GRE 和 VXLAN 对比
| Feature | VXLAN | GRE |
|---|---|---|
| Segmentation | 24-bit VNI (VXLAN Network Identifier) | Uses different Tunnel IDs |
| Theoretical scale limit | 16 million unique IDs | 16 million unique IDs |
| Transport | UDP (default port 4789) | IP Protocol 47 |
| Filtering | VXLAN uses UDP with a well-known destination port; firewalls and switch/router ACLs can be tailored to block only VXLAN traffic. | Firewalls and layer 3 switches and routers with ACLs will typically not parse deeply enough into the GRE header to distinguish tunnel traffic types; all GRE would need to be blocked indiscriminately. |
| Protocol overhead | 50 bytes over IPv4 (8 bytes VXLAN header, 20 bytes IPv4 header, 8 bytes UDP header, 14 bytes Ethernet). | 42 bytes over IPv4 (8 bytes GRE header, 20 bytes IPv4 header, 14 bytes Ethernet). |
| Handling unknown destination packets, broadcasts, and multicast | VXLAN uses IP multicast to manage flooding from these traffic types. Ideally, one logical Layer 2 network (VNI) is associated with one multicast group address on the physical network. This requires end-to-end IP multicast support on the physical data center network. | GRE has no built-in protocol mechanism to address these. This type of traffic is simply replicated to all nodes. |
| IETF specification | http://tools.ietf.org/html/draft-mahalingam-dutt-dcops-vxlan-01 | http://tools.ietf.org/html/rfc2784.html |