Cisco student needs help please???

Unanswered Question
Jan 15th, 2009

Hi guys,

Iam in year one ccna and for my first assignment I have to design a network with:

3 departments each in there own subnet salesX50 hosts, WarehouseX30 hosts and AdminX20 hosts.

There is a lot of other stuff i have to do for the assignment but I'm really struggling to design it.

Its sort of up to me, what demands each department have on the network so Ive put that there are two shared databases and file transfers from the sales department to the warehouse (trying to keep it simple, but not too simple)

At the moment (with packet tracer) I have a generic cisco router with 4 fast ethernet ports where three of which are connected to cisco switches for the stated departments/subnets. (every connection is 100mbps)

I need help with:

Should I stick with cat 5 100mbps utp or because of the 50 hosts in the sales department should I go for cat 6 gigabit or fibre ( just for the connection from the switches to the router to prevent bottlenecks)???

And what are my options with cisco routers, I'm not familiar with them so if you can give me any models I can go research

Please help me any sort of input is really needed, cheers.

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Overall Rating: 5 (4 ratings)
DELL ACORD Thu, 01/15/2009 - 06:49

What kind of traffic are you going to support?

Are there any servers involved?

Are you going to implement any kind of QoS?

Most Cisco routers are robust enough to support enough routing on a stick with a single interface.

danabersoch Thu, 01/15/2009 - 07:56

I will have one server hosting two databases (customer and stock databases) with all departments having access to them. there wont be anything complex or high demand like voip or video nor will I be implementing QoS.

Also the warehouse dep will be downloading files from the sales for the following day's orders, without to much affect on the rest of the network, my worry would be bottlenecks at the sales gateway??

danabersoch Thu, 01/15/2009 - 09:42

If you could tell me if a 100mbps connection will be good enough or if I would need somthing faster between the routers and the switches ????

and if you happen to know of any models that would fit the bill that would be brilliant???

lcleverley Sat, 01/17/2009 - 11:53

Your "design" decision is not what switches or routers to use but how you would break down your addressing structure. This is what they're trying to elicit from you...

50 Hosts Sales

30 Hosts Warehouse

20 Hosts Admin

danabersoch Sat, 01/17/2009 - 16:59

Ive already done all the addressing which was pretty straight forward, Ive handed in a draft submission using a generic router and not much of actuall models (because I don't know what to use and nothing stands out) and my tutor told me to do more work on real devices.

Joseph W. Doherty Sat, 01/17/2009 - 16:56

For 100 hosts, you could run your whole network as L2. Nothing wrong with using subnets, but if you do, for LAN performance, would recommend a L3 switch for LAN routing vs. a typical router. Selection of L2 or L3 switches would depend on feature needs and placement of devices. If you can place all you network devices together, you might consider stackable switches, either 3750 series (L3) or the new 2975 (L2).

For a non-stackable L3 switch, you'll want to look at the 3560 series. Cisco offers various non-stackable L2 switches. (If you have seperate L2 and L3 switches, you might want to select both that support Etherchannels to allow for interdevice bandwidth growth.

As for connection speeds, you would likely want gig between network devices (hopefully copper to keep costs down) and gig to server hosts. User hosts are normally okay at 100 Mbps, but if you can afford it, would recommend gig copper ports on your network devices and gig cabling plant. Recommend, if possible, Cat6, or at least Cat5E, so you have the option for gig.

danabersoch Sun, 01/18/2009 - 04:16

Thank you for your reply

My big problem is that, even though using a layer 3 switch is the best option (this is the advice i got from other forums) we havn't covered them yet (this is my first assignment and I started this course in sept) nor have we done routing on a stick or Vlans (sorry for the lack of knowledge).

So, please correct me if Im wrong, the only way I can keep the departments in seperate subnets and in there own broadcast domains is to have my central device as a router, and this is where Im struggling!! thanks again - good advice!

