Dynamic Host Configuration Protocol - DHCP

DHCP (Dynamic Host Configuration Protocol) is a protocol that lets network administrators manage centrally and automate the assignment of IP (Internet Protocol) configurations on a computer network. When using the Internet's set of protocols (TCP/IP), in order for a computer system to communicate to another computer system it needs a unique IP address. Without DHCP, the IP address must be entered manually at each computer system. DHCP lets a network administrator supervise and distribute IP addresses from a central point. The purpose of DHCP is to provide the automatic (dynamic) allocation of IP client configurations for a specific time period (called a lease period) and to eliminate the work necessary to administer a large IP network.

Work Of DHCP:

When a client needs to start up TCP/IP operations, it broadcasts a request for address information. The DHCP server receives the request, assigns a new address for a specific time period (called a lease period) and sends it to the client together with the other required configuration information. This information is acknowledged by the client, and used to set up its configuration. The DHCP server will not reallocate the address during the lease period and will attempt to return the same address every time the client requests an address. The client may extend its lease with subsequent requests, and may send a message to the server before the lease expires telling it that it no longer needs the address so it can be released and assigned to another client on the network.

Firewall

A Hardware Firewall is a network device that is connected upstream from a server. The Firewall blocks unwanted traffic from a server before the traffic ever reaches the server. The main advantage to having a Hardware Firewall is that a server only has to handle 'good' traffic and no resources are wasted dealing with the 'bad' traffic.Configuring a Firewall is as simple as creating a set of rules to allow access to certain ip addresses and ports from specific internet addresses.

Adding a Firewall to a Server:

To add a Firewall to a server, click on the link under the Security->hardware firewall tab in the customer portal. This page will display a list of servers on the account and which servers are eligible to be protected by a Firewall, which ones are already protected by a Firewall, and which ones cannot be protected by a Firewall due to network configuration.

To add a Firewall to your server, assuming the server is eligible for a Firewall, click the 'add' link and instructions will be displayed on how to have Firewall protection added to the server. Once a Firewall has been added to a server, an 'edit' link will be available to configure the Firewall.

Common Ports:

 
FTP - 21
SSH - 22
Telnet - 23
SMTP - 25
DNS - 53
HTTP - 80
POP3 - 110
IMAP - 143
HTTPS - 443
MSSQL - 1433
MySQL - 3306
Remote Desktop - 3389
PostgreSQL - 5432
VNC Web - 5800
VNC Client - 5900
Urchin - 9999 or 10000

CIDR - Classless Inter Domain Routing

Classless Inter Domain Routing (CIDR) was invented to keep the Internet from running out of IP Addresses. The IPv4, a 32-bit, addresses have a limit of 4,294,967,296 (232) unique IP addresses. The classful address scheme (Class A, B and C) of allocating IP addresses in 8-bit increments can be very wasteful. With classful addressing scheme, a minimum number of IP addresses allocated to an organization is 256 (Class C). Giving 256 IP addresses to an organization only requiring 15 IP addresses is wasteful. Also, an organization requiring more than 256 IP addresses (let's say 1,000 IP addresses) is assigned a Class B, which allocates 65,536 IP addresses. Similarly, an organization requiring more than 65,636 (65,634 usable IPs) is assigned a Class A network, which allocates 16,777,216 (16.7 Million) IP addresses. This type of address allocation is very wasteful.

With CIDR, a network of IP addresses is allocated in 1-bit increments as opposed to 8-bits in classful network. The use of a CIDR notated address can easily represent classful addresses (Class A = /8, Class B = /16, and Class C = /24). The number next to the slash (i.e. /8) represents the number of bits assigned to the network address. The example shown above can be illustrated with CIDR as follows:

   216.3.128.12, with subnet mask of 255.255.255.128 is written as
   216.3.128.12/25

   Similarly, the 8 customers with the block of 16 IP addresses can be
   written as:

   216.3.128.129/28, 216.3.128.130/28, and etc.

With an introduction of CIDR addressing scheme, IP addresses are more efficiently allocated to ISPs and customers; and hence there is less risk of IP addresses running out anytime soon.