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]> > *Cc:* Bocci, Matthew (Nokia - GB) <[email protected]>; [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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