Joseph W. Doherty Sun, 01/18/2009 - 05:00

Correct, to have your departments in separate subnets (and broadcast domains) does require routing (this also assumes you do want to be able to communicate between them). The device, itself, doesn't have to be a "router". L3 or multilayer switches can route, some dedicated security devices can route, many host systems can route. The placement of the device doesn't have to be "central" plus you could have more than one (routing device). (Central L3 deployment likely would be best for your network, if you're going to support L3. Again, for a network of your size, L2 would likely be fine from a performance viewpoint. Most larger network subnets contain as many or more hosts as yours. However, the other main advantage of using routing in a network of your size might be to implement security between the subnets since you seem to be planning on having logical subnet groups.)

The reason a L3 switch usually would be considered the best option is because they're "inexpensive" for the performance and features they offer. Most of the small Cisco "routers" have much less performance but are much richer in features, which often makes them a better choice for low bandwidth (several Mbps vs. 100s to 1,000s of Mbps) WAN connections.

Usage of VLANs or routing on a stick would depend much both on your selection of devices and physical topology. You might not need to implement VLANs and/or routing on a stick, or you might need one or both. If departments wouldn't need to share the same physical device, you may not need VLANs. If the L3 device has sufficient physical ports to interconnect any downstream L2 switches, you don't need to route on a stick. (What's also often confusing when seen for the first time in mixing L2 and L3 on the same device, as often done with a multilayer switch.)

danabersoch Sun, 01/18/2009 - 11:45

Cheers again,

Ive been looking at the basics of Vlans and how it works, by assigning the Vlan number to the appropriate ports.

I'm not going to have more than one department to switches.

Im now thinking:

Have switches in each area, Gigabit uplinks to the central device,

the central device being a layer 2 switch OR a L3 switch,,,,,

My new problems for these solutions:

Mainly Packet tracer -

I have got the three area switches with the uplink to the central L2 switch and then to a router (reason - because I think I just read somwhere that connecting the switch to a router is how we get connection between the different Vlans)

Ive put put the Vlans in the Vlan database then assigned the port the appropriate Vlan number and I can't ping one vlan host from a different vlan - need help with - trunk or access and how to configure the connection to the router.

I can imagine the whole point of a multilayer switch is to do all this in one device (Hope so) so I configure the Vlan database in the central multilayer switch (e.g? Vlan name - Sales, Vlan number - 10 etc) and what else do I have to do (remebering that I have to keep them in seperate broadcast domains but still have connectivity). Thanks a lot for your replies and thanks in advance!!

Joseph W. Doherty Sun, 01/18/2009 - 12:42

If your area switches only host one subnet, you don't need to define VLANs on them. (Managed switches will likely have a native default VLAN for all ports.)

A central router, with ports for each area switch, you just define the subnet on the router's link to the switch.

A central L2 switch will need to define VLANs for the downlink ports. To get traffic between VLANs, you need to connect a router. If the router has mutiple ports, it can connect an interface to each VLANs. (If you can do this, not much point in having a central L2 switch unless you extend VLANs across multiple switches.) Otherwise, you define a VLAN trunk port and connect that to the router (which then sees the VLANs as separate logical interfaces).

A central L3 switch, supporting different area switches, will either need to place downlink ports into different VLANs, or you might define the ports like you would on a router. The L3 switch then either routes between the "routed ports" or between VLANs (a separate router wouldn't be needed).

danabersoch Sun, 01/18/2009 - 15:05

Cheers I will have another play tomorrow and let you know how I get on, thanks a lot for the help

danabersoch Mon, 01/19/2009 - 09:57

Ive got a layer 2 central switch with downlinks to area switches.

On the L2 central I have 3 Vlan names and numbers and then assigned the Vlan number to the correct interfaces.

I then have configured an interace on the central switch as a trunk to a router.

I still can't ping from one Vlan/subnet to another? Is this down to the gateway address and what address do I give the interface on the router?

The network addresses are:

Sales /26

Warehouse /26

Admin /26

danabersoch Mon, 01/19/2009 - 10:33

Ive just done a bit more research on Vlans and routing on a stick.

I believe to have found what I think is the answer to the previous Q, do I have to configure addresses and subnets to sub interfaces on the router as logical gateway addresses for each subnet?

