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IP addressing

by Leima123 / December 1, 2009 3:15 PM PST

Hi all, I recently started trying to understand how networks are setup, primarily because of a school project I have to make in which I have to simulate the creation of a network from scratch in an enterprise, I don?t need something very elaborate, just basics. I?ve read some useful posts on this forum and I thought I might as well ask something that I have not understand quite well yet. I?m supposed to include at least 200 PCs in the network I?ll simulate, so I?m thinking I should just use a single real ip address from an ISP on a router, then connect this router to five different switches, all of which will have 40 PC?s connected to them, I guess this way the real IP address would be setup on the router and then I would be able to setup virtual addresses to every computer that is connected to a switch. Now my questions are:
1. Is it ok to use a single real IP address for such a high number of computers? The router would only really be connected only to five switches and I?m guessing it should be a very fast connection, like 100mbps or something.
2. Is it ok to setup the network just like that? Or do I need some kind of server or those layer 3 switches I?ve been hearing about?
3. In case I used more than a single real Ip address, how would I connect them? Would they each need a router? And in that case, how would the routers communicate with each other?
Any help would be really appreciated Silly

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IP addressing simplified
by fazalrehman / December 1, 2009 7:01 PM PST
In reply to: IP addressing

I m not so much expert in networking but I have been working in this field for about
two years. I have been involved in network deployments as well as administration and I suggest
u the following points for your questions

basically the network ip addressing scheme is such a way that u use the ISP ip on WAN
interface of the router only. on Lan and pc,s u should use private IP addresses

now in the case of 200 computers u must use a server the server can be server 2003 or
2008. this is necessary to manage such a large number of systems at a single place.

when u use single IP on Wan interface and large number of private IP addresses then u have to\
enable nat overloaded on your router. some of the routers has by default enabled Nat. but
in some cases u have to configure it manually.

if u need any further help u can contact with me i will provide help to u to my best.

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New Question
by Leima123 / December 2, 2009 1:35 AM PST

Tnx for your reply, I understand what you're saying, except for the part about the server. What would the server be used for? Is it to provide services such as DNS and stuff? If so, how is this setup, do I connect the server to the main router aswell and give it an Ip address?

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use of server
by fazalrehman / December 3, 2009 12:38 AM PST
In reply to: New Question

in practical networks of large number of nodes server is must. usually it is recommended that for computers greater than 100 a central server must be used.
a sever is basically a computer which has windows server installed in it. it performs all of the central operations including dns,dhcp, identity and access solutions, file services, internet security service,
windows deployment services and a lot of other services. server operating system is quite user friendly and u can learn it easly by spending some time on it.

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enterprise routing
by bill091 / December 2, 2009 1:56 AM PST
In reply to: IP addressing

Depends on if you just want a true enterprise design or if you want something a small company can afford.

The enterprise design would be a

Internet facing router
l3 switch
l2 switch

The theory being you want to separate the function. The internet router generally is 2 routers running BGP to 2 ISP. The firewall and l3 switch are generally pairs to avoid failure of hardware.

Although 200 addresses is still below the point it is recommended you split the subnet. A enterprise design try to prevent one switch/user from messing up other users. In this case you could use the layer3 switch to have each layer2 switch have its own subnet and route rather than switch between the subnets.

In general you will have no issue with a sharing a single address assuming its your more normal traffic with no inbound connection from the internet. Traffic wise 100m is overkill for 200 users. I run offices with 2000 users behind 100m. The key to remember is that in a true business internet access does not include porn,filesharing,streaming media.

You most likely cannot get more than a tiny block of real IP. You generally have to prove a need. You only want machines that provide a service to a outside customer having a real internet address. Even then all kinds of tricks are used to share addresses between these machines.

When you get a block of real ip's you generally have to route them. With a small number you can just static route them. For large number or even with large numbers of private IP's you run a routing protocol between your routers or really L3 switches.

Part of the reason enterprise class equipment is expensive is it supports lots of options.

In the simple case you could use a consumer router with a built in 5 port switch and then hang the 5 48 port switches off it and use the router to do all the nat and DHCP. It will work but not good. You would have to verify things like maximum number of nat entries,mac table sizes etc etc. Still all it takes is a user to plug a crossover cable between 2 of your 48 port switches and everything goes down since most inexpensive equipment does not support spanning tree.

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by Leima123 / December 2, 2009 5:32 AM PST
In reply to: enterprise routing

Tnx alot, that explanation helped me quite a bit, there's just one more question I would like to ask you, in the enterprise setup you mention, in that case the layer 3 switch would be the one to handle dhcp right? while the router would be the one to handle nat addressing

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lyl3 switch
by bill091 / December 2, 2009 6:01 AM PST
In reply to: Tnx

Generally there is a server or other dedicated device to do DHCP but it can be the router if you like.

Depends on who make the equipment but NAT and DHCP can only be done with a router not a l3 switch.

This is the key difference between a L3 switch and a router. A L3 switch is designed to work fast generally at full port speed with no delay so any feature that cannot be done at speed is not included. This means most layer 3 switches cannot do NAT,DHCP,VPN, etc.

Other than this a router and a layer 3 switch are the same thing.

Now to get around this limitation on DHCP there is a feature called DHCP helper that tell the switch to send the DHCP request to a router or other device.

Where you do the nat depend on a number of things. If you have a single IP and a single ISP router then the router is the best location. If you have multiple ISP you run into the issue of the traffic going out one ISP and coming back in the other. Nat does not like that a lot. Many routers have special features to handle this but it is more common to let the firewall do the nat in these designs.

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by Leima123 / December 2, 2009 10:38 AM PST
In reply to: lyl3 switch

Thanks alot, your posts have really helped me

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