Today we will cover:

1
Today we will cover

• TCP/IP Model
• VLANs Trunking

2
TCP/IP Model

• See diagram on board
• The U.S. Department of Defense (DoD) created the
  TCP/IP reference model because it wanted a
  network that could survive anything, like a
  nuclear war
• Weve been over TCP
• Internet Protocol (IP)

3
Internet Protocol Definition

• IP is a layer 3 protocol that offers a
  connectionless service that provides best-effort
  delivery across a network
• Ex post office
• IP looks for a way to move the packets to their
  destination.
• IP is packet-based networking
• Layer 3 packets

4
TCP/IP Model Layers In Depth

• Application
• Handles high-level protocols, encoding, and
  dialogue control.
• Ex Telnet, FTP, LPD, SNMP, TFTP, SMTP, NFS, X
  Window
• Transport (Host-to-Host)
• Reliability, flow control, and error correction.
• Ex TCP, UDP

5
TCP/IP Layers (cont.)

• Internetwork (Internet)
• Defines logical addressing and routing.
• Ex ICMP, ARP, RARP, IP
• Network Interface (Network access)
• Defines the protocols and hardware required to
  deliver data across some physical network.
• EX Ethernet, Token Ring, FDDI

6
VLANs Trunking

• .

7
Switching

• Switching is a generic term that can be applied
  to Layer 2, Layer3, Layer 4, or any layer
• To switch is to filter or forward data
• A switch is a network device that filters,
  forwards, and floods frames based on the
  destination address of each frame.

8
Switching

• A Layer 2 LAN switch, like a bridge, performs
  switching filtering based on the MAC address
  (DLL)
• Remember
• Bridge software-based
• Switch hardware-based
• All the ports on a bridge or a Layer 2 switch
  belong to the same Layer 3 network (i.e., the
  same IP network), so a broadcast by one station
  is forwarded by all the Layer 2 switches or
  bridges to all other stations.

9
Switching

• A Layer 3 switch acts on a packet in the same way
  that a traditional router does.
• Layer 3 switches are basically a cross between a
  LAN switch and a router.
• Each port on the switch is a separate LAN port
• But, the forwarding engine, the ASIC (application
  specific integrated circuit), calculates and
  stores routes based on Layer 3 addresses (IP
  addresses), NOT MAC addresses

10
Switching

• A Layer 3 switch is a switch that performs
  hardware-based routing using Layer 3 (network)
  addresses.
• Routers software-based
• A Layer 3 switch is a cost effective alternative
  to the traditional router. (Usually)

11
Switching

• Layer 4 switching is Layer 3 hardware-based
  routing that uses Layer 4 info
• Forwarding based on
• MAC addresses (Layer 2)
• Source/destination IP addresses (Layer 3)
• TCP/UDP (Layer 4) application port numbers
• More to come on different layer switching

12
VLAN Concepts Basics

• Think of a LAN and a broadcast domain as being
  basically the same thing.
• Simple collision/broadcast model (p. 246, 247
  INTRO)
• Without VLANs, a switch treats all interfaces on
  the switch as being in the same broadcast domain
  all connected devices are in the same LAN.

13
VLAN Basics (cont.)

• With VLANs, a switch can put some interfaces
  (ports) into one broadcast domain and some into
  another.
• Essentially, the switch creates multiple
  broadcast domains the individual broadcast
  domains are called virtual LANs.
• Example see board (p. 264 INTRO)

14
Motivations for using VLANs

• To group users by department, or by groups that
  work together, instead of by physical location
• To reduce overhead by limiting the size of each
  broadcast domain
• To enforce better security

15
VLAN Configuration

• Two methods
• Port-based (done with cables)
• MAC-based (high admin overhead at first)
• Network address (logical or IP address)
• Dynamic vs. static
• Dynamic done with VLAN Management Policy Server
  (VMPS) database maps MAC addresses to VLANs
• Static
• Created by administrator

16
VLAN Configuration

• We will cover VLAN switch commands in a few weeks

17
Trunking w/ ISL 802.1q

• Trunking a method to support multiple VLANs
  that have members on more than one switch
• Example see board (p. 265 INTRO)
• Cisco switches support two different trunking
  protocols
• Cisco Inter-Switch Link (ISL)
• IEEE 802.1Q