Jon Marshall Mon, 01/19/2009 - 10:49


Yes you do if you do not have a L3 capable switch. So your config on the router would look something like -

Sales /26 - vlan 10

Warehouse /26 - vlan 11

Admin /26 - vlan 12

the interface on the router is fa0/1

int fa0/1

no ip address

int fa0/1.10

encapsulation dotq1 10

ip address

int fa0/1.11

encapsulation dotq1 11

ip address

int fa0/1.12

encapsulation dot1q 12

ip address

a sales client will have it's default-gateway set to

a warehouse client

an admin client

and as you correctly say in your previous post the port on the switch that int fa0/1 connects into must be configured as an 802.1q trunk.


danabersoch Tue, 01/20/2009 - 06:41

Cheers Jon

I found the commands on how to config the subinterfaces and Im back on track with this asignment.

I appreciate the advice guys and will be using a lot of it.

I will post progress or failures if or when it occurs!!

danabersoch Fri, 01/30/2009 - 03:06

I have managed to find all the comands and I have come up with a design and all the hosts can ping each other (packet tracer). I have attached my topology diagram for your guys approval, please comment, cheers.

Joseph W. Doherty Fri, 01/30/2009 - 04:45

What you show should work. However, assuming the 2821 had 3 interfaces, you could use it where you have the central switch and save the cost of one switch. Or, if you replaced the central switch with a L3 switch, you likely wouldn't need the separate router. (This would likely provide better LAN routing performance.) Or, if there was also a WAN to deal with, you might retain the 2821 (or smaller router, e.g. 2801, 1841, etc.) to connect to it along with replacing the central L2 switch with a L3 switch. (In the latter, you could either route between the router and the L3 switch, or have both logically on the same subnets. [The last, I'm sure, is confusing but remember L3 switches tend to also be L2 switches.])

If you're wondering which is the "best" design, that depends on the requirments you're attempting to meet.


Another variation would be to use a L3 switch in the place where you're using the 2821. This would seem stange until you consider that if your uplinks from the switches are gig, the small 8 port 3560 offers 100 Mbps ports but only one gig port. Using it in a router on the stick configuration, like the 2821, might be less expensive than providing a gig port L3 switch to replace the central L2 switch yet offer much faster LAN routing than a 2821 (or any 2800 or 3800 ISR). Real designs also need to account for actual device capabilities.

danabersoch Fri, 01/30/2009 - 05:31

I totally get what you mean with layer three switches and I also get the jist of what they do, BUT I can't use them as Im early on in the course.

Youve got me a bit worried on the fact I wouldnt need that central switch but here is what Ive tried to express in the assignment:

(oh yeah the 2821 has only 2 interfaces abut loads of expansion slots)

The reason for the 2821 over cheaper routers - cos of the gig interfaces for the trunk.

The reason for vlan and routing on a stick - with a router being the central device it would be expensive to add more departments or even a server but as it is there would be no cost (for devices) for new vlans or subnets!

The cost of the central switch is equal to one expansion module for the router

Please tell me if this is enough of a reason to go with this design

Joseph W. Doherty Fri, 01/30/2009 - 05:54

That's good thinking about both the cost of add-on modules for the 2821 vs. a basic switch and later expansion!

However, on your possible later network expansion point, either router ports or another switch could be obtained later. Plus you're assuming new subnets/VLAN would require a new interface. Assuming you needed to split/grow VLAN 10, without adding new equipment, you could trunk up just the VLANs from that physical switch. In otherwords, easy growth without even the need to buy additional interfaces or switches.

Yes, the 2821 has gig interfaces, but the 2821 doesn't ofter the performance to substain gig bandwidth. In fact, it can not really substain 100 Mbps interfaces. It could subtain the perfomance of 2 or 3 10 Mbps interfaces.

To use a Cisco router that can actually support multiple gig bandwidth, you might need the new ASR series. A single gig trunk might be supported by a 7200 with NPE-G2.

If you can't use a L3 switch in your design (yet) that's fine. You're correct, that a central switch by saving interfaces on the router (assuming trunking) might be less expensive than the additional interfaces, but again, you're also sharing that trunked interface's bandwidth. (Always trade-offs.)

danabersoch Mon, 03/09/2009 - 10:29

I got a distinction on this assignment, woooohooo,

thanks for all your imput, helped me out loads!!!


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