IP Networking. What is a Network?. A connection between two or more computers so they may exchange information/resources. Using a network ‘medium’, computers pass information from one to another in an organized fashion using communication rules governed by ‘protocols’. Network Medium.
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A connection between two or more computers so they may exchange information/resources.
Using a network ‘medium’, computers pass information from one to another in an organized fashion using communication rules governed by ‘protocols’.
Refers to the tool used to carry the transmitted signals from one computer to the next. Typically Unshielded Twisted Pair cabling is the most common (aka 10BaseT or 100BaseT).
TCP/IP, IPX/SPX, Apple Talk, NetBEUI, etc.
The most common type of network is the Local Area Network in which computers situated in a common physical enclosure are connected together. A typical office scenario would be the most common example.
When two buildings need to be connected together a Wide Area Network is needed. Typically joining two LANs together creates a WAN.
How do we join them?
Our NCL family of products is used to join two LANs and create a WAN…
…while our LMS product line provides a wireless Last Mile Solution for ISPs and home/small business users.
Two Network Interfaces:
Issues such as antenna selection, cabling, distance, Line of Sight, configuration, etc. must all be considered.
These topics covered in the RF Networking section.
Issues such as what type of protocol to use, medium and configuration must be considered.
How do I choose??
Used when connecting two segments of the same network together via the wireless link.
In Bridge Mode, the NCL product supports all protocols.
Used when connecting two different networks together.
The NCL/LMS products support TCP/IP when functioning in Route Mode.
Take advantage of Route Tables to route packets from one network to another.
Network ID: 192.168.10.0
Network ID: 10.32.0.0
Due to the popularity of the Internet and internet services such as e-mail and web pages, the TCP/IP protocol has become the protocol of choice for most networks.
It also allows the network administrator to use SNMP, DHCP and other services to help manage the network.
Transmission Control Protocol/Internet Protocol
Suite of protocols that, when used together, allow computers to pass data between one another. Each protocol in the suite performs a specific function in the communication process.
- used for connection based communication
- used for resolving IP addresses to MAC addresses
- used for remotely monitoring network devices
- used for addressing and routing data to the destination
DHCP, RIP, ICMP, UDP, FTP, HTTP, etc….
In 1978 the International Standards Organization introduced an architectural model that would allow all networks to be able to communicate with each other. This model is called the Open Standards Interconnect Reference Model (OSI).
All manufacturers have developed their product according to this standard. Understanding the OSI model will help you to understand how communication on a network happens.
Represents a layered approach to networking. Each layer of the model handles a different portion of the communications process. The OSI Model simplifies how hardware and software work together, as well as providing a specific method of how components should function.
The OSI model consists of 7 Layers.
Converts incoming signals into bits and converts outgoing bits into signals by managing the interface between the computer and the network medium.
Data Link (Layer 2)
Responsible for creating the frame type used on the network (ie. Ethernet vs. Token Ring). Also provides error checking to determine when data needs to be re-transmitted.
Network Layer (Layer 3)
Defines protocols for routing data by opening and maintaining a path on the network between systems to ensure that data arrives at the correct destination node.
Controls the movement of data between systems, defines protocols for structuring messages, and supervises the validity of transmissions by performing error checking.
Session Layer (Layer 5)
Coordinates communication between systems, maintaining sessions for as long as needed and performing security, logging, and administrative functions.
Presentation Layer (Layer 6)
Defines how information is formatted for display or printing, how data is encrypted, and translation of other character sets.
The highest layer of the model, defines the way applications interact with the network.
As data is sent through the model, a header is added at each layer. On the receiving end the data is passed from Layer 1 to Layer 7 with the headers being stripped off as they go until the Application receives the data to be processed.
TCP / IP
Session (Layer 5)
Transport (Layer 4)
Network (Layer 3)
Data Link (Layer 2)
Physical (Layer 1)TCP/IP Model
TCP/IP has it’s own reference model which relates to the OSI Model. By understanding the two models it is easy to see how the various protocols participate in the communication process.
FTP, SNMP, HTTP, SMTP, Telnet, PING
ICMP IP ARP
For a packet of information to reach it’s destination it must be addressed with the destinations address, much the same way a regular mail letter needs an address before you put it into the post box.
Where peoples homes have street addresses, with IP networking each computer has an IP address.
255 Consumers Road
On any given network (or street) no two computers (or homes) can have the same address. If so, then where would the packet (or mail) be delivered!?!?
