Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis-09.txt - questions about Solicit Prefix Delegation

Alexandre Petrescu <alexandre.petrescu@gmail.com> Fri, 14 July 2017 19:50 UTC

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To: =?UTF-8?B?VsOtemRhbCBBbGXFoQ==?= <ales.vizdal@t-mobile.cz>
Cc: Ted Lemon <mellon@fugue.com>, dhcwg <dhcwg@ietf.org>, "Bernie Volz (volz)" <volz@cisco.com>
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From: Alexandre Petrescu <alexandre.petrescu@gmail.com>
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Date: Fri, 14 Jul 2017 21:50:09 +0200
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Subject: Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis-09.txt - questions about Solicit Prefix Delegation
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Le 14/07/2017 à 21:26, Vízdal Aleš a écrit :
> 
> 
>> On 14 Jul 2017, at 21:15, Alexandre Petrescu 
>> <alexandre.petrescu@gmail.com> wrote:
>> 
>>> Le 14/07/2017 à 20:35, Ted Lemon a écrit : So are the DHCP 
>>> clients you are talking about setting the IP header hop count to
>>>  0/1, or the DHCP header hop-count field to 0/1?   That is, what
>>>  is the behavior you are concerned about, and why do you think it
>>>  might cause a problem in this case?
>> 
>> Some clients I am talking about issue DHCP Solicit with Hop Limit 
>> field in the IPv6 base header (not DHCP UDP header) with value 1.
>> 
>> This Solicit is sent on a cellular network.  The cellular network 
>> encapsulates at some point in IPv4, and further decapsulates.  The
>>  encapsulation protocol is called "GTPU" by some non-wireshark 
>> packet dump format, with fields like "TEID", "GTP_TPDU_MSG".  This
>>  cellular network does not offer IPv4 access to end user, it only 
>> offers IPv6.
>> 
>> There is no GTP RFC.
> 
> GTP aka GPRS Tunnelling Protocol has been specified by 3GPP.
> 
> It starts at the eNodeB and terminates at the PGW where the DHCP 
> server/relay would sit.

You see, I am also told that my "MT" ("Mobile Terminal"?) terminates
GTP.  I guess both are possible (terminate some times at eNodeB and
other times at MT).

Or otherwise the expression "terminate at" may have different meanings
to different people.

>> There is an RFC for "Generic Packet Tunnelling in IPv6".  This RFC
>>  says that encap/decap decrements the Hop Limit.
>> 
>> This raises a potential speculation that the network drops an 
>> incoming packet that has Hop Limit 1.
>> 
>> It may be that the GTP encapsulation (no RFC) does not decrement 
>> the Hop Limit of a packet-to-be-encapsulated.  In this case there 
>> is no problem with DHCP Solicit having Hop Limit 1.
> 
> It shall keep the packet as-is, since it is not visible from 
> user/data-plane point of view.

I dont understand that.  Not sure what you mean by user-data planes.

The IP Hop Limit is in the IP header.  Some IP tunnelling mechanisms do
touch the Hop Limit of the encapsulated packet.  Why would GTP be
different than the other IP tunnelling mechanisms?

> I suggest a deep dive into 3GPP specs ...

It is certainly advantageous to understand the 3GPP specs.

But I'd rather consider putting that into an Internet Draft.

Alex

> 
>> Alex
>> 
>> 
>> 
>>> On Fri, Jul 14, 2017 at 8:32 PM, Alexandre Petrescu 
>>> <alexandre.petrescu@gmail.com 
>>> <mailto:alexandre.petrescu@gmail.com>> wrote: Le 13/07/2017 à 
>>> 23:14, Ted Lemon a écrit : On Jul 13, 2017 16:01, "Alexandre 
>>> Petrescu" <alexandre.petrescu@gmail.com 
>>> <mailto:alexandre.petrescu@gmail.com> 
>>> <mailto:alexandre.petrescu@gmail.com 
>>> <mailto:alexandre.petrescu@gmail.com>>> wrote: My oppinion is to
>>>  make DHCP spec Hop Limit > 1.  In order to make sure that the 
>>> encap/decap of DHCP Solicit in IPv4 GTP happening on a cellular 
>>> link does not drop it to 0 upon decap. If a link local sourced 
>>> multicast with a hop limit of one is dropped between sender and 
>>> receiver, ip is broken on that link, ne c'est pas? If that link 
>>> is a real link then yes - ip is broken on that link. But if the 
>>> link is a virtual link - like when on a tunnel - then it may be 
>>> that tunnel works or no. Alex
>> 
>> _______________________________________________ dhcwg mailing list 
>> dhcwg@ietf.org https://www.ietf.org/mailman/listinfo/dhcwg
> 
> Zásady komunikace, které společnost T-Mobile Czech Republic a.s. 
> užívá při sjednávání smluv, jsou uvedeny 
> zde<http://www.t-mobile.cz/dcpublic/Zasady_komunikace_pri_sjednavani_smluv_cz.pdf>.
>
>
> 
Není-li v zásadách uvedeno jinak, nepředstavuje tato zpráva konečný
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> communication principles which T-Mobile Czech Republic a.s. applies 
> when negotiating contracts are defined 
> here<http://www.t-mobile.cz/dcpublic/Zasady_komunikace_pri_sjednavani_smluv_en.pdf>.
>
>
> 
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>