[e2e] Lost Layer?
Fred Baker (fred)
fred at cisco.com
Tue Feb 11 10:47:00 PST 2014
On Feb 11, 2014, at 6:29 AM, Joe Touch <touch at isi.edu>
> On 2/11/2014 1:09 AM, Fred Baker (fred) wrote:
>> In real operational networks, in 2014, we have at least three common
>> sub-layers within the network layer. One is what we call the
>> Internetwork Layer and should be called, perhaps, the Inter-network
>> sub-layer. It provides the end to end datagram service that TCP and
>> other transports ride atop. ...
> The layer that TCP rides over that spans heterogeneous network technologies is IP, the Internet(working) layer.
>> ...Another might, by analogy, be called the
>> Intra-network sublayer. It connects systems that are not necessarily
>> directly connected, but use the same technology and are operated by a
>> common administration.Switched Ethernets, 802.11 networks, MPLS,
>> ATM, Frame Relay, and X.25 are all examples of Intra-network
> In ISO that's the link layer (the Internet originally called these subnetworks), the homogeneous network technology span.
In IEEE/ANSI politics circa 1985, there was an understanding that the network layer belonged to ANSI, and the link layer belonged to IEEE. IEEE 802 started work on 802.1 through 802.5, including two different ways to build networks out of what at the time were called Packet Repeaters or Bridges. They bypassed the understanding by calling them MAC Layer bridges, and they justified the appellation by noting that the bridges operated on the link layer header, whether transparently or by source-route bridging.
X.25 was a place where the nomenclature battle was fought heavily. In Europe, X.25 was, at the time, *the* network, and the definitive network layer. To the ARPA folks, it was an API that allowed someone to inject a packet into a network; it might come out a different API that was not X.25. In CSNET, IP ran atop X.25, and IP was the API that allowed someone to select which X.25 destination they might go to.
Get over it. X.25 is a network, and the Internet is a Network, and one often runs over the other. As in X.25/TCP/IP/CSNET and other bizarre things.
ISO had nothing to do with that.
>> And then there is what one might call the virtualization
>> sublayer, which is when, whatever we call it, we use an IP tunnel
>> between the Internetwork and Intranetwork layers. Static IP/IP and
>> GRE/IP tunnels, LISP, Mobile IP, L2TP,
> Tunnels don't map to any static definition of layers, exactly because they can always be placed between any pair of layers - including other tunnel layers. A tunnel is link, not a network. A set of tunnels can represent a network to the layer above it.
> This last reality is why it's so easy to get tunneling wrong. E.g., a tunnel can transit a "largest" packet - which defines the tunnel MTU; that MTU is *not* the 'largest unfragmented message' that can transit the tunnel. We don't have a concept of 'natural chunksize', and confusion between that and the largest message transmissible is the reason for a lot of really badly crafted tunnel specs.
> So all these layers end up being defined by the layer above and the layer below, e.g., if IP runs over them, they had better act a lot like what RFC3819 expects, or things will (and do) work badly. (that relative relationship is what RNA is all about).
8 issues in virtual infrastructure
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