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I want to assign my virtual machines MAC addresses so that I can configure DHCP reservations for them so that they always get the same IP address regardless of which host hypervisor they are running on or operating system they are running.
What I need to know is what range of MAC addresses can I use without fear that one day some device may be connected to our network with that MAC?
I have read the Wikipedia article on MAC addresses and this section seems to indicate that if I create an address with the form 02-XX-XX-XX-XX-XX then it is considered a locally administered address.
I would assume this means that no hardware manufacturer would ever use an address starting with 02 so I should be safe to use anything that starts with 02 for my virtual machines?
Thanks for the help.
Chris MagnusonI am using MS SQL Server 2008 and I am trying to extract first 3 octets of an IP address I tried the solution Extract 1st Three Octets of an IPV4, but SUBSTRINGINDEX is not built-in function name. As stated above, a Class A address has the first octet as the network portion and the remaining 3 octets as the host portion. Therefore, a Class A network mask is defined as 255.0.0.0. A Class B address has the first and second octets as the network portion and the third and fourth octets.
Chris Magnuson6 Answers
There are actually 4 sets of Locally Administered Address Ranges that can be used on your network without fear of conflict, assuming no one else has assigned these on your network:
Replacing x with any hex value.
Sam CoganSam CoganThe complete list of assigned mac prefixes can be found here:http://standards.ieee.org/regauth/oui/oui.txt
There are several prefixes marked private on that list, 02 is not one of them. If you use one of those, you should be relatively safe. Keep in mind that other devices, software, etc. may also use that prefix, in which case your chance of a conflict goes up slightly.
If you are using randomly generated suffixes, your odds of collision are pretty astronomical.
Paul McMillanPaul McMillanIn case you are using VMware products (ESXi / Workstation / vCenter / ...), the valid range of manually assigned MAC addresses is:
For Xen virtual machines you can use anything starting with 00:16:3E, and that's the default which many management tools will generate.
How Do I Know What To Set The Last 3 Octets Of Manual Mac Address 1
Kamil KisielKamil KisielI know this is old, but the way I read this is like so (as I am doing this now for Hyper-V 2012 and in an MSP environment....)
The order of the Hexadecimal digits is transmitted in pairs in reverse order on the ethernet wire.Thus, A3:xx:xx:xx:xx:xx is transmitted as 1100 0101:xx:xx:xx:xx:xxThe 3 is transmitted before the A, making the two least significant bits transmitted first both 1's. This is according to http://standards.ieee.org/develop/regauth/tut/macgrp.pdf
How Do I Know What To Set The Last 3 Octets Of Manual Mac Address List
Therefore, it appears that the above is correct. I understand the wiki article referenced above as well, but believe 06 is a poor example and not the way the bits are transmitted on the wire.
Here is a screen capture of the relevant piece of the above linked PDF:
This would make the ranges start as follows for Unicast:x2:, x6:, xA:, xE:And as follows for Multicast:x3, x7,xF.
It seems Virtualbox version 5 uses locally administered addresses beginning with 0A-00-27 ( while in previous versions it was using 08-00-27 ).
By the way when assigning MAC addresses manually just keep in mind that 00-03-FF is used by Virtual-PC VMs like mentioned here:http://blogs.technet.com/b/medv/archive/2011/01/24/how-to-manage-vm-mac-addresses-with-the-globalimagedata-xml-file-in-med-v-v1.aspxand 00-15-5D is used by Hyper-V VMs like mentioned here:http://technet.microsoft.com/en-us/library/jj590655.aspx
protected by Community♦Jun 2 '17 at 0:05
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The Internet Protocol (IP) was developed in the 1960s to provide packet fragmentation and reassembly across a packet-switched network. This packet-switched network became what we now call the Internet.IP addressing is used to uniquely identify hosts on an internetwork. An internetwork is made of LANs and WANs that are connected with a router or routers. To send data from a host on network A to a host on network B, a logical network addressing protocol must be used. IP is the most popular logical addressing protocol. However, IPX in the Novell stack and Datagram Delivery Protocol (DDP) in the AppleTalk stack can also be used. Although you can find many other types of routed protocols that provide the same functionality as IP, they aren’t as efficient as IP in larger networks.
The dreaded IP address
Before we conquer IP addresses, I want to define some of the terminology used in this Daily Drill Down:
- Bit: One digit; either one or zero.
- Byte: 8 bits. This term is interchangeable with octet.
- Octet: 8 bits. This term is interchangeable with byte.
- Network address: Address with all host bits turned off.
- Broadcast address: Address with all host bits turned on.
To fully understand IP addressing, you must be familiar with binary-to-decimal conversion. To find the decimal equivalent of a binary number, you must add the binary values. Binary numbers use eight bits to create a byte. Each bit in the byte has a certain value, and if a bit is turned on (assigned a value of 1), then the byte takes on that decimal value. Each bit has a value that starts at 1 and doubles in value from right to left. Table 1 shows an example of converting a byte to a decimal value.
| 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 | Decimal value |
| 0 | 0 | 0 | 1 | 1 | 0 | 1 | 0 | Binary number |
In the above example, there are three bits that are turned on (1s). Add each of these values to get the bytes decimal value (16+8+2=26). Let’s take a look at another example in Table 2.
| 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 | Decimal value |
| 0 | 1 | 1 | 0 | 1 | 0 | 0 | 0 | Binary number |
The IP address
IP addressing is not hard-coded into a machine. It is known as a software or logical address because of the way an administrator must statically configure each host (either manually or with DHCP). The basic design of an IP address allows hosts on different networks to communicate with each other, regardless of the type of network on which they are located.
