Network Switching

1. Chapter 3
Network Switching
CISCO Networking II
By Chhay Buntha
Root Bridge
FWD FWD
DP
BLK
RP
RP

2. • Local Area Network (LAN) ត្រូវបានបង្កើរង ើ្សត្ាប់ត្បព័នធ network of computers
ដែលសថិរងៅទីតាំ្ដរមួយ
• LAN ាន broadcast domain ដរមួយ, ងៅងពលដែល ាន computer ណាមួយ
broadcast information, broadcast នឹ្ទទួលបានសត្ាប់ត្រប់កាំព្យូទ័រ។
Local Area Network
Chapter3
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By Chhay Buntha

3. Hub or Layer-2 switches belong to only one broadcast domain.
A Layer-2 switch will forward both broadcasts and multicasts out every port but the
originating port.
Only Layer-3 devices separate broadcast domains. Because of this, Layer-2
switches are poorly suited for large, scalable networks. The Layer-2 header provides
no mechanism to differentiate one network from another, only one host from
another.
Broadcast Domain
Chapter3
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By Chhay Buntha

4. • By default, a switch will forward both broadcasts and multicasts out every port but
the originating port.
• However, a switch can be logically segmented into separate broadcast domains,
using VLAN.
• Each VLAN represents a unique broadcast domain:
• Traffic between devices within the same VLAN is switched.
• Traffic between devices in different VLANs requires a Layer-3 device to
communicate.
Virtual Local Area Network (VLAN)
Chapter3
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By Chhay Buntha

5. • A VLAN is a logical group of network devices that appears to be on the same LAN
• Configured as if they are attached to the same physical connection even if they
are located on a number of different LAN segments.
• Is a group of hosts with a common set of requirements that communicate as if
they were attached to the same broadcast domain regardless of their physical
location.
Virtual Local Area Network (VLAN)
Chapter3
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By Chhay Buntha

6. • VLANs can logically segment users into different subnets (broadcast domains)
• Broadcast frames are only switched on the same VLAN ID.
• This is a logical segmentation and not a physical one, workstations do not have
to be physically located together. Users on different floors of the same building, or
even in different buildings can now belong to the same LAN.
Virtual Local Area Network (VLAN)
Chapter3
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By Chhay Buntha

7. • ង ោះបីងៅទីតាំ្ង្្េ្គ្នាក៏អាចទាំនាក់ទាំន្គ្នាបាន
• អាចកាំណរ់ទាំហាំរបស់ broadcast domain និ្សកមមភាពរបស់វាមិនឲានងត្ចើនងពកងៅ
កនុ្ network មួយ
• ានសវរថភាពសត្ាប់កាំព្យូទ័រ ងត្រោះអាចដប្ដចកកាំព្យូទ័រណា អាច connect ងៅកាំព្យូទ័រណា
បានខ្លោះ
• មិនចាំបាច់របណាាញដខ្្េថ្មីងែើម្បីឲបានក្លាយជា network ដរមួយង្្េ្ពី network ែទទ
ងទៀរ
Benefits of VLANs
Chapter3
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By Chhay Buntha

8. A traditional LAN រត្មូវឲ users ាំ្
អស់ានIP subnet (broadcast
domain) ែូចគ្នាងែើម្បីអាចconnected
ជាមួយគ្នាបានកនុ្ switch ដរ មួយ។
Traditional LAN
Chapter3
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By Chhay Buntha

9. Sample of VLAN
Chapter3
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By Chhay Buntha

10. • Divide the LAN into subnets
• Use routers to link the subnets
BUT
• Routers are expensive
• Routers are slower than switches
• Subnets are restricted to limited
physical areas
• Subnets are inflexible.
ដំណ ោះស្រាយណោយណស្ររើ Router
Chapter3
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By Chhay Buntha

11. ងោយានក្លរ configure VLANs, users
ែូចគ្នា អាចានងៅទីតាំ្ង្្េ្គ្នាក៏បាន
ងហើយងៅដរ អាចទាំនាក់ទាំន្ជាមួយគ្នា
បានែដែល និ្រក្ា IP subnet
(broadcast domain)ែូចគ្នាង ោះបីងៅទី
តាំ្ង្្េ្គ្នាក៏ងោយ។
ងយើ្ត្រូវក្លរ Router ងែើម្បីឲ VLAN ង្្េ្
គ្នាអាចទាំនាក់ទាំន្គ្នាបាន
ដំណ ោះស្រាយណោយណស្ររើ VLAN
Chapter3
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By Chhay Buntha

