Networking

Connecting two LANs: Which solution is right?

The first step in extending a corporate LAN to branch offices in the same metropolitan area is settling on the best strategy. When a member in India faced this challenge, he turned to the Technical Q&A for help. Here's one member's response.

When network administrators are called upon to expand an existing LAN across a city, one of the problems they face is deciding which of the many possible approaches they should take. In a recent post to our Technical Q&A forum, Amar Kasurde of India asked for information about the various options.

Kasurde needs to expand his office network to a branch in the same metropolitan area but about 25 km away. In both offices, he has Windows 98 machines connected to NetWare 3.12 servers.

What is the best way to connect them? Would a metropolitan area network (MAN) be his best solution? What about a WAN with leased lines?

Every question has an answer
The question seems simple enough. Unfortunately, there's no simple right or wrong answer. An analysis of the possibilities is needed before a decision can be made.

Member eBob weighed in with a few possible suggestions, defining the options under consideration as:
  • A MAN
  • A dedicated, routed WAN
  • A VPN

He discussed each of these in his post to Kasurde.

MAN
In his response, eBob defined a MAN as a LAN extension that typically supports the 10- or 100-Mbps speeds of a typical Ethernet LAN. He noted, however, that networks rarely move data at that rate. A MAN might fill the need if there is someone to provide those services in his location, he said, but a very high-speed link is required, and the cost is high.

"Your provider, likely your PTT [postal, telegraph, and telephone—a generic reference to the agency that is responsible for these services at a governmental level], will provide all of the required gear. This usually takes the form of a small switch at each of your sites that terminates the 'bridge' link across the provider's high-speed (typically fiber) network. These switches, of course, connect with the existing LAN infrastructure at each of your sites," eBob wrote.

WAN
A second alternative is to use a leased line (T1/E1, frame relay, ISDN) to connect the main office and the branch office.

"You will need to implement a suitable router at each of your sites. The details depend on the specific technology you choose (and which is available in your area). This is connected to your LAN infrastructures at each end and to the adjoining PTT connection. You will need to contract with a local 'expert' to configure and maintain your routers. Again, your local provider (likely your PTT) will be able to provide this type of service. However, you can also look for private companies to help you with the details of managing a routed WAN."

VPN
The third possibility eBob discussed was the construction of a VPN connection across the Internet.

"Again, you normally use routers at each site, but rather than leasing a piece of infrastructure from the PTT between sites, you connect each site to the Internet using a suitable ISP. You then have your equipment configured to communicate in a secure fashion (hence 'virtually private'). Optimally, you will use the same ISP for each site. Find one who can assist you with the VPN configuration and with managing your new network gear."

Parting advice
At the end of his response to Kasurde, eBob had a suggestion that's somewhat universal in scope.

He cautioned that if Kasurde wasn't familiar with all the facets of each of these options, he should be careful in selecting a partner. The partner should be reliable and will likely be the PTT, but it could be a third party with a good reputation.

"Your biggest hurdle will be this partnering activity," eBob wrote.

What do you think about this advice?
Did eBob give Amar Kasurde the advice you would have given him? Do you know of other possibilities? Post a comment in the discussion below to add your opinion to this matter.

 
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