2. 2
Layer 2 Switching
ï Switching breaks up large collision domains into
smaller ones
ï Collision domain is a network segment with two or
more devices sharing the same bandwidth.
ï A hub network is a typical example of this type of
technology
ï Each port on a switch is actually its own collision
domain, you can make a much better Ethernet LAN
network just by replacing your hubs with switches
3. 3
Switching Services
ï Unlike bridges that use software to create and manage a
filter table, switches use Application Specific Integrated
Circuits (ASICs)
ï Layer 2 switches and bridges are faster than routers
because they donât take up time looking at the Network
layer header information.
ï They look at the frameâs hardware addresses before
deciding to either forward the frame or drop it.
ï layer 2 switching so efficient is that no modification to the
data packet takes place
4. 4
How Switches and Bridges
Learn Addresses
Bridges and switches learn in the following ways:
âą Reading the source MAC address of each
received frame or datagram
âą Recording the port on which the MAC address
was received.
In this way, the bridge or switch learns which addresses
belong to the devices connected to each port.
8. 8
Switch Features
ï± There are three conditions in which a switch will flood a
frame out on all ports except to the port on which the
frame came in, as follows:
ï¶Unknown unicast address
ï¶Broadcast frame
ï¶Multicast frame
10. 10
Learning Addresses
âą Station A sends a frame to station C.
âą Switch caches the MAC address of station A to port E0 by
learning the source address of data frames.
âą The frame from station A to station C is flooded out to all
ports except port E0 (unknown unicasts are flooded).
11. 11
Learning Addresses (Cont.)
âą Station D sends a frame to station C.
âą Switch caches the MAC address of station D to port E3 by
learning the source address of data frames.
âą The frame from station D to station C is flooded out to all ports
except port E3 (unknown unicasts are flooded).
13. 13
âą Station D sends a broadcast or multicast frame.
âą Broadcast and multicast frames are flooded to all ports
other than the originating port.
Broadcast and Multicast
Frames
14. 14
Forward/Filter Decision
ï± When a frame arrives at a switch interface, the destination hardware
address is compared to the forward/ filter MAC database.
ï± If the destination hardware address is known and listed in the
database, the frame is sent out only the correct exit interface
ï± If the destination hardware address is not listed in the MAC
database, then the frame is flooded out all active interfaces except
the interface the frame was received on.
ï± If a host or server sends a broadcast on the LAN, the switch will
flood the frame out all active ports except the source port.
24. 24
Loop Avoidance
âą Redundant links between
switches are a good idea
because they help prevent
complete network failures
in the event one link stops
working
âą However, they often cause
more problems because
frames can be flooded
down all redundant links
simultaneously
âą This creates network loops
25. 25
Network Broadcast Loops
ï± A manufacturing floor PC sent a
network broadcast to request a
boot loader
ï± The broadcast was first received
by switch sw1 on port 2/1
ï± The topology is redundantly
connected; therefore, switch sw2
receives the broadcast frame as
well on port 2/1
ï± Switch sw2 is also receiving a
copy of the broadcast frame
forwarded to the LAN segment
from port 2/2 of switch sw1.
ï± In a small fraction of the time,
we have four packets. The
problem grows exponentially
until the network bandwidth is
saturated
28. 28
Overview
ï±Redundancy in a network is extremely important
because redundancy allows networks to be fault tolerant.
ï±Redundant topologies based on switches and bridges
are subject to broadcast storms, multiple frame
transmissions, and MAC address database instability.
ï±Therefore network redundancy requires careful
planning and monitoring to function properly.
ï±The Spanning-Tree Protocol is used in switched
networks to create a loop free network
29. 29
âą Provides a loop-free redundant network topology by
placing certain ports in the blocking state.
Spanning-Tree Protocol
30. 30
Spanning Tree Protocol
ï±Spanning Tree Protocol resides in Data link Layer
ï±Ethernet bridges and switches can implement the IEEE 802.1D
Spanning-Tree Protocol and use the spanning-tree algorithm to
construct a loop free network.
32. 32
Selecting the Root Bridge
ï±The first decision that all switches in the network make, is to identify the
root bridge.
ï±When a switch is turned on, the spanning-tree algorithm is used to identify
the root bridge. BPDUs are sent out with the Bridge ID (BID).
ï±The BID consists of a bridge priority that defaults to 32768 and the switch
base MAC address.
ï±When a switch first starts up, it assumes it is the root switch and sends
BPDUs. These BPDUs contain BID.
ï±All bridges see these and decide that the bridge with the smallest BID value
will be the root bridge.
ï±A network administrator may want to influence the decision by setting the
switch priority to a smaller value than the default.
33. 33
Spanning Tree Protocol
Terms
ï±BPDU Bridge Protocol Data Unit (BPDU) - All the switches exchange information to use in the
selection of the root switch
ï±Bridge ID - The bridge ID is how STP keeps track of all the switches in the network. It is determined by
a combination of the bridge priority (32,768 by default on all Cisco switches) and the base MAC address.
ï±Root Bridge -The bridge with the lowest bridge ID becomes the root bridge in the network.
ï±Nonroot bridge - These are all bridges that are not the root bridge.
ï±Root port - The root port is always the link directly connected to the root bridge or the shortest path to
the root bridge. If more than one link connects to the root bridge, then a port cost is determined by checking
the bandwidth of each link.
ï±Designated port - A designated port is one that has been determined as having the best (lowest) cost.
