Subject: [OSPF] OSPF Hybrid Broadcast and P2MP Interface Type

From: Acee Lindem <[email-masked]>
Date: Thu, 6 Jan 2011 13:18:56 -0500

Speaking as WG Co-Chair, 

I think we are ready to ask whether or not we want to make this a WG document. If you feel one way or another, please share your opinion. 

Speaking as WG member, 

I think this is a reasonable approach which could be readily implemented. It also seemed there was some interest at the WG meeting in this capability. Hence, I would support its adoption (though I don't feel that strongly). 

Thanks,
Acee

---

From: "Alvaro Retana (aretana)" <[email-masked]>
Date: Thu, 6 Jan 2011 14:58:32 -0600

> From: [email-masked] [mailto:[email-masked]] On Behalf
Of
> Acee Lindem
> Sent: Thursday, January 06, 2011 1:19 PM
...

Acee:

Happy New Year!!

> Speaking as WG Co-Chair,
> 
> I think we are ready to ask whether or not we want to make this a WG
> document. If you feel one way or another, please share your opinion.

I'm going to say "no".

While I do believe that the definition of this type of hybrid interface
is interesting, the proposed solution has significant limitations
related to its application to "radio networks".  It is constrained to a
specific case (not the general case).  To quote Jeffrey form a prior
thread: "The premise is that we have a broadcast network but one can
reach some stations with a metric that is different from when reaching
others.  If that premise is not satisfied, then it's a different topic
(and out of the scope)."

Also, an interface with similar characteristics has already been
defined, implemented and deployed in radio networks.  Take a look at the
OSPF-MANET Interface definition in rfc5820 -- I'm quoting a little piece
of the text below.  Note that the OSPF-MANET interface can satisfy the
premise above as well as other types of configurations.

Thanks!

Alvaro.

-------------------

3.1. OSPF-MANET Interface

   Interfaces are defined as the connection between a router and one of
   its attached networks [OSPF].  Four types of interfaces have been
   defined and supported in [OSPF] and [OSPFv3]: broadcast, Non-
   Broadcast Multi-Access (NBMA), point-to-point, and point-to-
   multipoint.

   The point-to-multipoint model has been chosen to represent MANET
   interfaces.  (The features designed in this document MAY be included
   on other interface types as appropriate.)  The MANET interface allows
   the following:

   o  OSPF treats all router-to-router connections over the MANET
      interface as if they were point-to-point links.

   o  Link metric can be set on a per-neighbor basis.

   o  Broadcast and multicast can be accomplished through Layer 2
      broadcast or Layer 2 pseudo-broadcast.

      *  The MANET interface supports Layer 2 broadcast if it is able to
         address a single physical message to all of the attached
         neighbors.  One such example is 802.11.

      *  The MANET interface supports Layer 2 pseudo-broadcast if it is
         able to pick up a packet from the broadcast queue, replicate
         the packet, and send a copy over each point-to-point link.  One
         such example is Frame Relay.

   o  An API must be provided for Layer 3 to determine the Layer 2
      broadcast capability.  Based on the return of the API, OSPF
      classifies the MANET interfaces into the following three types:
      MANET broadcast, MANET pseudo-broadcast, and MANET non-broadcast.

   o  Multicast SHOULD be used for OSPF packets.  When the MANET
      interface supports Layer 2 broadcast or pseudo-broadcast, the
      multicast process is transparent to OSPF.  Otherwise, OSPF MUST
      replicate multicast packets by itself.

---

From: "Jeffrey (Zhaohui) Zhang" <[email-masked]>
Date: Thu, 6 Jan 2011 17:05:51 -0500

Alvaro,

Indeed we wanted to distinguish from the OSPF MANET interface.

When the underlying network is clearly not a MANET but a broadcast one, there is no need to implement the complicated procedures specified in RFC 5820 - a simple enhancement as specified in this draft will do. It simplifies operators' job (monitoring and debugging) as well.

Additionally, while radio network is one example, it is not the only one.

Thanks.

Jeffrey

> -----Original Message-----
> From: Alvaro Retana (aretana) [mailto:[email-masked]] 
> Sent: Thursday, January 06, 2011 3:59 PM
> To: Acee Lindem; [email-masked]
> Cc: Jeffrey (Zhaohui) Zhang
> Subject: RE: [OSPF] OSPF Hybrid Broadcast and P2MP Interface Type
>

---

From: "Alvaro Retana (aretana)" <[email-masked]>
Date: Thu, 6 Jan 2011 16:26:21 -0600

> From: Jeffrey (Zhaohui) Zhang [mailto:[email-masked]]
> Sent: Thursday, January 06, 2011 5:06 PM
...
> When the underlying network is clearly not a MANET but a broadcast
one,
> there is no need to implement the complicated procedures specified in
> RFC 5820 - a simple enhancement as specified in this draft will do. It
> simplifies operators' job (monitoring and debugging) as well.

You don't need to implement everything in the rfc to support the
interface functionality.  Most of the work in the rfc is oriented at
reducing the overhead on the wire (Incremental Hellos, Smart Peering) or
at addressing the cases where not all the nodes are visible (Overlapping
Relays).  

If you don't care about reducing the overhead and can guarantee that all
the nodes are visible, then the interface definition is enough. ;-)
That reduces to taking advantage of the broadcast characteristics for
flooding, but using p2p adjacencies -- which would be a lot easier to
operate because it is clearer what the relationship between the peers
w/the different metrics is.

In my mind the problem in your document is already solved.

Alvaro.

---

From: "Jeffrey (Zhaohui) Zhang" <[email-masked]>
Date: Thu, 6 Jan 2011 17:41:18 -0500

Alvaro,

1. does it require N or two adjacencies for a non-DR/BDR? I assumed N?
2. what exactly does one have to implement for the scenario targeted by the draft?

Thanks.
Jeffrey

> Sent: Thursday, January 06, 2011 5:26 PM
> To: Jeffrey (Zhaohui) Zhang; Acee Lindem; [email-masked]

---

From: Anton Smirnov <[email-masked]>
Date: Fri, 07 Jan 2011 02:33:27 +0100

Alvaro said more or less what I feel. We already have no less than 3
experimental RFCs dedicated to specifics of radio networks. IMO by
implementing selected bits of those RFCs such as incremental Hellos one
can achieve effectiveness greater than in this proposal.
   It is true that proposed solution is simple (simpler than any bit of
MANET RFCs). But on the other hand problem it solves is also very
specific. It is still not clear to me if there will be wide
need/interest in implementing this narrowly specialized enhancement.
Also, if MANET extensions pick up popularity and become widely
implemented then more complex but more efficient solution will win.

Anton

On 01/06/2011 09:58 PM, Alvaro Retana (aretana) wrote:
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