From owner-nanog@merit.edu Mon Oct 24 15:33:02 2005
Date: Mon, 24 Oct 2005 13:31:17 -0700
Subject: Re: What is multihoming was (design of a real routing v. endpoint id
seperation)
Stephen Sprunk wrote:
[snip]
>> Other people use this term in very different ways. To some people
>> it means using having multiple IP addresses bound to a single
>> network interface. To others it means multiple websites on one
>> server.
>
>
> That is virtual hosting in a NANOG context. Some undereducated MCSEs
> might call it multihoming, but let's not endorse that here.
Unfortunately, this is a common and "standards blessed" way to refer to
any host with multiple interfaces/addresses (real or virtual). For example,
from the "Terminology" section, 1.1.3, of RFC1122, "Requirements for
Internet Hosts -- Communication Layers," says,
Multihomed
A host is said to be multihomed if it has multiple IP
addresses. For a discussion of multihoming, see Section
3.3.4 below.
*sigh* Multi-homing simply means 'having external connections to more than
one network' -- be it a network with multiple, disjoint, ingress/egress paths,
or a host with interfaces (real or virtual) on distinct LAN subnets (even if
those subnets are agregated into a single net somewhere upstream.
A host with multiple adresses utilizing the _same_ netblock/netmask _should_
_not_ be called multi-homed (because there is only one path to that host), it
is simply a single-homed host with multiple identities. might be called
"poly-ip-any" or some such. <grin>
As became clear when we wrote the draft that became RFC 3582, apparently simple terms such as "transit provider" and "multi-homing" mean surprisingly different things to different people.
The important thing is not who is right, and not which definition is the best, but that everybody uses the same definitions so that they can talk to each other without running around in circles.
Joe
Robert Bonomi wrote:
From owner-nanog@merit.edu Mon Oct 24 15:33:02 2005
Date: Mon, 24 Oct 2005 13:31:17 -0700
Subject: Re: What is multihoming was (design of a real routing v. endpoint id
seperation)
Stephen Sprunk wrote:
[snip]
Other people use this term in very different ways. To some people
it means using having multiple IP addresses bound to a single
network interface. To others it means multiple websites on one
server.
That is virtual hosting in a NANOG context. Some undereducated MCSEs might call it multihoming, but let's not endorse that here.
Unfortunately, this is a common and "standards blessed" way to refer to
any host with multiple interfaces/addresses (real or virtual). For example,
from the "Terminology" section, 1.1.3, of RFC1122, "Requirements for
Internet Hosts -- Communication Layers," says,
Multihomed
A host is said to be multihomed if it has multiple IP
addresses. For a discussion of multihoming, see Section
3.3.4 below.
*sigh* Multi-homing simply means 'having external connections to more than one network' -- be it a network with multiple, disjoint, ingress/egress paths,
or a host with interfaces (real or virtual) on distinct LAN subnets (even if
those subnets are agregated into a single net somewhere upstream.
A host with multiple adresses utilizing the _same_ netblock/netmask _should_
_not_ be called multi-homed (because there is only one path to that host), it
is simply a single-homed host with multiple identities. might be called
"poly-ip-any" or some such. <grin>
Depends who you ask. Again, RFC1122 says (section 1.1.1),
A host is generally said to be multihomed if it has more than
one interface to the same or to different networks.
And also section 3.3.4.1,
A multihomed host has multiple IP addresses, which we may
think of as "logical interfaces". These logical interfaces
may be associated with one or more physical interfaces, and
these physical interfaces may be connected to the same or
different networks.
As far as a "multihomed host" is concerned, RFC1122 sure seems to call
anything with multiple IPs multihomed. Multihomed is a trait of the host
independent of any network topology around the host.
But whatever. It just means people need to be clear what they are talking
about when they say "multihomed." As is clear from this thread, there is
not clear agreement on what the precise meaning is.
OK... As entertaining as the debate on the definition of "multihomed host"
is so far, I'd like to point out that on NANOG, we are generally NOT
concerned with that term. The term that we are most interested in
is "multihomed network".
I would submit that host multihoming is irrelevant to the charter of
NANOG and that the definition of a "multihomed network" is a network
or collection of networks that meet the definition of an autonomous
system (whether an ASN is assigned to them or not) which are
topologically adjacent to more than one network or collection
of networks which each meet the definition of an autonomous
system, but, are not, themselves, a single autonomous system
or part of the same autonomous system as the network in question.
To attempt to translate that into English:
Autonomous System: One or more networks which are topologically
contiguous and share a common routing policy.
Whether an ASN is assigned to an Autonomous System or not is a different
matter.
If an autonomous system is topologically adjacent to two or more other
autonomous system, then, the networks within that autonomous system
can generally be said to be multihomed for the purposes of discussions
on NANOG. Technically, the AS is multihomed, but, we often use the
term network to mean AS or network.
Owen