You have been recently promoted to the position of a Network Administrator of a

Question

You have been recently promoted to the position of a Network Administrator of a network which has 15 Windows Servers 2012 EE & 200 Windows 7 workstations.   Your company will give a tour to the students in a local college for students who are studying computer networking. Your supervisor asks you to prepare a presentation on DHCP. She wants you to explain to the students why do you need to implement DHCP and what are the new features in Windows Server 2012. You also are to explain the four steps in DHCP: DORA, what each letter stand for and what happens in each step. Some of the additional insights that you have been asked to include are: Why do you need DHCP Relay agent in some networks? How will DHCP provide support for laptop users while they connect remotely? If an initial design of DHCP was running out of DHCP addresses, what steps will you take to remedy the situation? What are the differences between sub-netting and super-netting? Will you recommend the students to run the DHCP server from a Domain Controller? Please justify your answer.

Explanation / Answer

1) Need for DHCP:

Any protocol is essentially a software that runs on a specific computer and manages all the "talking" with other computers in the "protocol language". In order for the same software to run on different machines there is a need to initialize the protocol with parameters specific to that machine and to the local network before starting proper operation. Initialization can be done during booting (if the protocol is embedded in the operating system) or it can be triggered by a specific application (if the protocol is embedded into the application).

Take for example the TCP/IP protocol stack: first of all, the IP protocol needs to know the IP address of the computer. Moreover, it needs to know the network subnet-mask, IP-addresses of the default router, the printer, the DNS and perhaps some other servers etc.

Those parameters can be configured manually and locally for each and every computer. Using a mechanism like that introduces some problems:

All those reasons lead to the need in an automated mechanism for TCP/IP protocols' configuration and DHCP is the currently most advanced mechanism for doing so.

2) Features in windows server 2012

1. Multiserver support in Server Manager: it embraces the cloud concept ana hence the new Server Manager can manage multiple servers, and it provides an all-new dashboard that lets you drill down into local and remote servers.
2. Server Core is the default: Windows Server 8 uses the minimalist Server Core as the default server environment, marking a huge change away from dependence on the GUI for management.
3. Ubiquitous PowerShell management: Going hand-in-hand with the move away from the GUI is the move to PowerShell as the primary management tool.
4. Built-in NIC teaming: capability to provide NIC teaming natively in the OS. The new built-in Windows Server 8 NIC teaming works across heterogeneous vendor NICs and can provide support for load balancing as well as failover over NICs from different vendors.
5. SMB 2.2: The Windows Server Message Block (SMB) file sharing protocol has also been significantly enhanced
6. Data deduplication: provides built-in data deduplication, a feature typically found in high-end SANs
7. Expanded cluster scalability: Windows Failover Clustering has also taken a big jump in scalability. can support up to 63 nodes and up to 4,000 virtual machines (VMs) per cluster, effectively leap-frogging VMware's VM cluster support.
8. Multiple concurrent Live Migrations
9. Storage Live Migration
10. Live Migration without shared storage

3) DHCP:DORA
STEP 1. D- Discover: When a machine boots up in lan and it doesnt have an IP address configured , it would send a DHCP discover broadcast to the network. It will have a destination IP of 25.255.255.255. It also includes it mac address encapsculated in the package. The layer 2 destination would be ff:ff:ff:ff:ff:ff, ie to add devices in the network. The switch port which received the package would then forward it to all other ports in the switch except on the one from which the request is received.

STEP 2. O- Offer: If there is a dhcp server listening on the network, it will respond back to the DHCPrequest package with an offer package. The offer package is again a broadcast to 255.255.255.255, but it will have the destination mac address set to the DHCP client's mac address. The source mac address will be that of the DHCP server. The offer package will contain the IP address,DNS,gateway etc as well

STEP 3. R- Request: The dhcp client will get similar offers from all dhcp servers in the network and it will typically accept the first one that it receives.It will then send a request to the DHCP for the offered IP address.

STEP 4. A-Acknowledge: When DHCP received the DHCp Request from the client for the IP address, it will send back a DHCP aknowledge, thereby allocating that IP address to the client


4) DHCP Relay Agents:
A relay agent is a small program that relays DHCP/BOOTP messages between clients and servers on different subnets. DHCP/BOOTP relay agents are part of the DHCP and BOOTP standards and function according to the Request for Comments (RFCs), standard documents that describe protocol design and related behavior.

5) DHCP support for laptop users:
Our laptops can be connected to the local router or internet. The DHCP assigns the IP addresses to them accordingly using DORA process. Below are the steps that a laptop user or service provider must follow.
1. Registering for DHCP
2. Obtaining your Ethernet or Wireless Hardware Address
3. Configuring your Laptop to use DHCP

6) If running out of IP Addresses for DHCP:
If initial design of DHCP runs out of IP addresses, we could change the subnet mask (eg. if subnet mask is 255.255.255.0 then we could change it to 255.255.254.0 or so according to our need to increase number of IP addresses)

7)Difference between subnetting and supernetting:
Process of dividing an IP network in to sub divisions is called subnetting. Subnetting divides an IP address in to two parts as the network (or routing prefix) and the rest field (which is used to identify a specific host).For example, in IPv4, 192.60.128.0/22 indicates that 22 bits are allocated for the network prefix and the remaining 10 bits are reserved for the host address.
Supernetting is the process of combining several IP networks with a common network prefix. Supernetting was introduced as a solution to the problem of increasing size in routing tables. Supernetting also simplifies the routing process. For example, the subnetworks 192.60.2.0/24 and 192.60.3.0/24 can be combined in to the supernetwork denoted by 192.60.2.0/23. In the supernet, the first 23 bits are the network part of the address and the other 9 bits are used as the host identifier.

8) Running DHCP server from domain controller:
We should not recommend students to run DHCP servers from domain controllers for security and performance reasons.
DHCP server service runs under "Local System Account" - one of most powerful account on Windows machine (even more than Admin). Someone can use DHCP server service to bring down complete box. DHCP server service also used to register records in DNS, which again allow records to register with Admin accounts (DC), again not recommended from security point of view.
It can hurt performance if we use very less DHCP lease period (Less then 8 hours).

Hence students should not be recommended to run DHCP servers from domain controllers.

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