CCNA- part 8 switch

1. SWITCHING

2. Disadvantages of Hub:-
• It is physical layer device and it works
with 0’s and 1’s bits.
• It works with broadcasting.
• It works with shared bandwidth.
• In hub one broadcast domain and one
collision domain.
• Collisions are identified using access
methods called CSMA/CD.

3. Switch:-
• It is a data-link layer device and works
with frames.
• It is intelligent device and works with
physical address (MAC).
• It works with flooding and unicast.
• It has one broadcast domain and
number of collision domains depend
upon the no. of ports.
• It maintains MAC address table.

4. • Collision Domain:-
A collision domain is a set of NICs for
which a frame send by one NIC could result
in a collision with a frame sent by an other
NIC in the same collision domain.
• Broadcast Domain:-
A broadcast domain is a set of NICs for
which a broadcast frame sent by one NIC is
received by all other NICs in the same
broadcast domain.

5. Bridge
• Bridges are software
based.
• Bridge have lesser no.
of ports (max 16).
• Generally used for
connecting two different
topology.
• Bridges are half duplex.
• Store and forward
method is used for
switching
Switch
• Switches are hardware
based.
• Switches have higher
no. of ports (max 100).
• Generally used for
connecting single
topology.
• Switches are half and
full duplex.
• Store and forward, cut
through, fragment free
mode are used for
switching.

6. Types of switches:-
• Manageable switches:-
on manageable switch an IP address can
be assign and configuration can be made. It
has a console port.
• Un-Manageable switches:-
On un-manageable switch an IP address
ca not be assigned and configuration can not
made.

7. Cisco produces three layers Switches:-
(Cisco’s hierarchal structure )
• Core Layer Switches:-
They are used in enterprise level, ISP, Big
organizations.
e.g.switch series 7000, 8000, 10000……….
• Distribution Layer Switches :-
They are used in medium organization.
e.g.switch series 3000, 5000…
• Access Layer Switches :-
They are used in home or small organization
e.g.switch series 1900, 2900………

8. Switching Method:-
• Cut-through switching.
• Fragment-free switching.
• Store-and-Forward switching.

9. Cut-through switching:-
• In this method switch switches a frame
as soon as it sees the destination MAC
address in the frames (first-14byte).
• No security.
• Error correction will not take place.
• Latency is low.
• A default switching method for the core
layer switches.

10. Fragment-free switching:-
• In this it will switches a frame after the
switch sees at least 64-bytes.
• Medium security.
• Error checking on 64-bytes of frames.
• Latency is medium.
• This is the default switching method for
the access-layer switches like 1900,
2900 series.

11. Store-and-Forward switching:-
• In this switch pulls whole frame in the
switch, checks the CRC and then
switches.
• 100% security.
• Error checking takes place.
• Latency is high.
• This is the default method for distribution
layer switches.

12. Switch Functions
– Address learning
– Forward/filter decision
– Loop avoidance

13. How Switches Learn Host
Locations
MAC Address Table
A B
A B
0260.8c01.1111
C D
C D
0260.8c01.2222
0260.8c01.3333
0260.8c01.4444
E0 E1
E2 E3
• Initial MAC address table is empty.

14. How Switches Learn Host
Locations
A B
A B
0260.8c01.1111
D C
C D
0260.8c01.2222
0260.8c01.3333
0260.8c01.4444
MAC Address Table
E0: 0260.8c01.1111
E0 E1
E2 E3
• Station A sends a frame to station C.
• Switch caches the station A MAC address to port E0 by
learning the source address of data frames.
• The frame from station A to station C is flooded out to
all ports except port E0 (unknown unicasts are
flooded).

15. STP – Spanning Tree Protocol
• Spanning Tree Protocol is used to
eliminate loops when redundant links
are present
– Redundant topology eliminates single
points of failure
– Redundant topology causes broadcast
storms, multiple frame copies, and MAC
address table instability problems.

16. Redundant Topology
Segment 1
Segment 2 2
Server/Host X Router
Y

17. Broadcast Storms
Segment 1
Segment 2
Server/Host X Router
Y
Broadcast
Switch A
A
Switch
B
Host X sends a Broadcast

18. Broadcast Storms
Segment 1
Segment 2
Server/Host X Router
Y
Broadcast
Switch A Switch
B
Host X sends a Broadcast

19. Broadcast Storms
Segment 1
Switch A Switch
B
Segment 2
Server/Host X Router
Y
Broadcast
• Switches continue to propagate broadcast
traffic over and over.

20. Solution: Spanning-Tree Protocol
x Block
• Provides a loop-free redundant network topology by
placing certain ports in the blocking state.

21. Spanning-Tree Port States
• Spanning-tree transits each port
through several different states:
Blocking
(20
Seconds)
Listening
(15
Seconds)
Learning
(15
Seconds)
Forwarding

22. Spanning-Tree Operations
• One root bridge per network
• One root port per nonroot bridge
• One designated port per segment
100BaseT
Designated Port (F) Root Port (F)
Root Bridge Nonroot Bridge
SW X SW Y
x
Designated Port (F) Nondesignated Port (B)
10BaseT