260 Consumers Road
255 Consumers Road
265 Consumers Road
An IP address consists of two parts: a NetID portion and a HostID Portion
A house address consists of two parts: a street name and a house number
Obviously there could be two similar addresses in the world, the only difference being the cities each is located. Identifying the city tells the mail carrier how to handle the packet.
In the computer world the same holds true. The Subnet Mask associated with the computer defines which network it belongs to.
255 Consumers Road
265 Consumers Road
IP: 10.32.0.100 SM 255.255.255.224
The Subnet Mask determines what NetID the computer has.
Every device on a TCP/IP network requires a unique IP address. The IP address is commonly represented in ‘Dotted Decimal Notation’.
In reality, the IP address is really a 32-bit binary number. A computer would view the above IP address as:
Each ‘quarter’ of the IP address is called an Octet, because each quarter is made up of an 8-bit binary number.
Each bit in a binary number is assigned a decimal value. The more bits available in a binary number, the larger the decimal value of the number becomes.
128 64 32 16 8 4 2 1
1 1 0 0 1 1 1 1
When converting from decimal to binary, always start from the left and add bits to the right.
Warriors of the Net
Remember: the Application Layer of the TCP model is responsible for interacting with applications.
Many applications have a certain protocol they rely on to get the job done. Some common applications and their associated protocols would be:
Web Browser – HTTP
SNMP Manager – SNMP
E-Mail Program – SMTP
Hyper Text Transfer Protocol (HTTP) is the protocol used to transfer the data used to create Web Pages in your browser. To the end user the use of the protocol goes unnoticed, but to the application it is very important.
Another common protocol is the File Transfer Protocol (FTP). When transferring files over the Internet this protocol is used to create a connection oriented session to transfer the data. TCP is used to create the session and guarantee delivery of packets.
Telnet is a protocol commonly used to remotely administer Routers and other network devices from a remote location. It allows you to establish a session with the other machine and emulate keystrokes on the machine from your remote computer. All components of the LMS are manageable through Telnet sessions.
The LMS and NCL products are both configurable through a Telnet session to the unit.
Simple Network Management Protocol (SNMP) is used to remotely monitor or modify devices on your IP network. Unlike Telnet where you are actually emulating keystrokes on the unit, with SNMP you are polling devices for information. Depending on the security you set the units up with you can:
1. View information on the unit
2. View and edit information on the unit
SNMP relies on a Management Station to ask questions to Agents which respond to the questions appropriately.
The data that a Management station requests from an agent is held in a MIB (Management Information Base). Basically it is a list of questions that the management system can ask an agent.
Managers and Agents use the MIB tables as a lookup to send data back and forth.
Both the LMS and the NCL both have their own MIBs which are installed at the management station. That way the management station will know what information it can poll the agent for.
When the delivery of packets needs to be guaranteed the Transmission Control Protocol (TCP) is used at this layer to establish a ‘connection oriented’ session between the two computers.
The session tracks packets by monitoring when a packet is sent, in what order it is sent, and by notifying the sender when it is received. If for some reason packets are lost, the sending machine will resend the data. All of this ‘chatter’ between the two computers causes TCP to have more overhead than it’s counterpart UDP.
The User Datagram Protocol (UDP) is a non-connection based protocol that does not require a session to be established before transmitting data. Packets are not guaranteed and are also not retransmitted if lost in transit.
Because of the low overhead of UDP it is most commonly used with applications that depend on speed and where the guarantee of delivery is not very important. SNMP applications and real-time audio/video applications are good examples of applications that use UDP as a carrier.
TCP is typically used for transferring large amounts of data, where the application requires acknowledgement that the data has been received.
SNMP applications and real-time audio/video applications are good examples of applications that use UDP as a carrier.
Remember: the Internet Layer of the TCP model is responsible for addressing and routing of packets.
Every packet a computer generates must be addressed with an IP address. There are two possible ‘types’ of destination IP addresses a packet could possibly have:
When a computer is sending data to a computer on the same logical network as it is located on, the two computers are said to be ‘local’ to each other.
When a computer is sending data to a computer on a different logical network than the one it is located on, the two computers are said to be ‘remote’ to each other. In this case, a router must be present on each network to allow data packets to travel back and forth between the two.
The NetID is what the sending computer looks at to determine if the destination is local or remote to it.
IF (Destination NetID) = (Local NetID) then destination is local
IF (Destination NetID) < > (Local NetID) then destination is remote
How do we determine the NetID?
Upon boot up, all computers determine their own NetID by ANDing their IP address and their Subnet Mask.
