Re: [lisp] Meanign of R bit

[Margaret Wasserman <mrw at sandstorm.net>]

Hi Dino,

You and Joel are digging into the details of the R-bit here, but  
personally I don't understand why we need an R-Bit at all?

Could you please explain the purpose of the R-bit and what the  
structure of the LISP header will be when it is set?

From what I've heard so far, it sounds like the R-bit is a one-bit  
version field, where (at least some) of the fields in the LISP header  
will have other purposes when it is set.  If so, why do we believe we  
need to use a version bit for that purpose, rather than using one the  
other extensions methods we've discussed (new UDP port or control- 
plane signaling)?

Thanks,
Margaret


On Aug 31, 2009, at 5:52 PM, Dino Farinacci wrote:

> > What is supposed to happen if an ETR receives a packet with an R  
> > bit set to 1, and the N and L bits set to some combination other  
> > than 00?
> > Is that an error?
>
> The R-bit is allowed to user the other 2 fields as long as the  
> enable-bits for each one is set to 0.
>
> > I would think it would make more sense to state that if the R bit  
> > is set, the N and L bits are considered reserved, meaning that they  
> > must be set to 0 on transmission, and ignored upon reception.
>
> Well, we *could* run with the R-bit to 1 and still do echo-noncing  
> perhaps if the N bit is used. Since we are defining a bit for the  
> future (and don't know how its going to be used -- which I don't  
> like to do generally) it's hard to say how the Research header will  
> work when the standard header is also being used.
>
> > That leaves us free to assign a meaning to the R bit, and decide  
> > when we do so how to use the other two bits.
>
> We (Luigi, Damien, Noel, Andrew, Dave, Darrel, Vince, and Dino)  
> talked about this but agreed to keep the semantics for each bit.
>
> Dino
>
> > Yours,
> > Joel
>
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