GRE (Generic Routing Encapsulation) and VXLAN (Virtual eXtensible Local Area Network) are two protocols used to create tunnels, but they have different purposes, features, and use cases. Let’s look at the main differences:
1. Main Purpose
- GRE:
- A general-purpose tunneling protocol designed to encapsulate a wide range of network protocols (IP, MPLS, etc.) inside IP.
- Used primarily to create point-to-point tunnels (e.g. VPN).
- VXLAN:
- A protocol designed to create overlay networks on top of existing IP networks.
- Main purpose – extending VLANs in data centers with support for up to 16 million network segments.
2. Encapsulation
- GRE:
- Encapsulates the original packet in a new IP header.
- Suitable for any type of traffic (multicast, IPv6, etc.).
- VXLAN:
- Uses UDP to encapsulate Ethernet frames.
- Adds a VXLAN header (with VLAN ID) and a UDP header on top of the base IP.
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3. Scalability
- GRE:
- Limited in scalability as it does not provide the means for segmentation or large-scale use of networks.
- VXLAN:
- Provides enormous scalability thanks to the VXLAN Identifier (VNI, 24 bits) that supports up to 16 million unique network segments. This makes VXLAN preferable for large data centers.
4. Compatibility
- GRE:
- Simple and supported by almost all network devices and operating systems.
- VXLAN:
- Requires UDP support and VXLAN compatibility on end devices (e.g. virtual switches or routers).
5. NAT Compatibility
- GRE:
- Does not support NAT transit directly, as GRE packets do not contain ports. This makes them problematic in NAT networks.
- VXLAN:
- Uses UDP, which allows NAT traversal, making VXLAN preferable in NAT networks.
Usage:
- GRE:
- Connecting offices via VPN.
- Tunneling non-standard protocols.
- VXLAN:
- Network virtualization in cloud infrastructures.
- Expansion of L2 segments in data centers.
Thus, GRE is more focused on universal encapsulation, and VXLAN is designed for scalable network virtualization solutions.