Verify data flows as shown in the routing table shown above. Run Windows Task Manager and select 'Network' tab. And then browser or download file or youTube.. check the data flows via the network card with lowest Matric would flow the most data.

 

 

 

 

Would all the IP packets goes through NIC with the lowest metric value ?

 

No, not necessarily. The metric value is used by the routing algorithm to determine the best route for a given IP packet, but it is not the only factor that is taken into account. The routing algorithm also considers the network topology, link speed, congestion, and other factors when selecting the best route.

 

When you have multiple NICs, you can use the metric value to influence the routing decision, but it is not a guarantee that all IP packets will go through the NIC with the lowest metric value. The routing algorithm may choose a different route based on the other factors.

 

In addition, some applications may bind to a specific NIC or IP address, which can override the routing algorithm's decision. Therefore, it is important to test the routing configuration and ensure that the IP packets are being directed to the desired NIC.

 

 

 

Is there any way to distribute IP traffics among multiple NIC ?

 

There are different methods for distributing IP traffic among multiple NICs to increase network performance and availability. Here are a few common techniques:

  • Round-robin: In this method, the network traffic is evenly distributed among the available NICs in a rotating order. Each incoming packet is sent to the next NIC in the sequence. This technique is simple and effective for load balancing, but it does not take into account the load on each NIC, so it may not be optimal for high-traffic environments.
  • Link aggregation (also known as NIC bonding or teaming): This technique combines multiple NICs into a single logical interface to increase bandwidth and redundancy. The NICs are configured to operate in parallel, so the network traffic is spread across all of them. Link aggregation requires support from the NIC drivers and the network switch to work properly.
  • Policy-based routing: This method allows you to define different routing policies for specific traffic types, such as based on the source or destination IP address, port number, or protocol. Each policy can be associated with a different NIC or routing table, allowing you to distribute traffic based on specific criteria. This technique requires more advanced configuration and management.

These methods can be used separately or in combination, depending on your network requirements and infrastructure. It's important to test and monitor the network performance to ensure that the traffic is being distributed effectively and evenly.