Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis-09.txt - questions about Solicit Prefix Delegation - src LL vs GUA
Alexandre Petrescu <alexandre.petrescu@gmail.com> Wed, 18 October 2017 16:01 UTC
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To: "Bernie Volz (volz)" <volz@cisco.com>
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From: Alexandre Petrescu <alexandre.petrescu@gmail.com>
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Date: Wed, 18 Oct 2017 18:01:14 +0200
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Subject: Re: [dhcwg] I-D Action: draft-ietf-dhc-rfc3315bis-09.txt - questions about Solicit Prefix Delegation - src LL vs GUA
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Le 18/10/2017 à 16:25, Bernie Volz (volz) a écrit : > Hi Alex: > > Does it really matter what the Client’s source address Yes it is guidance that I need. Alex is as long as > the client can receive packets sent to that address (by a relay or > server that is on that link)? These are link-local packets and so no > router should be involved in them (that’s what the relay agent is > there for – to forward the packets to servers not on the local > link). > > - Bernie > > On 10/18/17, 10:06 AM, "Alexandre Petrescu" > <alexandre.petrescu@gmail.com> wrote: > > Bernie, > > Le 13/07/2017 à 19:38, Bernie Volz (volz) a écrit : [...] > >> Regarding Link Local vs GLA in Solicit, I think following the >> specification would be recommended. Use link-local. > > But the I-D 3315bis says this: >> Clients and servers exchange DHCP messages using UDP [RFC0768]. >> The client uses a link-local address or addresses determined >> through other mechanisms for transmitting and receiving DHCP >> messages. > ^^^^^^^^^^^^^^^^ > > This "other mechanisms" means that a GUA generated with SLAAC could > be used as an src in a DHCPv6 Solicit. > > > [...] >> Note also that section 13.1 (for the unicast, GLA case) assumes >> the message was not multicast (section 18.4 about UseMulticast >> Status talks about "Reception of Unicast Messages"). > > Hm, that lokks like a relatively less explicit if not outright > silent assumption(?) Or maybe I did not look well enough in the > I-D? > > There is a particular equipment manufacturer's simulator software, > and potentially real hardware, that uses GUA in src and dst multicast > with link scope ff02::1:2.547, in the DHCPv6 Solicit. > > If this behaviour is standard (src GUA and dst ff02::1:2) then it > should be in the draft. If it's not standard: it should get > corrected in the simulated and in the real implementation. > > Because other software than the one from the particular equipment > manufacturer uses src LL and dst ff02::1:2. > > Side note: > >> I think section 13.1 was written with the assumption that >> determining the destination address of a packet is harder than >> obtaining the source address; hence the assumption is that if a GLA >> is used as the source address, it was not a multicast [to the >> link-local multicast address]. Today, kernels typically provide the >> ability to get the destination address, not just the source address >> (though it takes a bit more code to do so). > > The picture may be different on point-to-point links like cellular > links. It's multicast, but it's just two nodes and they are always > seeing each other. Besides, one of the nodes allocates an address > to the other node by other means than SLAAC, and it knows it. > > Alex > >> >> >>> I can say e.g. some (I believe Cisco) client puts a GUA in the >>> src of aDHCPv6 Solicit. >> >> That's a bit of a broad statement as Cisco has many different >> devices (and many different operating systems and versions) ... >> perhaps if you could indicate which device(s) and software versions >> you've found this to be the behavior on, I can perhaps follow up. >> >> I will also add that in many cases when devices are doing DHCPv6, >> they will only have a LL so it may also depend on the network >> configuration. >> >> - Bernie >> >> -----Original Message----- From: Alexandre Petrescu >> [mailto:alexandre.petrescu@gmail.com] Sent: Thursday, July 13, >> 2017 12:01 PM To: Bernie Volz (volz) <volz@cisco.com> Cc: >> dhcwg@ietf.org Subject: Re: [dhcwg] I-D Action: >> draft-ietf-dhc-rfc3315bis-09.txt - questions about Solicit Prefix >> Delegation >> >> Bernie, >> >> Le 12/07/2017 à 23:33, Bernie Volz (volz) a écrit : >>> Hi: >>> >>>> What is the Hop Limit that a Solicit should contain in the >>>> IPv6 header? >>> >>> ND uses hop limit of 255 so the destination can check that it is >>> 255 on receipt (whereas 1 could have been anything and forwarded >>> many times). >>> >>> But I'm not sure if that is a the best practice when you don't >>> want the packet forwarded. I would think that if the destination >>> is a link-local multicast, it really doesn't matter as nothing >>> should forward the packet (and if something is misconfigured to >>> forward the packet, you're probably in deeper trouble than just >>> with DHCPv6). >>> >>> RFC 4861 has: >>> >>> 11.2. Securing Neighbor Discovery Messages >>> >>> The protocol reduces the exposure to the above threats in the >>> absence of authentication by ignoring ND packets received from >>> off-link senders. The Hop Limit field of all received packets >>> is verified to contain 255, the maximum legal value. Because >>> routers decrement the Hop Limit on all packets they forward, >>> received packets containing a Hop Limit of 255 must have >>> originated from a neighbor. >>> >>> I don't know off hand if there's any place this is documented >>> (what to use for hop limit with link-local). >> >> I think your explanation makes sense about ND. >> >> But, about DHCP, I need to know whether a DHCP Solicit with >> HopLimit 1 is valid or not. >> >> As I said earlier, some DHCP clients set it at 255 whereas others >> at 1. >> >> In some setting, the DHCP Solicit is encapsulated in IPv4. Some >> of the decapsulation RFCs say that the HopLimit is decremented. >> >> In that setting, it is not clear whether decrementing the hop >> limit happens, or not. >> >> But I want to make sure the client which sets HopLimit at 1 >> (odhcp6c) is the right way to do. >> >> I think a good place to clarify this is in the DHCP spec. >> >> The spec could say that the HopLimit has some preferred value. >> >>>> Is IA_NA with empty fields a valid option in a Prefix >>>> Delegation Solicit, or must IA_NA be absent altogether? (the >>>> intention is to only request the Prefix, because the address >>>> comes from RA). >>> >>> Not sure what an "empty" IA_NA is. Whether you include an IA_NA >>> or not with IA_PD is the client's choice. If it what's an >>> address (such as for management) on the upstream link, than it >>> should include an IA_NA. This is covered in the text in 6.3 >>> (IA_PD only) vs 6.4 (IA_PD and IA_NA, typically). >> >> Noted. >> >>>> Is ORO with empty fields illegal in a Prefix Delegation >>>> Solicit? (the intention is to get the DNS server from RA, but >>>> some client puts an empty ORO there). >>> >>> An empty ORO is fine (it should not cause problems, but is >>> obviously useless). Though if they are following the rfc3315bis >>> and doing what they should, there would not be an empty ORO. >> >> Noted. >> >>>> Is it ok to use a GUA in the src address of a Solicit Prefix >>>> Delegation? >>> >>> See 13.1 of draft-ietf-dhc-rfc3315bis-09 ... the source address >>> here should be link-local. >> >> Well, that contradicts some trial. >> >> I can say e.g. some (I believe Cisco) client puts a GUA in the src >> of a DHCPv6 Solicit. Other DHCP clients have this optional between >> LLA or GUA. The operator I work with wants it to be a GUA. >> >> As such, I dont know what is the way forward: should the spec get >> updated? shoudl the operator change? should the Cisco >> implementation change? >> >> Alex >> > >
- [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