The presentation introduces to local ethernet networks. Explains physical and data link OSI layers of ethernet networks. Few fundamental terms are also explained: - duplex and half duplex communication - collision domain - ethernet switch logic - VLAN tags

1. Andriy Berestovskyy
2017
( ц ) А н д р
і й Б е р е с
т о в с ь к и
й
networking hour
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berestovskyy
Networking Fundamentals
Local Networks

2. Networking Fundamentals
● Computer Networks
● Networking Models
● > Local Networks
● Internet
● IPv4 Routing
● Transport Protocols
2

3. Krakusa 11, 1st floor
Local Area Network
3
Krakusa 11, 2nd floor Krakusa 11, 3rd floor
How?
Interconnects hosts within a limited area and has its network
equipment and interconnects locally managed

4. Typical SOHO LAN
4
Internet
Switch
Access Point
Router
SOHO?
Distance?

5. Small Office/Home Office (SOHO) — category of business that
involves from 1 to 10 workers
— Wikipedia
5

6. Building 1
Typical Corporate LAN
6
Corporate
Network
Floor 2
Floor 1
Distance?

7. Building 1
Typical Corporate Network
7
Corporate
Network
Building 2
Building 3
Building 4
Distance?

8. Ethernet Physical Layer
8
Application
Presentation
Session
Transport
Network
Data Link
Physical
Frame
Bits
MAC Data FCS
IP Data
TCP Data
Packet
Segment
Data
7
6
5
4
3
2
1
Hi!
Salut!

9. Typical Ethernet Physical Layers
9
10 Mbps
Speed
100 Mbps
1 Gbps
Name
1 Gbps
10 Gbps
Medium Distance
10BASE-T Twisted Pair 100 m
100BASE-T Twisted Pair 100 m
10 Mbps10BASE2 Coaxial Cable 100 m
1000BASE-T Twisted Pair 100 m
1000BASE-LX SM Fiber 5 km
10GBASE-LR SM Fiber 10 km
10 Gbps10GBASE-ER SM Fiber 40 km
Ethernet
Fast Ethernet
10 Gigabit Ethernet
Gigabit Ethernet
More?

10. Switch
Ethernet Link Over a Twisted Pair
10
Host
Cable
RJ-45
Connector
RJ-45
Connector
RJ-45
Port
RJ-45
Port

11. Switch
Fast Ethernet Straight Cable
11
Host
TX RX
RX TX
1
2
3
6
Twisted Pair
Twisted Pair
1
2
3
6
Host
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
Switch
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
MDI* MDI-X*
* Media Dependent Interface (Crossover)

12. Host
Fast Ethernet Crossover Cable
12
Host
TX TX
RX RX
1
2
3
6
Twisted Pair
Twisted Pair
1
2
3
6
Host
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
Host
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
MDI MDI

13. Cable Usage?
13
Access Point
Host
Router
Switch
Hub
Host Access Point Router Hub Switch

14. Cable Usage
14
Access Point
CrossHost
Router
Switch
Hub
Host
Cross
Access Point
Cross
Router
Straight
Hub Switch
Cross Cross Cross
Cross Cross Cross
Cross Cross
Cross Cross
MDI MDI-X
Straight
Straight Straight
Straight Straight
Straight Straight
Straight Straight
Straight
Straight
MDI-X

15. Gigabit Ethernet Cable Pinout
15
Host
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
Host
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
MDI MDI
Host
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
Switch
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
MDI MDI-X

16. Host BHost A
10BASE2 Physical Layer
16
Data Data
0 V
+1 V
-1 V
Data 1 0 1 0 0 1 1 1 0 0 1
Source: https://en.wikipedia.org/wiki/Manchester_code
● Manchester encoding
● Half duplex
Duplex?
BNC T-Connector BNC T-Connector
Why?

17. Half Duplex Communication
17
send or receive :(
or
What if
both?

18. Collision
18
Host A Host B

19. Collision occurs when several demands are made simultaneously on
equipment that can handle only one at a time
— Wikipedia
19

20. Collision domain — section of a network where
data packets can collide with one another
— Wikipedia
20
Broadcast
domain?

21. Shared Medium Collision Domain
21
Host A
Host B
Host C
Host D
10Base2 Ethernet
over Coaxial cable
Collision
domain?
C
B
A
D
1 1

22. Collision Domain
Shared Medium Collision Domain
22
Host A
Host B
Host C
Host D
C
B
A
D
2
10Base2 Ethernet
over Coaxial cable
1 1
Solutions?

23. CSMA/CD
Carrier-Sense Multiple Access with Collision Detection
media access control method:
1. IF medium is not idle THEN goto 1
2. Start transmission + monitor for a collision
3. IF collision occurred THEN wait, goto 1
23

24. Repeater Hub
TX
Host A
10BASE-T Physical Layer
24
TX RX
RX TX
RX
TX
0 V
+1 V
-1 V
Data 1 0 1 0 0 1 1 1 0 0 1
● Manchester encoding
● Half duplex
Why?
RX
TX
RX

25. Repeater Hub Collision Domain
25
Host A
Host B
Host C
Host D
Repeater Hub
Collision
domain?
10Base-T Ethernet
over a Twisted Pair
A
B
A
C
1
1

26. Collision Domain
Repeater Hub Collision Domain
26
Host A
Host B
Host C
Host D
Repeater Hub
A
B
A
C
1
1
A
C
A
B
2
A
C
A
B
2

27. Switch
RX
TX
Host A
10GBASE-T Physical Layer
27
TX RX
More info: https://en.wikipedia.org/wiki/Pulse-amplitude_modulation
RX TX
RX
TX
0 V
+1 V
-1 V
Data*
1
0
1
0
0
1
1
1
0
0
1
0
● PAM-16 encoding*
● Full duplex
Why?
TX
RX
CPU
0000
* oversimplification!
0010
0100
0110
1111
1101
1011
1001
RAMRAM
1
1
1
1
1
1
0
1
0
0
0
1
0
1
0
0
1
1
1
1
0
1
1
1
1
0
0
1
1
0
0
0
What for?