A designated port will be marked as a forwarding port
ï±Nondesignated Port - A nondesignated port is one with a higher cost than the designated port.
Nondesignated ports are put in blocking mode
ï±Forwarding Port - A forwarding port forwards frames
ï±Blocked Port - A blocked port is the port that will not forward frames, in order to prevent loops
34. 34
âą Bpdu = Bridge Protocol Data Unit
(default = sent every two seconds)
âą Root bridge = Bridge with the lowest bridge ID
âą Bridge ID =
âą In the example, which switch has the lowest bridge ID?
Spanning-Tree Protocol
Root Bridge Selection
35. 35
âą One root bridge per network
âą One root port per nonroot bridge
âą One designated port per segment
âą Nondesignated ports are unused
Spanning-Tree Operation
36. 36
Selecting the Root Port
ï¶The STP cost is an accumulated total path cost based on the rated
bandwidth of each of the links
ï¶This information is then used internally to select the root port for that
device
37. 37
âą One root bridge per network
âą One root port per nonroot bridge
âą One designated port per segment
âą Nondesignated ports are unused
Spanning-Tree Operation
38. 38
Switching Methods
1. Cut-Through (Fast Forward)
The frame is forwarded through the switch before the entire frame is
received. At a minimum the frame destination address must be read before
the frame can be forwarded. This mode decreases the latency of the
transmission, but also reduces error detection.
2. Fragment-Free (Modified Cut-Through)
Fragment-free switching filters out collision fragments before forwarding
begins. Collision fragments are the majority of packet errors. In Fragment-
Free mode, the switch checks the first 64 bytes of a frame.
3. Store-and-Forward
The entire frame is received before any forwarding takes place. Filters are
applied before the frame is forwarded. Most reliable and also most latency
especially when frames are large.
41. 41
Physical Startup of the Catalyst
Switch
ï±Switches are dedicated, specialized computers, which contain a CPU,
RAM, and an operating system.
ï±Switches usually have several ports for the purpose of connecting
hosts, as well as specialized ports for the purpose of management.
ï±A switch can be managed by connecting to the console port to view
and make changes to the configuration.
ï±Switches typically have no power switch to turn them on and off. They
simply connect or disconnect from a power source.
42. 43
Verifying Port LEDs During Switch
POST
ï±Once the power cable is connected, the switch initiates a
series of tests called the power-on self test (POST).
ï±POST runs automatically to verify that the switch functions
correctly.
ï±The System LED indicates the success or failure of POST.
43. 44
Switch Command Modes
ï±Switches have several command modes.
ï±The default mode is User EXEC mode, which ends in a greater-
than character (>).
ï±The commands available in User EXEC mode are limited to those
that change terminal settings, perform basic tests, and display
system information.
ï±The enable command is used to change from User EXEC mode
to Privileged EXEC mode, which ends in a pound-sign character
(#).
ï±The configure command allows other command modes to be
accessed. Â Â
45. 46
Tasks
ïSetting the passwords (Password must be between 4
and 8 characters)
ïSetting the hostname
ïConfiguring the IP address and subnet
mask
ïErasing the switch configurations
47. 48
Switch Configuration
ï± There are two reasons to set the IP address information on the switch:
ï To manage the switch via Telnet or other management software
ï To configure the switch with different VLANs and other network functions
ï See the default IP configuration = show IP command
Configure IP Address
sw1(config-if)#interface vlan 1
sw1(config-if)#ip address 10.0.0.1 255.0.0.0
sw1(config-if)#no shut
sw1(config-if)#exit
sw1(config)ip default-gateway 10.0.0.254
48. 49
Configuring Interface
Descriptions
ï± You can administratively set a name for each interface on the
switches
SW1#config t
Enter configuration commands, one per line. End with CNTL/Z
SW1(config)#int e0/1
SW1(config-if)#description Finance_VLAN
SW1(config-if)#int f0/26
SW1(config-if)#description trunk_to_Building_4
SW1(config-if)#
ï± Setting Port Security
Sw1(config-if)#switchport port-security mac-address mac-address
ï¶ Now only this one MAC address is allowed on this switch port
49. 50
Switch Configuration
Connect two machine to a switch
To view the MAC table
sw1#show mac-address-table dynamic
Sw1#sh spanning-tree
Sw1(config)#spanning-tree vlan 1 priority ?
Sw1(config)#spanning-tree vlan 1 priority 4096
Erase the configuration
51. 52
VLANâs
ï± A VLAN is a logical grouping of network users and
resources connected to administratively defined ports on
a switch.
ï± Ability to create smaller broadcast domains within a layer
2 switched internetwork by assigning different ports on the
switch to different subnetworks.
ï± Frames broadcast onto the network are only switched
between the ports logically grouped within the same
VLAN
ï± By default, no hosts in a specific VLAN can communicate
with any other hosts that are members of another VLAN,
ï± For Inter VLAN communication you need routers
52. 53
VLANs
ï±VLAN implementation combines Layer 2 switching and Layer 3 routing
technologies to limit both collision domains and broadcast domains.
ï±VLANs can also be used to provide security by creating the VLAN
groups according to function and by using routers to communicate
between VLANs.
ï±A physical port association is used to implement VLAN assignment.
ï±Communication between VLANs can occur only through the router.
ï±This limits the size of the broadcast domains and uses the router to
determine whether one VLAN can talk to another VLAN.
