On Sep 13, 2005, at 11:23 AM, Danial Thom wrote:
its not clear why Chuck keeps answering since he
clearly doesn't understand the question.
I'm willing to try and help people, even if the questions being asked
aren't entirely clear. If you want to believe this reflects a lack
of understanding on my part, that's OK:
you're welcome to hold that opinion.
You can, of course, multihome with one nic, and
Spanning Tree and "collision domains" have
nothing to do with anything, simply by routing to
the correct router.
A machine with one NIC can be attached to a "multihomed network".
But a machine with one NIC is not a "multihomed machine". [1]
"Multi-homing" refers to having more
than one network egress (ie 2 or more upstream
providers) and the ability to "decide" which one
to send specific traffic to.
Sure. This definition of "multihoming" is applicable to the network
as a whole, not to each and every individual device on the network.
A multihomed network can lose one of its upstream connections and
still retain full connectivity, because there is an alternate path
available via the second (or additional) upstream connections.
In order to construct such a network, you need two or more routers,
each of which is a "multihomed machine" by the classic definition
(ie, has two physical network interfaces connected to two different
physical networks), and you commonly use BGP to coordinate routing
with the upstream providers, just as you might use VRRP or CARP to
provide a single fault-tolerant virtual router IP for the systems on
the LAN which will continue to function even if one of the routers
fails.
--
-Chuck
[1]: I am aware that some people would disagree with this.
For example, Microsoft's IIS documentation apparently describes a
webserver hosting more than one domain as "multihomed" rather than
using Apache's terminology of "name-based virtual hosts". There are
people who believe that using "ifconfig alias" to configure
additional IPs on a NIC creates a multihomed system, but there is no
physical redundancy involved and there is no isolation of traffic.
I find such usages of the term "multihomed" to be misleading at best,
and at worst sometimes even represent a deliberate effort to confuse
people expecting the additional reliability and redundancy of a truly
multihomed network architecture:
What happens to a machine with a single NIC when that NIC fails?
Do you see any difference between this and a machine with two or more
NICs?
(The latter retains network connectivity, the former does not.)
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