Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis-09.txt - questions about Solicit Prefix Delegation
"Bernie Volz (volz)" <volz@cisco.com> Sat, 15 July 2017 09:25 UTC
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From: "Bernie Volz (volz)" <volz@cisco.com>
To: Alexandre Petrescu <alexandre.petrescu@gmail.com>
CC: Ted Lemon <mellon@fugue.com>, Vízdal Aleš <ales.vizdal@t-mobile.cz>, dhcwg <dhcwg@ietf.org>
Thread-Topic: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis-09.txt - questions about Solicit Prefix Delegation
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Date: Sat, 15 Jul 2017 09:25:44 +0000
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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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>But IPv6 in 3GPP is a wholly different beast for which few specs - if >any- exist at IETF. Yes, but it would seem then that they would have issues with pretty much all multicast, unless applications that send multicast have taken steps to set a different hop limit for their packets. I would guess that applications that use non-link local multicast would set the hop limit (perhaps to "default" which I think is typically around 60). BTW: While it is only 1 data point, I checked a RedHat Enterprise Linux 7.0 system and: IPV6_UNICAST_HOPS is 64 IPV6_MULTICAST_HOPS is 1 (See RFC 3493 for details on these parameters.) See https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt - it seems there is a means to change the default unicast hop limit, but not the multicast one? - Bernie -----Original Message----- From: Alexandre Petrescu [mailto:alexandre.petrescu@gmail.com] Sent: Saturday, July 15, 2017 4:48 AM To: Bernie Volz (volz) <volz@cisco.com> Cc: Ted Lemon <mellon@fugue.com>; Vízdal Aleš <ales.vizdal@t-mobile.cz>; dhcwg <dhcwg@ietf.org> Subject: Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis-09.txt - questions about Solicit Prefix Delegation Le 15/07/2017 à 08:45, Bernie Volz (volz) a écrit : > I agree with Ted. > > And, it does appear that kernels will default to 1 for a hop limit > with > multicast: > > “By default, IP multicast datagrams are sent with a hop limit of one, > which prevents the datagrams from being forwarded beyond a single > subnetwork.” Again it's ok with native IP on native links like IP-over-Ethernet. But IPv6 in 3GPP is a wholly different beast for which few specs - if any- exist at IETF. And DHCP-PD is probably the only part of DHCP that is considered in these 3GPP networks. In DHCP-PD it would be perfectly fine to use GUA in the src and dst ll. This is under discussion. > Thus, it is the multicast destination (ff02::1:2 for DHCPv6 packets) > that controls the (default) hop limit. > > Also note that 2460bis has: > > Hop Limit 8-bit unsigned integer. Decremented by 1 by > > each node that forwards the packet. When > > forwarding, the packet is discarded if Hop > > Limit was zero when received or is > decremented > > to zero. A node that is the destination of > a > > packet should not discard a packet with hop > > limit equal to zero, it should process the > > packet normally. > > RFC 2460 only has the 1^st sentence, so it was clarified as to what a > node that receives a packet should do if the hop count is 0 – process it. In IPv6 tunnelling both encap and decap decrement - leading to -1. Alex > > * Bernie > > *From: *Ted Lemon <mellon@fugue.com> > *Date: *Saturday, July 15, 2017 at 6:36 AM > *To: *Alexandre Petrescu <alexandre.petrescu@gmail.com> > *Cc: *Vízdal Aleš <ales.vizdal@t-mobile.cz>, "dhcwg@ietf.org" > <dhcwg@ietf.org>, Bernie Volz <volz@cisco.com> > *Subject: *Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis-09.txt - > questions about Solicit Prefix Delegation > > Alexandre, it appears to me that you are asking the DHC working group > to make a change to the DHCPv6 spec in order to solve a problem you don't > know exists in an IPv6 layer 2 implementation. I think that this is > wrong-headed on two fronts. First, you are speculating that the > problem exists. Find out whether the problem exists, don't speculate. > Second, the problem is not in DHCP, if it does exist--it is in an IP > implementation. So fix the implementation--don't ask for a change to > the DHCP spec. > > On Fri, Jul 14, 2017 at 9:50 PM, Alexandre Petrescu > <alexandre.petrescu@gmail.com <mailto:alexandre.petrescu@gmail.com>> wrote: > > > > Le 14/07/2017 à 21:26, Vízdal Aleš a écrit : > > On 14 Jul 2017, at 21:15, Alexandre Petrescu > <alexandre.petrescu@gmail.com > <mailto: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> > <mailto: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>> > <mailto: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 <mailto: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 > > návrh na uzavření či změnu smlouvy ani přijetí takového návrhu. > The 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>. > > > Unless otherwise stated in the principles, this message does not > > constitute the final offer to contract or an amendment of a contract > or acceptance of such offer. >
- [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis-09.… internet-drafts
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Templin, Fred L
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Bernie Volz (volz)
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Bernie Volz (volz)
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Ted Lemon
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Ted Lemon
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Bernie Volz (volz)
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Ted Lemon
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Vízdal Aleš
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Ted Lemon
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Bernie Volz (volz)
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Bernie Volz (volz)
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Vízdal Aleš
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Ted Lemon
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Vízdal Aleš
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Ted Lemon
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Vízdal Aleš
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Ted Lemon
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Ted Lemon
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Bernie Volz (volz)
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Bernie Volz (volz)
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Ted Lemon
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… 神明達哉
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Bernie Volz (volz)
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… 神明達哉
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Bernie Volz (volz)
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Alexandre Petrescu
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Bernie Volz (volz)
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Templin, Fred L
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Ted Lemon
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Templin, Fred L
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Roy Marples
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Ted Lemon
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Ted Lemon
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Roy Marples
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Bernie Volz (volz)
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Roy Marples
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… Ted Lemon
- Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis… mohamed.boucadair