ï±NOTE: This is the only way a switch can break up a broadcast domain!
53. 54
A VLAN = A Broadcast Domain = Logical Network (Subnet)
VLAN Overview
âą Segmentation
âą Flexibility
âą Security
54. 55
History
ï±11 Hosts are connected to the switch
ï±All From same Broadcast domain
ï±Need to divide them in separate logical segment
ï±High broadcast traffic reasons
ï±ARP
ï±DHCP
ï±SAP
ï±XWindows
ï±NetBIOS
55. 56
Definition
ï± Logically Defined community of interest that limits a
Broadcast domain
ï± LAN are created on the software of Switch
ï± All devices in a VLAN are members of the same
broadcast domain and receive all broadcasts
ï± The broadcasts, by default, are filtered from all ports on
a switch that are not members of the same VLAN.
56. 57
Security
ï± A Flat internetworkâs security used to be tackled by connecting hubs
and switches together with routers
ï± This arrangement is ineffective because
ï± Anyone connecting physical network could access network resources
located on that physical LAN
ï± Can observe the network traffic by plugging network analyzer into the
HUB
ï± Users could join a workgroup by just plugging their workstations into the
existing hub
ï± By creating VLANâs administrators have control over each port and
user
57. 58
How VLANs Simplify Network
Management
ï± If we need to break the broadcast domain we need to connect a
router
ï± By using VLANâs we can divide Broadcast domain at Layer-2
ï± A group of users needing high security can be put into a VLAN so
that no users outside of the VLAN can communicate with them.
ï± As a logical grouping of users by function, VLANs can be
considered independent from their physical locations.
58. 59
VLAN Memberships
ï± VLAN created based on port is known as Static VLAN.
ï± VLAN assigned based on hardware addresses into a
database, is called a dynamic VLAN
61. 62
Dynamic VLANs
ï± A dynamic VLAN determines a nodeâs VLAN assignment
automatically
ï± Using intelligent management software, you can base
VLAN assignments on hardware (MAC) addresses.
ï± Dynamic VLAN need VLAN Management Policy Server
(VMPS) server
62. 63
LAB â Creating VLAN
ï± Connect two computers on a switch
ï± Ping and see both are able to communicate
ï± Create two vlans and configure static VLANâs so both ports are on separate VLANâs
ï± Test the communication between PCâs
port1 port5
To see the existing VLAN
#Show vlan
To create VLAN
#vlan database
Switch(vlan)#vlan 2 name red
Switch(vlan)#vlan 3 name blue
Assigning ports to VLAN
Sw(config)# int fastEthernet 0/1
Sw(config-if)#switch mode access
Sw(config-if)#switchport access vlan2
63. 64
LAB â Deleting VLAN
port1 port5
To delete VLAN
Sw(config)# no vlan 2
Sw(config)# no vlan 3
To bring port back to VLAN 1
Sw(config-if)#switchport mode acces
Sw(config-if)#switch port access vlan1
For a Range
Sw(config)#int range fastethernet 0/1 - 5
Sw(config-if)#switch port access vlan1
64. 65
ï±VLANs can span across multiple switches.
ï±Trunks carry traffic for multiple VLANs.
ï±Trunks use special encapsulation to distinguish between
different VLANs.
VLAN Operation
65. 66
Types of Links
ï± Access links
ï± This type of link is only part of one VLAN
ï± Itâs referred to as the native VLAN of the port.
ï± Any device attached to an access link is unaware of a VLAN
ï± Switches remove any VLAN information from the frame before
itâs sent to an access-link device.
ï± Trunk links
ï± Trunks can carry multiple VLANs
ï± These carry the traffic of multiple VLANs
ï± A trunk link is a 100- or 1000Mbps point-to-point link between
two switches, between a switch and router.
68. 69
Frame Tagging
ï Can create VLANs to span more than one connected switch
ï Hosts are unaware of VLAN
ï When host A Create a data unit and reaches switch, the switch adds a
Frame tagging to identify the VLAN
ï Frame tagging is a method to identify the packet belongs to a particular
VLAN
ï Each switch that the frame reaches must first identify the VLAN ID from the
frame tag
ï It finds out what to do with the frame by looking at the information in the filter
table
ï Once the frame reaches an exit to an access link matching the frameâs VLAN
ID, the switch removes the VLAN identifier
69. 70
Frame Tagging Methods
ï± There are two frame tagging methods
ï Inter-Switch Link (ISL)
ï IEEE 802.1Q
ï± Inter-Switch Link (ISL)
ï proprietary to Cisco switches
ï used for Fast Ethernet and Gigabit Ethernet links only
ï± IEEE 802.1Q
ï Created by the IEEE as a standard method of frame
tagging
ï it actually inserts a field into the frame to identify the VLAN
ï If youâre trunking between a Cisco switched link and a
different brand of switch, you have to use 802.1Q for the
trunk to work.
70. 71
ï± Performed with ASIC
ï± ISL header not seen
by client
ï± Effective between
switches, and
between routers and
switches
ISL trunks enable VLANs across a backbone.
