IP addressing is based on the principle that it is physical hardware independent. As a logical addressing scheme, this allows two networked systems that are not attached physically to the same network to be able to communicate with each other. This is how a person can surf the Internet from their home over the phone lines using a modem, but the servers that they visit may be attached to Ethernet LAN's at their facilities. The server transmits and receives information through Ethernet and has a MAC address, the modem does not have an Ethernet MAC address and does not transmit Ethernet frames so how would the two ever be able to exchange data? By making the payload of the modem's packets and the Ethernet NIC's packets an embedded IP packet. Then a router equipped with a modem and a NIC can peek inside the modem's packet at the intended destination and determine that the packet should be extracted from the modem transmission and should be repackaged and rebroadcast as the data payload of an Ethernet frame for the server to receive on the LAN.

Another feature of logical addressing schemes is that they are not permanently assigned to the node like physical MAC addresses are. This allows the node to take on a new address if and when necessary or for another node to take on the address of a retired one, such as a major server upgrade in which it is completely replaced by a new one. This is very difficult or impossible and certainly impractical to do at the physical MAC layer, but it is part of the functionality of the network addressing layer.

Another boon provided to networks at the network addressing layer is the ability to route a packet not only as described above from one physical transmission media to another but also across multiple routers until the packet arrives at its destination network and ultimately its destination node. This is possible because the network address consists of two parts: the network number and the node number. Routers keep tables that are periodically updated by communicating with each other using their own routing protocols. The routing tables indicate one or more choices for forwarding a packet to another router so that it can ultimately arrive at its intended destination. Without a network number, if IP addressing were a "flat" addressing scheme, then the routers of the world would have no clue of which would be the better choice amongst each other for forwarding a particular packet and then how would a packet ever get across the planet to its destination? It wouldn't.

The IPX protocol is much easier to understand as far as the network number and the node numbers so this will be explained first. Then IP will be tackled. In IPX the network number is assigned at the server and is an eight hexadecimal digit number meaning that it is 4 bytes long or a 32-bit value. Here is one of the most popular choices in all of the Novell NetWare networks of the world: DEADBEEF. A valid 8 digit hex number. The node address used in IPX is the physical MAC address of the system. This is a 48-bit or 6 byte or 12 hex digit number obtained from the network interface card of the system. IPX is very fast and robust since a system can request to join a network and in the Ethernet transmission the server will already know the node address that the system will use. For example, if the system has a node address of 00-E0-81-DE-0B-51 then its IPX address will be: DEADBEEF:00E081DE0B51. Address Resolution from IPX to MAC is not an issue for IPX networks since the MAC is also the node portion of the IPX address. And that is all there is to IPX addressing. Network administrator assigns the 32-bit unique network number and nodes provide their own 48-bit node number from the MAC address. The network numbers and the node numbers are fixed in size and location within the IPX address.

However, in IP addressing this is not the case at all. The network number and the node number are fixed in location within the IP address but they are NOT fixed in size within it and this combined with the way IP addresses are written leads to all of the confusion concerning IP addressing. Just like IPX, IP must consist of both a network number and a node number in order to be capable of being routed at all. A station's IP address consists entirely of a 32-bit assignable number. The MAC address is not involved in it and it is completely assignable by the administrator or software. As such accidental replication of a used number is much more likely than in IPX where it is in theory impossible due to the fact that MAC's must be unique on the earth. And the IPX number is going to automatically be assigned to be the MAC by the network stack so human user error in the assignment is eliminated as well.

The IP address is a 32-bit number that is split into two parts bitwise. Yet it is never represented as a binary value. It is not even represented as a hex value which would have helped at least somewhat. Instead it is represented as a decimal value for each byte within it. So the binary IP address: 00110011 11110000 01010111 11010110 would be written as each 8-bit byte converted to decimal and then each of these numbers separated by periods: 51.240.87.214 This notation method for representing IP addresses is referred to as the dotted decimal notation. It is perfectly fine except for the fact that bits within it cannot be easily distinguished, yet the IP address is split along an arbitrary dividing line within it into the network number containing all of the bits to the left and the node number composed of all of the bits to the right of where they are divided. This leads to network and node numbers that are not immediately obvious especially if the split is not at the edge of two bytes (at one of the periods).

