A Little Bit About Networking

I pretty much know nothing about networking, but after reading a chapter about it in award-winning book “Release It!” — I figured I could summarize some high-level information.

• In a data center, mostly all servers are “multihomed” (meaning it is a server with more than one IP address, thereby existing on several networks simultaneously). This improves security and performance by separating high-volume traffic (e.g. backup traffic) from production traffic.
• Backup transfers involve huge volumes of data in bursts that do not affect application users if running.
• Bonding or teaming is a configuration for a network with multiple production interfaces that share a common IP address. The operating system will ensure that an individual packet goes out over only one of the interfaces, but the real advantage of bonded interfaces is that they can automatically balance outbound traffic.
• An important security protection is having a network designated for administrative access. Obviously, this would help in the event of a firewall breach.
• It was interesting to learn about the real-world use of multiple interfaces. An application listening on a socket will listen for connection attempts on any interface. In the case of Java’s ServerSocket class, three of their four constructors bind to every interface on the server. The fourth constructor can define which interface to bind to. Binding to all interfaces is not really ideal since it would allow connections to the backup or administration networks. Applications that are given a name or IP address can determine which ones to latch onto.
• A virtual IP address is an IP address that can be moved from network card. A network card sends and receives messages on behalf of the operating system and applications using that machine. If a server hosting a critical application goes down, the cluster server will take note of the failure and then start up the application on a secondary server. The IP address then becomes associated with a new MAC address (otherwise known as “physical addresses” or “hardware addresses,” is a binary number used to uniquely identify computer network adapters); each network card has a MAC address. Since clients connect to the name for the virtual IP address, and not the node that currently holds the IP address, the client has a pretty seamless connection. As great as this sounds, the downside of a virtual IP address is the loss of an in-memory data. If it has not been committed, it won’t transfer over to the machine.