On 8/15/2016 4:42 PM, Reith, Lothar wrote: > > Hi Joe, > > > > I must admit I am puzzled a bit because you provided the reference to > RFC3819 which states: “this document defines a subnetwork > i.e., subnet
> as a layer 2 network, > That's exactly what I state below... > which is a > > network that does not rely upon the services of IP routers to forward > packets between parts of the subnetwork.” > A L2 network - by definition - doesn't require IP forwarding inside. I'm not sure what the issue is. This is consistent with what I say below. Joe > > > Lothar > > > > *Von:*Joe Touch [mailto:[email protected]] > *Gesendet:* Dienstag, 16. August 2016 01:07 > *An:* Reith, Lothar <[email protected]>; David Allan I > <[email protected]> > *Cc:* Bocci, Matthew (Nokia - GB) <[email protected]>; [email protected] > *Betreff:* Re: AW: AW: [nvo3] FW: Call for interest on NVO3 use case draft > > > > > > > > On 8/15/2016 3:54 PM, Reith, Lothar wrote: > > Hi Joe, > > > > thanks for the references to these RFCs, in particular to RFC 3819 > which I was not aware of. > > > > I think the references make very clear, that the term “subnet” is > overloaded and therefore context dependent in meaning. > > > It's almost always more useful to be clear about the way in which the > term is used, but IMO "subnet" is an L3 term that refers to > addressing. Everything else derives from that. > > > I do not want to bother you with a detailed analysis, but my > observation is as follows: > > > > The meaning of the term subnet is context dependent > > - Layer-2 subnet in the sense of an object that forwards packets > > - Layer-3 subnet in the sense of an object that forwards packets > > - network prefix in the sense of an object that is a portion of an > address plan, more precisely a subtree of a binary tree. > > > L2 doesn't have subnets; a specific L2 *is* a subnet to L3. > > L3 subnets are defined by having a common bit-aligned address prefix. > > > Adding to this ambiguity is the fact that subnet number (IPv4) > and subnet ID (IPv6) relate to the Layer-3 subnet context of > “subnet” only > > That's because subnet is an L3 term. > > > (not to the layer 2 subnet context) > > There is no L2 subnet. An L3 subnet is often - but not always - mapped > to a single L2 *network*. > > > but do not identify a layer-3 subnet as a global identifier, > rather play the role of a locator in the binary subtree with local > significance only. This appears to be similar to the locator ID > separation problem addressed by LISP. > > That's exactly because LISP turns the encapsulation layer into what is > effectively an L2 network. The problem of mapping the inner and outer > addresses in LISP is the same as ARP, except that it requires > determining LISP egress rather than destination. > > That's why we called the protocol to solve this "BARP" - it combines > BGP and ARP - when we developed it for what we called "recursive > routers" in the late 90s in our X-Bone system. > > > Given this and Dave’s additional comments regarding: “please > provide a use case please” may I kindly ask you to provide a use > case with “context tag” or perhaps using the term network prefix > instead of subnet where appropriate. > > > > In particular I would be interested in a use case describing your > stated requirement for “revisitation, where a single node > participates multiple times in an overlay”. Could you please > clarify the cardinality relations in this use case, e.g. do you mean > > - One physical interface to appear like multiple physical > interfaces (such as a single physical NIC to appear as multiple > VNICs)? > > - One physical interface (typically Ethernet Interface or > station) to be associated with one MAC addresses at Layer 2, > where multiple IP addresses are associated with that MAC address, > where said IP addresses belong to multiple Layer3 subnets., thus > multiple Layer3 subnets associated with the same Layer2 subnet? > > - One physical interface (typically Ethernet Interface or > station) to be associated with multiple MAC addresses at Layer 2, > where each of that MAC addresses is assigned one IP address (one > to one relation between Layer3 subnet and Layer2 subnet, but > multiple layer2 subnets on the same physical interface (Ethernet > station i.e. PNIC or VNIC)? > > First, if you're thinking about physical anything, you're limiting > yourself to one layer of virtualization. That's unnecessary. > > So let's assume that when you say "physical" you really mean "in the > lowest layer of virtualization" (i.e., the base case of what is > ultimately a recursive structure - e.g., see www.isi.edu/rna > <http://www.isi.edu/rna>, which is a generalization of the X-Bone > architecture). > > When I say "revisitation", I mean one base L3 interface that acts like > multiple NVO3 L3 interfaces. > > That is accomplished by associating it with multiple virtual L2 (L2 > over L3), each virtual-L2 of which is associated with one virtual L3. > > None if this is what you're describing above; you're stuck at the base > layer L2, which is below where NVO3 operates. > > Joe > > > > > > Best Regards, Lothar > > PS: Given that we live in times of emerging software defined > networks, it is increasingly important WHAT an orchestration > software defines when it defines a “network” or a “subnet”, and > rapidly becoming irrelevant what context tag was not explicitly > spelled out in an IETF RFC. So I recommend to analyse WHAT it is, > that the OpenStack method “create network” creates. It may be an > empty binding between a L2-subnet and a L3-subnet with all details > and sizes yet undefined, but with a handle in form of a globally > unique identifier in the form of a UUID, and the problem solved is > the lack of a global identifier that