ISL Tagging
71. 72
LAB-Creating Trunk
Create two VLAN's on each
switches
#vlan database
sw(vlan)#vlan 2 name red
sw(vlan)#vlan 3 name blue
sw(vlan)#exit
sw#config t
sw(config)#int fastethernet 0/1
sw(config-if)#switch-portaccess vlan
2
sw(config)#int fastethernet 0/4
sw(config-if)#switch-portaccess vlan
3
To see Interface status
#show interface status
10.0.0.3
10.0.0.4
1 2 3 41 2 3 4
10.0.0.1
10.0.0.2
24 12
Trunk Port Configuration
sw#config t
sw(config)#int fastethernet 0/24
sw(config-if)#switchport trunk
encapsulation dot1q
sw(config-if)#switchport mode trunk
* 2950 Only dot1q Encapsulation
72. 73
Assigning Access Ports to a
VLAN
Switch(config)#interface gigabitethernet 1/1Switch(config)#interface gigabitethernet 1/1
âą Enters interface configuration mode
Switch(config-if)#switchport mode accessSwitch(config-if)#switchport mode access
âą Configures the interface as an access port
Switch(config-if)#switchport access vlan 3Switch(config-if)#switchport access vlan 3
âą Assigns the access port to a VLAN
74. 75
Verifying the VLAN Port
Configuration
Switch#show running-config interface {fastethernet |
gigabitethernet} slot/port
Switch#show running-config interface {fastethernet |
gigabitethernet} slot/port
âą Displays the running configuration of the interface
Switch#show interfaces [{fastethernet | gigabitethernet}
slot/port] switchport
Switch#show interfaces [{fastethernet | gigabitethernet}
slot/port] switchport
âą Displays the switch port configuration of the interface
Switch#show mac-address-table interface interface-id [vlan
vlan-id] [ | {begin | exclude | include} expression]
Switch#show mac-address-table interface interface-id [vlan
vlan-id] [ | {begin | exclude | include} expression]
âą Displays the MAC address table information for the specified
interface in the specified VLAN
75. ï±A messaging system that advertises VLAN configuration information
ï±Maintains VLAN configuration consistency throughout a common
administrative domain
ï±Sends advertisements on trunk ports only
VTP Protocol Features
76. 77
VLAN Trunking Protocol
(VTP)
ï±Benefits of VTP
ï±Consistent VLAN configuration across all switches in
the network
ï±Accurate tracking and monitoring of VLANs
ï±Dynamic reporting of added VLANs to all switches in
the VTP domain
77. 78
âą Forwards
advertisements
âą Synchronizes
âą Not saved in
NVRAM
âą Creates VLANs
âą Modifies VLANs
âą Deletes VLANs
âą Sends/forwards
advertisements
âą Synchronizes
âą Saved in NVRAM
âą Creates VLANs
âą Modifies VLANs
âą Deletes VLANs
âą Forwards
advertisements
âą Does not
synchronize
âą Saved in NVRAM
VTP Modes
78. 79
VTP Operation
âą VTP advertisements are sent as multicast frames.
âą VTP servers and clients are synchronized to the latest update identified
revision number.
âą VTP advertisements are sent every 5 minutes or when there is a change.
79. 80
VTP Pruning
âą VTP pruning provides a way for you to preserve
bandwidth by configuring it to reduce the amount of
broadcasts, multicasts, and unicast packets.
âą If Switch A doesnât have any ports configured for VLAN
5, and a broadcast is sent throughout VLAN 5, that
broadcast would not traverse the trunk link to Switch A.
âą By default, VTP pruning is disabled on all switches.
âą Pruning is enabled for the entire domain
80. 81
âą Increases available bandwidth by reducing unnecessary flooded traffic
âą Example: Station A sends broadcast, and broadcast is flooded only toward
any switch with ports assigned to the red VLAN
VTP Pruning
81. 82
VTP Configuration Guidelines
â Configure the following:
âą VTP domain name
âą VTP mode (server mode is the default)
âą VTP pruning
âą VTP password
Switch(config)#vtp mode server
Switch(config)#vtp domain gates
SwitchA#sh vtp status
82. 83
wg_sw_1900#configure terminal
Enter configuration commands, one per line. End with CNTL/Z
wg_sw_1900(config)#vtp transparent
wg_sw_1900(config)#vtp domain switchlab
wg_sw_1900(config)#vtp [server | transparent | client] [domain
domain-name] [trap {enable | disable}] [password password]
[pruning {enable | disable}]
Creating a VTP Domain
Catalyst 1900
Catalyst 2950
wg_sw_2950#vlan database
wg_sw_2950(vlan)#vtp [ server | client | transparent ]
wg_sw_2950(vlan)#vtp domain domain-name
wg_sw_2950(vlan)#vtp password password
wg_sw_2950(vlan)#vtp pruning
83. 84
Verifying the VTP
Configuration
Switch#show vtp statusSwitch#show vtp status
Switch#show vtp status
VTP Version : 2
Configuration Revision : 247
Maximum VLANs supported locally : 1005
Number of existing VLANs : 33
VTP Operating Mode : Client
VTP Domain Name : Lab_Network
VTP Pruning Mode : Enabled
VTP V2 Mode : Disabled
VTP Traps Generation : Disabled
MD5 digest : 0x45 0x52 0xB6 0xFD 0x63 0xC8 0x49 0x80
Configuration last modified by 0.0.0.0 at 8-12-99 15:04:49
Switch#
84. 85
Verifying the VTP
Configuration (Cont.)
