[rbridge] Updated charter

[erik.nordmark at sun.com (Erik Nordmark)]

Michael Smith wrote:

>>The solutions that have been discussed will replace the L2 
>>headers (at least in some cases, and encapsulate in another 
>>L2 header in some cases), and not decrement the L3 TTL, which 
>>is different than a bridge (which doesn't replace the L2 
>>header) and a router (which decrements TTL).
> 
> 
> Some specific examples may help clarify, but the above statement sounds like
> the traditional bridge of yore i.e. bridges with ethernet and token ring
> interfaces that swap MAC headers to the appropriate canonical format and
> encapsulating bridging packets over ATM and Frame Relay using RFC1483 and
> RFC1490.

I guess there is a difference between the theory of bridges, captured in 
IEEE standards, and what products actually do. I don't think the IEEE 
standards talk about what bridges between e.g. Ethernet and Token Ring 
do, but I recall products doing somethings like handling bit-order 
issues with the addresses in arp packets, and the need to fragment IP 
packets due to the different MTUs.

Radia's rbridge draft (I think) talks about optimizations for IP where 
the IP packet would transit a cloud of rbridges unmodified, but where 
the L2 header might be different on exit than on entry. This isn't a 
problem for IP, since IP doesn't look at the L2 header, but can't be 
applied to non-IP (aka unknown to the rbridge) protocols.

    Erik
From erik.nordmark at sun.com  Wed Feb  2 16:57:05 2005
From: erik.nordmark at sun.com (Erik Nordmark)
Date: Wed Feb  2 16:59:05 2005
Subject: [rbridge] Updated charter
In-Reply-To: <[e-mail]>
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	<[e-mail]>
Message-ID: <[e-mail]>

Joe Touch wrote:

> The basis of the Internet is a single address layer that spans different 
> link layers. There are numerous problems stemming from the rbridge 
> basically needing to proxy the semantics of two different L2 systems.

The Internet architecture assumes very little about the L2 
infrastructure. For instance, it works with L2s that preserve the same 
L2 header (Ethernet being one example) but also over L2s that only use 
local identifiers (such as DLCIs in frame relay).

I don't see how running IP over a L2 where the L2 headers are different 
when received than when transmitted will cause problems, as long as the 
protocols involved in L2 address resolution are handled correctly.

So perhaps you can list the numerous problems.

> What you're proposing is a router that doesn't decrement the TTL.

No. And I think it is in the interest of clarity, especially during 
these formative times, that we don't reuse old terms for new things.
So please call it a hybrid, a rbridge, a frobnits, but not a router or a 
bridge, since that will confuse things with the routers and bridges that 
exist today.

> That's 
> not the same as a bridge that uses routing (vs. spanning tree) 
> internally; the former doesn't include L2 semantics, the latter does. 
> The latter presumes a single L2 semantics, which is easy to verify. The 
> former (as you suggest) allows multiple L2s, but does NOT preserve L2 
> semantics.

What we are talking about is a hybrid, which includes L2 semantics but 
might not preserve L2 semantics when carrying IP packets.

> That means a lot of IP will break where/when the L2s have different 
> semantics, e.g., NBMA vs. broadcast. We don't have a uniform L2 
> emulation protocol on which to base an interoperability layer (the PILC 
> WG noted some of its expected properties, but didn't spec it out as 
> such). This work seems like it should avoid L2 translation until that 
> canonical virtual L2 can be spec'd.

I don't think anybody has argued that the protocol will support any L2. 
What's being suggested is that it support some degree of non-uniformity.
And since we are assuming that ARP/ND be used for L2 address resolution 
there is an unstated assumption that all such L2 support 
broadcast/multicast.

> That the routing inside the rbridge is opaque to things outside the 
> rbridge.

OK, that I understand.


I think there is a range of semantics that are possible for the hybrids, 
and the WG needs to discuss them.
At one end we have what you seem to be arguing for, which I'll call 
strict IEEE 802 bridge equivalence,
This means that the cloud of interconnected hybrids behave the same way 
as an IEEE compliant bridge. I think this means that not only are the L2 
headers not modified, but also that the packets are delivered on the 
ports where an IEEE 802 bridge would deliver them (i.e. all ports for 
broadcast and multicast).

At another end of the scale we have what I'd call "IP works". In this 
case the cloud of interconnected hybrids collectively exhibit behavior 
so that IPv*/ARP/ND/DHCP etc work as expected.

Note that there are probably interesting points between these scales. 
One is what existing switch products do for multicast, which is to do 
IGMP/MLD snooping to limit the spread of multicast.
Presumably there are others as well.