12. • All hosts in a VLAN have addresses in the same subnet. A VLAN is a subnet.
• Broadcasts are kept within the VLAN. A VLAN is a broadcast domain.
• Layer 2 switches cannot route between VLANs.
VLANs
Chapter3
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By Chhay Buntha

13. • VLAN 1: default Ethernet LAN, all ports start in this VLAN.
• VLANs 1002 – 1005 automatically created
• Numbers 2 to 1001 can be used for new VLANs
• Up to 255 VLANs on Catalyst 2960 switch
• Extended range 1006 – 4094 possible but fewer features
• VLAN information is stored in the VLAN database.
• vlan.dat in the flash memory of the switch.
VLAN ID និងព័ត៌មានណសេងណ ៀត
Chapter3
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By Chhay Buntha

14. • Each switch port intended for an end device is configured to belong to a VLAN.
• Any device connecting to that port belongs to the port’s VLAN.
• There are other ways of assigning VLANs.
• Ports that link switches can be configured to carry traffic for all VLANs (trunking)
VLANs on Port
Chapter3
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By Chhay Buntha

15. • Has the switch IP address.
• Used for telnet/SSH or web access for management purposes.
• Better not to use VLAN 1 for security reasons.
Management VLAN
Chapter3
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By Chhay Buntha

16. • Layer 2 switch keeps VLANs separate.
• Router can route between VLANs. It needs to provide a default gateway for each
VLAN as VLANs are separate subnets.
• Layer 3 switch has a switch virtual interface (SVI) configured for each VLAN.
These act like router interfaces to route between VLANs.
Traffic between VLANs
Chapter3
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By Chhay Buntha

17. • Access ports are used when:
• Only a single device is connected to the port
• Multiple devices (hub) are connected to the port, all belonging to
the same VLAN
• Another switch is connected to this interface, but this link is only
carrying a single VLAN (non-trunk link).
• Trunk ports are used to:
ងែើម្បី បញ្ជូន packets សត្ាប់ត្រប់ VLANs។ ត្បងេទ ports ាំ្ងនោះ រឺានងៅចងនាាោះពី switch មួយងៅក្លន់
switch មួយងទៀរ។
ត្បងេទ Links ាំ្ងនោះត្រូវក្លរែឹកជញ្ជូន packets ពីត្រប់ VLANs ាំ្អស់ រឺវាែឹកជញ្ជូន VLANs ជាងត្ចើន, ងត្រោះ
VLANs ាំ្ងនាោះអាចចរាចរងៅក្លន់ switches ជាងត្ចើនងទៀរ។
Configuring port
Chapter3
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By Chhay Buntha

18. • Both switches have the same 5 VLANs.
• Do you have a link for each VLAN?
• More efficient for them to share a link.
Trunking
Chapter3
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By Chhay Buntha

19. • Traffic for all the VLANs travels between the switches on a shared
trunk or backbone
Trunking
Chapter3
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By Chhay Buntha

20. Trunk and Access Port
Chapter3
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By Chhay Buntha

21. Make a port into a trunk port and tell it which VLAN
is native.
SW1(config)#int fa0/1
SW1(config-if)switchport mode trunk
SW1(config-if)switchport trunk native vlan 99
By default native VLAN is 1.
Configure trunk port
Chapter3
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By Chhay Buntha

22. SW1(config)#vlan 20
SW1(config-vlan)#name Finance
SW1(config-vlan)#end
VLAN will be saved in VLAN database rather than
running config.
If you do not give it a name then it will be called
vlan0020.
Create VLAN
Chapter3
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By Chhay Buntha

23. SW1(config)#int fa 0/14
SW1(config-if)#switchport mode access
SW1(config-if)#switchport access vlan 20
SW1(config-if)#end
Assign port to VLAN
Chapter3
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By Chhay Buntha

24. List of VLANs with ports
Show VLAN brief
Chapter3
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By Chhay Buntha

25. show vlan brief (list of VLANs and ports)
show vlan summary
show interfaces vlan (up/down, traffic etc)
Show interfaces fa0/14 switchport (access mode,
trunking)
Show commands
Chapter3
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By Chhay Buntha

26. SW1(config)#int fa 0/14
SW1(config-if)#no switchport access vlan
SW1(config-if)#end
The port goes back to VLAN 1.
If you assign a port to a new VLAN, it is
automatically removed from its existing VLAN.
Remove port from VLAN
Chapter3
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By Chhay Buntha

27. SW1(config)#no vlan 20
SW1(config)#end
VLAN 20 is deleted.
Any ports still on VLAN 20 will be inactive – not on
any VLAN. They need to be reassigned.
Delete VLAN
Chapter3
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By Chhay Buntha