1 & 1 = 1
1 & 0 = 0
0 & 0 = 0
22.214.171.124 a Network ID
The sending computer also ANDs the destination IP address of each packet with it’s own Subnet Mask to determine whether the packet is local or remote.
Dest IP: 126.96.36.199
188.8.131.52 a Local Network ID
Dest IP: 184.108.40.206
220.127.116.11 a Remote Network ID
By determining if the destination was Local or Remote, we are then able to address the packet properly.
When local, we stamp the packet with the destination IP address.
If remote we not only stamp it with the destination IP address, but we also stamp it with the default gateway (aka Router) IP address.
Now the Internet Layer can pass the packet to the lower layers of the OSI Model … right??
Unfortunately at the next layer (Data Link), a different addressing scheme is used. This layer uses the MAC address to determine if packets are to be forwarded to the upper layers, therefore we must also address each packet with the MAC address of the final destination.
Now that we know the destination IP address, how do we determine the MAC address needed?
Address Resolution Protocol allows a computer to send a broadcast on the network which basically says:
“I need to send a message to 192.168.9.2. Can the computer with this IP address please respond to this message and send your MAC address to 44-32-F9-00-00-01”
This message is sent as a broadcast on the network so that every computer on the network receives it. A broadcast message is sent with the MAC address of FF-FF-FF-FF-FF-FF. Every computer reads the message, but only the computer with a matching IP address will respond.
After the resolution takes place and a response is received, the requesting computer will then add the resolved MAC address to its ARP table, for future data transmission.
A typical ARP table contains the IP and corresponding MAC address. By storing this in memory, if the MAC has already been resolved, a broadcast message (which slows down the network) does not need to be sent.
This table is usually flushed every few minutes, but can be made to stay resident in memory.
If IP has determined the destination to be Local, ARP will look for the MAC address of the destination.
If IP has determined the destination to be Remote, ARP will look for the MAC address of the Default Gateway.
Given the previous information, we can now conclude how a computer communicates with both Local and Remote hosts.
1. Determine if IP is Local or Remote
2. Is there already an entry in ARP table? If not, send an ARP
1. Determine if IP is Local or Remote
5. This process continues until the final destination is reached.
In all networking environments one rule must be followed…..
No two computers can have the same IP address at any one time
An IP conflict occurs in this situation, with neither computer being able to communicate on the network. There are ways of assigning IPs without causing conflicts.
The best way to resolve any potential IP conflicts on your network is with the use of a DHCP Server.
Dynamic Host Configuration Protocol
A DHCP Server is a computer on your network that hands out IP addresses to hosts as they come online on the network.
TCP/IP is a ‘high maintenance’ protocol, and the DHCP server takes much of the management away from the Network Administrator.
Using a DHCP Server will allow automatic configuration of all these parameters (and more) without any manual intervention.
A client broadcasts a request on the network which only a DHCP server will reply to.
The request basically says “The computer with MAC address ?? Needs an IP address. Please send me one!”
The DHCP server responds with at least an IP address and Subnet Mask. Other options are configurable as well at the Network Administrators option.
An important thing to remember is that, by default, most routers will not forward broadcast messages. If your DHCP server is located on ‘the other side’ of a router, generally a DHCP Relay Agent must be installed on the network to act as an intermediary between the client and the server.
The Relay Agent is already configured with an IP address, and hence can get directly to the DHCP Server by knowing the IP Address of the server.
Both the LMS and the NCL (when in route mode) can be configured to act as DHCP Relay Agents, thereby avoiding any issues with DHCP broadcast messages across networks.
As most users know, sometimes things just don’t go right when logging onto a network, or surfing the web, etc. Most of us have seen messages that resemble the following:
To report any error messages regarding IP and the delivery of packages, the ICMP (Internet Control Message Protocol) is used. There are two basic types of messages: error and query
Most companies are taking advantage of the advanced features available through routers and are using Private IP addressing. This reduces both the setup and administrative costs of the network.
There are still rules that must be followed when choosing your own IP addresses, especially if you choose to connect to the internet eventually.
The disadvantage to this addressing scheme is that it requires an organization to use a Network Address Translator (NAT) at their router for global Internet access. However, the use of the private address space and NAT make it much easier for clients to change their ISP without the need to ‘renumber’ their network.
Public IP addresses are assigned and administered by the Network Providers (Telephone Companies, ISPs) and the whole orchestration of addressing is ultimately managed by a single organization known as Network Solutions.
For the most part, IP Addresses are given in chunks to Internet Service Providers who in turn hand them out to their clients.
By simply looking at the first octet of an IP address, it’s class is easily determined. This will help answer other questions such as how many HostIDs are available, what is the default Subnet Mask, etc.
