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New Member

One or two networks??

Due to a recent merger I have been tasked with looking at consolidating two networks. Before the merger we have two discrete networks (both 22 bit mask) connected via a Cisco 2651XM router. Our WAN connection is shared via this router apart from that the two networks are seperate. We now have 500 people in one network and 450 people on the other network needing to share data/resources.

The 500 person network comprises of 4912G backbone switch with 2948 and 2980 switches. Two data centres connected via 2 x 1Gbs tunnel. Connects into 2651 via cat5+ @ 100Mb/s full duplex.

The 450 person network comprises of a mixed switch/hub environment with one data centre, connecting 3 'offices' via fibre. This network connects into 2651 via fibre 100Mb/s full-duplex. The fibre run is approximately 250m .

What would be the best network layout for both networks to be able to access each other and users to be free to roam. Do I swap the 2651 connection to a layer 3 switch and use fast uplinks or keep the 2651 as the network intersection. Both networks are IP, running Windows 2000/NT and IBM AS400.

Do I go fully switched one network or keep the two seperate networks?

We have an 8 core fibre between the two offices of which 2 core is currently used to connect to the router.

Any help/advise/pointers appreciated.


New Member

Re: One or two networks??

I would certainly want 1000 users on more than two broadcast domains. 3 data centres as well... The 2651 may do it but im sure you need L3 switching here.

Do you have a budget ? your 2900's and cat5K are end of sale.

New Member

Re: One or two networks??


There has been no talk of a specific budget but I did mention it would cost money - it needs to be done so I guess I would suggest two options - the preferred solution (most expensive!) and the bare minimum solution.

My current thinking is buying a 5500 (or 6500) layer 3 switch and put this in-front of the two networks with the router hanging off for WAN traffic/access. The layer 3 switch would be used to route between the two networks?

Any thoughts?



New Member

Re: One or two networks??

What about a 450x with a layer 3 supervisor engine.

New Member

Re: One or two networks??

I was just looking at that via the Cisco products .. a 4506 might do the job but will it cope with 1000 users?

New Member

Re: One or two networks??

Hello Gary,

The way we do things here is we have a separate vlan for the datacenters and use layer 3 switches (cat6506) for cores. We have layer 2 (cat6506/9) for datacenter and 4006s for IDFs (user switches)....If you have any NMS tools that can determine bandwidth or RMON tools to determine traffic flows might help you out further.

I would definitely try to determine what your bandwidth outbound and across your WAN would be before making your final decision. You would hate to have the company buy some gear and still have performance below expectations.

Also we have found that creating separate networks not only reduces the broadcast domains but allows for increased security (ACLs) when needed (broadcast storms, virus, controlling server access).

Good Luck,


New Member

Re: One or two networks??


Thanks for that. I configured MRTG to do some traffic stats on the interfaces - doesn't give protocols but will give a feel for the traffic between networks and over the WAN.

Once I have a couple of weeks of stats, I'll be in a better position to make my mind up.



New Member

Re: One or two networks??


This is a recommendation on the cheap side, I seem to always put together three options, one cheap, one moderate cost and one cadilac(expensive). It usually turns out that the cheap solution is what non-network people want, unless you have hard data that spending the money will help the business side explicitly, save cost, improve efficiency in real dollars etc...

Since your 2651XM are capable of doing 802.1Q trunking, I would start to break up the vlan on each side of your networks. Reducing the broadcast domain should help with local traffic levels on your current switches.

It gives you the ability to create a vlan that would be unique to your data centers on each side, thereby isolating traffic for network management, backup , server farms etc...

You might find that spending money on replacing the hubs with switches at one of your sites is the biggest bang for the buck/euro.

I would get the most out of what you have, with out spending too much time or money and then analyse your bottle necks. You can pretty much predict where the bottle necks will be, but if management rearranges the resources, the bottle necks can move. And if they move to a spot where you have not spent money, you might need to come back to managment requesting more funds for upgrades.

An additional thought, management may move most equipment to one data center and reduce cost of both staff and hardware. In that case, one site becomes a satalite office with only one data center. I see it happen often with mergers and acquisitions.


PS with the 2650's you may be near the top end of their recommended use with sites of your size, but when you analyze your actual traffic patterns, you may find they are capable of handling your current data with no issues.