Budget for the extra bytes without VTEP fragmentation
05Encapsulation makes the underlay IP packet larger. Maximum Transmission Unit (MTU) is the largest IP packet a link can carry without fragmentation in this example.
Separate case: an intermediate router fragments the encapsulated packet. The receiving VTEP may discard the fragments, so fragmentation is not a guaranteed delivery repair.
Source for this drawing: RFC 7348 · Read RFC section 4.3 ↗
New to this? Start hereA quick picture + helpful background
A message needs an address.
Think of a packet as a small addressed envelope. Devices pass it onward; transport protocols decide what delivery promises an application gets.
Helpful first, if these ideas are unfamiliar
These pictures are analogies to help you learn. The linked RFC explains the actual rules.
Terms in this drawing
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
A VTEP MUST NOT fragment VXLAN packets; a path that fits the wrapper avoids relying on fragments.
- VTEPs MUST NOT fragment VXLAN packets. An intermediate router may fragment an encapsulated packet, but the receiving VTEP MAY silently discard those fragments.
- It is RECOMMENDED to configure physical-network MTUs large enough for the added encapsulation. Path MTU Discovery MAY also be used.
- With no VLAN tags or IP options: an inner 1500-byte IP packet plus 14-byte inner Ethernet header becomes a 1550-byte outer IPv4 packet. The outer Ethernet header and FCS are outside that IP MTU measurement.
Chosen values: 1514 inner-frame bytes excluding inner FCS;8 VXLAN+8 UDP+20 IPv4 add 36 bytes, making 1550 outer-IP bytes. Adding 14 outer Ethernet+4 new FCS makes 1568 link-frame bytes, excluding preamble/inter-frame gap. No claim of a universal 1600-byte underlay MTU is made.
Read the RFC section ↗