The fact that the network number portion and the node number portion of the IP address are not fixed in size within the 32-bit IP address is one of the major sources of confusion for the networking novice. The reason that the dividing point is different from one number to another was to allow for greater flexibility in the size of networks when TCP/IP was first created. Since a 32-bit number was chosen which in theory can uniquely identify over 4 billion network nodes, this was at the time larger than the world's population. Now obviously the number is inadequate which is why IP version 6 is being developed and endorsed by the computing industry. IPv6 as it is called uses a 128-bit node address. This allows for a total of 2¹²⁸ which is roughly 340,000,000,000,000,000,000,000,000,000,000,000,000 (almost enough for each windows DLL to have its own IP address) IPv6 addresses are expressed in hex with colons separating each four hex digits such as: 1234:CA99:B402:EEFF:00CD:A120:84D4:368A. The move to IPv6 has however stalled because so many existing systems only understand IPv4 and the cost to convert especially in hardware like routers has proven to be prohibitive. All new equipment and software (i.e. Windows Vista) does include optional IPv6 support.

Nevertheless, continuing the line of thought; if the IP address had been assigned a fixed width of 16-bits for the network number and then 16-bits for the node number, this would have allowed the world only 65,536 total IP networks. In other words, only 65,536 businesses, governments, committees, non-profit organizations, etc. would be allowed on the Internet. There are this many in any big city alone. Furthermore, the 16-bit node number would allow each agency to have up to 65,536 nodes. Certainly way too many for most businesses especially single office based businesses. But, some companies and agencies do need that many node addresses, in fact many need even more than that. Others need far fewer than this and this is why the sliding network number-vs-node number size was implemented in IP addressing from the beginning.

To solve the problem IP addressing was originally divided into classes. If an IP address falls within a certain number range it is considered a certain class of address. Some classes allow for very large numbers of nodes while others are allow for small numbers of nodes. The classes were not chosen arbitrarily but were instead based on the values of certain bits within the network number of IP address itself. Again these clearly defined values are not easily discernable when the numbers are converted to decimal. All class "A" IP network address numbers begin with the leftmost bit, the highest place value digit within the number, also known as the "Most Significant Bit" or MSB of the entire 32-bit IP address number equal to zero. This is very clear in binary: 00110011 11110000 01010111 01010110 of the example above is easily seen to be a class "A" address when viewed in binary as the routers view it. But when viewed in dotted decimal notation: 51.240.87.214 this fact is not nearly so abundantly clear (that the MSB bit is a zero).

The range of possible first octets that have a zero as the topmost bit is: 00000000 to 01111111 or when converted to decimal: 0 to 127. Zero is understood in IP addressing to refer to a missing node number leaving only the network number and since the network number starts from the leftmost bit down, the top octet cannot be zero since there would be no number at all to the left of it to specify the network number. In other words, there is no valid network number of zero. The network number 127 has been reserved for the local host's internal adapter address for testing purposes and is not a valid IP address and routers will reject it if they receive a packet with a destination of 127.x.x.x. So this leaves the numbers 1 to 126 as valid class "A" starting octet values. Class "A" licenses are intended for very large networks, as such they were divided such that the top 8-bits define the network number and the bottom 24-bits define the node number. This means that there are exactly 126 class "A" networks and all of these are already in use on the Internet. Each of these networks can support up to 16,777,214 nodes or computers within the network. We'll see why that's 16,777,214 rather than 16,777,216 nodes momentarily. Some examples of owners of class "A" IP network licenses are General Electric who owns 3.x.x.x, IBM owns 9.x.x.x, M.I.T. owns 18.x.x.x, and the United Stated Postal Service owns 56.x.x.x.

Now if the first octet starts with the binary digits 10... then this defines a class "B" IP address license. By the way, remember that once the local area network is attached to the Internet there cannot be any duplicate addresses. Therefore, the addressing of the Internet is centrally organized and administered to ensure that addresses are not duplicated on the Internet. The organization that handles this used to be the IANA - Internet Assigned Numebrs Authority, but the control has been moved to the ICANN - Internet Corporation for Assigned Names and Numbers. This is why they are refered to as licenses because someone can not just pick a number out of a hat and go online with it, they must apply for it, pay a fee to these organizations (they are non-profit but the cash doesn't seem to bother them) and then use it.

