Chapter 5 Intro to Routing & Switching

 Upon completion of this chapter, you should be able to:  Describe the operation of the Ethernet sublayers.  Identify the major fields of the Ethernet frame.  Describe the purpose and characteristics of the Ethernet MAC address.  Describe the purpose of ARP.  Explain how ARP requests impact network and host performance.  Explain basic switching concepts.  Compare fixed configuration and modular switches.  Configure a Layer 3 switch.

5.1.1

 Most widely used LAN technology  What 2 layers does it operate at?  Data link & physical  What are the 2 sublayers of the data link?  LLC & MAC

 IEEE  Helps communicate with network layer  Adds control info  Performs it in software

 Encapsulates the data  Adds MAC addresses  Adds error detection to frame  Media Access Control  Placing the frames on the media  Ethernet is a logical bus; physical star  Signal passes to all  Can send whenever  Can be collisions

 Ethernet is contention-based/non-deterministic  Data contends or shares for a spot on the media  Doesn’t know when it’ll get access to it  Listens for signal on media  No signal = transmit data  Transmit at same time= collision  Devices do not keep track of whose turn it is  More collisions= less throughput  SOLUTION: CSMA/CD & CSMA/CA

 Listens for silence  Silence= transmit data  If devices transmit at same time, collision  Backoff random time, listen for silence, retransmit  Collision detection not a problem much anymore  Using switches & full-duplex, this is not a problem anymore

 Wireless  Listen for silence  Sends Ready to Send message to AP  Gets a Clear to Send message from AP  Sends data

 Used to identify frame  Each host has a unique address  Burned into NIC hardware  48-bits / 12 hex digits / 6 bytes  1 st 24 bits OUI; 2 nd 24 bits serial #

 How many bits is a MAC address?  48 bits  What is the OUI in this MAC? A2:07:CC:F6:AD:32  A2:07:CC  What does a wireless network use to avoid collisions?  CSMA/CA  What sublayer places the frames on the media?  MAC

 The OUI is how many bytes? 33  Ethernet shares access to the media. It contends for the media and does not take turns transmitting. Not taking turns means the network is…  Nondeterministic  Is the MAC address found in hardware or software?  Software End of Day One

5.1.2

 Min. frame size is 64 bytes; max is 1522 bytes  Data is bytes  > 64 bytes is considered a collision fragment & will be dropped



 What important addresses are encapsulated into a frame?  Source & destination MAC  What does the preamble used for?  Timing/synchronization  What is the minimum frame size?  64 bytes  What happens if a frame is less than 64 bytes?  Considered a fragment & dropped

 How many bits in a MAC address?  48 bits  How many hex digits?  12  The first 6 hex digits are what?  The OUI  The OUI would then be the 1 st ____ bytes. 33  What sublayer is used to communicate with the upper layers?  LLC

5.1.3

 IP Address:  32 bits, 4 octets  8 bits in each octet   Written in decimal   Value in each octet from  That’s a total of 256 numbers.

 Add up the values of the binary 1’s  156  

 Ipconfig /all  Hexadecimal (Base 16)  0-9, A-F (10-15)  16 total #’s

 Handouts

 Begin with a 0x  0xA4

 One to one communication

 One to all in a network  Dest. MAC address will be all F’s  DHCP & ARP use broadcasts

 One to a group in a network  Remote gaming or video conference  Dest. IP will be  Dest. MAC will begin with E



 What kind of message gets sent from one PC to a group within a network?  Multicast  Identify each as unicast, multicast, or broadcast:

5.1.4

 MAC address  Burned into NIC (DOES NOT CHANGE)  Similar to the name of a person  Physical address  IP address  Similar to the address of a person  Based on where the host is actually located  Logical address  Both the physical MAC & logical IP addresses are required for a computer to communicate just like both the name and address of a person are required to send a letter

 Destination IP NEVER changes!  Source & Destination MAC changes at each router interface

 Wireshark

 How do you change your MAC address?  Get a new NIC  T or F. The destination IP address changes during transmission.  False  What happens to the source & destination MAC addresses as you go from router to router across the Internet?  They change (router port substituted)

 What is IEEE 802.2?  LLC sublayer  What is IEEE 802.3?  Ethernet/MAC sublayer  What is a layer 2 address?  MAC address  What is a layer 3 address?  IP address

