Connecting Switches together?

[tylerr96]

We are trying to get a network set up for a school.

We know that there will be one main datacenter and 2 secondary ones, laid out similar to this:

MAINDATACENTER
I
I
I
⌐----------------------¬
DC2 DC3

How would we connect the datacenters to each other? The datacenters would just essentially be switches that will be serving clients, but I don't understand how just 1 CAT5 cable would be sufficient to connect the two to the main. Is there a special type of cable?

-Tyler

 

[lyleb]

Switches are normally connected with CAT 5 cables.

 

[tylerr96]

Switches are normally connected with CAT 5 cables.

Yes, but if I have 100 clients off of a secondary datacenter working on the internet at one time, I don't get how all those clients would be able to get back to the main datacenter and the router by just one cat5 cable.

-Tyler

 

[jinkguns]

Hi Tyler,

I'm a Core Network Engineer for a service provider and I'm also currently going through the Cisco Certified Network Professional tests now. So I'd like to think I know a few things about switches.

It sounds like you lack a basic understanding of network topology, but if I am wrong, I sincerely apologize for that assumption.

Cat5/6 is the most common medium in any networking environment. For example, my company only uses fiber optic cable on 10 Gig Ethernet connections, everything else is Cat6, although we were using Cat5 until a few years ago and there is a lot of Cat5 still in production.

Cat6 is a standard that was created for gigbit ethernet. The only difference between Cat6 and Cat5 is the number of twists per a specific distance in the twisted pairs. If your ports are 100 megabit ethernet you should be fine using Cat5.

Now as for not understanding how your 100 clients can work on the internet at one time through just one Cat5 cable, that's kind of the whole point of networking. Aggregating connections and simplifying architecture. Your clients send packets which are switched and routed to the destination. That's why you don't need to have one cable going to every possible destination, and are instead concentrated at switches and hubs.

If your connection to the internet is less then 100mb (which I'm absolutely sure it is, even our fiber customers don't contract pass 50mb/s), then you should be fine. This also assumes that your intra-network traffic (client to client) won't need to exceed 100mb/s.

I'm more concerned about the size of your broadcast domains. In what you describe you are running two data centers on switches, and then probably connecting to a router for your outbound traffic. This would mean that all of your clients are on the same virtual "Wire" meaning that all packets they transmit are not separated, meaning that a special type of packet, broadcast packets, are transmitted to all end points when one of the clients wants to match a MAC address to a IP address. This is going to create a large amount of overhead and congestion.

Any data center environment should really be running on VLANs (VLANs create virtual networks on top of your physical topology) both for decreasing the size of broadcast domains as well as for security reasons. You don't want a client PC to be able to intercept packets destined for a financial accounting or records server, which will be really easy to do if they are on a "dumb" switched network without VLANs.

Finally, while the one cat5 cable will be fine depending on what throughput you require, I would recommend running a second one for redundancy, but ONLY if your switches support spanning tree protocol, which prevents a packet from looping across a redundant connection. If you connect a redundant cable between to switches, they will replicate the packet over and over again, and will crash the entire network in seconds.

Also, unless the ports on the switches are crossover-X auto sensing, the Cat5 cable will need to be a crossover cable. Not a straight through as most pre-packaged Cat5 cables are. This is because your between to like (layer 2) devices. The only difference being the pin order on each end of the cable.

In closing, for this type of project, I really recommend you contract the work to a experienced network engineer.

 

[garnr1]

Hi jinkguns,

I'm just wondering is there any limit of how many computers can be connected to switch, then from the switch via 1 x single Cat6 cable to a modem? If you want fast internet speeds for multiple computers connected to the switch what needs to be done from a networking perspective? Is it simply a matter off adding another Cat6 cable from the switch to the modem to increase speed available at the switch?

Any help would be hugely appreciated!

Kind Regards,

Rhys

 

[garnr1]

Hi Tyler,

I'm a Core Network Engineer for a service provider and I'm also currently going through the Cisco Certified Network Professional tests now. So I'd like to think I know a few things about switches.

It sounds like you lack a basic understanding of network topology, but if I am wrong, I sincerely apologize for that assumption.

Cat5/6 is the most common medium in any networking environment. For example, my company only uses fiber optic cable on 10 Gig Ethernet connections, everything else is Cat6, although we were using Cat5 until a few years ago and there is a lot of Cat5 still in production.

Cat6 is a standard that was created for gigbit ethernet. The only difference between Cat6 and Cat5 is the number of twists per a specific distance in the twisted pairs. If your ports are 100 megabit ethernet you should be fine using Cat5.

Now as for not understanding how your 100 clients can work on the internet at one time through just one Cat5 cable, that's kind of the whole point of networking. Aggregating connections and simplifying architecture. Your clients send packets which are switched and routed to the destination. That's why you don't need to have one cable going to every possible destination, and are instead concentrated at switches and hubs.

If your connection to the internet is less then 100mb (which I'm absolutely sure it is, even our fiber customers don't contract pass 50mb/s), then you should be fine. This also assumes that your intra-network traffic (client to client) won't need to exceed 100mb/s.

I'm more concerned about the size of your broadcast domains. In what you describe you are running two data centers on switches, and then probably connecting to a router for your outbound traffic. This would mean that all of your clients are on the same virtual "Wire" meaning that all packets they transmit are not separated, meaning that a special type of packet, broadcast packets, are transmitted to all end points when one of the clients wants to match a MAC address to a IP address. This is going to create a large amount of overhead and congestion.

Any data center environment should really be running on VLANs (VLANs create virtual networks on top of your physical topology) both for decreasing the size of broadcast domains as well as for security reasons. You don't want a client PC to be able to intercept packets destined for a financial accounting or records server, which will be really easy to do if they are on a "dumb" switched network without VLANs.

Finally, while the one cat5 cable will be fine depending on what throughput you require, I would recommend running a second one for redundancy, but ONLY if your switches support spanning tree protocol, which prevents a packet from looping across a redundant connection. If you connect a redundant cable between to switches, they will replicate the packet over and over again, and will crash the entire network in seconds.

Also, unless the ports on the switches are crossover-X auto sensing, the Cat5 cable will need to be a crossover cable. Not a straight through as most pre-packaged Cat5 cables are. This is because your between to like (layer 2) devices. The only difference being the pin order on each end of the cable.

In closing, for this type of project, I really recommend you contract the work to a experienced network engineer.

 

[taitai]

Hi, I have seen a situation where in the patch panel cabinet there are two patch panels one for cat5 and the other for cat 6 points, so do all of them go to the same switch or you will have to have 2 switches which will connect to the router?

Thank you,

 

[ngrego]

Using cat5e or cat6 cables on trunk ports will only make a difference if your switch has corresponding trunk ports. A cat6 cable plugged onto a cat5 or cat5e port will only give you the maximum speed of the port itself. Networks with a large number of connected end users will experience congestion or bottlenecks if the trunk (backbone) can't transport the data fast enough. If optic fiber is not an option you could bridge two or more ports to maximize trunk bandwidth.
You can connect two switches to your router, but how well it will work for you depends on the router itself. Keep in mind that with such a setup the router will have to do the switching work and also the routing work. If its a high end router it will possibly do, but a home or small office router may not be able to cope.