Back to the business at hand; a "B" address is divided so that the topmost 16 bits comprise the network number and the bottom 16 bits comprise the node address. This means that the numbers from: 10000000 00000000 to 10111111 11111111 are valid class "B" network numbers or in dotted decimal from: 128.0.x.x to 191.255.x.x. There are 64 possible first octets (128 to 191) each of which can have any second octet from 0 to 255 (256 possibilities) So 64 x 256 = 16,384 possible class "B" networks. Exxon has a class "B" network. Microsoft has one also. All class "B" licenses on the Internet are taken already. Since each address has a 16-bit node number this allows 65,534 nodes on these networks. However, 2¹⁶ = 65,536. Why is each license always losing two possible nodes? When the node address is zero this is interpreted to mean no specified node at all, the address now refers to "this network" rather than any specific node within it. As described above a zero is not a valid network address because node address bits left all zeros leaves only the network address so it can be easily identified. And because of this, no node can have a node address of zero. Also no node can have a node address of all 1's because when the node address is all ones this is the broadcast address for the entire network and all nodes are the recipients of a packet whose destination node number is all ones. Therefore, the all zeros address and the all ones addresses cannot be used by any specific node and must be thrown out leaving 65,534 possible valid node addresses on a class "B" network (or any other class network for that matter).

Class "C" licenses were intended for small organizations and the topmost bits must be 110... In a class "C" license the top 24-bits define the network number and the bottom 8 bits define the node number. This allows the numbers 11000000 00000000 00000000 up to 11011111 11111111 11111111 for valid network numbers or in dotted decimal: 192.0.0.x to 223.255.255.x There are 32 possible first octet values and each of these can be followed by any number in the second octet (256 possibilities) and any number in the third octet (256 possibilities) so 32 x 256 x 256 = 2,097,152 possible class "C" network numbers. Since the node numbers are 8 bits wide this allows host addresses from 0 to 255 but remember that zero is not a valid host address and 255 is all ones and would represent the braodcast address for that network and therefore cannot be assigned to a specific node either. This leaves 254 possible nodes on a class "C" network so these licenses are intended for small organizations. There are only a few class "C" networks numbers left and they are dwindling so fast that they may already be gone by the time of this writing.

Class "D" licenses are not for private use but are instead used for Internet multicasting. A system can join a multicast automatically and also relinquish membership at any time. Class "D" licenses start with 1110... and any other combination of bits in the topmost octet so the class "D" addresses range from 11100000.x.x.x to 11101111.x.x.x or 224.x.x.x to 239.x.x.x This defines 16 numbers in the first octet and 256 possibilities in the second octet with 256 possibilities in the third octet with 256 possibilities in the fourth octet. So 16 x 256 x 256 x 256 = 268,435,456 total multicast addresses.

If the four topmost bits are 1111... then the possible network numbers are 11110000 to 11111111 or 240.x.x.x to 255.x.x.x The 255.255.255.255 is a general IP broadcast to any recipient so the class "E" licenses really effectively range from 240.x.x.x to 254.x.x.x and are experimental addresses and are not for use on the Internet.

To recap:

Modern IP addressing has moved to CIDR - Classless Inter-Domain Routing, style of addressing. In CIDR the 32-bit IP address can be divided at any point not just at the full octet boundaries like the old class addressing scheme. Then the bits to the left of the division point are the network number and the bits to the right are the node number. Overall the CIDR address must fall within the general category of the old class addressing scheme or else the whole thing would collapse. This means that the old class "A", "B", and "C" IP addressing licenses are in essence CIDR 8, CIDR 16 and CIDR 24 licenses. Since all class "A" and "B" licenses are gone and the number of "C" licenses is dwindling rapidly, the only CIDR licenses available will be higher than CIDR 24. "CIDR Slash 24" means that the top 24 bits are the network number and the bottom 8 bits are the host number, so a "CIDR Slash 24" network is equivalent to the class "C" license of the old IP address licensing system. A "CIDR Slash 26" network means the top 26 bits represent the network number leaving the bottom 6 for the host number. This means that the remaining class "C" licenses are in effect being subnetted and the subnets are being sold to the Internet customers who want them. With a "Slash 26" network leaving a 6-bit node address there are: 2⁶ = 64 numbers are available for use, but all zeros represents the network itself and is not a valid host number and all 1's represents the broadcast address for the network and is also not a valid host number. This leaves 62 hosts for the Internet customer that purchases a CIDR "Slash 26" license. Here is an example of a 26-bit CIDR address range license:

The CIDR 26 ("Slash 26") Network Number (206.149.11.64):

11001110 10010101 00001011 01000000

The lowest valid host number (206.149.11.65):

11001110 10010101 00001011 01000001

The highest valid host number (206.149.11.126):

11001110 10010101 00001011 01111110

The broadcast address for this network (206.149.11.127):

11001110 10010101 00001011 01111111

The yellow bits are the 26 bits that form the network number portion of the CIDR IP address class license, they borrow the top two bits of the classic class "C" host number (the fourth byte) so this particular CIDR network number has a non-zero fourth byte value in it. Note how the decimalized IP address numbers reflect the presence of the used bits in the network number forming unusual network number, lowest available host address, highest available host address, and broadcast addresses for this network.

Since the network number and the node number are not fixed in size within the IP address, how can the machines tell what part is the network number and what part is the node number? This is done with the second essential component of the IP configuration of any IP network node: the subnet mask (the first essential component of a node's IP configuration is its IP address).

The subnet mask is used by the machine to determine which part of the IP address is the network number and which part is the node number. This is done by using the subnet mask to perform a logical AND operation on the IP address using the subnet mask. For example, the logical AND operator's truth table looks like this:

AND is a "bitwise" operator. It can be done with large binary numbers and the AND is done only to the bits in the columns and does not need borrows or carries like addition or subtraction. Now an AND mask works like this: any bits that you want stripped away from a number are AND'ed with zero and any bits that you want to keep are AND'ed with one. So given the byte 01010101 if the bottom four bits need to be stripped away the AND mask would be 11110000:

    01010101
AND 11110000
    01010000

The subnet mask is in fact a plain and simple AND mask. For a class "A" license, the subnet mask must retain the first dotted octet, while stripping the 2nd, 3rd and 4th so it must be: 11111111.00000000.00000000.00000000 or in decimal dotted octet notation: 255.0.0.0 and when applied to any class "A" license, this subnet mask will strip away the host number. For example:

    IP Address:  120.120.120.120
    Subnet Mask: 255.0.0.0
    IP Address in binary:  01111000.01111000.01111000.01111000
    Subnet Mask in binary: 11111111.00000000.00000000.00000000
                 AND "sum" 01111000.00000000.00000000.00000000

    AND "sum" in decimal: 120.0.0.0

So the subnet mask tells the machine which part of the IP address is the network number and which part is the host number. The machine can quickly perform this AND "sum" operation on any IP address and compare the network number to its own. If they match, then the address is a "local" one, the address belongs to another node on its own network. If they do not match, then the node is a "foreign" one, it belongs to a node on a different network.

The classic subnet masks are then:

Class "A" - 11111111.00000000.00000000.00000000 = 255.0.0.0
Class "B" - 11111111.11111111.00000000.00000000 = 255.255.0.0
Class "C" - 11111111.11111111.11111111.00000000 = 255.255.255.0

The CIDR subnet masks are a little more tricky. The only good way to figure them out so that they make sense, is to figure them out in binary, and then convert them to decimal. Let's figure out a "slash 26" CIDR subnet mask: "Slash 26" means that the leftmost 26 bits are the network number so; these must be ones, and the rest to the right must be zeros that make it a 32-bit number. We will put the periods in every 8 bits to make the final conversion to decimal easy:

  CIDR "slash 26" Network number bits:

  11111111.11111111.11111111.11

  Now the remaining bits are zeros and must make it exactly 32-bits wide:

  11111111.11111111.11111111.11000000

  Now convert each octet to decimal:

  255.255.255.192

  This is the correct subnet mask for any CIDR "slash 26" network.

In IP networks, nodes assume that they can send a packet directly to any node on their own network and they also assume that they CANNOT send a packet to a "foreign" node that resides on a different network. Whenever the machine sets up a transmission of a network layer IP packet, the target address is first checked by AND'ing it with the subnet mask, the network number is then checked with its own network number. If the target of the transmission is determined to be a foreign node, then the machine will NOT just go ahead and transmit the packet. It will assume that this is impossible because the target is on a different IP network. Instead the machine will send the packet to the local router whose job is to forward foreign traffic to other routers that will ultimately get the packet to the correct foreign network. This means that the machine needs the third essential element of its IP configuration in place: the address of the local router which is called the default gateway in IP terminology.

