Very Simple Introduction to Switching in a Cisco Network

1. Introduction to Cisco
Switching – Part 1

2. Contents
 OSI Model
 Packet traversal across a network
 Switch frame forwarding and address learning
 Useful commands

3. The OSI Model

4. The OSI Model
Layer 1 - Physical
• Puts bits on the wire
• Electrical signalling

5. The OSI Model
• Communication between adjacent
devices
• Uses MAC address to determine
destination of frame
Layer 2 - Data Link

6. The OSI Model
• Routes packets across different networks
• Uses IP address to determine destination
of packet
Layer 3 - Network

7. The OSI Model
• Provides services to the data stream
including window size, flow control and
port numbers
Layer 4 - Transport

8. The OSI Model
OSI TCP/IP

9. High Level IP Packet Network TraversalIP Address 10.10.10.1
MAC Address AAAA.AAAA.AAAA
IP Address 192.168.0.1
MAC Address FFFF.FFFF.FFFF
IP Address 10.10.10.254
MAC Address BBBB.BBBB.BBBB
IP Address 192.168.0.254
MAC Address EEEE.EEEE.EEEE
IP Address 172.16.16.1
MAC Address CCCC.CCCC.CCCC
IP Address 172.16.16.2
MAC Address DDDD.DDDD.DDDD

10. High Level IP Packet Network TraversalIP Address 10.10.10.1
MAC Address AAAA.AAAA.AAAA
IP Address 192.168.0.1
MAC Address FFFF.FFFF.FFFF
IP Address 10.10.10.254
MAC Address BBBB.BBBB.BBBB
IP Address 192.168.0.254
MAC Address EEEE.EEEE.EEEE
IP Address 172.16.16.1
MAC Address CCCC.CCCC.CCCC
IP Address 172.16.16.2
MAC Address DDDD.DDDD.DDDD

11. High Level IP Packet Network TraversalIP Address 10.10.10.1
MAC Address AAAA.AAAA.AAAA
IP Address 192.168.0.1
MAC Address FFFF.FFFF.FFFF
IP Address 10.10.10.254
MAC Address BBBB.BBBB.BBBB
IP Address 192.168.0.254
MAC Address EEEE.EEEE.EEEE
IP Address 172.16.16.1
MAC Address CCCC.CCCC.CCCC
IP Address 172.16.16.2
MAC Address DDDD.DDDD.DDDD

12. High Level IP Packet Network TraversalIP Address 10.10.10.1
MAC Address AAAA.AAAA.AAAA
IP Address 192.168.0.1
MAC Address FFFF.FFFF.FFFF
IP Address 10.10.10.254
MAC Address BBBB.BBBB.BBBB
IP Address 192.168.0.254
MAC Address EEEE.EEEE.EEEE
IP Address 172.16.16.1
MAC Address CCCC.CCCC.CCCC
IP Address 172.16.16.2
MAC Address DDDD.DDDD.DDDD

13. High Level IP Packet Network TraversalIP Address 10.10.10.1
MAC Address AAAA.AAAA.AAAA
IP Address 192.168.0.1
MAC Address FFFF.FFFF.FFFF
IP Address 10.10.10.254
MAC Address BBBB.BBBB.BBBB
IP Address 192.168.0.254
MAC Address EEEE.EEEE.EEEE
IP Address 172.16.16.1
MAC Address CCCC.CCCC.CCCC
IP Address 172.16.16.2
MAC Address DDDD.DDDD.DDDD

14. High Level IP Packet Network TraversalIP Address 10.10.10.1
MAC Address AAAA.AAAA.AAAA
IP Address 192.168.0.1
MAC Address FFFF.FFFF.FFFF
IP Address 10.10.10.254
MAC Address BBBB.BBBB.BBBB
IP Address 192.168.0.254
MAC Address EEEE.EEEE.EEEE
IP Address 172.16.16.1
MAC Address CCCC.CCCC.CCCC
IP Address 172.16.16.2
MAC Address DDDD.DDDD.DDDD

15. Frame Forwarding and Address Learning
 Every Interface of every device has a
unique MAC address
 MAC addresses sit at Layer 2 of the
OSI model. They are used to deliver
traffic to devices on the same
network segment
 Switches keep a table in memory of
what MAC addresses are connected
to what ports
IP Address 10.10.10.254
MAC Address BBBB.BBBB.BBBB

16. Frame Forwarding and Address Learning
 From Power-On a switch has no
MAC addresses in its tables
 It learns which MAC addresses are
on which port by recording the
SOURCE address of incoming frames
 If it knows the port the destination
MAC is on it forward the frame out
of that port only
 If it doesn’t know the port then it
forwards the frame out of every
port other than the one it was
received on

17. Command – show ip interface brief

18. Command – show interface <interface
name>

19. Command – show mac-address-table