28. Erasing the startup configuration does not get rid
of VLANs because they are saved in a separate file.
SW1#delete flash:vlan.dat
Switch goes back to the default with all ports in
VLAN 1.
You cannot delete VLAN 1.
Delete VLAN database
Chapter3
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By Chhay Buntha

29. SW1(config)#int fa0/1
SW1(config-if)#switchport mode trunk
SW1(config-if)#switchport trunk native vlan 99
SW1(config-if)#switchport trunk allowed vlan add 10,
20, 30
SW1(config-if)#end
Configure trunk
Chapter3
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By Chhay Buntha

30. On one interface of router you can have many sub-interfaces. And
those are call VLAN interfaces.
To enable sub-interface using command below:
R1(config)#int f0/0
R1(config-if)#no shut
R1(config-if)#exit
R1(config)#int f0/0.10
R1(config-subif)#encapsulation dot1Q 10
R1(config-subif)#ip address 192.168.10.1
255.255.255.0
Create VLAN Interface on Router
Chapter3
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By Chhay Buntha

31. • IEEE 802.1D
• A loop-prevention protocol
• Allows L2 devices to communicate with each other to discover
physical loops in the network.
• Algorithm that creates a loop-free logical topology.
• STP creates a tree structure of loop-free leaves and branches that
spans the entire Layer 2 network.
• The purpose of STP is to avoid and eliminate loops in the network
by negotiating a loop-free path through a root bridge.
• STP determines where are the loops and blocks links that are
redundant.
• Ensures that there will be only one active path to every destination.
Spanning Tree Protocol (STP)
Chapter3
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By Chhay Buntha

32. STP executes an algorithm called
Spanning Tree Algorithm (STA).
• STA chooses a reference
point, called a root bridge.
• Then determines the
available paths to that
reference point.
• If more than two paths
exists, STA picks the best
path and blocks the rest
Spanning Tree Protocol (STP) (Cont.)
Chapter3
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By Chhay Buntha
Root Bridge
FWD FWD
DP
BLK
RP
RP

33. - Used to aggregate bandwidth between multiple L2/L3 interfaces
- Etherchannel increases bandwidth and provides redundancy by aggregating
individual links between switches
- Etherchannel loadbalances traffic over all the links in the bundle.
- Up to 8 links can be used to combine in to one logical link.
- Etherchannel can be configured as layer 2 or layer3.
- Port-channel is the logical interface of the physical interfaces.
Etherchannel or Port Channel
Chapter3
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By Chhay Buntha

34. Ether Channel is a port link aggregation technology developed by Cisco, which
provides fault-tolerant high-speed links between Switches, Routers, and Servers.
Ether Channel technology can be used to increase the bandwidth between two
devices that support Ether Channel technology and Ether Channel technology
provides automatic recovery for the loss of a link by redistributing the load across
the remaining links.
Ether Channel or Port Channel
Chapter3
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By Chhay Buntha

35. - Etherchannel can be dynamically configured between switches using two
protocols.
- PAgP (Port Aggregation Protocol)
- LACP (Link Aggregation Control Protocol)
Etherchannel Modes:
Chapter3
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By Chhay Buntha
Mode Result
On PAgP and LACP disabled (negotiation disable) (Manual)
Auto Passively listen for PAgP (Dynamic)
Desirable Actively negotiate PAgP (Dynamic)
Passive Passively listen for LACP (Dynamic)
Active Actively negotiate LACP (Dynamic)

36. On - On
Desirable - Desirable
Desirable - Auto
Active - Active
Active - Passive
Successful combination of etherchannel would be:
Chapter3
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By Chhay Buntha
switch(config)#int range f1/1 – 4
Switch(config-if-range)#channel-group 2 mode ?
active Enable LACP unconditionally
auto Enable PAgP only if a PAgP device is detected
desirable Enable PAgP unconditionally
on Enable Etherchannel only
passive Enable LACP only if a LACP device is detected

37. Most configurations are done on the EtherChannel interface
ensuring consistency throughout links.
Relies on existing switch ports – no need for upgrades.
Load-balances between links on the same EtherChannnel.
Creates an aggregation viewed as one logical link by STP.
Provides redundancy because the overall link is viewed as one
logical connection. If one physical link within channel goes down,
this does not cause a change in the topology and does not require
STP recalculation.
Advantage of EtherChannel
Chapter3
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By Chhay Buntha

38. However, simply trunking two or more ports between the switches will
not work, as this creates a switching loop. One of two things will occur:
Spanning Tree Protocol (STP) will disable one or more ports to
eliminate the loop.
If STP is disabled, the switching loop will result in an almost
instantaneous broadcast storm, crippling the network
Ether Channel or Port Channel
Chapter3
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By Chhay Buntha