Use the following chart to read the first octet:
After determining the IP Class, we can now determine how many octets (or bits) are allocated to the NetID and HostID.
Remember: Each octet contains 8 bits
With each IP Class there is also a default Subnet Mask associated with each. They are as follows:
Class A – 255.0.0.0
Class B – 255.255.0.0
Class C – 255.255.255.0
As can be seen, there is a direct relationship between the default subnet mask and the number of octets available for the NetID and the HostID.
…and knowing that the first 3 octets are for the NetID and the last octet is for the HostID with a Class C Address we can deduce the following…
IP: 18.104.22.168 11001111.00010111.10101111.00000010
SM: 255.255.255.0 11111111.11111111.11111111.00000000
By following the rule, we can clearly identify both the NetID and the HostID.
NetID – 22.214.171.124
HostID – 2
Now that we know how to determine the class and interpret the Subnet Mask, we can use that information to determine how many Hosts per network we can have.
By determining the # of bits in the HostID portion of the address and figuring out how many combinations of 1s and 0s there could possibly be will tell us how many HostIDs are available to us.
For example, with a default class C address 8 bits are available for the HostID (remember the default Class C Subnet Mask!)
00000000, 00000001, 00000010, 00000011, … , 11111110, 11111111
Using the following formula is much easier than counting!
Number of HostIDs = 2n-2
where n = # bits available for the HostID (or the # of 0s in the subnet mask)
* subtract 2 because a Host ID of all 0s or all 1s is not allowed
The following table summarizes the number of hosts available to each default IP Class:
216 –2 = 65,534
Quite often an ISP will divide up a Class C address into smaller segments, since rarely does a client need the full 254 addresses a Class C address comes with.
The ISP will divide up the Class C address by ‘subnetting’ it.
Subnetting is a way of manipulating the Subnet Mask and dividing up an IP address into smaller more manageable NetIDs.
Say an ISP had two customers who wanted to connect their networks wirelessly to the Internet. Each customer had 20 computers on their networks and weren’t planning on adding any more computers in the future.
The ISP has the NetID of 126.96.36.199 which it can distribute to customers.
How do we divide this up into two segments for distribution to the customer??
By default 8 bits are assigned to the HostID. If we take bits away from the HostID and allocate them to the NetID, it will give us more bits to create more NetIDs.
Subnetting involves modifying the Subnet Mask and taking bits away from the HostID to allow for more Network IDs.
In our example we need at least 2 NetIDs. In order to create 2 NetIDs we will borrow 1 bit from the HostID portion of the subnet mask.
IP: 188.8.131.52 11001000.01100100.00001010.00000000
IP: 184.108.40.206 11001000.01100100.00001010.00000000
Basically, the more bits you borrow, the more NetIDs you can create, but the fewer HostIDs per network you are allowed.
Use the following formula to determine the # of bits you need to borrow:
# of new NetIDs = 2n
where n = # bits borrowed from the HostID
In our example we need to borrow at least one bit and possibly up to 3 bits. If we borrow more than three bits we will not have enough hosts per network to support the 20 hosts on each network.
Lets assume we borrow 3 bits. That will leave us 3 bits available for the NetIDs…
.00100000, .01000000, .01100000, .10100000, .11000000, .11100000
… and 5 bits available for the HostID in each network.
The easiest way to calculate the NetID of each new network after subnetting is to take the decimal value of the last borrowed bit and add it to the original NetID.
Original NetID: 220.127.116.11
New Subnet Mask: 255.255.255.224
Decimal Value = 32
Original NetID: 18.104.22.168
+ 32 = 22.214.171.124
+ 32 = 126.96.36.199
+ 32 = 188.8.131.52
+ 32 = 184.108.40.206
+ 32 = 220.127.116.11
+ 32 = 18.104.22.168
+ 32 = 22.214.171.124
That leaves us with 5 bits for HostIDs in each network.
126.96.36.199 with HostIDs from 1-30
188.8.131.52 with HostIDs from 33 - 62
184.108.40.206 with HostIDs from 65 - 94
220.127.116.11 with HostIDs from 97 - 126
18.104.22.168 with HostIDs from 129 - 156
22.214.171.124 with HostIDs from 161 - 190
126.96.36.199 with HostIDs from 193 - 222
188.8.131.52 with HostIDs from 224 - 253
The main rule to remember with the HostID is that, in binary, a HostID of all 1s or all 0s is invalid…hence the reason for the –2 in our formula 2n – 2.
