VLAN interfaces on FreeBSD; performance issues

[Charles Swiger]

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.)