RE: Different terms for the same or more secure?

["Isaac Van Name" <ivanname () southerlandsleep com>]

Okay, you caught me... got my early morning rant of useless information out
of the way.  :-)  Can't really dispute much of what was said, but I'll try
anyways.  B-)

> > I guess I meant a subnet created with a VLAN - an attempt to go along
> > with the word choices of the original poster.

Of course.  For the sake of clarity, I took it upon myself to nitpick.  :-)

> > VLANs seperate broadcast domains only. A broadcast does not traverse a
> > router - unless its told to pass them (DHCP over WAN links for
> > instance). On a switch, each port is its own collision domain, unlike
> > a hub.

You're right; a broadcast does not traverse a router unless explicitly told
to do so.  However, this statement alone does not necessarily mean that it
is more accurate to say a VLAN separates broadcast domains.  True, this is
what you will find on any site defining a VLAN... and it is the literal
definition.  For the sake of understanding how a VLAN fits into the whole
picture, though, I have to say it seems more accurate to say a VLAN
"creates" a broadcast domain, which inherently separates itself from the
broadcast domain that the switch lies on (just like a physical broadcast
domain would).  It's like saying that opening a new browser window separates
your browser into two windows... true, but not quite how we'd think of it
using generic human nature.  But, of course... this is not saying anyone is
wrong; this is simply arguing for the sake of an almost-inconsequential
increase in accuracy.  ...Nitpicking again.

Oh, and you're right about the switch... I generalize an individual switch
environment as a collision domain because I don't know a better way to refer
to them.  I'm sure someone will assist me with that dilemma.

> > >  It separates IP addresses like a subnet,

> > No, your subnetting (IP Addressing) scheme does that.

My turn to cater to the original poster.  True, a VLAN does not subnet IP
addresses because a broadcast domain doesn't, either.  However, in most
cases where a VLAN was used, I've seen it used just this way... to create
separate "subnets" on a switch.  To steal your phrase, "vlaned subnets".
Not truly a subnet, but rather a broadcast domain containing a single
subnet, in those cases.

> > Collision domains are a physical layer issue, I *believe* and has
> > nothing to do with upper layer protocols (like VLANs).

Probably so, but I wouldn't know.  This falls back on my tendency to term a
switch as a single collision domain.  The point I was trying to raise is
that a VLAN doesn't function as a switch would, but rather as a router
would.  Of course, there is always a counterargument for this as a router
functions on a different layer than a VLAN, right?

> > Trunk lines allow the switch to pass multiple VLANs across the same
> > port. If you define a VLAN to a switch you almost always have to have
> > a trunk line connecting that switch to a router (unless you're in a
> > chassis with an MSFC) since, in the Cisco world anyway, you always
> > have vlan1 and you don't want to use it for your normal traffic.

Right.  No argument here.  :-)

Well, I'm sure there will be a rebuttal on some of this; this, however, is
what makes mailing lists interesting.  Just to keep on the track of reaching
a conclusion for the original poster, though, I'm obligated to ask:  Hylton,
what else is not clear?

Isaac Van Name

-----Original Message-----
From: Brian Loe [mailto:knobdy () gmail com] 
Sent: Thursday, August 31, 2006 9:23 AM
To: Isaac Van Name
Cc: security-basics () securityfocus com
Subject: Re: Different terms for the same or more secure?

On 8/31/06, Isaac Van Name <ivanname () southerlandsleep com> wrote:
> > > If its physically subnetted then there's a router between the subnets.
> > > Logically seperated subnets, I suppose, would be vlaned subnets
> > > (virtual being logical - not real/physical).
>
> Right, router separates subnets because switches send packets out of a
> subnet into a router, and then out from there.  Not really understanding
the
> "vlaned subnets" phrase, though, considering the following excerpt...

I guess I meant a subnet created with a VLAN - an attempt to go along
with the word choices of the original poster.


> > > The only thing a VLAN does is break up broadcast domains. Subnets, on
> > > the other hand, are controlled and limited by your IP addressing
> > > scheme - and provide nothing, a router or other such device (firewall
> > > for instance) is divide them up.
>
> If a VLAN breaks up broadcast domains, then what is a vlaned subnet?  Not
to
> be picky about phrasing, but "logically separated subnets" in this
instance
> would be simply "vlaned LANs".  But, then we get into the whole thing
about
> exactly what a VLAN does... and, it seems to me, a VLAN does not break up
> broadcast domains.  A router does that.  A VLAN creates a broadcast domain
> on a switch that contains a collision domain... but the VLAN is not part
of
> the collision domain.  What separates a switch's collision domain and a
> VLAN's broadcast domain?  About 3 hops.  :-P  Joking... VLANs are
> fascinating in that they defy normal networking logic to bring you an
> alternative that fits situations that defy (some) networking logic.

VLANs seperate broadcast domains only. A broadcast does not traverse a
router - unless its told to pass them (DHCP over WAN links for
instance). On a switch, each port is its own collision domain, unlike
a hub.

>  It separates IP addresses like a subnet,

No, your subnetting (IP Addressing) scheme does that.

> but isn't a collision domain.

Collision domains are a physical layer issue, I *believe* and has
nothing to do with upper layer protocols (like VLANs).

>  It contains its own broadcast domain, but is
> adjacent to a collision domain and doesn't have to get "routed" from a
> router to a switch to do so... because it's based off of the switch.  A
VLAN
> uses a trunk line to have traffic directed to it as if it's a router.

Trunk lines allow the switch to pass multiple VLANs across the same
port. If you define a VLAN to a switch you almost always have to have
a trunk line connecting that switch to a router (unless you're in a
chassis with an MSFC) since, in the Cisco world anyway, you always
have vlan1 and you don't want to use it for your normal traffic.

> I can't think anymore... I need coffee.  If I misrepresented any
particular
> piece of information, please feel free to correct me; I learn the same way
> everyone else does.

I hear ya...



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