is not a locator or address. > > > > > > *Von:*Joe Touch [mailto:[email protected]] > *Gesendet:* Sonntag, 14. August 2016 01:45 > *An:* Reith, Lothar <[email protected]> > <mailto:[email protected]>; David Allan I > <[email protected]> <mailto:[email protected]> > *Cc:* Bocci, Matthew (Nokia - GB) <[email protected]> > <mailto:[email protected]>; [email protected] <mailto:[email protected]> > *Betreff:* Re: AW: [nvo3] FW: Call for interest on NVO3 use case draft > > > > > > > > On 8/13/2016 4:20 PM, Reith, Lothar wrote: > > Hi Joe, Dave, dear all, > > > > I think that the term “subnet” is indeed only defined in a context > sensitive way. > > > > Unfortunately there is no distinction made between a L2-subnet > (aka a broadcast domain, or a MEF EVC, or o broadcast domain > equivalent achieved without broadcast such as EVPN) and a > L3-subnet (the object that does not appear in any information > model that I am aware of, but which has a size which is defined > by a subnet-mask and which supports the use case of “change the > IP-address range assigned to that subnet”. > > The reason that L2 broadcast domain and L3 subnet (as per RFC1812) > coincide is that is the basis of most L3:L2 mapping mechanisms, > e.g., ARP (RFC826) or ARP emulation (RFC1577). > > And the concept of an L3 subnet is pervasive in many RFCs, being > the basis of hierarchical IP forwarding since its inception. > There's even a specific RFC advising on the design of L2 subnets > to support L3 subnets (3819). > > > > Part of the reason for complexity is the lack of a proper > definition of this object in the information model. > > > > If I am wrong – I would be happy to be corrected by someone who > can point me to an authoritative definition of the term subnet as > an object that supports the use case “change address range > assigned to subnet” without specifying how the subnet is built as > layer 2 construct (e.g. as Ethernet yellow cable, VLAN in a > Switched Ethernet domain, VXLAN overlay, EVPN, MEF EVC or ATM > point to point link). > > > Subnet in L3 in IPv4 is defined as per RFC 4632 > > Subnet in L3 in IPv6 is defined as per RFC 4291 > > These are very old and fundamental concepts to the Internet > architecture. Any notion of virtualizing L3 needs to deal with them. > > Joe > > > > > > Thanks to OpenStack for finally fixing the problem by introducing > the method “create network”, which creates – exactly – this > missing object in an abstract way. > > > > So Dave’s question is very valid, simply because the term > “subnetting” is not properly defined – unless the authors point to > a reference RFC where the term is defined in an authoritative way. > > > > Lothar > > > > > > > > *Von:*nvo3 [mailto:[email protected]] *Im Auftrag von *Joe Touch > *Gesendet:* Samstag, 13. August 2016 19:30 > *An:* David Allan I <[email protected]> > <mailto:[email protected]> > *Cc:* Bocci, Matthew (Nokia - GB) <[email protected]> > <mailto:[email protected]>; [email protected] <mailto:[email protected]> > *Betreff:* Re: [nvo3] FW: Call for interest on NVO3 use case draft > > > > > > On 8/13/2016 9:52 AM, David Allan I wrote: > > Hi Joe > > > > And the use case for wanting to do subnet emulation is….? > > > You want the properties of a subnet and/or to emulate the behavior > of a shared link, i.e., to limit the scope of various protocols, > including IP routing, IPv6 automatic addressing, L2 address > translation (virtualizing L2 underneath a virtual L3 is needed to > support revisitation, where a single node participates multiple > times in an overlay), and basically any subnet-based resource > discovery. > > Joe > > > > > > > That‘s my question > > Dave > > > > *From:*Joe Touch [mailto:[email protected]] > *Sent:* Friday, August 12, 2016 8:20 PM > *To:* David Allan I <[email protected]> > <mailto:[email protected]> > *Cc:* [email protected] <mailto:[email protected]>; Bocci, Matthew (Nokia > - GB) <[email protected]> <mailto:[email protected]> > *Subject:* Re: [nvo3] FW: Call for interest on NVO3 use case draft > > > > The typical use case is to support subnet emulation, e.g., a group > of links over which broadcast is emulated as with LANE. > > > On Aug 12, 2016, at 7:11 PM, David Allan I > <[email protected] <mailto:[email protected]>> > wrote: > > My point would be that introducing additional complexity in an > overlay should have a use case associate with it. It would not be > something you would do gratuitously…. > > > > SO I’m looking for the draft to provide a use case for this vs. > simply mentioning subnetting without any context J > > > > Cheers > > Dave > > > > *From:*nvo3 [mailto:[email protected]] *On Behalf Of *Joe Touch > *Sent:* Friday, August 12, 2016 5:07 PM > *To:* David Allan I <[email protected] > <mailto:[email protected]>>; [email protected] > <mailto:[email protected]>; Bocci, Matthew (Nokia - GB) > <[email protected] <mailto:[email protected]>> > *Subject:* Re: [nvo3] FW: Call for interest on NVO3 use case draft > > > > > > > > On 8/12/2016 4:16 PM, David Allan I wrote: > > 4.2 Why I would subnet my overlay could use some explanation. I > normally think of subnetting as a convenient address > summarization technique dependent on topology, and with an overlay > I don’t have a topology. > > > The topology of an overlay is determined by its tunnels, just as > the topology of the underlying net is determined by its links. > > A subnet in an overlay corresponds either to a single multipoint > tunnel or to a set of tunnels that transparently acts as such - > just as a subnet in the Internet base network corresponds to a > shared access link or a set of links that transparently act as > such (e.g., switched ethernet). > > Joe > > > > > > > > >
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