Hi Ron, I will say again that the minimum IPv6 link MTU is 1280 bytes and so the design must account for tunnel paths that include links with such a small MTU. The design must also account for nested tunnels-within-tunnels, where the MTU seen by the first tunnel ingress may be reduced by potentially many layers of additional encapsulation.
But again, the point is that the tunnel ingress cannot legitimately send PTBs that report a size smaller than 1280 *and* perpetually drop packets smaller than 1280 which is exactly the behavior your text is permitting. Thanks - Fred [email protected] > -----Original Message----- > From: Ronald Bonica [mailto:[email protected]] > Sent: Tuesday, March 31, 2015 1:21 PM > 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, > > In the last network that I operated, all interior links had MTU greater than > 9k. If I configured a GRE tunnel between two points in that > network and detected a GMTU less than 1280, it would have indicated one of > the following: > > - Phenomenal brokenness > - An ICMP PTB-based attack in progress > > In such cases, operators need some flexibility in how their networks would > behave. Why deny them this flexibility by taking away the > configuration option? > > Isn't it an operator's prerogative to discard any packet that might degrade > network performance? > > > Ron > > > -----Original Message----- > > From: Templin, Fred L [mailto:[email protected]] > > Sent: Tuesday, March 31, 2015 3:01 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 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
