> -----Original Message----- > From: Brian E Carpenter [mailto:[email protected]] > Sent: Wednesday, June 01, 2016 1:14 PM > To: Xuxiaohu; Joe Touch > Cc: joel jaeggli; Fred Baker (fred); Wassim Haddad; [email protected] > Subject: Re: [Int-area] Call for adoption of draft-xu-intarea-ip-in-udp-03 > > I think I detest fragmentation, or rather re-assembly, as much as anybody, > whether designing hardware or software solutions. And of course, in a closely > managed environment, you can ensure that the outer MTU is sufficient to > contain the inner MTU. That isn't the point. The point is that designing a > protocol
It said in the draft that "... this specification defines an IP-in-UDP encapsulation method dedicated for Softwire service (including both mesh and hub-spoke modes). " Softwire networks are well-managed SP networks. I would like to add a dedicated Applicability Statement section to emphasize it if the current statement seems not enough. Best regards, Xiaohu > proposed as a general-purpose protocol for the Internet, that might be used > for > a hundred years, we can't guarantee that it will always be deployed in such a > managed environment. In fact, we can pretty much guarantee that it will be > used in completely unmanaged (or badly managed) ways. > > This isn't theory. We've seen it a lot where IPv6 has been tunneled across > IPv4 islands, with lots of MTU and fragmentation failures. That's even simpler > than IP in UDP in IP. > Regards > Brian > > On 01/06/2016 16:09, Xuxiaohu wrote: > > > > > >> -----Original Message----- > >> From: Brian E Carpenter [mailto:[email protected]] > >> Sent: Wednesday, June 01, 2016 4:01 AM > >> To: Xuxiaohu; Joe Touch > >> Cc: joel jaeggli; Fred Baker (fred); Wassim Haddad; [email protected] > >> Subject: Re: [Int-area] Call for adoption of > >> draft-xu-intarea-ip-in-udp-03 > >> > >> On 31/05/2016 20:13, Xuxiaohu wrote: > >>> > >>> > >>>> -----Original Message----- > >>>> From: Brian E Carpenter [mailto:[email protected]] > >>>> Sent: Tuesday, May 31, 2016 4:46 AM > >>>> To: Joe Touch > >>>> Cc: joel jaeggli; Xuxiaohu; Fred Baker (fred); Wassim Haddad; > >>>> [email protected] > >>>> Subject: Re: [Int-area] Call for adoption of > >>>> draft-xu-intarea-ip-in-udp-03 > >>>> > >>>> And being pedantic... > >>>> On 31/05/2016 06:12, Joe Touch wrote: > >>>>> > >>>>> > >>>>> On 5/29/2016 4:23 PM, joel jaeggli wrote: > >>>>>>>> I.e., you MUST support source fragmentation at the ingress at > >>>>>>>> the outer > >>>>>>>> IPv6 layer (because UDP doesn't have support for fragmentation > >>>>>>>> and reassembly). If you make this requirement, you can handle > >>>>>>>> IPv6 over the tunnel. > >>>>>> Yeah I don't support it for this reason. getting IP fragments > >>>>>> back together in the same place a reassembled is hard is in some > >>>>>> cases especially when you hash. (see frag drop) given > >>>>>> alternatives that better address such situations it seems hard to > >>>>>> justify. > >>>>> > >>>>> If you intend to support recursive IP tunneling* and believe that > >>>>> IP has a minimum MTU, then you have to accept reassembly. > >>>> > >>>> If you intend to support recursive datagram tunneling and believe > >>>> that any path has a minimum MTU, then you have to accept reassembly. > >>>> > >>>> This is physics, and nothing to do with design details. > >>>> > >>>> (Something I discovered in about 1983, when implementing OSI/CLNP > >>>> at CERN over a homebrew network with 128 byte packets.) > >>> > >>> Reassembly on the tunnel egress may be acceptable at that old time. > >>> However, > >> due to the considerable improvement in network bandwidth capability, > >> the practice acceptable at the old time may have become outdated today. > >> > >> I don't understand what network capacity has to do with the physical > >> and mathematical fact that packets larger than N bytes will not fit > >> into a packet limited to N bytes. > > > > This article > (http://learning.nil.com/assets/Tips-/The-Never-Ending-Story-of-IP-Fragmentati > on.pdf) may be useful for you to understand why network capability is a key > factor to be considered for fragmentation and reassembly on routers (here > routers are not software routers or CPU-only routers which were dominant in > the old time). Of course, you could also have a look at the current > fragmentation > and reassembly implementations of major router vendors if you believed that > article is a little bit old. > > > > Xiaohu > > > >> That was true in 1983 and will still be true in 2083. > >> > >> Brian > >> > >>> See the MAP implementation experience shared by Ole recently. > >>> > >>> Xiaohu > >>> > >>>> Brian > >>>> > >>>>> > >>>>> Joe > >>>>> > >>>>> * where "recursive IP tunneling" is IP in [zero or more other > >>>>> protocols] in IP. > >>>>> > >>>>> _______________________________________________ > >>>>> Int-area mailing list > >>>>> [email protected] > >>>>> https://www.ietf.org/mailman/listinfo/int-area > >>>>> _______________________________________________ Int-area mailing list [email protected] https://www.ietf.org/mailman/listinfo/int-area