Switch#show vtp countersSwitch#show vtp counters
Switch#show vtp counters
VTP statistics:
Summary advertisements received : 7
Subset advertisements received : 5
Request advertisements received : 0
Summary advertisements transmitted : 997
Subset advertisements transmitted : 13
Request advertisements transmitted : 3
Number of config revision errors : 0
Number of config digest errors : 0
Number of V1 summary errors : 0
VTP pruning statistics:
Trunk Join Transmitted Join Received Summary advts received from
non-pruning-capable device
---------------- ---------------- ---------------- ---------------------------
Fa5/8 43071 42766 5
85. 86
VLAN to VLAN
ï±If you want to connect between two
VLANs you need a layer 3 device
86. 87
Router on Stick
10.0.0.3
20.0.0.3
1 2 3 41 2 3 4
10.0.0.2
20.0.0.2
24 12
Create two VLAN's on each
switches
#vlan database
sw(vlan)#vlan 2 name red
sw(vlan)#vlan 3 name blue
sw(vlan)#exit
sw#config t
sw(config)#int fastethernet 0/1
sw(config-if)#switch-portaccess vlan 2
sw(config)#int fastethernet 0/4
sw(config-if)#switch-portaccess vlan 3
To see Interface status
#show interface status
Trunk Port Configuration
sw#config t
sw(config)#int fastethernet 0/24
sw(config-if)#switchport trunk
encapsulation dot1q
sw(config-if)#switchport mode trunk
Router Configuration
R1#config t
R1(config)#int fastethernet 0/0.1
R1(config-if)#encapsulation dot1q 2
R1(config-if)#ip address 10..0.0.1 255.0.0.0
R1(config-if# No shut
R1(config-Iif)# EXIT
R1(config)#int fastethernet 0/0.2
R1(config-if)# encapsulation dot1q 3
R1(config-if)#ip address 20..0.0.1 255.0.0.0
R1(config-if# No shut
Router-Switch Port to be made as Trunk
sw(config)#int fastethernet 0/9
sw(config-if)#switchport trunk enacapsulation
dot1q
sw(config-if)#switchport mode trunk
10.0.0.1
20.0.0.1
FA0/0
9
87. 88
Fig. 3 NAT (TI1332EU02TI_0003 New Address Concepts, 7)
88. 89
New Addressing Concepts
Problems with IPv4
Shortage of IPv4 addresses
Allocation of the last IPv4 addresses was for the year 2005
Address classes were replaced by usage of CIDR, but this is not sufficient
Short term solution
NAT: Network Address Translator
Long term solution
IPv6 = IPng (IP next generation)
Provides an extended address range
Fig. 2 Address shortage and possible solutions (TI1332EU02TI_0003 New Address Concepts, 5)
89. 90
NAT: Network Address Translator
NAT
Translates between local addresses and public ones
Many private hosts share few global addresses
Public Network
Uses public addresses
Public addresses are
globally unique
Private Network
Uses private address range
(local addresses)
Local addresses may not
be used externally
Fig. 4 How does NAT work? (TI1332EU02TI_0003 New Address Concepts, 9)
90. 91
NAT Addressing Terms
ï± Inside Local
ï¶ The term âinsideâ refers to an address used for a host inside an
enterprise. It is the actual IP address assigned to a host in the private
enterprise network.
ï± Inside Global
ï¶ NAT uses an inside global address to represent the inside host as
the packet is sent through the outside network, typically the Internet.
ï¶ A NAT router changes the source IP address of a packet sent by an
inside host from an inside local address to an inside global address
as the packet goes from the inside to the outside network.
93. 94
NAT Addressing Terms
ï± Outside Global
ï¶ The term âoutsideâ refers to an address used for a host outside
an enterprise, the Internet.
ï¶ An outside global is the actual IP address assigned to a host that
resides in the outside network, typically the Internet.
ï± Outside Local
ï¶ NAT uses an outside local address to represent the outside host
as the packet is sent through the private network.
ï¶ This address is outside private, outside host with a private
address
95. 96
Types Of NAT
ï±There are different types of NAT that can
be used, which are
ï¶Static NAT
ï¶Dynamic NAT
ï¶Overloading NAT with PAT (NAPT)
96. 97
Static NAT
ï± Static NAT - Mapping an unregistered IP address to a registered
IP address on a one-to-one basis. Particularly useful when a
device needs to be accessible from outside the network.
ï± In static NAT, the computer with the IP address of
192.168.32.10 will always translate to 213.18.123.110.
97. 98
Dynamic NAT
ï± Dynamic NAT - Maps an unregistered IP address to a registered IP
address from a group of registered IP addresses.
ï± In dynamic NAT, the computer with the IP address 192.168.32.10
will translate to the first available address in the range from
213.18.123.100 to 213.18.123.150.
98. 99
Overloading NAT with PAT
(NAPT)
ï± Overloading - A form of dynamic NAT that maps multiple unregistered
IP addresses to a single registered IP address by using different ports.
This is known also as PAT (Port Address Translation), single address
NAT or port-level multiplexed NAT.
ï± In overloading, each computer on the private network is translated to
the same IP address (213.18.123.100), but with a different port number
assignment..
99. 100
Static NAT Configuration
âą For each interface you need to configure INSIDE or OUTSIDE
Fig. 2 Address shortage and possible solutions (TI1332EU02TI_0003 New Address Concepts, 5)
E0
B
A 10.0.0.1
S0
200.0.0.1
C
Internet10.0.0.2
10.0.0.3
10.0.0.254
R1(config)#Int fastethernet 0/0
R1(config-if)# IP NAT inside
R1(config-if)##Int s 0/0
R1(config-if)# IP NAT outside
R1(config-if)# Exit
R1(config)# ip NAT inside source static 10.0.0.1 200.0.0.1
To see the table
R1(config)#show ip nat translations
R1(config)#show ip nat statistics
101. 102
Dynamic NAT
ï± Dynamic NAT sets up a pool of possible inside global
addresses and defines criteria for the set of inside
local IP addresses whose traffic should be translated
with NAT.