Any time a machine attempts to send packets to a foreign address it will check its own configuration for the address of the default gateway. If this value is left blank, it can cuase considerable delays and the failure to make any transmissions addressed to foreign network nodes. To properly configure IP on any node then it must have at the very least these three essential configuration elements set:

  Minimum Functional IP Configuration for any node:
  1) IP Address   - must be unique in the network, in fact in the world if the machine
                    is to be connected directly to the Internet
  2) Subnet Mask  - must conform to the class license of the local machine's IP address
                    whether it is a classic license or a CIDR license
  3) Default Gateway - allows the machine to transmit packets to foreign nodes, even if
                    there is no local router, the machine can have this set to itself,
                    this allows it to quickly determine what to do with foreign packets
                   (i.e. discard them because it knows it is not a router) and many
                    commands and functions look for the value of this parameter and will
                    fail if it is left blank.

Now for the gory details. Here is the structure of an IP packet:

Bit0	4	8	12	16	20	24   Bit31
IP Version	IHL	TOS		Total Length
Identification				Flags	Fragment Offset
TTL		Protocol		Header Checksum
Source IP Address
Destination IP Address
Options					Padding
Data

These packets can be thought of as a 32-bit technology because of the 32-bit IP address, but many fields are not actually 32-bits in size. Each field and its practical function for the intersystem communication will now be explained.

	IP version – This is a 4-bit field that holds the version of IP being imeplemented in the packet. This is an IP version 4 packet, but IP version 6 is being developed.
	IHL – Internet Header Length, this 4-bit number is a count of how many double words (32-bit numbers) are in this header. The minimum for a valid IP packet is 5.
	TOS – Type of Service, this is an abstract QoS (Quality of Service) descriptor which is bit fielded as follows:

Here are a few precedence value meanings: 000 = Routine, 001 = Priority, 010 = Immediate, 011 = Flash, 100 = Flash Override, etc. In bits 3, 4, and 5 a zero indicates normal a 1 means "expedite." For example if bit 3 = 1, the packet says "reduce delays in handling this packet." If bit 5 = 1, the packet says "ensure that this packet is sent with high reliability."

	Total Length – 16 bit number representing the number of bytes in the packet including this header and the data. 576 byte packets are routine. Especially with ISPs.
	Identification – A packet ID if fragmented to guide the driver in reconstruction.
	Flags – 3 bits as follows, Bit 0 = Reserved, Bit 1 = 0 means "May Fragment," Bit 1 = 1 means "Don't Fragment", Bit 2 = 0 means "Last fragment," Bit 2 = 1 means "more fragments follow."
	Fragment Offset – 13 bit number that describes this fragment's position in increments of 8 bytes, the first having an offset of zero.
	TTL – Time to Live, how many router hops the packet may take before being destroyed as “undeliverable.” The TTL field is intended to measure seconds, but each router must decrement the field by at least 1 upon retransmitting it even if it was handled in a microsecond. Any handler that receives a packet with a TTL of zero must discard it.
	Protocol – Describes well known Service Access Points for the handling of the packet.
	Header Checksum – This is calculated against the rest of the header then inserted here. This must be changed by routers as well. Because they alter the TTL value.
	Source IP Address – The Actual IP address of the sender
	Destination IP Address – The actual IP address of the intended target system.
	Options – There are a large number of options that can be specified in a packet, but the original sender does not have to specify any options, but if it does then all handlers must attempt to honor them.
	Padding – Intended to bring the size of the header to an even 32 bit boundary before the beginning of the data.
	Data – the actual content being transmitted.