28. Switch Collision Domain
28
Host A
Host B
Host C
Host D
Collision
domain?
A
B
A
C
1
1

29. Switch Collision Domains
29
Host A
Host B
Host C
Host D
A
B
A
C
1
A
B
1
A
C
Switch eliminates collisions by breaking down collision domain
2

30. Collision Domain Switch
RX
TX
Host A
Switch Stores & Forwards
30
TX RX
RX TX
RX
TX
TX
RX
CPU
RAMRAM
A
C A
B
Switch stores Ethernet frame in RAM and then forwards it
Pros/Cons?

31. Ethernet Data Link Layer
31
Application
Presentation
Session
Transport
Network
Data Link
Physical
Frame
Bits
MAC Data FCS
IP Data
TCP Data
Packet
Segment
Data
7
6
5
4
3
2
1
Hi!
Salut!

32. Ethernet Frame Format
32Source: https://en.wikipedia.org/wiki/Ethernet_frame
Ethernet
Frame
Bits
2
1
7
Preamble, 7 octets
Start of Frame, 1 octet
6
Destination MAC, 6 octets
6
Source MAC, 6 octets
4
Optional 802.1q (VLAN) Tag, 4 octets
Ethertype, 2 octets
46-1500 4
Frame Check Sequence, 4 octets
12
Interframe gap, 12 octetsPayload, 46-1500 octets
72 — 1530 octets
64 — 1522 octets
TrailerHeader

33. Optional 802.1q (VLAN) Tag
33
Payload
...
MAC Destination
MAC Destination MAC Source
MAC Source
Ethertype
0 32
14Bytes
Frame Check Sequence
Payload
...
MAC Destination
MAC Destination MAC Source
MAC Source
Ethertype
0 32
18Bytes
Frame Check Sequence
0x8100 VIDPCP D
PCP — Priority Code Point (Class of service) (3 bits)
DEI — Drop Eligible Indicator (1 bit)
VID — VLAN Identifier (12 bit)
Protected by Frame
Check Sequence

34. Ethernet MAC Address
34* OUI — Organizationally Unique Identifier
6
Destination MAC, 6 octets
6
Source MAC, 6 octets
4 46-1500 4
123456Intel 825992
789abcIntel I350
123456Cavium
2
2
Family Name First Name
NIC IDOUI*2
24 bits 24 bits
b7
0: globally unique
1: locally managed
b6
0: unicast
1: multicast
654321
b5 b4 b3 b2 b1 b0

35. Ethernet Type
35
6 6
Ethertype, 2 octets
4 46-1500 4
1
Eth
Type
IPv4
IPv4 Payload
Eth
Ethertype = 0x8000
2
Eth
Type
IPv6
IPv6 Payload
Eth
Ethertype = 0x86DD

36. Per-VLAN Switch Logic
36
Host A
Host B
Host C
Host D
D
A
Why? PortMAC
1
2
3
4
MAC Table
Learn!

37. 1A
Per-VLAN Switch Logic
37
Host A
Host B
Host C
Host D
D
A
1
PortMAC
1
2
3
4
MAC Table
2
1. Check Ethernet FCS
2. Add A to MAC table
3. No D in MAC table:
○ what to do?

38. 1A
Per-VLAN Switch Logic
38
Host A
Host B
Host C
Host D
D
A
1
PortMAC
1
2
3
4
MAC Table
2
D
A
D
A
3
3
“Unknown unicast”
D
A
3
1. Check Ethernet FCS
2. Add A to MAC table
3. No D in MAC table:
○ send to all ports
Problems?

39. 1A
Per-VLAN Switch Logic
39
Host A
Host B
Host C
Host D
4
Port
D
MAC
1
2
3
4
MAC Table
2
A
D
1
1. Check Ethernet FCS
2. Add D to MAC table
3. A in MAC table:
○ send to port 1
A
D
3

40. 1. Receive frame, check Ethernet FCS
2. Add/update source MAC in MAC table
3. If multicast bit is set:
a. forward to all ports, but the source
4. If destination is in MAC table:
a. forward to the specific port
5. Else, forward to all ports
Per-VLAN Switch Logic Summary
40

41. Local Networks Checklist
1. LAN?
2. Ethernet?
3. Ethernet physical layers?
4. Straight through vs crossover cables?
5. Duplex?
6. Collision?
7. Collision domains for hub, switch?
8. CSMA/CD?
9. Ethernet header?
10. 802.1q tag?
11. Switch logic?
41

42. References
1. Kevin Wallace. CCNP Routing and Switching ROUTE 300-101 Official Cert Guide. Cisco Press, 2014
2. David Hucaby. CCNP Routing and Switching SWITCH 300-115 Official Cert Guide. Cisco Press, 2014
3. RFC 1122. Requirements for Internet Hosts — Communication Layers.
4. IANA Protocol Numbers: http://www.iana.org/assignments/protocol-numbers
42