RE: multihomed host

["Michel Py" <michel@arneill-py.sacramento.ca.us>]

> Yoshihiro Ohba wrote:
> I don't know if there is an official definition, but I
> have usually heard the term "multihomed host" used to
> refer to multi-interface systems that do not function
> as routers (i.e. they don't forward packets).

Here is my reading of this:

1. Multi-interface host:
> Margaret Wasserman wrote:
> I don't know if there is an official definition, but I
> have usually heard the term "multihomed host" used to
> refer to multi-interface systems that do not function
> as routers (i.e. they don't forward packets).

I agree with Margaret. A host that has multiple interfaces connected to
multiple subnets *is* a multihomed host, but...


2. A host that has multiple interfaces with addresses in the same subnet
(either to increase throughput or to provide redundancy) is *not* a
multihomed host.


3. Single interface, multiple address host:
> Bill Sommerfeld wrote:
> For what it's worth, I've occasionally heard the
> term used in an application-layer context to refer
> to hosts having multiple IP addresses rather than/in
> addition to multiple interfaces.

For v4, I agree with Bill *if* the multiple addresses belong to
different subnets.

For v6, this is blurry. Would you call multihomed a host that has both a
link-local and a regular unicast address on the same interface? I don't
think so.

On the other hand,
> Yoshihiro Ohba wrote:
> There may be some scenario in which a single-interface
> host is connected to multiple ISPs on the same link, which
> seems to be not covered in the usual definition for
> "multihomed host". I don't know what to call the model,
> but is such a model already common? Or is there any
> ongoing work on this model?

This is possible as of today; a host that has multiple PA addresses is
certainly considered a multihomed host. However, this alone is not a
multihoming solution.


4. A host that has a single address but is part of a multihomed site:
This would be the case for hosts belonging to a multihomed LIR, or the
case of hosts connecting to a MHAP network. I do not call these hosts
multihomed.

In other words: semantically speaking, the fact that the host is
connected to a multihomed router does not make the host itself
multihomed, IMHO.

Michel.