ï± The dynamic entry in the NAT table stays in there as
long as traffic flows occasionally.
ï± If a new packet arrives, and it needs a NAT entry, but
all the pooled IP addresses are in use, the router
simply discards the packet.
Fig. 2 Address shortage and possible solutions (TI1332EU02TI_0003 New Address Concepts, 5)
102. 103
Dynamic NAT
ï± Instead of creating static IP, create a pool of IP
Address, Specify a range
ï± Create an access list and permit hosts
ï± Link Access list to the Pool
Fig. 2 Address shortage and possible solutions (TI1332EU02TI_0003 New Address Concepts, 5)
103. 104
Dynamic NAT Configuration
âą For each interface you need to configure INSIDE or OUTSIDE
S0
200.0.0.1/200.0.0.254
Internet
E0
B
A 10.0.0.1
C
10.0.0.2
10.0.0.3
10.0.0.254
Create an Access List
R1(config)# Access-list 1 permit 10.0.0.0 0.255.255.255
Configure NAT dynamic Pool
R1(config)# IP NAT pool pool1 200.0.0.1 200.0.0.254 netmask 255.255.255.0
Link Access List to Pool
R1(config)# IP NAT inside source list 1 pool pool1
104. 105
PAT
ï± Overloading an inside global address
ï± NAT overload only one global IP shared among all hosts
Fig. 2 Address shortage and possible solutions (TI1332EU02TI_0003 New Address Concepts, 5)
E0
B
A 10.0.0.1
C
10.0.0.2
10.0.0.3
10.0.0.254 200.0.0.1
Internet
Shared Global IP
200.0.0.1:1025
200.0.0.1:1026
200.0.0.1:1027
113. 114
PAT LAB
R1#config t
R1(config)# int e 0
R1(config-if)# ip nat insde
R1(config)# int s 0
R1(config-if)# ip nat outside
R1(config)#access-list 1 permit 192.168.10.0 0.0.0.255
R1(config)#ip nat inside source list 1 interface s 0 overload
ï¶ To see host to host ping configure static or
dynamic routing
To check translation
#sh ip nat translations
S0
S0E0
E0
192.168.10.2
A B
200.0.0.2
192.168.10.1
200.0.0.1
192.168.20.2
192.168.20.1
R2#config t
R2(config)# int e 0
R2(config-if)# ip nat insde
R2(config)# int s 0
R2(config-if)# ip nat outside
R2(config)#access-list 1 permit 192.168.20.0 0.0.0.255
R2(config)#ip nat inside source list 1 interface s 0 overload
ï¶ To see host to host ping configure static or
dynamic routing
To check translation
#sh ip nat translations
Editor's Notes
<number>
Emphasize: The next few slides discuss the basic function of a bridge/switch:
1. How it learns the location of the hosts by reading the source MAC address of incoming frames.
2. How it makes forwarding/filtering decisions.
There are three conditions in which a switch will flood a frame out on all ports except to the port on which the frame came in, as follows:
Unknown unicast address
Broadcast frame
Multicast frame
3. How STP is used to avoid loops in a switched/bridged network.
<number>
Slide 1 of 3
Emphasize: The 1900en max MAC address table size is 1024. Once the table is full, it will flood all new addresses until existing entries age out.
The command to change the MAC address table aging time is, as follows:
wg_sw_a(config)#mac-address-table aging-time ?
<10-1000000> Aging time value
The default is 300 sec.
The MAC address table is also referred to as the CAM table (Content Address Memory) on some switches.
<number>
Slide 2 of 3
<number>
Slide 3 of 3
Emphasize: Once C replies, the switch will also cache station Câs MAC address to port E2, as shown in the next slide.
<number>
<number>
The server in the figure sends a unicast frame to Router C. Since itâs a unicast frame, Switch A forwards the frame, and Switch B provides the same serviceâit forwards the unicast. This is bad because it means that Router C receives that unicast frame twice, causing additional overhead on the network.one: The MAC address filter table will be totally confused about the deviceâs location because the switch can receive the frame from more than one link.
<number>
Emphasize: A looped topology is often desired to provide redundancy, but looped traffic is undesirable. The Spanning-Tree protocol was originally designed for bridges. Today, it is also applied to LAN switches and routers operating as a bridge. Spanning-Tree protocol ensures that all bridged segments are reachable but any points where loops occur will be blocked.
a company called Digital Equipment Corporation
(DEC) created the original version of
Spanning Tree Protocol (STP)
. The IEEE later
created its own version of STP called 802.1D. All Cisco switches run the IEEE 802.1D version
of STP, which isnât compatible with the DEC version.
STP uses the spanning-tree algorithm (STA) to first create a
topology database, then search out and destroy redundant links.
<number>
Emphasize: Using the default Spanning-Tree protocol timers setting, the times it takes to go from the blocking state to the forwarding state is 50 sec (20 + 15 + 15).
Blocking A blocked port wonât forward frames; it just listens to BPDUs. The purpose of the
blocking state is to prevent the use of looped paths. All ports are in blocking state by default
when the switch is powered up.
