I’m currently performing a high-level survey of the products available in the Virtualization software space. Since the development of Xen, there has been an explosion of software to allow you to run more than one server on the same host. This series of posts will begin with a quick introduction to what Virtualization is, what it is used for and summarize with a survey of vendors and products.
I’ll be looking at three different kinds of virtualization software:
Another question from the Ask InetDaemon mailbag:
I can't connect to the Internet. My computer keeps getting the address 169.254.x.x. Why?
Time for another question from the mailbag:
Why is the Loopback address always in the range of 127.0.0.0 to 127.255.255.255 ?
This range of IP addresses is reserved by the Internet Assigned Names Authority (IANA) for use as the Internet host loopback address. All Internet connected hosts (hosts running Internet Protocol) can use this adress for local loopback processing. This address range is typically used for special purposes such as testing the network interfaces and the network software.
A ping sent to any address should always work if at least one interface is enabled. Here is an example of what happens on a Windows XP host when you ping an address in the 127.0.0.0 – 127.255.255.255 range:
Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.
C:\Documents and Settings\inetdaemon>ping 127.127.127.127
Pinging 127.127.127.127 with 32 bytes of data:
Reply from 127.0.0.1: bytes=32 time<1ms TTL=128
Reply from 127.0.0.1: bytes=32 time=-63ms TTL=128
Reply from 127.0.0.1: bytes=32 time=-63ms TTL=128
Reply from 127.0.0.1: bytes=32 time=63ms TTL=128
Ping statistics for 127.127.127.127:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = -63ms, Average = 1073741808ms
The current list of reserved blocks of IP address space and their designated use are listed in RFC 3330 and RFC 1918.
Cisco routers have a virtual loopback interface and this should not be confused with the loopback address, even though the loopback address can be used on the Cisco loopback interface.
Another reader asks:
What is the difference between an IP datagram and a TCP segment?
Mostly, its terminology used in the standards documentation, though upon transmission a TCP segment gets created first from the application layer data and an IP datagram contains the TCP segment in the payload section of the IP datagram. I’ve got lots of tutorials on these subjects in this website.