Today we will cover:
• TCP/IP Model
• VLANs & Trunking
TCP/IP Model
• See diagram on board
• The U.S. Department of Defense (DoD)
created the TCP/IP reference model
because it w...
Internet Protocol Definition
• IP is a layer 3 protocol that offers a
connectionless service that provides besteffort deli...
TCP/IP Model Layers In Depth
• Application
– Handles high-level protocols, encoding, and
dialogue control.
– Ex: Telnet, F...
TCP/IP Layers (cont.)
• Internetwork (Internet)
– Defines logical addressing and routing.
– Ex: ICMP, ARP, RARP, IP

• Net...
VLANs & Trunking
.
“Switching”
• “Switching” is a generic term that can be
applied to Layer 2, Layer3, Layer 4, or any
layer
• To switch is t...
Switching
• A Layer 2 LAN switch, like a bridge, performs
switching & filtering based on the MAC address
(DLL)
• Remember:...
Switching
• A Layer 3 switch acts on a packet in the same
way that a traditional router does.
• Layer 3 switches are basic...
Switching
• A Layer 3 switch is a switch that performs
hardware-based routing using Layer 3
(network) addresses.
– Routers...
Switching
• Layer 4 switching is Layer 3 hardwarebased routing that uses Layer 4 info
• Forwarding based on:
– MAC address...
VLAN Concepts & Basics
• Think of a LAN and a broadcast domain
as being basically the same thing.
– Simple collision/broad...
VLAN Basics (cont.):
• With VLANs, a switch can put some
interfaces (ports) into one broadcast
domain and some into anothe...
Motivations for using VLANs:
• To group users by department, or by
groups that work together, instead of by
physical locat...
VLAN Configuration
• Two methods:
– Port-based (done with cables)
– MAC-based (high admin overhead at first)
– Network add...
VLAN Configuration
• We will cover VLAN switch commands in a
few weeks
Trunking w/ ISL & 802.1q
• Trunking – a method to support multiple
VLANs that have members on more than
one switch
• Examp...
Cisco Inter-Switch Link (ISL)
• Cisco created ISL before the IEEE
standardized a trunking protocol
• ISL is Cisco propriet...
ISL Header
• The ISL header includes several fields, but most
important, the ISL header VLAN field provides a
place to enc...
ISL Header (cont.)
• Also, the source and destination
addresses in the ISL header use MAC
addresses of the sending and rec...
IEEE 802.1Q
• Years after Cisco created ISL, IEEE created the
802.1Q standard.
• 802.1Q uses a different style of header t...
ISL & 802.1Q Compared:
• Both support a separate instance of
spanning-tree for each VLAN.
– What is purpose of STP?
Passing Traffic Between VLANs
• Layer 2 switching refers to the typical switchprocessing logic found at the DLL
• When VLA...
Traffic Between VLANs (cont.):
• Layer 3 Forwrding Using a Router:
– Switches do not forward frames between different
VLAN...
VLAN Traffic (cont.)
• Layer 4 switching
– The key to understanding Layer 4 switching is
to remember the function of TCP a...
VLAN Traffic (cont.):
• Layer 5-7 Switching:
– Also called
• Layer 7 Switching
• Application Layer Switching (named for TC...
VLAN Traffic (cont.)
• Multilayer Switching:
– A switch that concurrently performs switching
based on multiple layers.
– F...
Comparison of Switching Layers:
• L2 Switching
– (no VLAN to another)

• L3 Switch
• L4 Switch
• L5-L7 Switch
• Multilayer...
Comparison Notes
• L2 switching is the only option in the table
that does not allow forwarding from one
VLAN to another.
•...
VTP
• Will be added shortly
VTP Pruning
• Will be added shortly.
Quiz Time
.
1
• What are the four layers of the TCP/IP
model?
2
• What two protocols function at the
transport (host-to-host) layer of the TCP/IP
model?
3
• What are some protocols that operate at
the TCP/IP Internet layer?
4
• What is a Layer 3 switching device?
5
• What are VLANs?
6
• For VLANs to communicate with each
other, what network component is
needed?
7
• What are the two most common trunking
protocols supported by Cisco switches?
Next Meeting March 22
• IP & Addressing Fundamentals
• Subnetting
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Vlan1

  1. 1. Today we will cover: • TCP/IP Model • VLANs & Trunking
  2. 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 • We’ve been over TCP… • Internet Protocol (IP)
  3. 3. Internet Protocol Definition • IP is a layer 3 protocol that offers a connectionless service that provides besteffort 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. 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. 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. 6. VLANs & Trunking .
  7. 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. 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. 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. 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. 11. Switching • Layer 4 switching is Layer 3 hardwarebased 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. 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. 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. 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. 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. 16. VLAN Configuration • We will cover VLAN switch commands in a few weeks
  17. 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. 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. 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. 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. 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. 22. ISL & 802.1Q Compared: • Both support a separate instance of spanning-tree for each VLAN. – What is purpose of STP?
  23. 23. Passing Traffic Between VLANs • Layer 2 switching refers to the typical switchprocessing 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. 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. 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. 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. 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. 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. 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. 30. VTP • Will be added shortly
  31. 31. VTP Pruning • Will be added shortly.
  32. 32. Quiz Time .
  33. 33. 1 • What are the four layers of the TCP/IP model?
  34. 34. 2 • What two protocols function at the transport (host-to-host) layer of the TCP/IP model?
  35. 35. 3 • What are some protocols that operate at the TCP/IP Internet layer?
  36. 36. 4 • What is a Layer 3 switching device?
  37. 37. 5 • What are VLANs?
  38. 38. 6 • For VLANs to communicate with each other, what network component is needed?
  39. 39. 7 • What are the two most common trunking protocols supported by Cisco switches?
  40. 40. Next Meeting March 22 • IP & Addressing Fundamentals • Subnetting
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