Re: [Bier] comments for draft-zhang-bier-bierin6-04.txt

Hi Tony,
I think that the example of LL BFD, i.e. single-hop BFD, is in fact
opposite, not in support of TTL/HC = 1. RFC 5881, following on the
extensive discussion of the GTSM in RFC 5082, requires that TTL/HC for the
single-hop BFD be set to 255 and BFD packet discarded by a receiver if
TTL/HC != 255. I'll note that we had an extensive discussion with IESG on
the TTL/HC value in the case of BFD over VXLAN. We've agreed that a VXLAN
tunnel is as single-hop IP and thus TTL/HC MUST be set to 255. Not sure if
all this information was helpful. My $.02

Regards,
Greg

On Thu, Mar 12, 2020 at 8:57 AM Tony Przygienda <tonysietf@gmail.com> wrote:

>
>
>> >    If the neighbor is directly connected, The destination address in
>> >    IPv6 header SHOULD be the neighbor's link-local address on this
>> >    router's outgoing interface, the source destination address SHOULD be
>> >    this router's link-local address on the outgoing interface, and the
>> >    IPv6 TTL MUST be set to 1.
>>
>> I've started a thread on 6man/6ops re. link-local-tunnel traffic as i
>> have the same also in my ANIMA draft, and in implementations i have
>> seen quite some issues tunneling traffic HW accelerated across IPv6
>> link-local addresses and TTL=1.
>>
>> Would welcome implementers in BIER to chime in if they would see this
>> as an issue.
>>
>> If folks feel supporting this HW accelerated might be more complicated
>> than non-link-local tunnels, then it might be useful to change the
>> text to also allow/require support for using the BFR address even for
>> subnet adjacent BFR. In that case one would not use HL=1, and that
>> too i have seen to be a problem in HW accelerated forwarding plane:
>> HL/TTL=1 -> MUST punt (software processing).
>>
>
> really? I'm surprised, actually, LL with TTL=1 for link local is an
> absolutely common case since years for e.g. BFD and other thinks like BGP
> sessions in many topologies so if a silicon does not support that it's a
> strange IPv6 silicon. But yes, supporting LL properly in IPv6 is non
> trivial (spec allows to have e.g. same LL on multiple interfaces in a
> node). The spec here says SHOULD and not MUST so it's perfectly find using
> any addresses (one could probably even use BFR prefix but that would lead
> to ECMP non-deterministic behavior which may or may not be OK depending on
> deployment).  If that needs to be spelled out (albeit it's redundant) I'm
> not opposed to that.
>
> Please cc: bier working group on any discussion you are starting with 6man
> on the side ... Unless I missed my morning mail input ...
>
> --- tony
>
>
>
>
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