Hi Sandeep, You are correct, that a VXLAN GPE implementation can be backward compatible to VXLAN by looking at the P-bit. Which is why we originally were sharing the same UDP port as VXLAN. The problem comes up when a VXLAN (only) VTEP gets a VXLAN GPE packet with the P-bit set, it has no idea what the P-bit means and subsequently ignores the bit (as the VXLAN RFC says it should). This means it expects an Ethernet frame to be directly following the VXLAN header...but since this the VXLAN GPE, the protocol field can be specifying some other protocol besides Ethernet. The VXLAN implementation would misinterpret the data and potentially misdeliver the data.
If the tunnels between VTEPs are always point to point using a control plane, this scenario can be avoided, but if multicast is used, then you cannot mix VXLAN-only VTEPs (which are not forward compatible) with VLAN GPE VTEPs. So, the new UDP port was assigned to prevent a VXLAN GPE packet accidentally being sent to a VXLAN-only VTEP. Note that using the new UDP port is optional if this issue is not a problem in your environment based on not having a mix of VTEPs, or relying on a control plane to prevent this. - Larry From: nvo3 <[email protected]<mailto:[email protected]>> on behalf of "Sandeep Kumar (Sandeep) Relan" <[email protected]<mailto:[email protected]>> Date: Monday, September 21, 2015 at 4:24 PM To: "[email protected]<mailto:[email protected]>" <[email protected]<mailto:[email protected]>> Subject: [nvo3] destination UDP port : draft-ietf-nvo3-vxlan-gpe-00 Hello, Concern/Query : What is the need to have another Destination UDP port number ? Reference : draft-ietf-nvo3-vxlan-gpe-00 (VXLAN - GPE) This draft mentions that : IANA has assigned the value 4790 for the VXLAN-GPE UDP port. Further, this draft specifies: P Bit: Flag bit 5 is defined as the Next Protocol bit. The P bit MUST be set to 1 to indicate the presence of the 8 bit next protocol field. When P=1, the destination UDP port MUST be 4790. P = 0 indicates that the payload MUST conform to VXLAN as defined in [RFC7348<https://tools.ietf.org/html/rfc7348>], including destination UDP port - 4789 What is the need for having another IANA assigned UDP destination port number ? I don't see any strong reasons on the need of another IANA assigned UDP destination port number ? I believe, the P Bit can take care of distinguishing between RFC 7348 VXLAN packet from VXLAN-GPE packets. Appreciate, any insight/ background on the requirement to define another new UDP destination port number for future VXLAN packets ? Thanks & regards Sandeep Relan
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