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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