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

[Tony Przygienda <[e-mail]>]

>
> >    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