Linux GRE Configuration

GRE is a tunneling protocol that encapsulates various network layer protocols inside point-to-point connections. It is used to create virtual private networks (VPNs) and to transport packets over IP networks.

• Encapsulation: GRE encapsulates packets within an outer IP packet, allowing the transport of protocols that might not be natively supported by the underlying network.
• Simplicity: GRE is straightforward and lightweight, making it easy to implement.
• Use Case: Commonly used for creating VPNs, connecting geographically dispersed networks, and enabling compatibility between different network protocols.

Required Linux Modules

root@dent-1:~# lsmod
Module                  Size  Used by
ip_gre                 32768  0
gre                    16384  1 ip_gre

Basic GRE configuration

Topology

Configuration

• config enp0s4 link on both devices with the required ip addresses.
• create tun1 GRE link on both sides.
• add route to the remote destination and set tun1 as nexthop device.

ONM-CLI

dent-1(config-links-iproute2)# link enp0s4
dent-1(config-[name='enp0s4'])# ip 1.1.1.2/24
dent-1(config-[name='enp0s4'])# admin-status up
dent-1(config-[name='enp0s4'])# exit
dent-1(config)# links-iproute2
dent-1(config-links-iproute2)# gre tun1
dent-1(config-gre[name='tun1'])# admin up
dent-1(config-gre[name='tun1'])# tunnel-info local 1.1.1.2
dent-1(config-gre[name='tun1'])# tunnel-info remote 1.1.1.4
dent-1(config-gre[name='tun1'])# tunnel-info pmtudisc on
dent-1(config-gre[name='tun1'])# exit
dent-1(config-links-iproute2)# exit
dent-1(config)# routes-iproute2
dent-1(config-routes-iproute2)# route 192.168.1.0/24
dent-1(config-[prefix='192.168.1.0/24'][table='main']# nexthop tun1
dent-1(config-nexthop[dev='tun1'])# commit

IPROUTE2

ip address add 1.1.1.2/24 dev enp0s4
ip link add name tun1 up type gre local 1.1.1.2 remote 1.1.1.4
ip route add 192.168.1.0/24 table main metric 0 tos default nexthop dev tun1 weight 1

NETCONF

<config>
    <links xmlns="urn:okda:iproute2:ip:link" xmlns:yang="urn:ietf:params:xml:ns:yang:1" yang:operation="none">
        <link>
            <name>enp0s4</name>
            <ip>
                <address>1.1.1.2/24</address>
            </ip>
        </link>
        <gre yang:operation="create">
            <name>tun1</name>
            <admin-status yang:operation="create">up</admin-status>
            <tunnel-info yang:operation="create">
                <local yang:operation="create">1.1.1.2</local>
                <remote yang:operation="create">1.1.1.4</remote>
                <pmtudisc yang:operation="create">on</pmtudisc>
            </tunnel-info>
        </gre>
    </links>
    <routes xmlns="urn:okda:iproute2:ip:route" xmlns:yang="urn:ietf:params:xml:ns:yang:1" yang:operation="none">
        <route yang:operation="create">
            <prefix>192.168.1.0/24</prefix>
            <table>main</table>
            <metric>0</metric>
            <tos>default</tos>
            <netns>1</netns>
            <nexthop yang:operation="create">
                <dev>tun1</dev>
            </nexthop>
        </route>
    </routes>
</config>

Verify

• If we ping from PC1 to PC2 we can see that the traffic is encapsulated with GRE tunnel.