Feature: Layer 3 IPv4 Routing

Feature: Layer 3 IPv4 Routing

Introduction

Starting from firmware version v1.7.0, supported GigaCore switches supported Layer 3 unicast routing or Switch Virtual Interfaces. This is an advanced functionality which can be useful to eliminate external routers or make routing more efficient by leveraging the routing capabilities of the switches for local network traffic.
Alert
Inter-VLAN routing is advanced functionality. This not only requires configuration of the GigaCore switches, but also of the end devices which you would like to use for routing. These devices need a matching IPv4 address and gateway IP.

Requirements

  1. Firmware version v1.7.0 or newer
    1. A Layer 3-capable GigaCore switch.
    2. A Layer 3 IP interface has been configured for the groups between which you would like to route.

    Limitations

    Info
    1. Inter-VLAN routing is only possible for unicast IPv4 traffic
    2. Enabling or disabling routing is a global option. When enabled, routing will be possible between ALL groups with Layer 3 functionality enabled.
    3. The GigaCore does not support additional rules or firewalling to block or allow certain types of traffic from going to a certain group.

    Configuration

    Web interface

    Assuming that Layer 3 IP interfaces have already been configured:
    1. Browse to the web interface of the GigaCore through a port and with an IP address on which configuration is possible. Typically this is through ports indicated with the blue LED of the management group.
    2. Go to 'Device settings' configuration in the sidebar
    3. Find the 'Routing' configuration section
    4. Click the checkbox to enable Layer 3 routing.
    5. Once enabled, an info message will list the groups between which routing is possible.
    6. Optionally configure a default gateway, which should be the IP address of an upstream router.
      1. The IP address has to fall within one of the configured subnets. 
      2. This default gateway IP configuration will override the default gateway setting from the 'IP settings' configuration section.
    7. Click 'Apply' within the routing section.

    Explanation

    What is routing?

    Routing is used to route packets between different Groups (VLANs). To accomplish this, every Group gets assigned an IPv4 address. With this address, an Switch Virtual Interface (SVI) is created.

    What is an SVI (Switch Virtual Interface)?

    An SVI (Switch Virtual Interface) is a logical Layer 3 interface on a switch, associated with a specific Group (VLAN). It allows the switch to route IP packets between groups, enabling inter-group (inter-VLAN) unicast routing.

    When IP routing is enabled, the switch uses SVIs to serve as gateways for devices within each group. Each SVI is assigned:

    • A VLAN ID (e.g., 200, 300). This is determined by the group configuration

    • An IP address. This is the configured Layer 3 IP address. This address has to be used as the default gateway by devices in that group.

    What is a (default) gateway?

    A gateway is a network device (usually a router or switch with routing capabilities) that connects a local network to other networks.
    A default gateway is the IP address a device sends traffic to when the destination is outside its own subnet—it’s the device’s path to reach external networks or the internet. The default gateway IP address is configured to match the IP address of the gateway in the network. A default gateway only has to be configured if a communication is necessary between the device and devices in other networks.

    Example

    GigaCore

    Let’s say a GigaCore 30i switch has the following configuration:
     Group (VLAN)  SVI IP Address  Description
    Group 2 (200) 10.2.0.10/16 SVI for Group 2 (gateway)
    Group 3 (300) 10.3.0.10/16 SVI for Group 3 (gateway)
    Default Gateway 10.2.0.1 IP of the upstream router. Used by the switch to reach external networks

    Devices

    • Device A in Group 2, IP: 10.2.0.20/16, Gateway: 10.2.0.10

    • Device B in Group 3, IP: 10.3.0.30/16, Gateway: 10.3.0.10

    • (Optional) Upstream router in Group 2, IP 10.2.0.1/16

      • This is the default gateway. Any traffic for which no route is known by the GigaCore, will be forwarded towards the default gateway.


    Routing behavior

    When Device A wants to send a packet to Device B:

    1. It sends the packet to its default gateway 10.2.0.10 (SVI on the switch).

    2. The GigaCore 30i routes it to Group 3 using its SVI 10.3.0.10.

    3. The packet is delivered to Device B.

    If Device A tries to send a packet to an unknown network, like 1.1.1.1:

    • The switch doesn't have a direct route.

    • It forwards the packet to its own default gateway, 10.2.0.1, for further routing (e.g., to the internet).

    Packet example with IP and MAC address changes

    Let’s examine the packet flow in detail:

    Device A (Group 2) sends an IP packet to 10.3.0.30 (Device B):

    • Source MAC: AA-AA-AA-AA-AA-AA (Device A)

    • Destination MAC: BB-BB-BB-BB-BB-BB → unknown by Device A, so it's actually set to MAC of SVI 10.2.0.10, e.g., GC-02-02-02-02-02

    • Source IP: 10.2.0.20 (Device A)

    • Destination IP: 10.3.0.30 (Device B)

    Link 1 (Device A → GigaCore 30i):
    1. Src MAC: AA-AA-AA-AA-AA-AA
    2. Dst MAC: GC-02-02-02-02-02
    3. Src IP:  10.2.0.20
    4. Dst IP:  10.3.0.30
    Routing happens now on the switch. The GigaCore will determine the most appropriate route to reach IP 10.3.0.30. The MAC addresses will change. IPs remain unchanged.
    1. Src MAC: GC-03-03-03-03-03  (MAC of SVI 10.3.0.10)
    2. Dst MAC: BB-BB-BB-BB-BB-BB  (Device B)
    3. Src IP:  10.2.0.20
    4. Dst IP:  10.3.0.30

    Conclusion

    1. SVIs enable the GigaCore switch to act as a router between groups (VLANs).
    2. Each group has an SVI that acts as the gateway for devices.
    3. MAC addresses are rewritten during routing; IP addresses remain unchanged.
    4. If the destination IP doesn’t match any known routes, the switch forwards the packet to its default gateway (e.g., 10.2.0.1), continuing the path toward external networks.

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