Re: [v6ops] new draft: draft-taylor-v6ops-fragdrop

[Brian E Carpenter <[e-mail]>]

On 29/10/2012 15:08, Joe Touch wrote:
> How does that differ substantively from RFC 4821's advice? See esp. Sec.
> 8 of that doc, which seems just as accurate for the current situation.

Joe,

I have never thought that 4821 was specific enough, because it leaves
quite a bit of the recipe open. The application writer just wants to do
open/send/receive/close and have somebody else take care of this stuff.

    Brian

> 
> Joe
> 
> On 10/28/2012 11:51 PM, Lorenzo Colitti wrote:
>> On Mon, Oct 29, 2012 at 5:08 AM, Mark Smith <[e-mail]
>> <mailto:[e-mail]>> wrote:
>>
>>     I don't really disagree with that either, it's more that
>>     fragmentation is a current capability of IPv6, so I think the IETF's
>>     recommendation should be that it is enabled by default on the
>>     Internet. I think that recommendation fits the robustness principle
>>     too - "..., be liberal in what you accept from others".
>>
>>     If the IETF recommends against forwarding fragments, then I think
>>     that creates the obligation to provide advice and methods on what do
>>     instead,
>>     which might include specifying a standardised UDP fragmentation
>>     method, and provide alternative methods for protocols that utilise
>>     IP layer
>>     fragmentation.
>>
>>     Fragments may still be in use, however they may not used much at the
>>
>>     application layer. OSPFv2 and OSPFv3 uses them instead of
>>     implementing it's own fragmentation mechanism (and that may be
>>     across multiple hops in the case of a OSPF virtual link), and they
>>     are likely to be commonly used in IPsec and GRE tunnels (PMTUD
>>     across the tunnel path and having the tunnel MTU adjusted to it is a
>>     more advanced capability).
>>
>>
>> Ok, so how about stating the following, then?
>>
>> 1. Fragments are unreliable on the Internet today.
>> 2. If you're an application developer and your apps need to run on the
>> Internet, then fragments will likely not work in many cases. If you want
>> your application to work in these cases, you should either use
>> application-layer fragmentation, use path MTU discovery, or limit
>> yourself to small packets instead of sending fragments.
>> 3. If you control the network (e.g., if you're the network operator),
>> and want to use fragments for tunnels or other purposes, go ahead, but
>> note that in other people's networks, they might be filtered.
>>
>> Your suggestion of providing a generic UDP segmentation mechanism is a
>> fine idea, and one that we discussed before this draft was written, but
>> our feeling was that such a solution would be impossible to agree on
>> until we have a problem statement. This draft ("FYI: some operators
>> filter fragments. Keep that in mind.") was supposed to be the problem
>> statement.
>>
>>
>> _______________________________________________
>> v6ops mailing list
>> [e-mail]
>> https://www.ietf.org/mailman/listinfo/v6ops
>>
> _______________________________________________
> v6ops mailing list
> [e-mail]
> https://www.ietf.org/mailman/listinfo/v6ops
>