18
Cisco Inter-Switch Link (ISL)

• Cisco created ISL before the IEEE standardized a
  trunking protocol
• ISL is Cisco proprietary it can only be used
  between two Cisco switches
• ISL encapsulates each frame in an ISL header
  trailer

19
ISL Header

• The ISL header includes several fields, but most
  important, the ISL header VLAN field provides a
  place to encode the VLAN number.
• By tagging a frame with the correct VLAN number
  inside the header, the sending switch can ensure
  that the receiving switch knows which VLAN the
  encapsulated frame belongs to
• This is called Frame Tagging

20
ISL Header (cont.)

• Also, the source and destination addresses in the
  ISL header use MAC addresses of the sending and
  receiving switch, not the node device that
  originally sent the frame.

21
IEEE 802.1Q

• Years after Cisco created ISL, IEEE created the
  802.1Q standard.
• 802.1Q uses a different style of header than does
  ISL for tagging frames with a VLAN number.
• 802.1Q does not encapsulate it adds an extra
  4-byte header to the middle of the original
  Ethernet header
• Called Frame Tagging as well
• 802.1Q forces a recalculation of FCS
• See frame example

22
ISL 802.1Q Compared

• Both support a separate instance of spanning-tree
  for each VLAN.
• What is purpose of STP?

23
Passing Traffic Between VLANs

• Layer 2 switching refers to the typical
  switch-processing logic found at the DLL
• When VLANs are used, an L2 switch uses the same
  logic, but per VLAN.
• There is a MAC address table for each VLAN.
• Unicasts sent inside one VLAN cannot be
  forwarded out ports in another VLAN.
• Broadcasts cannot traverse VLANs (need a router
  for that)

24
Traffic Between VLANs (cont.)

• Layer 3 Forwrding Using a Router
• Switches do not forward frames between different
  VLANs!!!!
• A router does this!!!
• Forwarding Using a Layer 3 Switch
• The term Layer-3 switch refers to a switch that
  also has routing features
• The router internal to the switch performs the
  same routing function as a router.
• L3 switches use
• ASICs
• Software used to run other processes, like
  routing protocols

25
VLAN Traffic (cont.)

• Layer 4 switching
• The key to understanding Layer 4 switching is to
  remember the function of TCP and UDP port numbers
  (see p. 155 INTRO for examples).
• With Cisco switches you can enable a feature
  called NetFlow switching, which performs
  accounting based on Layer 4 information (like
  port numbers) while forwarding traffic like a
  Layer 3 switch.

26
VLAN Traffic (cont.)

• Layer 5-7 Switching
• Also called
• Layer 7 Switching
• Application Layer Switching (named for TCP/IP
  Model)
• L5-L7
• Looks past the Layer 4 header, into application
  layer headers, to make switching decisions
• A feature Cisco calls Content Delivery Networks
  (CDN).

27
VLAN Traffic (cont.)

• Multilayer Switching
• A switch that concurrently performs switching
  based on multiple layers.
• For instance, most L3 switches also perform L2
  switching inside a VLAN and L3 switching for
  traffic between VLANs.

28
Comparison of Switching Layers

• L2 Switching
• (no VLAN to another)
• L3 Switch
• L4 Switch
• L5-L7 Switch
• Multilayer

• Forwards based on MAC address.
• Based on destination IP address for traffic to
  another VLAN.
• Typically based on port numbers.
• Based on Application Layer (TCP/IP Model)
• Concurrent switching on multiple layers.

29
Comparison Notes

• L2 switching is the only option in the table that
  does not allow forwarding from one VLAN to
  another.
• External router, connected to L2 switch router
  forwards like always, based on destination IP
  address.

30
VTP

• Will be added shortly

31
VTP Pruning

• Will be added shortly.

32
Quiz Time

• .

33
1

• What are the four layers of the TCP/IP model?

34
2

• What two protocols function at the transport
  (host-to-host) layer of the TCP/IP model?

35
3

• What are some protocols that operate at the
  TCP/IP Internet layer?

36
4

• What is a Layer 3 switching device?

37
5

• What are VLANs?

38
6

• For VLANs to communicate with each other, what
  network component is needed?

39
7

• What are the two most common trunking protocols
  supported by Cisco switches?

40
Next Meeting March 22

• IP Addressing Fundamentals
• Subnetting