Fred,
Some (if not most) operators maintain networks in which all links have MTU
greater than or equal to 1500. In those networks, the very detection of a GMTU
smaller than 1280 indicates brokenness. Those operators, the alternative
behavior may be preferable to the default.
Ron
> -----Original Message-----
> From: Templin, Fred L [mailto:[email protected]]
> Sent: Tuesday, March 31, 2015 1:30 PM
> To: Ronald Bonica; [email protected]; [email protected]
> Cc: Zuniga, Juan Carlos; [email protected]; intarea-
> [email protected]
> Subject: RE: [Int-area] Start of WGLC for draft-ietf-intarea-gre-ipv6
>
> Hi Ron,
>
> > -----Original Message-----
> > From: Ronald Bonica [mailto:[email protected]]
> > Sent: Tuesday, March 31, 2015 10:18 AM
> > To: [email protected]; [email protected]
> > Cc: Zuniga, Juan Carlos; Templin, Fred L;
> > [email protected]; [email protected]
> > Subject: Re: [Int-area] Start of WGLC for draft-ietf-intarea-gre-ipv6
> >
> > Hi Fred,
> >
> > Inline.....
> >
> > Ron
> >
> >
> > > Hi Juan Carlos,
> > >
> > > Final passage of Section 3.1 says:
> > >
> > > ?However, in an alternative configuration, the GRE ingress MAY:
> > >
> > > o discard the IPv6 packet
> > >
> > > o send an ICMPv6 Packet Too Big (PTB) [RFC4443] message to the IPv6
> > > packet source. The MTU field in the ICMPv6 PTB message is set to
> > > the GMTU.?
> > >
> > > This means that there may be circumstances when the GRE ingress
> > > sends a PTB reporting a size less than 1280. According to RFC2460,
> > > Section 5, the standard behavior for a host that receives such a PTB is:
> > >
> > > ?In that case, the IPv6 node
> > > is not required to reduce the size of subsequent packets to less than
> > > 1280, but must include a Fragment header in those packets?
> > >
> > > So, hosts that obey RFC2460 Section 5 will see a perpetual black
> > > hole if the GMTU is smaller than 1280 which is probably not what we
> want.
> >
> >
> > [RPB]
> > All true. This is why the WG decided to make this the alternative behavior
> and not the default behavior.
>
> Behavior that is broken is still broken regardless of whether it is
> alternative or
> default.
>
> > > ?draft-templin-6man-linkadapt? attempts to provide guidance to hosts
> > > on how to react to PTB messages that report a small size. But, as of
> > > right now,
> > > RFC2460 Section 5 is the normative behavior.
> > [RPB]
> >
> > Absolutely correct. The procedures described in Section 5 or RFC 246 are
> normative.
> >
> > I don't how this impacts the WG's LC decision regarding the current draft.
>
> Broken behavior should not be specified, whether alternative or default.
>
> Thanks - Fred
> [email protected]
>
> >
> > Ron
> >
> > >
> > > Thanks ? Fred
> > > [email protected]
> > >
> >
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