Listening The port listens to BPDUs to make sure no loops occur on the network before passing
data frames. A port in listening state prepares to forward data frames without populating
the MAC address table.
Learning The switch port listens to BPDUs and learns all the paths in the switched network.
A port in learning state populates the MAC address table but doesnât forward data frames.
Forwarding The port sends and receives all data frames on the bridged port. If the port is still
a designated or root port at the end of the learning state, it enters this state.
Disabled A port in the disabled state (administratively) does not participate in the frame forwarding
or STP. A port in the disabled state is virtually nonoperational.
Switch ports are most often in either the blocking or forwarding state. A forwarding port is
one that has been determined to have the lowest (best) cost to the root bridge. But when and if
the network experiences a topology change (because of a failed link or because someone adds
in a new switch), youâll find the ports on a switch in listening and learning states.
BPDUs are sent every two seconds,
BPDUs are sent every two seconds,
If more than one link connects to the root bridge, then a port cost is determined by checking the bandwidth of each link.The lowest-cost port becomes the root port. If multiple links have the same cost, the bridge with the lower advertising bridge ID is used. Since multiple links can be from the same device, the lowest port number will be used.
Emphasize: By default, the switch with the lowest MAC address will be the root bridge.
Note: The Catalyst switches support an instance of spanning tree per VLAN. Each VLAN will use a unique MAC address for spanning tree purposes. On the Catalyst 1900, the address it uses for spanning tree is the MAC address on the various ports. VLAN is discussed in the next chapter.
The IEEE 802.1d specification specifies for a 16-bit priority field. The Catalyst 1900 switch only supports the 802.1d Spanning-Tree protocol. The default priority on the Catalyst 1900 is 32768 in decimal or 8000 in hex, the midrange value.
BPDU contain the following fields:
Protocol ID version
Message type
Flags
Root ID
Cost of path
Bridge ID
Port ID
Message age
Max age
Hello time
Forward delay
Emphasize: The three general rules when dealing with STP are as follows:
1. One root bridge per network. The root is the bridge with the lowest bridge ID. All the ports on the root bridge are designated ports (forwarding).
2. For every non-root bridge, there is a root port (forwarding). The root port is the port with the lowest accumulated path cost to the root bridge.
3. For every segment, there is only one designated port. The designated port forwards traffic for the segment. The designated port has the lowest accumulated path cost to the root bridge.
Selecting the Root Port
If more than one link leads to the root bridge, then cumulative outbound port costs along the path to the root bridge becomes the factor used to determine which port will be the root port
Emphasize: The three general rules when dealing with STP are as follows:
1. One root bridge per network. The root is the bridge with the lowest bridge ID. All the ports on the root bridge are designated ports (forwarding).
2. For every non-root bridge, there is a root port (forwarding). The root port is the port with the lowest accumulated path cost to the root bridge.
3. For every segment, there is only one designated port. The designated port forwards traffic for the segment. The designated port has the lowest accumulated path cost to the root bridge.
Series â 1900 â Stopped
2900 â Will be used in LAB
3500 â layer 3 Switch
When the 1900 switch is first powered on, it runs through a power-on self-test (POST). At first, all port LEDs are green, and if upon completion the POST determines that all ports are in good shape, all the LEDs blink and then turn off. But if the POST finds a port that has failed, both the System LED and the portâs LED turn amber.
There are several benefits to using VLANs, including:
1. Increased performance
2. Improved manageability
3. Network tuning and simplification of software configurations
4. Physical topology independence
5. Increased security options
Increased performance
Switched networks by nature will increase performance over shared media devices in use
today, primarily by reducing the size of collision domains. Grouping users into logical
networks will also increase performance by limiting broadcast traffic to users performing
similar functions or within individual workgroups. Additionally, less traffic will need to be
routed, and the latency added by routers will be reduced.
<number>
Purpose:
Emphasize: A VLAN is a broadcast domain.
Note: In order to have inter-VLAN communications, a router is required.
<number>
Note: Once a port has been assigned to a VLAN, it cannot send or receive traffic from devices in another VLAN without the intervention of a Layer 3 device like a router.
The 1900 canât be configure as the VMPS.
A CiscoWorks 2000 or CWSI management station or a Catalyst 5000 switch can be configured as the VMPS.
In the future, dynamic VLANs may also offer membership based on other criteria such as protocol or application. Dynamic VLANs are covered in the Managing Cisco Switched Internetworks class.
VMPS
VMP S is a server process that supports dynamic ports. Dynamic ports enable end-user nodes to remain on the same VLAN after being moved and plugged into another physical port without the intervention of manual port reconfiguration. To support dynamic ports, there must be at least one Catalyst 5000 switch running VMPS per domain on the network.
When a workstation or other end-user node is attached to a dynamic port, the switch uses VMPS information to assign that port to a particular VLAN based on the MAC address of the network interface card in the device. When the device is moved and plugged into another port, VMPS provides configuration information from the MAC-VLAN mapping that allows the device to remain on the same VLAN as before without manual reconfiguration.
Without VMPS, each port is statically assigned to a single VLAN. Changing the VLAN assigned to a static port requires manually changing the VLAN assignment of the port. Thus, when you most a device and connect it to a different port, you need to manually reconfigure the port. You can use VlanDirector, CiscoView, or the command-line interface to do this reconfiguration; with VMPS, however, it is automatic.
<number>
Layer 3 of 3
Emphasize: A trunk is used to connect two switches together.
