IP Networking.

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 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.
Protocol The ‘language’, or set of rules, that govern the communication between two devices. The protocol determines the following: the type of error checking to be used data compression method, if any how the sending device will indicate that it has finished sending a message how the receiving device will indicate that it has received a message TCP/IP, IPX/SPX, Apple Talk, NetBEUI, etc.

Network Types 1. LAN 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.

Network Types 2. WAN 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?

Traditional Methods T1 T3 Fiber DSL Modem

WaveRider Methods Wireless What the hell Wireless

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.

WaveRider Product Two Network Interfaces: RF Interface (SMA connector)
Ethernet Interface (10BaseT)

RF Perspective Ethernet Perspective
Issues such as antenna selection, cabling, distance, Line of Sight, configuration, etc. must all be considered. These topics covered in the RF Networking section. Ethernet Perspective Issues such as what type of protocol to use, medium and configuration must be considered.

How to Implement? How do I choose?? Two options: Bridge Mode
Route Mode How do I choose??

Bridge Mode Used when connecting two segments of the same network together via the wireless link. In Bridge Mode, the NCL product supports all protocols. TCP/IP NetBEUI IPX/SPX AppleTalk

Route Mode 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. TCP/IP Network ID: Network ID:

TCP/IP: The Internet Protocol
Due to the popularity of the Internet and internet services such as 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. TCP/IP Transmission Control Protocol/Internet Protocol

DHCP, RIP, ICMP, UDP, FTP, HTTP, etc….
What is TCP/IP? 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. TCP - used for connection based communication ARP - used for resolving IP addresses to MAC addresses SNMP - used for remotely monitoring network devices IP - 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.

The OSI Reference Model
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.

Physical Layer (Layer 1)
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.

Transport Layer (Layer 4)
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.

Application Layer (Layer 7)
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.

FTP, SNMP, HTTP, SMTP, Telnet, PING
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. OSI TCP / IP Application (Layer7) Application Presentation (Layer6) Session (Layer 5) Transport (Layer 4) Transport Network (Layer 3) Internet Data Link (Layer 2) Network Interface Physical (Layer 1) FTP, SNMP, HTTP, SMTP, Telnet, PING TCP UDP ICMP IP ARP

Network Addressing 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 255 Consumers Road

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 Toronto, Canada 265 Consumers Road Melbourne, AUS

The Subnet Mask determines what NetID the computer has.
IP: SM: IP: SM Network Network The Subnet Mask determines what NetID the computer has.

IP Rules…so far All computers on a given network must have same NetID
No two computers can have the same HostID All computers on the same network must have the same subnet mask

IP Address 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.

Binary Numbers 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. = 207 Tip: When converting from decimal to binary, always start from the left and add bits to the right.

Review Test #1

Movie Warriors of the Net

Application Layer Protocols

HTTP FTP Telnet SNMP 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 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.

Transport Layer Protocols

TCP UDP Remember: the Transport Layer of the TCP model is responsible for delivery and movement of packets. There are two ways in which a packet can be delivered to another computer. Guaranteed with some sort of acknowledgement of delivery (ie. Registered Mail) Non-Guaranteed with no acknowledgment of delivery (ie. Regular Mail)

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.

Internet Layer Protocols

IP ARP DHCP ICMP 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: Local Remote

Local 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. Remote 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.

How do we determine the NetID?
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?

ANDing Upon boot up, all computers determine their own NetID by ANDing their IP address and their Subnet Mask. IP: SM: 1 & 1 = 1 1 & 0 = 0 0 & 0 = 0 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: SM: a Local Network ID Dest IP: SM: a Remote Network ID

Why did we do that? 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??

One More Step… 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?

ARP – Address Resolution Protocol
Address Resolution Protocol allows a computer to send a broadcast on the network which basically says: “I need to send a message to Can the computer with this IP address please respond to this message and send your MAC address to F ”

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
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.

Resolving a Local IP Address
1. Determine if IP is Local or Remote 2. Is there already an entry in ARP table? If not, send an ARP broadcast. Once address resolved, address the data packet with MAC and send.

When the IP is Remote 1. Determine if IP is Local or Remote
If remote, the source will send the data packet to its Default Gateway (Router), therefore the MAC of the router needs to be resolved. An ARP is sent requesting the MAC for the Router. (All nodes on a network would be preprogrammed with the IP of the router) Once the MAC of the router is resolved, the data is sent to the router. The data packet contains the IP of final destination. The router then goes through the same process of determining whether that IP is local or remote to it. 5. This process continues until the final destination is reached.

