Subject: RE: draft-rajahalme-ipv6-flow-label-00.txt

From: "Glenn Morrow" <[email-masked]>
Date: Wed, 2 Jan 2002 13:57:42 -0600

Brian,

Diff-serv itself is a sort of signaling and the field it operates on is
mutable is it not? I hope you at least agree that is is either configured or
signaled. I believe you can signal to routers and have routers that are not
configured or capable of handling the signaling ignore the signaling. IPv6's
option definitions were designed specifically for this filtering function.

So I guess what I'm saying is, the example you gave to indicate that the
fields should be immutable is not immutable itself and so I don't think the
reasoning holds up. Making the field mutable or not is disjoint from the
signaling or configuration argument in order to act on a field. With
diff-serv you either configure or signal to set up the behavior of its
operational field. The merits of configuration vs signaling might be argued
but IMO configuration (especially remote configuration) is a form of
signaling as well. I do see value in out of the box schemas for on-net
solutions; however, I don't think mutability will thwart this ability or
desire as long as the signaling or subsequent configuration can change the
default schema. 

I also don't understand why people are so terrified of mutability of certain
fields. The original point was that if there is a business reason to make a
field mutable or not, it will be mutable irrespective of what an RFC says.
It seems to me that making things immutable reduces the use of the fields in
question from a functional perspective. Mutability with signaling and at
least configuration seems to increase flexibility and extensibility. It
seems to me that for the long term we should not try to restrict the use of
fields but rather detail the use and expectations for particular
applications as their need arises. I don't see a problem with an RFC saying,
"for this particular network layer service, the field is expected to be
immutable as it traverses certain parts of the network or the whole
network". But this would be for just one type of network-layer service and
would leave the door open for other uses in the future.

regards,

Glenn

> -----Original Message-----
> From: Brian E Carpenter [mailto:[email-masked]]
> Sent: Sunday, December 23, 2001 9:17 AM
> To: Morrow, Glenn [RICH2:C330:EXCH]
> Cc: Margaret Wasserman; [email-masked]
> Subject: Re: draft-rajahalme-ipv6-flow-label-00.txt
> 
> 
> Glenn Morrow wrote:
> 
> > If "function A" wants the field immutable so be it. The 
> signaling for "function A" needs to convey the mutability 
> rules to affected parties
> > either implicitly or by optionality. 
> 
> This is broken. You can't signal to routers that aren't aware of
> the "function A", because they won't be aware of the relevant
> signalling either. Also, we need to be able to construct 
> signalling-free 
> solutions (such as diffserv) for scalability.
> 
> Immutability is the only viable answer.
> 
>   Brian
> 
> 
>