RE: Different terms for the same or more secure?



My pet peeve.

Quote From: Isaac Van Name
A broadcast does not traverse a
router - unless its told to pass them (DHCP over WAN links for
instance).

Since we are nitpicking, that statement is incorrect.
Routers NEVER pass broadcast traffic (unless they are configured as a
bridge of course, but that doesn't count). They can be told to listen
for broadcast on one interface and pass unicast on the other.
Proof: on cisco, when configuring the helper address, you must provide
the ip address of DHCP, DNS etc.
Also, drop a sniffer on your network, you'll see.


BTW, this was my first "post". How did I do?
lol

Dino Dogan
Network Engineer
NaviSys
499 Thornall Street
Edison, NJ 08837-2235
www.navisys.com
732.767.3828 PH
732.635.9576 FX

-----Original Message-----
From: Isaac Van Name [mailto:ivanname@xxxxxxxxxxxxxxxxxxxx]
Sent: Thursday, August 31, 2006 10:56 AM
To: Brian Loe
Cc: security-basics@xxxxxxxxxxxxxxxxx
Subject: RE: Different terms for the same or more secure?
Importance: Low

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@xxxxxxxxx]
Sent: Thursday, August 31, 2006 9:23 AM
To: Isaac Van Name
Cc: security-basics@xxxxxxxxxxxxxxxxx
Subject: Re: Different terms for the same or more secure?

On 8/31/06, Isaac Van Name <ivanname@xxxxxxxxxxxxxxxxxxxx> 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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education and the case study affords you unmatched consulting experience.
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