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
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Networking Fundamentals: Local Networks
1. Andriy Berestovskyy
2017
( ц ) А н д р
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berestovskyy
Networking Fundamentals
Local Networks
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
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
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!
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
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