Getting Started

There are only a few scenarios, such as when using multipath TCP, in which you require multiple default gateways on a host. In most cases, you configure only a single default gateway to avoid unexpected routing behavior or asynchronous routing issues.

NOTE To route traffic to different internet providers, use policy-based routing instead of multiple default gateways.

Prerequisites

1. The host uses NetworkManager to manage network connections, which is the default.
2. The host has multiple network interfaces.
3. The host has multiple default gateways configured.

Procedure

1. Display the routing table:

   • For IPv4, enter:

     # ip -4 route
     default via 192.0.2.1 dev enp1s0 proto static metric 101
     default via 198.51.100.1 dev enp7s0 proto static metric 102
     ...

   • For IPv6, enter:

     # ip -6 route
     default via 2001:db8:1::1 dev enp1s0 proto static metric 101 pref medium
     default via 2001:db8:2::1 dev enp7s0 proto static metric 102 pref medium
     ...

   Entries starting with default indicate a default route. Note the interface names of these entries displayed next to dev.

2. Use the following commands to display the NetworkManager connections that use the interfaces you identified in the previous step:

   # nmcli -f GENERAL.CONNECTION,IP4.GATEWAY,IP6.GATEWAY device show enp1s0
   GENERAL.CONNECTION:      Corporate-LAN
   IP4.GATEWAY:             192.168.122.1
   IP6.GATEWAY:             2001:db8:1::1
   
   # nmcli -f GENERAL.CONNECTION,IP4.GATEWAY,IP6.GATEWAY device show enp7s0
   GENERAL.CONNECTION:      Internet-Provider
   IP4.GATEWAY:             198.51.100.1
   IP6.GATEWAY:             2001:db8:2::1

   In these examples, the profiles named Corporate-LAN and Internet-Provider have the default gateways set. Because, in a local network, the default gateway is typically the host that is one hop closer to the internet, the rest of this procedure assumes that the default gateways in the Corporate-LAN are incorrect.

3. Configure that NetworkManager does not use the Corporate-LAN connection as the default route for IPv4 and IPv6 connections:

   # nmcli connection modify Corporate-LAN ipv4.never-default yes ipv6.never-default yes

   Note that setting ipv4.never-default and ipv6.never-default to yes, automatically removes the default gateway’s IP address for the corresponding protocol from the connection profile.

4. Activate the Corporate-LAN connection:

   # nmcli connection up Corporate-LAN

5. Verification steps

   • Display the IPv4 and IPv6 routing tables and verify that only one default gateway is available for each protocol:

     a. For IPv4, enter:

     # ip -4 route
     default via 192.0.2.1 dev enp1s0 proto static metric 101
     ...

     b. For IPv6, enter:

     # ip -6 route
     default via 2001:db8:1::1 dev enp1s0 proto static metric 101 pref medium
     ...