    Erik
From erik.nordmark at sun.com  Wed Feb  2 16:58:22 2005
From: erik.nordmark at sun.com (Erik Nordmark)
Date: Wed Feb  2 17:00:44 2005
Subject: [rbridge] Updated charter
Message-ID: <[e-mail]>


I generated an update because Margaret asked for one. As part of doing
that I've tried to capture something about what has been discussed on 
the list.

Next step is to figure out an agenda for Minneapolis.

    Erik


[Note: name change from IPVLX to TRILL]

TRansparent Interconnection of Lots of Links (TRILL)


While IEEE 802 bridges are attractive due to not needing explicit
configuration and allowing hosts to move within the bridged topology,
they are more limited than IP routers since bridges
only support IEEE 802 technologies, and the most common layer 2
interconnection method (dynamically created spanning tree
formation using bridges) is not as flexible and robust as layer 3 routing.

The WG will design a hybrid solution that combines the simplicity of
configuration while taking full advantage of complex topologies.

The design should have the following properties:
  - zero configuration of the hybrid devices
  - ability for hosts to move without changing their IP address
  - it should be possible to forward packets using pair-wise shortest paths,
    and exploit the redundant paths through the network for increased
    aggregate bandwidth
  - possible optimizations for ARP and Neighbor Discovery packets 
(potentially
    avoid flooding all the time)
  - support Secure Neighbor Discovery
  - the packet header should have a hop count for robustness in the presence
    of temporary routing loops
  - nodes should be able to have multiple attachments to the network
  - no delay when a new node is attached to the network
  - multicast should work (and after a re-charter it might make sense to
    look at optimizations for IP multicast)
  - be no less secure than existing bridges (and explore whether the 
protocol
    can make "L2 address theft" harder or easier to detect)

A required piece of the solution is an IP routing protocol which is extended
to carry L2 address reachability, handle broadcast, and is friendly to
zero-configuration. Likely candidate are the link-state routing protocols
since they can easily be extended to provide for broadcast, which is 
believed
to be difficult for distance vector protocols.
This working group will define the requirements on such routing protocol(s),
and select the routing protocol(s) to be used.  The intent is that the 
actual
extensions to the routing protocol(s) be performed in the WGs with 
expertise
in the routing protocol(s).

The working group will look into solutions that can interconnect different
layer 2 technologies, and also look at providing support for non-IP 
protocols,
even though one can not combine those two features together; the
interconnection of different layer 2 technologies (with different layer 2
address formats) will most likely only work for the IP family of protocols.
Whether the same or different address formats are used, there might be a 
need
to handle different MTUs.

The WG will design a protocol that combines the benefits of bridges
and routers in a way that will co-exist with existing hosts, IP routers
and bridges. The design must support both IPv4 and IPv6

The working group will not work any layer 3 aspects except to provide
  - Possible optimizations for ARP and ND packets (not always
    flooded everywhere)
  - Being able to carry IP broadcast and multicast packets (which might 
just
    fall out from supporting L2 multicast)
  - Defining the L3 operations needed to interconnect different L2 
technologies


The work consists of several, separable pieces:
  - Defining the requirement on the routing protocol(s), and select one or
    more routing protocols. The detailed specification of the extensions to
    a particular routing protocol will be left as an action item for the
    specific routing protocol WG.
  - Defining what information must be carried in an encapsulation header for
    data packets, and how to map that information to various link types 
(e.g.,
    IEEE LAN, Fibrechannel, MPLS)
  - Defining how address resolution (ARP and Neighbor Discovery) is 
performed,
    taking into account the desire to be compatible with Secure Neighbor
    Discovery.
  - Defining how the solution extends to the case when multiple layer 2
    technologies, that have different address format/length, are 
interconnected.

Deliverables
  - A short draft on the problem statement and goals
  - A document defining what information needs to be carried in routing
    protocols to support the rbridge concept, and other requirements on
    the routing protocols.
  - Encapsulation draft specifying what needs to be carried in general
    and the specific format to use on IEEE LANs
  - ARP and ND draft
  - Draft on interconnecting different types of layer 2 technologies
  - Threat analysis document

Goals and Milestones

Jun 05  Problem statement and Goals submitted to IESG for Informational
Sep 05  Routing protocol support requirements to IESG for Informational
Dec 05  Encapsulation document to IESG for Proposed Standard
Sep 05  ARP & ND to IESG for Proposed Standard
Mar 06  Interconnecting Layer 2 Technologies document to IESG for
         Proposed Standard
Dec 05  Threat analysis to IESG for Informational

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