The IP address is 32 bits long and is divided into dotted decimal. An example of an IP address is: 10.205.34.2. Each of the decimals is known as a byte and is 8 bits long. Therefore, an IP address is 4 bytes, or 32 bits long.
An IP address is hierarchal in design and is divided into two parts: network and host. An IP address not only defines the host on the internetwork but also describes the network on which the host is located. In the example above, 10 is the network and 205.34.2 is the host address.
The job of a router is to get packets to a network using the logical address. To get a packet to a host, the hardware address is used. If a packet has a destination IP address of 10.205.34.2, the routers in the internetwork will forward the packet to network 10. If the routing tables do not have an entry for network 10, the routers will discard the packet.
An IP address can only be configured within certain ranges. Although an IP address can be displayed in decimal from 0.0.0.0 to 255.255.255.255, only certain addresses can be used to configure hosts on an internetwork. It is imperative that you can look at an IP address and know whether it’s a valid host address.
Classes of IP addresses
The original designers of the IP stack came up with a hierarchical addressing scheme with five ranges, called classes. These ranges are named:
- Class A: IP address range from 0-127 in the first byte designed for very large companies.
- Class B: IP address range from 128-191 in the first byte designed for medium-size companies.
- Class C: IP address range from 192-223 in the first byte designed for small companies.
- Class D: IP address range from 224-239 in the first byte reserved for multicast addressing. Not used in the public sector.
- Class E: IP address range from 240-255 in the first byte reserved for scientific studies. Not used in the public sector.
Class A
In the four-byte Class A IP address, only the first byte is used to identify the network. The last three bytes are used to describe the hosts on each network: network.host.host.host. The Class A range is 0-127 in the first byte. Only 1-126 can be used to identify Class A networks because 0 and 127 are reserved.
To find the valid host addresses in a Class A network, you must find the network and broadcast address in the IP range. Since the Class A address only uses the first byte to identify the network, the last three octets are host bits.
To find the network and broadcast address, turn off the host bits and then turn them on again. For example, if we want to use the Class A network address of 10, the network address, broadcast address, and valid hosts are determined as shown:
- 10.0.0.0 is the network address because all of the host bits are turned off (0). The last three octets are zeros because the first octet is a 10, which is in the Class A range of 1-126.
- To find the broadcast address of the IP address, turn on the host bits: 10.255.255.255.
- The valid hosts are the numbers in between the network address and the broadcast address: 10.0.0.1 through 10.255.255.254.
Class B
The Class B range is 128-191. For example, if you find an IP address that begins with 152, then you know that it’s a Class B address. Class B addresses use the first two bytes to define the network and the last two bytes to define the hosts on each network: network.network.host.host.
For example, in the IP address 152.93.10.5, 152.93 is the network address and 10.5 is the host address. In this example, what are the network address, broadcast address, and valid host range? Remember, all you have to do is to find the host bits and turn them all off and then turn them all on. In a Class B address, the host bits are the third and fourth octets by default.
- 152.93.0.0 is the network address (all host bits off).
- 152.93.0.1 is the first valid host.
- 152.93.255.254 is the last valid host.
- 152.93.255.255 is the broadcast address (all host bits on).
Class C
In a Class C IP address, only the fourth octet is used to address hosts. The first three octets are used to define the network: network.network.network.host.
An example of a Class C address is 200.10.10.59. By glancing at this address, you can see that the network address is 200.10.10 and the host address is 59. To find the valid host range, turn all of the host bits off and then turn them on.
- 200.10.10.0 is the network address because all host bits are off.
- 200.10.10.1 is the first valid host.
- 200.10.10.254 is the last valid host.
- 200.10.10.255 is the broadcast address because all host bits are on.
Subnet masks
Subnet masks are used in IP configurations to tell hosts on the network which part is the network address and which part is the host address of an IP address. You cannot configure an IP address on a host without also configuring the subnet mask information.
Remember that a Class A IP address uses only the first byte to describe the network address and three bytes to describe the host addresses. In a subnet mask, the network portion consists of all ones (1s) and the host portion is all zeros (0s). Therefore, a default Class A subnet mask must be 255.0.0.0. Since the entire first byte is the network portion and must be all 1s, the decimal value is 255. IP will examine this mask to determine the host and network bits in an address.
In a Class B IP address, the first two bytes represent the network portion and the last two bytes are the host portion. Therefore, the default mask is 255.255.0.0.In a Class C IP address, the first three bytes represent the network portion and the last byte is the host portion. The default mask is 255.255.255.0.
This is an example of a Class A configuration of a host where 10 is the network address and 59.135.4 is the host address:
10.59.135.4
255.0.0.0
This is an example of a Class B configuration of a host where 130.59 is the network address and 135.4 is the host address:
130.59.135.4
255.255.0.0
Here is an example of a Class C configuration of a host where 210.59.135 is the network address and 4 is the host address:
210.59.135.4
255.255.255.0
The default gateway address is typically configured but is not required. It is the router address on the network. If no default gateway address is configured on the host, the host won’t be able to communicate outside its own local network.