terryboob,
The exercise is quite a big one and requires a bit of math.
Here's what I would have done (if anyone has an alternative method, feel free to post it).
Site No1 has 4 departments with 150,100, 92 and 58 users respectively.
We'll assign one subnet for each department. The subnet's size will depend on the number of users each department has.
150 users requires at least a /24 (255 IPs) subnet mask, or 255.255.255.0
100 users require a /25 (128 IPs) subnet mask, or 255.255.255.128
92 users require a /25 (128 IPs) subnet mask, or 255.255.255.128
58 users require a /26 (64 IPs) subnet mask, or 255.255.255.192
So, putting things into place, we can start building our map using the 172.16.0.0 network according to the above:
172.16.0.0 /24 (150 user department) [ ip range 172.16.0.1 - 172.16.0.254]
172.16.1.0/25 (100 user department) [ ip range 172.16.1.1 - 172.16.1.126]
172.16.1.128/25 (92 user department) [ ip range 172.16.1.129 - 172.16.1.254]
172.16.2.0/26 (58 user department) [ ip range 172.16.2.1 - 172.16.2.62]
Lastly, I've figured that if your using the three layer hierarchical model, that means you need access, distribution and core layer switches:
400 users / 48 (assuming 48 port switches) = around 9 access layer switches
I'd place two 24 port distribution switches and one core layer switch, plus the 2600 router.
In total, that's 9 + 2 +1 +1 = 13 IP's.
A /28 prefix or 255.255.255.240 subnet mask gives us 14 useable ip addresses. Here's the final network:
172.16.2.64/28 (13 ip's for our switches & router) [ ip range 172.16.2.65 - 172.16.2.78]
So, if my math calculations are correct, here's the total breakdown for your first site:
172.16.0.0 /24
172.16.1.0/25
172.16.1.128/25
172.16.2.0/26
172.16.2.64/28
You'll need to perform the same breakdown for your 2nd site, and then add your WAN link to that as well, which is quite easy as WAN links commonly use /30 (2 usable ip addresses) for point to point connections.
I hope that helps you towards your answer.
Cheers,
