Re: [Bier] BIER WG adoption of https://datatracker.ietf.org/doc/draft-zzhang-bier-php/

["Jeffrey (Zhaohui) Zhang" <[e-mail]>]

Hi Ice,

Thanks for your comments and questions. Please see below.

> -----Original Message-----
> From: BIER <[e-mail]> On Behalf Of IJsbrand Wijnands
> Sent: Wednesday, October 10, 2018 9:09 AM
> To: Antoni Przygienda <[e-mail]>
> Cc: [e-mail]
> Subject: Re: [Bier] BIER WG adoption of https://datatracker.ietf.org/doc/draft-
> zzhang-bier-php/
> 
> Dear WG,
> 
> This is an interesting area, but for me there is clarification needed to support
> this draft as a WG document.
> 
> * When doing PHP, the BIER header is removed. That also removes the Context
> (for the upstream Label) of the packet, that is required to map it to the correct
> VPN or application. To me it sounds like this proposal does not work for MVPN
> and EVPN, but only global table Multicast. I assume that when a upstream
> assigned label is at the bottom of the BIER header, the BIER header is removed,
> and the Upstream label is left in place. How does the egress router know this
> label is upstream or downstream? By adding a global unique downstream
> Label into the Upstream label space you can probably solve that, but it needs
> to be documented this is a restriction.

The draft does have the following:

   The procedures in this section can be applied only if, by means
   outside the scope of this document, it is known that one of the
   following conditions is met.

   o  The payload after BIER header is IPv4 or IPv6 (i.e., the Proto
      field in the BIER header is 4 or 6).
      Notice that in this case the Destination Address in the IPv4/IPv6
      header must be in the address space for the BIER layer.

   o  The payload after BIER header is MPLS packet with downstream-
      assigned label at top of stack (i.e., the Proto field in the BIER
      header is 2), For example, labels from a Domain-wide Common Block
      (DCB) are used as specified in [I-D.zzhang-bess-mvpn-evpn-
      aggregation-label].
> 
> * When there is no Upstream label below the BIER header, the Multicast
> packet is sent natively to the egress PE. How will the egress PE do the RPF
> check in order to accept the packet?

The egress RPF would either disable the RPF check or specify any "core interfaces" to be expected incoming interface. This is similar to using P2MP tunnels to send multicast traffic w/o signaling (a deployment scenario that has been supported by certain vendors already).

More importantly, I would expect MVPN/GTM/EVPN kind of deployment is the more appropriate scenario, where there will be a VPN/BD label used, which can associate the packets with a virtual RPF interface. If we're just transitioning an existing PIM deployment to using BIER, then there is no explicit set of edge routers (the premise of PHP is really that some edge routers, like VPN/EVPN PEs, cannot be upgraded to support BIER forwarding) - we can just run PIM if a router does not support BIER yet.

I can clarify this in the draft.

> 
> * This draft does require an upgraded software version of the Egress router in
> order to signal PHP, right?

Yes - at least it does not require hardware upgrade :-)

Thanks!
Jeffrey

> 
> Thx,
> 
> Ice.
> 
> > On 3 Oct 2018, at 23:39, Antoni Przygienda <[e-mail]> wrote:
> >
> > Based on consensus/request during IETF 102 this thread starts adoption
> request for https://urldefense.proofpoint.com/v2/url?u=https-
> 3A__datatracker.ietf.org_doc_draft-2Dzzhang-2Dbier-
> 2Dphp_&d=DwIGaQ&c=HAkYuh63rsuhr6Scbfh0UjBXeMK-
> ndb3voDTXcWzoCI&r=f7wsLGcfzAWDNS6XNTBZwj_OLAOsZZqdrR2IDAzeZqE&
> m=MHOYT0MTPnGU7-SyEX7XAKCB_PvAtekCQA8c_v34l88&s=eN3c_C-
> EyJQ3XqPzTCK6bVlK0US32ynkeG6QEsifoNQ&e=
> >
> > Please voice support/dissent/comments …
> >
> > --- tony
> >
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