Planning Domain Local and Global Accounts
The exact DNS server requirements of your organization will be based on the number of users, the amount of queries, and the amount of traffic that you see both externally and internally within your organization. As a general rule of thumb, a resource record (RR) will take up approximately 100 bytes of RAM. Thus, based on the number of users and records associ- ated with your organization, you can use this accordingly. If you are in an organization with 10,000 users, you will require 1,000,000 bytes of RAM just for resource records that can be accessed thousands of 70-680 times per second based on the amount of traffic ?owing back and forth between your network.
In general, the basic rule of DNS server requirements is that the DNS server must be highly available and accessible to all users in your organization. In an ideal world, this would mean you could place a DNS server in every subnet, and each server would have an incredibly light load. However, for an organization with, say, 500 subnets, this is not very realistic. This problem literally doubles when you consider that the first rule of thumb with network design is that you plan for the worst and then expect the worst. So, this means you will naturally need a backup DNS server for each server you are using. And, in your ideal ?500 subnet?design, you?d be using a paltry 1,000 servers purely for DNS?probably not a good idea.
Normally, DNS servers are accessed across a WAN link or across routers that are con- nected in such a way that allow for easy throughput. When placing your DNS servers in design questions on the certification exam, consider the speed or your WAN CCNA Exam links as well as the speed of the given switches in the topology, and place your DNS server in the most logi- cal area of your network in terms of accessibility.
It’s pretty unlikely that you will be asked about this on your exam, but a good tip to keep in mind for the real world is that Microsoft estimates that WINS servers can support approximately 4,500 queries per minute and register about 1,500 names per minute.
In short, network access refers to any method an external or internal user will need to imple-ment in order to securely or insecurely access a resource from a remote or internal location across a WAN or LAN. More simply put, network access refers to any user trying to access the network from any given location at any given time. Within Windows Server 2008, there are a myriad of ways for this to occur, such as VPNs, dial-up connections, RADIUS servers, or other such remote technologies.
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