Subject: RE: Ethernet as a shared (not broadcast) network?

From: "Gray, Eric" <[email-masked]>
Date: Wed, 5 Apr 2006 17:11:35 -0400

Bob,

	I wonder if it is likely that some of the confusion relating to 
"multi-link subnets" that Dave tries to address, in the draft below,
comes from a disagreement about the definition of a "link"?

	In Dave's draft, link is defined as "generally used to refer to 
a topological area bounded by routers which decrement the IPv4 TTL or 
IPv6 Hop Limit when forwarding the packet."

	Outside of a strictly layer three context, this is simply not
true.  However, it works for router folks because - even if a router
does have multiple interfaces into a single subnet (or collection of
subnets), the router "bridges" between those (two or more) links.  
This can be simply modeled as -

     _________|__________________________________
    |         |                                  |
    |         |                 .-----(link-2)---+---- 
    |       .-+-.             .-+-.              |
  --+-------+ R +--(LINK-1)---+ B +---(link-4)---+---- 
    |       `-+-'             `-+-'              |
    |         |                 `-----(link-3)---+----
    |_________|__________________________________|
              |

	In this model, LINK-1 is as Dave's draft defines it.  For this
reason, it is shown in upper-case.  The use of the term "link" for
the link-2, link-3 and link-4 (clearly in lower-case in the figure)
is just as legitimate a use of the term - but in a layer two sense,
only.  If we don't call the connections between bridges links, what
do we call them?

	Hopefully, it helps to look at this model, because it should
help to highlight the essential layer-two nature of having multiple
interfaces connecting to the same subnet(s).  By using a bridging
logical function to separate the LINK (per Dave's definition) from 
the physical interfaces connecting to a subnet (set), issues with
layer two propagation in that subnet are resolved by that function.

--
Eric

--> -----Original Message-----
--> From: Bob Hinden [mailto:[email-masked]] 
--> Sent: Wednesday, April 05, 2006 4:24 PM
--> To: Stephen Sprunk
--> Cc: IPv6 WG
--> Subject: Re: Ethernet as a shared (not broadcast) network?
-->
 
... [SNIP] ...

--> 
--> Bob
--> 
--> 
--> >> Dave Thaler also wrote a draft on the general topic that was   
--> >> presented at the internet area meeting in Dallas:
--> >>
--> >>   Issues With Protocols Proposing Multilink Subnets
--> >>
--> >>
http://www.ietf.org/internet-drafts/draft-thaler-intarea-multilink-subnet-is
sues-00.txt
--> >
--> > Very good reading; thanks for the pointer.
--> >

... [SNIP] ...

--> 
--> 
--> --------------------------------------------------------------------
--> IETF IPv6 working group mailing list
--> [email-masked]
--> Administrative Requests: https://www1.ietf.org/mailman/listinfo/ipv6
--> --------------------------------------------------------------------
--> 

--------------------------------------------------------------------
IETF IPv6 working group mailing list
[email-masked]
Administrative Requests: https://www1.ietf.org/mailman/listinfo/ipv6
--------------------------------------------------------------------

---

From: "Dave Thaler" <[email-masked]>
Date: Wed, 5 Apr 2006 14:17:07 -0700

Re "If we don't call the connections between bridges links, what
do we call them?"

We call them "segments".

Yes "link" is an overloaded term, which is why I was sure to clearly
define in what context I was using the term.  Other documents and
contexts may use different terminology.

-Dave

-----Original Message-----
From: Gray, Eric [mailto:[email-masked]] 
Sent: Wednesday, April 05, 2006 2:12 PM
To: Bob Hinden
Cc: IPv6 WG; Stephen Sprunk; Dave Thaler
Subject: RE: Ethernet as a shared (not broadcast) network?

Bob,

--
Eric

... [SNIP] ...

--> 
--> Bob
--> 
--> 
http://www.ietf.org/internet-drafts/draft-thaler-intarea-multilink-subne
t-is

... [SNIP] ...

--> 
-->