RE: Meta-issues: On the deprecation of the fragmentation function

Hi Ron,

> -----Original Message-----
> From: Ronald Bonica [mailto:rbonica@juniper.net]
> Sent: Wednesday, July 10, 2013 8:50 AM
> To: Templin, Fred L; Doug Barton
> Cc: ipv6@ietf.org
> Subject: RE: Meta-issues: On the deprecation of the fragmentation
> function
> 
> Fred,
> 
> There are alternatives....
> 
> Probably, the best alternative is for the tunnel ingress router to
> tunnel ingress router to discover the PMTU to the egress. When the
> tunnel ingress router receives a packet that is so large that it cannot
> be forwarded through the tunnel, it discards the packet and sends an
> ICMP PTB to the packet's originator. The packet's originator then
> modifies its sending behavior based upon its new estimate of the PMTU
> associated with the destination.

Sure, the tunnel ingress can probe the path to the egress; such a
probing method is already covered by SEAL. But, if the path MTU will
not accommodate a packet that after encapsulation is as large as
(1280 + HLEN) there is no alternative for the ingress other than to
start fragmenting since the ingress is not allowed to send a PTB
message reporting a size smaller than 1280. 

> So, for the purposes of MTU management, the tunnel is just another
> link.

True, but I want that link to have an unbounded MTU. In other
words, encapsulate and send everything regardless of its size
even if a little bit of fragmentation is necessary (but try to
tune out the fragmentation if possible).

You should really have a look at my new draft:

http://tools.ietf.org/html/draft-generic-6man-tunfrag-08

Thanks - Fred
fred.l.templin@boeing.com

>                                                      Ron
> 
> 
> 
> 
> > -----Original Message-----
> > From: Templin, Fred L [mailto:Fred.L.Templin@boeing.com]
> > Sent: Wednesday, July 10, 2013 10:59 AM
> > To: Ronald Bonica; Doug Barton
> > Cc: ipv6@ietf.org
> > Subject: RE: Meta-issues: On the deprecation of the fragmentation
> > function
> >
> > Hi Ron,
> >
> > > -----Original Message-----
> > > From: ipv6-bounces@ietf.org [mailto:ipv6-bounces@ietf.org] On
> Behalf
> > > Of Ronald Bonica
> > > Sent: Tuesday, July 09, 2013 5:33 PM
> > > To: Doug Barton
> > > Cc: ipv6@ietf.org
> > > Subject: RE: Meta-issues: On the deprecation of the fragmentation
> > > function
> > >
> > > Doug,
> > >
> > > Let's see if we can find some common ground.
> > >
> > > Assume that the IETF is considering a new protocol that doesn't run
> > > over TCP. In order to deal with MTU issues, the new protocol must
> do
> > > one of the following:
> > >
> > > a) implement PLMTUD or PMTUD
> > > b) restrict itself to sending PDUs so small that when they are
> > > encapsulated in an IPv6 header, the resulting packet will not
> exceed
> > > 1280 bytes
> > > c) rely on IPv6 fragmentation
> > >
> > > Is there ever a reason why c) is better than a) or b). For that
> > > matter, is c) ever an acceptable solution?
> >
> > Fragmentation at a tunnel ingress router is unavoidable. Proof:
> >
> >   - a tunnel configures a 1280 MTU
> >   - When its packets are encapsulated they emerge as (1280 + HLEN)
> >     (the length of the encapsulating headers)
> >   - the tunnel crosses a 1280 link somewhere in the path to the
> egress
> >   - the packet is dropped with a PTB signal sent back
> >   - the ingress now has two choices: 1) start fragmenting, 2) quit.
> >
> > Thanks - Fred
> > fred.l.templin@boeing.com
> >
> > >                                                   Ron
> > >
> > > > -----Original Message-----
> > > > From: Doug Barton [mailto:dougb@dougbarton.us]
> > > > Sent: Tuesday, July 09, 2013 2:41 PM
> > > > To: Ronald Bonica
> > > > Cc: ipv6@ietf.org
> > > > Subject: Re: Meta-issues: On the deprecation of the fragmentation
> > > > function
> > > >
> > > > On 07/09/2013 11:12 AM, Ronald Bonica wrote:
> > > > > Doug,
> > > > >
> > > > > It might be interesting to revisit what we mean by deprecating
> > > > > IPv6
> > > > fragmentation....
> > > > >
> > > > > It means that the IETF will not approve any new protocols that
> > > > > rely
> > > > upon IPv6 fragmentation. Nothing more, nothing less.
> > > >
> > > > Thanks for clarifying. FWIW, I understand what is being proposed,
> > > > and
> > > I
> > > > still think it's a bad idea.
> > > >
> > > > Doug
> > > >
> > > >
> > >
> > >
> > >
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> >
> 
> 