5.2.1

 ARP table of IP/MACs  Added from communication  Added from ARP requests  You have the dest. IP, not the MAC  ARP request is all F’s where?  Destination MAC  How is an ARP request sent?  Broadcast  Who replies to the ARP request?  Only one with matching dest. IP

 Windows-  Arp –a  Cisco router  Router# show ip arp

 If you want to access a remote server, and you don’t have the destination MAC, what gets substituted for it?  The default gateway’s MAC address  A router has ports with MAC addresses. How do you view the router’s ARP table?  Router#sh ip arp  What does ARP find? What do you know?  Finds the dest. MAC; you know the dest. IP

5.2.2

 Broadcasts  It’s a broadcast. If many devices started at same time, there’d be a flood of ARP requests which would cause a reduction in performance for a short period of time.  Security  ARP poisoning (or spoofing)  Attacker forges MAC address to have frames delivered to different computer  Solution: Use a switch

 Segments network into smaller collision domains  Replies go to one device only  Implement security too

5.3.1

 Full duplex, Half duplex, Auto  Must match setting of device  Half duplex uses CSMA/CD to avoid collisions

 Cisco uses cut-through switching  As soon as destination MAC is read, it forwards the frame  Fast-forward Lowest latency; in and out  Fragment-free Store first 64 bytes before forwarding Most errors & collision happen there (runts) If it makes it through, should be error-free

 Complete

 2 switches connect to each other. One port is 100Mbps and the other is 1000Mbps. What speed will that connection operate at?  100Mbps  What feature will allow you to use a straight- through cable to connect two switches together?  Auto-MDIX  Your switch port is connected to a hub with 3 computers on it. How many MAC addresses will be in the table for that port? 33

 Switch it!   Do it at least 4 times  Different scenario each time  Lab together  Draw network from MAC address table

5.3.2

 Fixed Configuration Switch  As is; no add-ons or changing  A 24 port switch will always be 24 ports  Modular  Add-in cards/ports  Stackable  Connected by special cable to act as one switch  Fixed may be stackable  PoE (Power over Ethernet)  Delivers power to a device, like an IP phone  We use this in school  More $$, faster forwarding rate

 Which type of switch can you add a card to add more Ethernet ports or add fiber ports?  Modular  You bought a 24 port switch and cannot add more ports to it. What kind of switch did you buy?  Fixed  You have the switch above and need more ports. You then buy more 24 port switches and connect them with a special cable. What kind of switch do you now have?  Fixed & stackable

5.3.3

 Looks like a switch  Combined with router functions  Adds in router functions  Knows which IP addresses are out each port too  Fast

 Make an Ethernet port a routed port  To connect to the ISP  Configure a port  What have we configured with an IP on a switch?  IP for remote management  This is similar

F0/6

  Configuring a Layer 3 Switch

 What address(es) does a layer 2 switch read?  MAC addresses  What address(es) does a layer 3 switch read?  IP & MAC  You want to connect your Layer 3 switch to your ISP instead of using a regular router. What must you configure one of the ports as?  Routed port  Which command enables the routing function on a switch port?  No switchport

 Complete the study guide handout  Take the quiz on netacad.com  Jeopardy review

In this chapter, you learned:  Ethernet is the most widely used LAN technology used today.  Ethernet standards define both the Layer 2 protocols and the Layer 1 technologies.  The Ethernet frame structure adds headers and trailers around the Layer 3 PDU to encapsulate the message being sent.  As an implementation of the IEEE 802.2/3 standards, the Ethernet frame provides MAC addressing and error checking.  Using switches in the local network has reduced the probability of frame collisions in half-duplex links.

 The Layer 2 addressing provided by Ethernet supports unicast, multicast, and broadcast communications.  Ethernet uses the ARP to determine the MAC addresses of destinations and map them against known IP addresses.  Each node on a network has both a MAC address and an IP address.  The ARP protocol resolves IPv4 addresses to MAC addresses and maintains a table of mappings.  A Layer 2 switch builds a MAC address table that it uses to make forwarding decisions.

 Layer 3 switches are also capable of performing Layer 3 routing functions, reducing the need for dedicated routers on a LAN.  Layer 3 switches have specialized switching hardware so they can typically route data as quickly as they can switch.

Chapter 5 Intro to Routing & Switching