ip add link returns RTNETLINK answers: File exists

Issue

• Customer wants to add multiple GRE Tunnels.
  https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux_OpenStack_Platform/5/html/Installation_and_Configuration_Guide/Compare_VXLAN_and_GRE_tunnels.html
  So he managed to add one, but the second returns the following:

 [root@host-a network-scripts]# ip link add GRE15_98 type gretap local 10.xxx.yyy.73 remote 98.xxx.yyy.9
 RTNETLINK answers: File exists