GRE Configuration Example
- Tracy Yang (Unlicensed)
NOTE:
GRE tunnel is a logical interface created by Linux kernel on software side. Once created, GRE tunnel stays in "UP" state unless it is shut down by CLI command "set l3-interface tunnel ddd disable".
As shown in Figure 1, if te-1/1/3 is disabled, the underlay routing of the associate GRE tunnel is broken. It is not necessary that tunnel l3-interface (TnXtunnel1) should be down. In this case, the state of GRE tunnel is "UP" in the display of show command run show l3-interface tunnel.
admin@R1# run show l3-interface tunnel tnl0
tnl0 State:UP
Tunnel Source: 100.168.3.1
Tunnel Destnation:: 100.168.10.2
Tunnel protocol/transport: gre-ip
Inet addr: 100.168.4.1
Traffic statistics:
5 sec input rate IPv4 0 packets/sec, IPv6 0 packets/sec
5 sec forwarding rate IPv4 0 packets/sec, IPv6 0 packets/sec
IPv4 Input Packets............................28
IPv4 Forwarding Packets.......................5
IPv6 Input Packets............................0
IPv6 Forwarding Packets.........
In this document we will demonstrate a sample use case for GRE tunnels using two PICOS switches. As shown in Figure 1, we have two Pica8 switches connected to each other through a public IPv4 network. A host is connected with each device.
Figure 1. GRE Tunnel Configuration
Switch configurations
Below is the switch R1 and R2 configurations.
R1 Configuration
Step 1: Configure L3 VLAN interface for GRE tunnel.
admin@R1# set vlans vlan-id 20 l3-interface "vlan20" admin@R1# set interface gigabit-ethernet ge-1/1/1 family ethernet-switching native-vlan-id 20 admin@R1# set l3-interface vlan-interface vlan20 address 100.168.3.1 prefix-length 24
Step 2: Configure L3 VLAN interface for PC1.
admin@R1# set vlans vlan-id 10 l3-interface "vlan10" admin@R1# set l3-interface vlan-interface vlan10 vrf "vrf1" admin@R1# set interface gigabit-ethernet ge-1/1/2 family ethernet-switching native-vlan-id 10 admin@R1# set l3-interface vlan-interface vlan10 address 192.168.5.2 prefix-length 24
Step 3: Enable IP routing on R1 and configure VRF.
admin@R1# set ip routing enable true admin@R1# set ip vrf vrf1 description "orange"
Step 4. Configure GRE tunnel name, IP, source IP, destination IP etc.
admin@R1# set l3-interface tunnel tnl0 address 100.168.4.1 prefix-length 24 admin@R1# set l3-interface tunnel tnl0 tunnel-mode "gre-ip" admin@R1# set l3-interface tunnel tnl0 source 100.168.3.1 admin@R1# set l3-interface tunnel tnl0 destination 100.168.10.2 admin@R1# set l3-interface tunnel tnl0 vrf "vrf1"
Step 5: Create static routes for the GRE tunnel.
admin@R1# set protocols static vrf vrf1 route 192.168.6.0/24 next-hop 100.168.4.2 admin@R1# set protocols static route 100.168.10.0/24 next-hop 100.168.3.2
Or we can create the static route using the tunnel name as the next hop.
admin@R1# set protocols static vrf vrf1 interface-route 192.168.6.0/24 interface tnl0
R2 Configuration
Step1. Configure L3 VLAN interface for GRE tunnel.
admin@R2# set vlans vlan-id 20 l3-interface "vlan20" admin@R2# set interface gigabit-ethernet ge-1/1/1 family ethernet-switching native-vlan-id 20 admin@R2# set l3-interface vlan-interface vlan20 address 100.168.10.2 prefix-length 24
Step 2: Configure L3 VLAN interface for PC2.
admin@R2# set vlans vlan-id 10 l3-interface "vlan10" admin@R2# set l3-interface vlan-interface vlan10 vrf "vrf1" admin@R2# set interface gigabit-ethernet ge-1/1/2 family ethernet-switching native-vlan-id 10 admin@R2# set l3-interface vlan-interface vlan10 address 192.168.6.2 prefix-length 24
Step 3: Enable IP routing on R1 and configure VRF.
admin@R2# set ip routing enable true admin@R2# set ip vrf vrf1 description "orange"
Step 4. Configure GRE tunnel name, IP, source IP, destination IP etc.
admin@R2# set l3-interface tunnel tnl0 address 100.168.4.2 prefix-length 24 admin@R2# set l3-interface tunnel tnl0 tunnel-mode "gre-ip" admin@R2# set l3-interface tunnel tnl0 source 100.168.10.2 admin@R2# set l3-interface tunnel tnl0 destination 100.168.3.1 admin@R2# set l3-interface tunnel tnl0 vrf "vrf1"
Step 5: Create static routes for the GRE tunnel.
admin@R2# set protocols static vrf vrf1 route 192.168.5.0/24 next-hop 100.168.4.1 admin@R2# set protocols static route 100.168.3.0/24 next-hop 100.168.10.3
Or we can also create the static route with the tunnel name as the next hop.
admin@R2# set protocols static vrf vrf1 interface-route 192.168.5.0/24 interface tnl0
Verify Configuration
- Run command run show l3-interface tunnel to display information about the GRE tunnel interface.
admin@R1# run show l3-interface tunnel tnl0
tnl0 State:UP
Tunnel Source: 100.168.3.1
Tunnel Destnation:: 100.168.10.2
Tunnel protocol/transport: gre-ip
Inet addr: 100.168.4.1
Traffic statistics:
5 sec input rate IPv4 1400 packets/sec, IPv6 0 packets/sec
5 sec forwarding rate IPv4 28 packets/sec, IPv6 0 packets/sec
IPv4 Input Packets............................28
IPv4 Forwarding Packets.......................5
IPv6 Input Packets............................0
IPv6 Forwarding Packets.......................0
- To verify the configuration on R1, we can use the command show l3-interface tunnel tnl0 as shown below.
admin@R1# show l3-interface tunnel tnl0
address 100.168.4.1 {
prefix-length: 24
}
tunnel-mode: "gre-ip"
source: 100.168.3.1
destination: 100.168.10.2
vrf: "vrf1"
- Similarly on R2, run the same command.
admin@R2# show l3-interface tunnel tnl0
address 100.168.4.2 {
prefix-length: 24
}
tunnel-mode: "gre-ip"
source: 100.168.10.2
destination: 100.168.3.1
vrf: "vrf1"
- Check to see if PC1 can reach PC2.
PC1# ping 192.168.6.1 PING 192.168.6.1 (192.168.6.1) 56(84) bytes of data. 64 bytes from 192.168.6.1: icmp_seq=1 ttl=64 time=3.064 ms 64 bytes from 192.168.6.1: icmp_seq=2 ttl=64 time=2.062 ms 64 bytes from 192.168.6.1: icmp_seq=3 ttl=64 time=1.060 ms
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