Hi Ron, > -----Original Message----- > From: Ronald Bonica [mailto:[email protected]] > Sent: Tuesday, March 31, 2015 11:38 AM > To: Templin, Fred L; [email protected]; [email protected] > Cc: Zuniga, Juan Carlos; [email protected]; > [email protected] > Subject: RE: [Int-area] Start of WGLC for draft-ietf-intarea-gre-ipv6 > > 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.
The minimum IPv6 MTU is 1280 bytes; that is how much the link must deliver no matter what. A GMTU smaller than 1280 does not indicate brokennesss; it can naturally happen if 1) there is a link with a small MTU in the path, or 2) there are multiple tunnel nesting levels, or both. As such, sustained dropping of packets less than 1280 is a no-no, and cannot be specified in a document like this. Thanks - Fred [email protected] > > 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] > > > > > > > _______________________________________________ Int-area mailing list [email protected] https://www.ietf.org/mailman/listinfo/int-area