If we look at our first NetID of 184.108.40.206 and the Subnet Mask of 255.255.255.224, when the HostID is all 0s we have the equivalent of the NetID…
…and with a HostID of all 1s we have the broadcast IP address for the network.
The main thing to remember about subnetting is that the more bits you borrow, the more NetIDs you can create, but the fewer hosts per subnet you will be allowed.
Use the following checklist to help simplify subnetting:
4. Determine the resulting NetIDs that will be used.
5. Determine the resulting HostIDs that will be used.
Quite often different terminology is used to identify the subnet mask. Instead of displaying the entire subnet mask, an integer is often used to identify how many bits are in use (ie. How many 1s are in the subnet mask).
255.255.255.0 = 24
255.255.255.224 = 27
255.255.192.0 = 18
WaveRider products allow the use of either representation when configuring the unit.
In this situation our NCL product will need to be installed in Route mode, since we are connecting different networks together.
A general ‘Rule of Thumb’, is to supply your networks Router with the first available IP address in your IP class. Our new network would look similar to this:
Routers connect different networks together.
A router operates at the Internet layer of the TCP Model. It uses IP addresses to determine how to route data from one network to another.
The router uses its routing table to figure out where to send the data destined for various networks. The IP packet contains the source and destination addresses for the packet being sent.
Since routers connect different networks together we can conclude the following:
Therefore, in our network we need to assign the radio segment of our radios an IP address also. For our example we will use:
192.168.10.0 / 24
We now have 4 different IP networks.
By default a router has entries for the networks to which it is attached as well as an entry for the ‘loopback’ address.
The Default Route Table for the 220.127.116.11 router would look like:
A similar entry would appear in the other routers as well
A static route is entered manually through the command line interface. To add a route so that packets could travel from #1 to #2 we would add the following to 18.104.22.168:
The entry is basically specifying what interface to send data to when destined for a specific NetID.
Data can now get from #1 to #2, but until we add a route from #2 to #1, the communication will only be in one direction.
ip route add 22.214.171.124 192.168.10.1 27
In order for #1 to send data to #3, and vice versa, similar entries at the 126.96.36.199 and 188.8.131.52 routers will have to be made.
ip route add 184.108.40.206 192.168.10.3 27
ip route add 220.127.116.11 192.168.10.1 27
We now have data flow from:
1 to 2 1 to 3 3 to 1 2 to 1
Finally we need to add entries so that #2 can talk to #3. The two most important rules to remember are:
Therefore, in our network for #2 to talk to #3, all traffic must be passed though the router at 18.104.22.168
With both the NCL and the LMS radios, in a routed network all traffic is passed through the ‘Master’ radio.
Because of this, the route tables at the ‘Stations’ can be simplified with the following entry:
ip route add 0.0.0.0 <master radio> 0
This entry basically tells the local router to forward any packet that it does not have a route entry for to the Master radio.
Since the Master has a route entry to all other networks, the data will still get to the intended destination.
With Dynamic Routing there is no need for the Network Administrator to manually add route entries. Using the Router Information Protocol (RIP) the routers broadcast their route tables onto the network.
Over time all routers will learn routes to all other networks via these broadcasts.
The LMS and the NCL product line both incorporate RIP v2 into the product.
The two most common ways of verifying that two nodes on your network are communicating are through the PING and the TRACERT command.
Both commands are run from the DOS window on a Windows machine and allow you to verify whether or not another IP address is accessible over the network. They are both very handy in troubleshooting by allowing you to determine which ‘link’ in the chain is causing problems.
PING uses ICMP Echo Request and Reply messages to connect to another machine. If the other machine is accessible it will reply to your request. If a reply is not sent then usually there is either a routing problem or an IP problem.
TRACERT is used to view all the hops that are taken when passing through routers to a given destination. It is useful in determining exactly which hop is causing the communication problems.
Most common type of cabling.
Twisting of the wires provides protection from crosstalk.
UTP commonly referred to as CAT3 or CAT5. The number helps determine the speed of the cable. (CAT3 = 10Mbps CAT5 = 100Mbps).
Supports cable runs up to 100 meters (328 feet).
Use RJ-45 connectors.
STP contains shielding which makes it less vulnerable to outside interference, but much harder to install than UTP.
AKA 10BaseT or 100BaseT
Use a ‘crossed over’ UTP cable when connecting a node to another node without using a hub, or when connecting 2 hubs together that do not have an ‘uplink’ port.
Use a ‘straight through’ UTP cable when attaching nodes to a hub/switch or when attaching two hubs using the ‘uplink’ port.