IP addresses also have a few reserved ranges that are called "private" address ranges. These will not be forwarded by Internet routers or true routers of any kind. These ranges can be used by anyone on any LAN even if it is attached to the Internet and therefore prevent machines that are attached to the Internet from transmitting real addresses that have been reserved for use by someone else on the Internet. They are:

Class "A" Private address range: 10.0.0.0 - 10.255.255.255
Class "B" Private address range: 172.16.0.0 - 172.31.255.255
Class "C" Private address range: 192.168.0.0 - 192.168.255.255

So anyone can set up a LAN using any of these IP address ranges at any time and they are completely set aside for this purpose. Note that an entire "A" license (10.x.x.x) has been set aside for anyone to use and it would support up to 16,777,214 nodes within that network. You may recognize the 192.168.x.x as the typical address range that your high speed Internet access router asigns to your own PC using its DHCP - Dynamic Host Configuration Protocol function. A DHCP server, can answer node requests to receive their IP configuration settings including but not limited to their IP address, subnet mask and default gateway. DHCP servers therefore can issue these settings and keep a record of the IP addresses that they have given out so that they will not give out duplicate IP addresses which would cause the nodes to fail. The device itself takes the typical router address of an IP range of host #1 (i.e. 192.168.0.1) This is in effect a form of native IP addressing "firewall" since no router on the Internet will ever forward any IP packet whose source or destination IP is 192.168.x.x This makes your machines relatively safe from external directed TCP/IP packet level attacks.

According to Microsoft, the IANA has reserved 169.254.0.0-169.254.255.255 for APIPA - Automatic Private IP Addressing. As a result, APIPA provides an address that is guaranteed not to conflict with routable addresses. This means that this class "B" license has also been reserved as a private address range and packets with these addresses in the source or destination fields will also be rejected by routers. They are APIPA addresses which means that machines can automatically assign themselves any random address within this range and begin to function on the local area network using TCP/IP and this function has been incorporated by Microsoft into their TCP/IP drivers since Windows 98. In the event that the machine is configured to get its TCP/IP configuration from a DHCP server, and this server is not responding or does not exist, the machine will set itself up with an APIPA address. Since they are in the same range and use the same subnet mask, all machines configuring themselves with APIPA addresses will be able to communicate on the LAN. However, while the LAN will work, Internet access will FAIL because this address range has been reserved as a private address range. The only techniques that can be used to successfully access the Internet when all of the machines on the LAN are using APIPA addresses (which have the native IP "firewall" features mentioned above) would be to set up some form of "proxy" server that has a real Internet address and that can go online properly. The same high speed Internet connectivity routers mentioned earlier that issue the 192.168.x.x addresses also have this "proxy" server functionality which is how your PC can browse the Internet. It does it by proxy (hence the name of the proxy server) in that its requests are received by the proxy server which then repackages a request using its real address and it transmits that onto the Internet. When the response arrives it repackages this and sends it back to the original machine.

What is the function of OSI model Layer 3?

Name 3 basic functions that layer 3 logical addressing provides to the network.

What is the name of the layer 3 protocol invented by Novell?

What is the length of an IPX address? How many total networks can there be using IPX? How many nodes on each network?

Explain why ARP is not needed in an IPX/SPX network.

What is the length in bits of an IP address? How many bits constitute the network number?

What is the term for the way IP addresses are expressed?

IPv6 addresses are how many bits? How are they expressed? Give an example.

List and describe the classic IPv4 classes. Mention the leading bits, total number of networks, total number of nodes and the subnet masks each has.

What are the three essential parameters required to configure any IP node properly?

How does the system use the subnet mask?

How does the system use the default gateway?

All machines within the network must have the ___________ subnet mask.

All machines within the network must have ___________ IP addresses.

All machines within the network must not leave the ___________ ___________ setting blank.

The two primary authorities of the Internet responsible for issuing valid IP addresses to those who want them are (spell them out):

Consider which classic classes of IP addresses can actually be used to give nodes their addresses on the Internet. How many total networks are there on the Internet? If a router's routing table has an entry for every possible IP network and each entry is 8 bytes, how much RAM does the router need to hold the routing table for the entire Internet? Does this seem large or small considering its scope?

What is the one field within the original IP packet that the source machine transmitted that is always modified by every router that handles it? Why do you think this is done?

The default IP configuration in Windows when the network interface drivers are loaded is to use DHCP. In the event there is no actual DHCP server to configure the network interface's IP settings, will the interface function? And if so how?

Counting the APIPA addresses, list all standard resevered for private use IP address ranges:

How many class "A" licenses are private? How many class "B" network numbers are private? how many class "C" network numbers are private? How many actual node addresses were lost to regular use on the Internet because they are part of these private ranges?

Why do typical high-speed Internet connectivity devices like DSL routers function like DHCP servers? What is one of the practical reasons that they issue addresses in the 192.168.0.0 range? These devices also have built into them what other server type function? Why would this be necessary?