Re: [pim] WG Last Call - draft-ietf-pim-bidir-06

[Pekka Savola <pekkas at netcore.fi>]

Sorry if I sounded a bit aggressive in my comments .. :)

On Fri, 21 May 2004, Isidor Kouvelas wrote:
> >More minor comments:
> >--------------------
> >
> >Bidir PIM introduces the Bidir_Capable PIM-Hello option that MUST be
> >included in all Hello messages from a Bidir-PIM capable router.  The
> >Bidir_Capable option advertises the router's ability to participate in
> >the Bidir-PIM protocol. The format of the Bidir_Capable option is
> >described in section 3.7.
> >
> >==> HELLO?!?!!?!?  Do you mean that every router in a domain that is
> >bidir-capable starts logging errors about every neighbor they have
> >which is not bidir-capable?!??  Say goodbye to incremental deployment 
> >and adding bidir capability on by default!
> 
> HIIIII!!!!! HOW ARE YOU?!?!?!?!?!
> First of all there is no incremental deployment for BIDIR-PIM.  Mixing
> BIDIR capable and legacy routers in a domain is a mis-config which the
> option helps detect. Obviously if on a BIDIR capable router you have
> BIDIR PIM disabled then you will not see such a message because you
> have a non capable neighbour.
> Now it is true that the option itself dates back to Dino's draft that
> did specify incremental deployment. The main reason we cannot remove it
> now is to keep existing code happy.

Sorry, what I meant is incremental _router software_ deployment.

In a network of 100 multicast routers, this implies either that:
 a) bidir-pim must always be disabled by default, or
 b) all the routers must be upgraded simultaneously.

If I'm not misunderstanding something, bidir-pim could be enabled by 
default (but not active until a group advertisement with bidir flag is 
sent) by a slightly different strategy .. see below.

> >The warning is should probably something that should be activated if a 
> >group has been configured as bidir, but your neighbor isn't, or if you 
> >try to use bidir forwarding algorithm towards the neighbor, and it 
> >isn't bidir-capable.
> 
> There is currently no way of knowing what the group to RP / protocol
> mapping is on a neighbouring PIM router. The assumption is that if the
> neighbour is BIDIR capable then it has made the same interpretation of
> the config / BSR advertisement.

I fail to see why this is relevant. The routers could stay "dormant", 
advertising bidir-pim capabilities but not using bidir-pim for 
anything until such time that config/BSR advertisement decrees that 
bidir-pim is to be used for a group, right?  Or is there something I'm 
missing?

When you get that BSR advertisement, only *then* you should start 
complaining if your neighbors aren't bidir-PIM -capable.
 
> >...
> >==> what is the BIDIR interdomain strategy?  There's no need for such, 
> >I think, because it'll "just work the same way as PIM-SM" if you use 
> >MSDP, but it would not hurt to spell it out.
> 
> It does not "just work". We scoped the mods at one point in time to
> see what would be required. There are significant changes to make
> source-only branches traverse a BIDIR domain.

So it should be spelled out I think..
 
-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings


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