Difference between Legacy Nexus VxLAN and ACI VxLAN

[Noovi]

Hi Guys,

i am preparing Cisco ACI and VxLAN in ACI.

I am having query for difference between Legacy Nexus VxLAN and ACI VxLAN? Can anyone give best answer?

[Robert Burns · Accepted solution]

ACI VXLAN (aka iVXLAN) just makes use some of the reserved fields in the VXLAN headers to identify source groups (EPGs) and some other ACI-specific classifiers.  You can take a look at this CiscoLive presentation if you want to understand the header differences.  https://www.ciscolive.com/c/dam/r/ciscolive/emea/docs/2019/pdf/BRKACI-3101.pdf
Robert

[RedNectar · Accepted solution]

Hi @Noovi ,

If you are asking from an academic point of view - just because you HAVE TO KNOW then I understand your question perfectly - and Robert's answer is a great place to go - particularly slide 20. I've pasted a copy of that slide below for your reference.  You could also check out this (now expired) RFC Draft 

BUT if you are asking the question because you are worried about any changes you might need to carry existing VXLAN traffic across ACI - then there is no need to worry. The iVXLAN encapsulation is for ACI only, existing VXLAN traffic that needs to be transported over ACI is trasported transparently and no changes need to be made on your part.

[njccnp]

Cisco documentation shows the following as the first 16 bits in the ACI VxLAN header. I assume this is outdated information?

GRRRIRRR  RDRRARRR

One example of this is https://www.ciscolive.com/c/dam/r/ciscolive/us/docs/2019/pdf/BRKDCN-2489.pdf

(Slide 18)

[RedNectar]

Hi @njccnp ,

Not sure if you are adding extra information to the question (which already has an accepted answer) or you are asking a new question.

IF you ARE asking a new question, then please, ask a new question. And include the reference to where you found the diagram. I for one would be very interested to see where you found it.

[njccnp]

I have edited my post to include an example of where this information is presented. I have seen it in several places. As I said, I assume that this is probably outdated, but I thought you or someone from Cisco might be able to confirm this. I apologize if I posted my question in the wrong place, but it won't let me delete the post.

[RedNectar]

Hi @njccnp 

You don't need to delete the post. Just create a new one (and maybe once created, edit your original to link to the new question).  In the meantime, I'll take a look at the reference.

[njccnp]

Okay, thanks. Usually the docs with the "RDRRARRR" flags refer to the ACI implementation as "VXLAN GBP," whereas most docs with the "DL,E,SP,DP" flags refer to it as "iVXLAN." However, some docs simply say "VXLAN." My assumption is that the header format changed, and that the term "iVXLAN" refers to the modified specs, while "VXLAN-GBP" is the older term, and refers to older (likely deprecated) specs.

[RedNectar]

Hi @njccnp ,

As much as I hate adding to a dead thread, I guess the following information is relevant to the original question, so here goes:

1. VXLAN is VXLAN - it is defined in RFC 7348
   1. In the RFC, only 1 bit in the first 24 bits of the VXLAN header is defined - the I bit, which indicates that the header contains a VXLAN Network Identifier (VNI - or often written as VNID)
      
      
2. The VXLAN Group Policy Extension draft RFC defined some more bits, most notably the G bit (Group bit), which indicated that
   
   1. the D and A bits, (D or DL is the "Don't Learn" bit, the A bit indicates that policy has been "Applied") should also be present, as well as a 16 bit Group Policy ID.
      1. the presence of these fields give definition to the first 24 bits of the VXLAN Header
   2. This draft referred to the newly defined header as the VXLAN Group Based Policy Extension (VXLAN-GBP) header
   3. AFAIK, only two technologies use this header, Security Group Tags (SGT - see slide 17 in your reference above) and ACI
      1. In ACI, the header is usually referred to as the iVXLAN header (the i indicating Insieme - the company that created ACI before it was bought (back) by Cisco.