Re: BFD over VXLAN: Trapping BFD Control packet at VTEP

Greg Mirsky <> Thu, 01 August 2019 12:40 UTC

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From: Greg Mirsky <>
Date: Thu, 1 Aug 2019 08:40:14 -0400
Message-ID: <>
Subject: Re: BFD over VXLAN: Trapping BFD Control packet at VTEP
To: Dinesh Dutt <>
Cc: rtg-bfd WG <>, "T. Sridhar" <>, Joel Halpern <>,, Martin Vigoureux <>,
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Hi Dinesh,
as I understand, Sridhar is on vacation. In the meantime, this is his
response to the question on using VTEP's MAC address as the destination MAC
in the inner Ethernet frame:

T. Sridhar
Sun, Jun 30, 7:13 PM
to Reshad, Martin,, Matthew, Sam, Jeffrey

Sorry - could not respond earlier.

Joel is right - the draft does impose a requirement on the inner MAC being
the same as the VTEP MAC and eats into the tenant MAC space which is not a
desirable approach. You *could* use VNI0 as the one only VNI to specify
this but that's not ideal either since we did not impose any restriction on
the VNI space.

Btw,  I also think I should modify the comment I had made below about using
the inner IP to be the same as the VTEP IP since there is no guarantee that
the inner MAC frame is an IP packet.


On 6/26/19, 6:59 PM, "Reshad Rahman (rrahman)" <> wrote:

    Thank you Sridhar. One concern which came up is wrt the use of the
destination VTEP MAC address as dest MAC in the inner IP header (see
attached email). Could you please comment on that aspect?


I understand that RFC 7348 maybe is not clear on that issue. I'd like to
understand how the existing implementations behave, process VXLAN header
and the inner Ethernet frame to minimize changes BFD over VXLAN may impose
on the implementation.


On Thu, Aug 1, 2019 at 12:48 AM Dinesh Dutt <> wrote:

> I don't understand his objection. My recommendation is to understand that
> before we propose new text. I fear otherwise that we'll have a new draft in
> a few months to address the issue of using non-mgmt VNI.
> Dinesh
> On Jul 31, 2019, 12:07 PM -0700, Greg Mirsky <>om>,
> wrote:
> Hi Dinesh,
> if I recall correctly, T.Sridhar has noted that VTEP's MAC must not be
> used as the destination MAC address in the inner Ethernet frame.
> Also, I should have been more precise in the proposed text, please see the
> updated version to stress that the management VNI MUST NOT be one of the
> tenant's VNIs:
> An operator MUST select a VNI number to be used as Management VNI.
> Management VNI number MUST NOT be one of the tenant's VNIs to prevent
> sending VXLAN packets received on Management VNI to a tenant. VNI number 1
> is RECOMMENDED as the default for Management VNI.
> On Wed, Jul 31, 2019 at 2:25 PM Dinesh Dutt <> wrote:
>> Hi Greg,
>> On Wed, Jul 31, 2019 at 9:20 AM Greg Mirsky <>
>> wrote:
>>> Hi Dinesh,
>>> thank you for your consideration of the proposal and questions. What
>>> would you see as the scope of testing the connectivity for the specific
>>> VNI? If it is tenant-to-tenant, then VTEPs will treat these packets as
>>> regular user frames. More likely, these could be Layer 2 OAM, e.g. CCM
>>> frames. The reason to use 127/8 for IPv4, and 0:0:0:0:0:FFFF:7F00:0/104 for
>>> IPv6 is to safeguard from leaking Ethernet frames with BFD Control packet
>>> to a tenant.
>>> You've suggested using a MAC address to trap the control packet at VTEP.
>>> What that address could be? We had proposed using the dedicated MAC and
>>> VTEP's MAC and both raised concerns among VXLAN experts. The idea of using
>>> Management VNI may be more acceptable based on its similarity to the
>>> practice of using Management VLAN.
>> If you use the inner IP address as the VTEP IP address, then use the MAC
>> address that the VTEP would respond with when replying to an ARP for that
>> VTEP IP address. If a VXLAN expert disagrees with this, could you kindly
>> tell me who it is so that I can understand their disagreement? So this
>> handles the case where the VNI is not a user-tenant VNI. If the VNI used in
>> the BFD packet is a user-tenant VNI, then the receiving VTEP MUST have an
>> IP address in that VNI (mapped to a VRF) else you cannot use that VNI in
>> the BFD packet. Why won't this combination address all the cases you've
>> listed? What am I missing? Define VNI 1 as a possible use, not VNI 0. I
>> objected to VNI 0 because there are too many switching siicon out there and
>> some of them will not be able to handle this scenario.
>> Dinesh
>>> Regards,
>>> Greg
>>> On Wed, Jul 31, 2019 at 12:03 PM Dinesh Dutt <> wrote:
>>>> Hi Greg,
>>>> As long as the inner MAC address is such that the packet is trapped to
>>>> the CPU, it should be fine for use as an inner MAC is it not? Stating that
>>>> is better than trying to force a management VNI. What if someone wants to
>>>> test connectivity on a specific VNI? I would not pick a loopback IP address
>>>> for this since that address range is host/node local only. Is there a
>>>> reason you're not using the VTEP IP as the inner IP address ?
>>>> Dinesh
>>>> On Wed, Jul 31, 2019 at 5:48 AM Greg Mirsky <>
>>>> wrote:
>>>>> Dear All,
>>>>> thank you for your comments, suggestions on this issue, probably the
>>>>> most challenging for this specification. In the course of our discussions,
>>>>> we've agreed to abandon the request to allocate the dedicated MAC address
>>>>> to be used as the destination MAC address in the inner Ethernet frame.
>>>>> Also, earlier using VNI 0 was changed from mandatory to one of the options
>>>>> an implementation may offer to an operator. The most recent discussion was
>>>>> whether VTEP's MAC address might be used as the destination MAC address in
>>>>> the inner Ethernet frame. As I recall it, the comments from VXLAN experts
>>>>> equally split with one for it and one against. Hence I would like to
>>>>> propose a new text to resolve the issue. The idea is to let an operator
>>>>> select Management VNI and use that VNI in VXLAN encapsulation of BFD
>>>>> Control packets:
>>>>> NEW TEXT:
>>>>> An operator MUST select a VNI number to be used as Management VNI.
>>>>> VXLAN packet for Management VNI MUST NOT be sent to a tenant. VNI number 1
>>>>> is RECOMMENDED as the default for Management VNI.
>>>>> With that new text, what can be the value of the destination MAC in
>>>>> the inner Ethernet? I tend to believe that it can be anything and ignored
>>>>> by the reciever VTEP. Also, if the trapping is based on VNI number, the
>>>>> destination IP address of the inner IP packet can from the range 127/8 for
>>>>> IPv4, and for IPv6 from the range 0:0:0:0:0:FFFF:7F00:0/104. And lastly,
>>>>> the TTL to be set to 1 (no change here).
>>>>> Much appreciate your comments, questions, and suggestions.
>>>>> Best regards,
>>>>> Greg