No two computers can have the same IP address at any one time
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.

Dynamic Host Configuration Protocol
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.

IP Configuration Options

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.

Broadcasts 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.

WaveRider Products 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 Error messages might include: Destination Unreachable Redirect Time Exceeded

Query messages might include:
Echo Request Echo Reply PING (Personal Internet Groper) is a protocol that uses ICMP to verify that a particular IP address exists on a network. One of the most common and easy to use troubleshooting methods available.

IP Addresses

How does a company pick it’s IP address?
Two options: Public IP addressing Private IP addressing 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. RFC 1918 clearly defines which NetIDs are allowed in a private addressing scheme: /8 /16 /16

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.

Determining the Address Class
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:

Remember: Each octet contains 8 bits
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 – Class B – Class C – a b.c.d a.b c.d a.b.c d 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.

By reading the subnet mask in binary…
SM: …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… a 1 in the SM means the corresponding bit in the IP address is used for the Network ID a 0 in the SM means the corresponding bit in the IP address is used for the Host ID

Example: IP: SM: By following the rule, we can clearly identify both the NetID and the HostID. NetID – HostID – 2

How many Hosts?? 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!)

How many possible combinations of 8 bits are there??
, , , , … , , 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.

Subnetting Example 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 200.100.10.0 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. Before Subnetting: IP: SM: After Subnetting: IP: SM:

where n = # bits borrowed from the HostID
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

Class C Subnetting

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… , , , , , … and 5 bits available for the HostID in each network.

What are the new NetIDs?? 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: New Subnet Mask: Decimal Value = 32

That leaves us with 5 bits for HostIDs in each network.
Fourth Octet Original NetID: + 32 = + 32 = + 32 = + 32 = + 32 = + 32 = + 32 = That leaves us with 5 bits for HostIDs in each network.

The New Networks 200.100.10.0 with HostIDs from 1-30

HostIDs 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 and the Subnet Mask of , 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.

This same theory holds true for all the NetIDs generated by subnetting.
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:

Subnetting Checklist Determine the number of NetIDs required currently and in the future. Determine the maximum number of hosts required per subnet currently and in the future. Define one Subnet Mask for the entire network that allows for the desired NetIDs and HostIDs. 4. Determine the resulting NetIDs that will be used. 5. Determine the resulting HostIDs that will be used.

Our New Network NetID: 200.100.10.0 SM: 255.255.255.224

Subnet Mask Interpretation
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). = 24 = 27 = 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:

#2 #1 #3

Routers 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:
A router needs at least two interfaces…one to connect each interface. A router needs at least two IP addresses…one for each interface. A router needs a populated route table to know how to direct traffic.

WaveRider Routers When acting as a router, the WaveRider product is connected to two networks: The ethernet network The radio network Therefore, in our network we need to assign the radio segment of our radios an IP address also. For our example we will use: / 24

We now have 4 different IP networks.
#2 #1 #3 We now have 4 different IP networks.

A similar entry would appear in the other routers as well
Default Route Entries 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 router would look like: A similar entry would appear in the other routers as well

Establishing Route Tables
The Routers do not know of other networks by default and must have their Route Tables built in order to forward traffic properly. Two methods for achieving this: Static Route entries Dynamic Route entries

Static Routing 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 : 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. #2 #1 ip route add

In order for #1 to send data to #3, and vice versa, similar entries at the and routers will have to be made. ip route add ip route add

We now have data flow from:
#2 #1 #3 We now have data flow from: 1 to to to to 1

Finally we need to add entries so that #2 can talk to #3
Finally we need to add entries so that #2 can talk to #3. The two most important rules to remember are: You can only pass data as far as the next router. You can only pass RF traffic to a radio which you have ‘Line of Sight’ with. Therefore, in our network for #2 to talk to #3, all traffic must be passed though the router at

Eventually the route tables in all routers would look like this:
#1 #2 #3

ip route add 0.0.0.0 <master radio> 0
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 <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.

The route tables will now look like this:
#1 #2 #3

Dynamic Routing 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.

Network Troubleshooting Basics

Verifying Communications
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.

What is the #1 cause of most Networking Problems??
BAD CABLING!!!

Twisted Pair Cabling 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.

Review Test

IP Networking.

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