How To Understand AWS GWLB GENEVE Encapsulation Overhead Variability

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When setting up your network with a Gateway Load Balancer (GWLB) on AWS, it’s important to understand the size of the encapsulation overhead introduced by the GENEVE protocol. According to AWS documentation, the GENEVE encapsulation adds about 68 bytes to each original packet. This means that to handle the maximum packet size comfortably, your appliances should support a minimum MTU (Maximum Transmission Unit) of 8,568 bytes. Planning for this size helps prevent issues with packet fragmentation or drops.

Although the GENEVE protocol allows for variable-length headers because of optional fields called TLV (Type-Length-Value), AWS specifies the typical encapsulation overhead as 68 bytes for GWLB. The documentation treats this as a standard size and does not specify that it changes based on configuration or optional fields. As of now, you can reliably use 68 bytes as the overhead in your planning.

It’s also worth noting that this overhead might be updated in future AWS releases, but such changes would be communicated clearly through AWS announcements and documentation updates.

For reliable operation, always design your network around the 68-byte encapsulation overhead. Make sure your appliances can support at least 8,568 bytes of MTU. Doing so helps ensure your network runs smoothly without unexpected packet drops or fragmentation issues.