https://www.juniper.net/documentation/en_US/junos/topics/topic-map/switches-interface-gre.html
| In Layer 2 service | GRE max MTU 1514 L2 header=14 Bytes IP header= 20 Bytes GRE header= 4 Bytes L2 customer packet: 1514- 38 = 1476 bytes Total= 38 Bytes of L2 overhead Ratio: 42/1514 = 2.8% |
| In Layer 3 service | L3 services L2 header=14 Bytes IP header= 20 Bytes GRE header= 4 Bytes L3 customer Header packet: 1514 - 38 = 1476 bytes Total= 24 Bytes of L2 overhead Ratio: 24/1514 = 1.6% |