[Year 12 SofDev] Network Diagrams - Physical or Logical

Sun Mar 30 21:58:27 EST 2008

Hi Folks,

 I would make a few observations here.

1. A network has a boundary as a network card. This is also known as a 
gateway ( there may be more than one gateway ). If the boundary is a router, 
one card ( router interface ) is in the network, and at least one other has 
to be in the "next" network otherwise you don't have a router. A router can 
be a computer ( min 2 cards ) or a purpose built router such as a Cisco 
router. A gateway device MUST have at least 2 NICs. The firewall sitting in 
the middle of a network troubles me. How will packets be checked for 
permission to ENTER the network if they are being sent to a device in the 
MIDDLE of the network ?

2. Routing ( deciding which interfaces a packet should be sent to once it 
has arrived at an interface ) is wasteful before the firewall does it's job. 
Why decide how to process a packet only to have it dropped by the firewall ? 
Therefore  the firewall should sit further out than the router or if in the 
one device the firewall function takes place first. If the firewall is happy 
to accept the packet, the routing table is then checked to see which 
interface the packet should now exit the router.

3. Some routers have firewall and inbuilt modem module capability. The modem 
would sit further out again if it was a separate device. But since these 
devices appear to be in one box the sequence of operations is sometimes not 
clear.

4. There may be alternate representations and conceptually the issue is that 
all traffic inbound must be forced to go through the firewall. How do we 
assure every packet will be forced through the firewall in the non 
sequential diagram as presented by Kevin ? If the inbound, default gateway 
from the router is the firewall, it can't route traffic with one network 
card except with some exotic configurations. Point 2 above is also still an 
issue.

5. Use of DMZ ( Demilitarised Zones ) could be worth investigating with 
students and explaining how they reduce the risk to networks.

6. Robert makes a good point regarding a conceptual understanding  to be 
sufficient rather than a distinction say, between routers and switches as 
far as what data units ( packets vs frames ) they handle. I would have 
thought the concrete would be much easier than the abstract for these kids. 
This is only IMHO. The method lecturer's advice from Dip Ed to always 
support a concept with a concrete example keeps ringing in my ear.

7. I don't recall anyone suggesting the reason for teaching these physical 
implementation details in Software Development ( router, switch, firewall, 
modem ) is in any way for preparation of these students for work. On the 
contrary, it is to understand the concepts and not to go home and implement 
a solution or build a network - unless they want to.

Now, give me a minute to take cover in the Demilitarized Zone before you 
launch your assault on my comments here .....

Are we supposed to be on holidays ?

Kind Regards
Kevork Krozian
Edulists Creator and Administrator
www.edulists.com.au
kevork at edulists.com.au

----- Original Message ----- 
From: "Neil Wallace" <neil at norwood.vic.edu.au>
To: "'Year 12 Software Development Teachers' Mailing List'" 
<sofdev at edulists.com.au>
Sent: Friday, March 28, 2008 2:24 PM
Subject: RE: [Year 12 SofDev] Network Diagrams - Physical or Logical

> You must also be marking SAC 1 now huh??? My comments below refer to the
> network diagram as a physical diagram. I use the DFD's and Data 
> Dictionaries
> for logical representations in this SAC.
>
> I get similar things Kevin, but I don't have a problem with the serial
> representation. In many practical instances that kids are familiar with
> firewall features are built into the switch and router. A home ADSL router
> that provides firewall, VoIP, wireless and switching (OK maybe hub) 
> services
> is an example.
>
> I usually walk the kids through what they may have at home, then tour the
> server room and switch cabinets when doing the network structure side of
> things.
>
> So, please all shoot me down if I am out of line here, but as long as the
> modem or router, firewall and switch are all in place in the network 
> diagram
> (in that order from external to internal) I feel OK with that.
>
> And we haven't got to talking about DeMilitarised Zones for safety in
> isolation of onsite servers yet either. . . .
>
> Enjoy your break.
>
> Neil Wallace
> Norwood Secondary College
>
> -----Original Message-----
> From: sofdev-bounces at edulists.com.au 
> [mailto:sofdev-bounces at edulists.com.au]
> On Behalf Of Kevin Feely
> Sent: Friday, 28 March 2008 1:14 PM
> To: sofdev at edulists.com.au
> Subject: [Year 12 SofDev] Network Diagrams - Physical or Logical
>
> Hi All
> Just to clarify one part of these things that i get a number of students
> representing firewalls inaccurately.
> I find some students like to connect them all up in series (see attached
> picture), so that from the switch they go to a firewall, then to a router
> then to the phone lines to the internet.
> Or even worse the go from the switch to a firewall and then to the 
> internet
> with no mention of a router or modem.
> I have always put, or seen installed, firewalls (hardware, naturally)
> connected  to the network switch (doesn't matter which one) and thats it.
> There is no "throughput". ie as you represent a server ,as basically thats
> what they are.
> The router (or modem if you want to go back a few years) is the throughput
> device, on one side the phone line (PSTN, ADSL, CABLE, ETC) and on the 
> other
> the network connection to switch via ethernet, to switch from pc via usb
> from router, or to switch from pc via serial from modem.
> Is this a problem to your students or is it just me?
>
> regards
> kevin
>
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