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

Greg Mirsky <> Wed, 31 July 2019 19:07 UTC

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From: Greg Mirsky <>
Date: Wed, 31 Jul 2019 15:07:28 -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,
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