A Fundamental Look at Networking Services Part II
In the first of this three part series, we discussed communications protocols and traffic as it traverses the Internet. Specifically, we examined IP, TCP, UDP and DHCP protocols as they are employed in network connections. This article will examine the concepts behind Network Address Translation – NAT. We will also discuss Domain Name Service – DNS, and its naming schemas and practices that allow Internet users to find web sites by names instead of IP addresses.
NAT and Tunneling
One of the biggest reasons we haven’t switched over to IPv6 addresses is the advancement of Network Address Translation – NAT – devices. Routers that perform NAT can deliver multiplexing services to thousands of nodes in a LAN and expose just one IP address to the outside Internet at large.
The working component behind NAT is Port Address Translation - PAT - which assigns a different TCP or UDP port to each networking connection. With PAT, a single computer can connect to numerous external servers and sites, all while using one internal IP address and one public IP address.
As a result, companies only have to purchase one public IP address for the NAT device instead of one IP address for each node in the LAN. The NAT router then creates logical socket connections with dynamic port assignments for each internal device, and includes that port information in packet headers that are sent over the Internet so it can keep track of which Internet incoming packets are destined for which internal node.
Tunneling protocols are most commonly associated with virtual private networks – VPNs. Tunneling is a transport service that allows a device such as a VPN switch to encapsulate packets from inside nodes and transmit them through public media, such as the Internet backbone. Devices that employ tunneling agree on an encryption scheme and effectively mask the contents of the packets they transport.
DNS and URL's
Domain Name Service – DNS – is a service that translates network addresses into domain names.
In the early days of the Internet you had to know the publicly assigned IP address of a web site and type that address in the address bar of a browser in order to connect to that site. It became apparent that people would not remember very many IP addresses, and domain name registration services were established so that we could effectively remember web sites by their names -- instead of the IP addresses of the servers that actually hosted the web sites.
To simplify the task or recording the exact DNS name and IP address of every Internet site, DSN names are grouped by their DNS extensions. DNS extensions are pre-approved categories, such as .com, .edu, .net, etc. They are controlled by the Internet Corporation for Assigned Names and Numbers -- ICANN.
Every country also has licensing control over its own DNS extension, such as uk for the United Kingdom and br for Brazil. On June 20 2011 ICANN approved a new set of DNS extensions.
A URL, or Uniform Resource Locator, is a web address that adheres to a rule or convention. For example, the common convention is a protocol (http or ftp for example), followed by a colon and two backslashes which designates a network path, then a server address or domain name.
URLs can also specify specific directories or locations inside a network by including additional share or device names separated by additional periods or backslashes either before the domain name or after it.
While most end users understand that they need to use a URL to find a network site, they may not know that DNS registrations are the lookup services that make those URL's discoverable. NAT/PAT and tunneling services have successfully maintained IPv4 networking services and prolonged the lifecycle of IPv4 addresses, which are consumed by DNS mappings and ultimately deliver the web site URLs.
The next forward facing topic is the emergence of IPv6. In June, 2011, the Internet Society -- a non-profit organization supporting Internet standards, education, and policy-making led a successful one-day trial run of websites utilizing the IPv6 Internet backbones. This effort included Google, Facebook and Yahoo. Suffice to say, we can expect a faster migration to IPv6 Internet services in the near future.
James Dalton is a Learn iT! Microsoft Certified Trainer with over 15 years of experience as a solutions developer, consultant, and teacher of networking, applications and Microsoft server solutions for many different colleges, universities and private companies in the San Francisco Bay Area. He holds numerous certifications, including Microsoft ITPro for Server 2008, SharePoint, Windows7.