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Simple Network Management Protocol (SNMP) is used as the transport protocol for network management. Network management consists of network management stations communicating with network elements such as hosts, routers, servers, or printers. The agent is the software on the network element (host, router, printer) that runs the network management software. Therefore when the word agent is used it is referring to the network element. The agent will store information in a management information base...

Simple Mail Transfer Protocol (SMTP) is used to send mail across the internet. There are four types of programs used in the process of sending and receiving mail. They are: MUA - Mail users agent. This is the program a user will use to type e-mail. It usually incorporates an editor for support. The user types the mail and it is passed to the sending MTA. MTA - Message transfer agent is used to pass mail from the sending machine to the receiving machine. There is a MTA program running on both...

Dynamic routing performs the same function as static routing except it is more robust. Static routing allows routing tables in specific routers to be set up in a static manner so network routes for packets are set. If a router on the route goes down the destination may become unreachable. Dynamic routing allows routing tables in routers to change as the possible routes change. There are several protocols used to support dynamic routing including RIP and OSPF. Routing costCounting route cost...

Internet Group Management Protocol (IGMP) is the protocol used to support multicasting. To use multicasting, a process on a host must be able to join and leave a group. A process is a user program that is using the network. Group access is identified by the group address and the interface (NIC). A host must keep track of the groups that at least one process belongs to and the number of processes that belong to the group. IGMP is defined in RFC 1112. IGMP messages are used by multicast routers...

Network interface cards are usually programmed to listen for three types of messages. They are messages sent to their specific address, messages broadcast to all NICs, and messages that qualify as a multicast for the specific card. There are three types of addressing: Unicast - A transmission to a single interface card. Multicast - A transmission to a group of interface cards on the network. Broadcast - A transmission to all interface cards on the network. RFC 919 and 922 describe IP broadcast...

Network File System (NFS)NFS, defined by RFC 1094, is a method for client systems to use a filesystem on a remote host computer. NFS uses the UDP protocol and is supported by RPC. Remote Procedure Call (RPC) RPC, defined by RFC 1057, is a set of function calls used by a client program to call functions in a remote server program. The port mapper program is the program used to keep track of which ports programs supporting RPC functions use. The port mappers port is 111. In Redhat Linux the portmapper...

BOOTP (Boot Protocol) may be used to boot remote computers over a network. BOOTP messages are encapsulated inside UDP messages and therefore its requests and replies are forwarded by routers. BOOTP is defined by RFCs 951 and 1542. The drawing below illustrates the data encapsulation: The diskless system reads its unique hardware address from its network interface card then sends a BOOTP request. The table below shows the BOOTP package format from most significant bit to least significant bit. Bit...

Dynamic Host Configuration Protocol (DHCP) This protocol is used to assign IP addresses to hosts or workstations on the network. Usually a DHCP server on the network performs this function. Basically it "leases" out address for specific times to the various hosts. If a host does not use a given address for some period of time, that IP address can then be assigned to another machine by the DHCP server. When assignments are made or changed, the DHCP server must update the information in the...

If you've understood most of this document so far, the principles of Virtual private networking (VPN) will be easy to understand. The most confusing part of VPN is that many acronyms show up. This is partly because VPN requires data encryption to be "private" and there are many encryption techniques and terms. Also there are many complicated security issues relating to VPN concerning encryption and user authentication. This section will first explain the concept and methodology behind...

Host Names Domain Name Service (DNS) is the service used to convert human readable names of hosts to IP addresses. Host names are not case sensitive and can contain alphabetic or numeric letters or the hyphen. Avoid the underscore. A fully qualified domain name (FQDN) consists of the host name plus domain name as in the following example:  computername.domain.com  The part of the system sending the queries is called the resolver and is the client side of the configuration. The nameserver...

Firewalls are mainly used as a means to protect an organization's internal network from those on the outside (internet). It is used to keep outsiders from gaining information to secrets or from doing damage to internal computer systems. Firewalls are also used to limit the access of individuals on the internal network to services on the internet along with keeping track of what is done through the firewall. Please note the difference between firewalls and routers as described in the second paragraph...

IP masquerading is a form of network address translation (NAT) which allows internal computers with no known address outside their network, to communicate to the outside. It allows one machine to act on behalf of other machines. It's similar to someone buying stocks through a broker (without considering the monetary transaction). The person buying stocks, tells the broker to buy the stocks, the broker gets the stocks and passes them to the person who made the purchase. The broker acts on behalf...