Routers in racks and data centers

[trauts14]

Probably a tough question to answer, but when I see a rack in a data center with multiple routers, does each rack have one router, or does one router go to a switch which in turn helps multiple racks? anybody have a brief explaination as to how many servers or racks a router can work with?

 

[jdabbs]

Probably a tough question to answer, but when I see a rack in a data center with multiple routers, does each rack have one router, or does one router go to a switch which in turn helps multiple racks?

Short answer: Depends.
Long answer: One router can support multiple racks, but there are other concerns that determine the router/rack ratio.

Traditional design: http://en.wikipedia.org/wiki/Hierarchical_internetworking_model
The purpose of the data center dictates the network infrastructure. A DC for an ISP would be very different from a DC for a hosting provider. My company has a lot of database servers, so our racks get by with a mix of megabit and gigabit switches. The traffic from these switches is aggregated at our core switches, which in turn forward the traffic to our firewalls (which assume routing duties on our internal networks). The only time traffic touches an actual router is at the ISP handoff.

anybody have a brief explaination as to how many servers or racks a router can work with?

You are looking at the wrong metric. You should be evaluating by throughput, packets per second, and if applicable, number of interfaces (if you need to terminate four T1s, and your router can only support one, you'll be looking at a new router).

 

[trauts14]

Thank you for the assistance. I wasn't sure how exaxtly that worked on a large scale. For example my small Cisco routerr goes to 2 switches in my house (I need a second switch for POE purposes), and then the router handles traffic from my gaming consoles, IP cams, cctv system etc..
This is simple for me to understand, but when I see pics of a Google DC for example I always wonder where the hell are the routers (on top portion of a rack?) and lord knows there must be a ton of routers. It is tough for a nonprofessional to grasp this architecture.

 

[jdabbs]

If servers compose most of the rack, top of rack is usually a switch.

The router:switch ratio for my facility is 1:9, and would be even lower if we weren't concerned about device-level redundancy.

 

[Nerre]

and lord knows there must be a ton of routers.

Why must there be a ton of routers?

A router is only needed between two separate IP networks, a Class A network can have 16 million IP addresses, a Class B network over 60 000.

In the old days, using hubs, you had to segment your networks into subnets, but with modern switches the "routing" takes places on the ethernet level so subnetting isn't as important any longer.


Edit: And one more thing: A router is merely a computer with two or more network interfaces, so any one of those rack mounted computers having more than one NIC can be a "router".

 

[coxhaus]

Routers are usually at WAN borders. Routers are not fast enough for switched networks. Local networks are usually switched networks. Local networks may be in different networks but they are switched networks when they are local in a corporate rack.