--- SOTL <sotl155360@earthlink.net> wrote:
> Hi All
>
> Laying on the couch thinking about this I believe that the following
> is
> correct:
>
> Lets assume a device with one what we shall call a line connection
> and 5
> output connection. This device will be a:
>
> Hub
> Non configurable
> If all packages into any one port go to all other ports.
>
> Switch
> Non configurable
> If an input package only goes to the port that contains the device
> that the
> package is directed to. Can not figure this one out how the switch
> knows to
> sent a package inputed to A to output B instead of C and what happens
> if you
> need it to also go to D?
>
> Router
> If you configure the device such that that a package in A go to which
> ever
> combination of ports you choose for outputs. By this one could
> configure all
> e-mail to go to ports A & B AFN to no other port, all html to port C
> and
> reject all other packages. You can configure this as you want.
>
> Frank
heres two views.
the device centric view:
hubs repeat everything they see on every port to every port. they are
essentially splitters / combiners for networks. hubs see data like
this: [stuff]
switches are like hubs with a brain. a switch forwards "stuff" from a
source interface (eg an ethernet interface) to a destination interface
by knowing the mac addresses associated with each interface. sometimes
those addresses are learned, other times they are programmed. switches
see data like this: [[source address][destination address][stuff]]
(some switches have additional functionality for controlling traffic
flow such as with vpn's. this functionality is programmable).
there is no way to send "stuff" to two and only two machines in this
device without something like vpn (where only two machines belong to
the virtual network). if you do need to send something out to all
machines (such as a request for dhcp to lease an ip address), then its
done with something called multicasting, which is "Stuff" that has
special destination mac (ff:ff:ff:ff:ff:ff) and ip (last octet is
usually 255, eg: 192.168.0.255) addresses that tell devices to send it
everywhere.
bridges are like hubs that connect different types of networks (eg,
ethernet to wireless). some bridges come with additional functionality
for filtering different types of traffic. this functionality is
programmable. basic bridges see data like this: [stuff]
routers are like switches that forward "stuff" from a source interface
to a destination interface based on an ip address (rather than a mac
address). routers are almost always programmed (i've never seen one
that wasn't), however, they are unique in the fact that some can
communicate directly with other routers to learn new routes (this is
what protocols such as bgp and rip are for). routers see data like
this: [[source & destination macs][[source ip][destination
ip][stuff]]].
a gateway is a kind of router that has a default interface (in fact,
its not a router, but it acts like one). if "stuff" has a destination
ip address that the router cant find on its own, then "stuff" is sent
to that default port in hopes that any devices connected to that
interface will know where to send that "stuff".
the protocol centric view (aka, the osi model layers 1 - 3):
pc's and routers have both ip addresses and mac addresses. some
switches and bridges have mac addresses, some dont. hubs have no
addresses. when a pc or router has "stuff" to send to another pc or
router, it starts by automagically preparing that data (handled by osi
layers 4 - 7).
that data is then wrapped in an ip packet (layer 3): [[source
ip][destination ip][stuff]]. this packet holds the information needed
by _routers_ to get "stuff" to its intended destination which is
identified by an _ip address_.
the ip addresses and "stuff" are wrapped again in an ethernet (or
802.11a|b|g) frame (layer 2): [[source mac][destination mac][ip
addresses & stuff]]. this frame holds the information needed by
_switches_ to get "stuff" to its intended destination which is
identified by a _mac address_.
finally, everything is sent over the media that carries your data
(radio waves, cat5 cable, etc): [mac & ip & stuff]. _bridges_ and
_hubs_ forward this blindly. they have no concept of addresses.
once this information reaches its first hop (a device that understands
addresses), that device _may_ opt to peel off and replace any mac or ip
information that will prevent stuff from getting to its destination
(eg, masquerading). the wireless gateway/router/bridge/switch you've
been talking about does this so you can have more than one device using
your internet connection at once.
as a gateway, it converts addresses as necessary so your isp can get
your "stuff" to the internet.
as a bridge, it converts information from one medium to another.
as a switch, it allows computers on the lan side to communicate with
eachother using mac addresses.
as a router, it allows computers on either the lan or wan sides to
communicate with eachother using ip addresses.
http (html), email (smtp / pop3), ftp, etc are all protocols that
reside in layers 4 - 7 and are all controlled and maintained by
software running on the source and destination computers rather than
networking devices. as far as a router / switch / bridge / hub is
concerned, all of the data in these protcols is "stuff". no decisions
are made on this data unless additional functionality exists in any of
these devices to control whether "stuff" should be dropped into a
bit-bucket or allowed to continue on. this is the job of a firewall
(which is also said to run on layers 4 - 7) and is not an inherant part
of any networking devices listed above.
There are some really good entry level networking books available that
go into great detail. anything related to the net+ and ccna
certifications would probably be very helpful to your understanding.
hope that helps.
>
>
>
>
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