A trunk carries traffic for multiple VLANs.
Only the Fast Ethernet ports on the 1900 can be configured as trunk port.
Trunking is off by default on the 1900 Fast Ethernet ports (fa 0/26 and fa 0/27).
Note: The 1900 supports DISL.
At the time of the beta, the core switch (2900xl) doesnât support DISL.
Access port â single VLAN
Trunk â Between switches and cannot be part of only one VLAN
Trunk port can carry multiple VLANS
Creating VLAN on each port should be consistent
Port can be anything
Trunk port is a fastethernet port
Since trunk need to carry this to all VLANâs there should be an ID
This ID is frame Tagging
Trunking allows you to make a single port part of multiple VLANs at the same time. This
can be a real advantage. For instance, you can actually set things up to have a server in two
broadcast domains simultaneously, so that your users wonât have to cross a layer 3 device
(router) to log in and access it.
The basic purpose of ISL and 802.1Q frame-tagging methods is to provide inter-switch VLAN communication..
<number>
Note: The 1900 only supports ISL trunking.
ISL is Cisco proprietary. 802.1Q is an IEEE standard.
Other trunk types:
LANE (VLANSs over ATM)
802.10 (FDDI trunk)
Two Switches are connected and there are four hosts machines
Configure 4 VM with 10.0.0.1 to 10.0.0.4
Ping and see all are pining
Have connected thru switches and connect switches using cross cable
Create VLAN red and blue on both Switches
Now see only the same VLANâs can communicate
<number>
Notes: VTP is a Cisco proprietary feature. VTP is a Layer 2 messaging protocol that maintains VLAN configuration consistency by managing the addition, deletion, and renaming of VLANs on a network-wide basis. VTP minimizes misconfigurations and configuration inconsistencies that can cause several problems, such as duplicate VLAN names, incorrect VLAN-type specifications, and security violations.
A VTP domain (also called a VLAN management domain) is one switch or several interconnected switches sharing the same VTP domain. A switch is configured to be in only one VTP domain. You make global VLAN configuration changes for the domain by using the Cisco IOS command-line interface (CLI), Cisco Visual Switch Manager Software, or Simple Network Management Protocol (SNMP).
By default, a 1900 switch is in the no-management-domain state until it receives an advertisement for a domain over a trunk link or you configure a management domain.
The default VTP mode is server mode, but VLANs are not propagated over the network until a management domain name is specified or learned. If the switch receives a VTP advertisement over a trunk link, it inherits the management domain name and configuration revision number. The switch then ignores advertisements with a different management domain name or an earlier configuration revision number.
When you make a change to the VLAN configuration on a VTP server, the change is propagated to all switches in the VTP domain. VTP advertisements are transmitted out all trunk connections, including Inter-Switch Link (ISL), IEEE 802.1Q, IEEE 802.10, and ATM LAN Emulation (LANE).
If you configure a switch from VTP transparent mode, you can create and modify VLANs, but the changes are not transmitted to other switches in the domain, and they affect only the individual switch.
<number>
Emphasize: Default VTP mode on the Catalyst switches is server. Be careful when adding new switches into an existing network. This is covered in more detail later.
<number>
Layer 2 of 2
Emphasize: The latest revision number is what the switches will synchronize to.
<number>
Emphasize: VTP prunning provides optimized flooding. Without VTP prunning, station Aâs broadcast will be flooded to all switches whether they have any port in the red VLAN or not.
Note: VLAN1 canât be prunned. STP, CDP, VTP updates are sent on VLAN1.
All switches in the switched network must support prunning or prunning will be disabled.
Each trunk port maintains a state variable per VLAN indicating if the switch has any port assigned to a particular VLAN or not.
<number>
Be cautious when adding a new switch into an existing domain.
Add a new switch in a Client mode to get the last up-to-date information from the network then convert it to Server mode.
Add all new configurations to switch in transparent mode and check your configuration well then convert it to Server mode to prevent the switch from propagating incorrect VLAN information.
Notes: All switches in a VTP domain must run the same VTP version.
The password entered with a domain name should be the same for all switches in the domain. If you configure a VTP password, the management domain will not function properly if you do not assign the management domain password to each switch in the domain.
A VTP version 2-capable switch can operate in the same VTP domain as a switch running VTP version 1, provided version 2 is disabled on the version 2-capable switch (version 2 is disabled by default).
Do not enable VTP version 2 on a switch unless all of the switches in the same VTP domain are version 2-capable. When you enable version 2 on a switch, all of the version 2-capable switches in the domain must have version 2 enabled. If there is a version 1-only switch, it will not exchange VTP information with switches with version 2 enabled.
If there are Token Ring networks in your environment, you must enable VTP version 2 for Token Ring VLAN switching to function properly.
Enabling or disabling VTP pruning on a VTP server enables or disables VTP pruning for the entire management domain.
In the lab, all the switches are set to VTP transparent mode.
<number>
Layer 2 of 2
Note: The two commands shown in the slide can also be combined into one command:
vtp domain switchlab transparent
What Does NAT Do?
NAT is like the receptionist in a large office. Let's say you have left instructions with the receptionist not to forward any calls to you unless you request it. Later on, you call a potential client and leave a message for that client to call you back. You tell the receptionist that you are expecting a call from this client and to put her through. The client calls the main number to your office, which is the only number the client knows. When the client tells the receptionist that she is looking for you, the receptionist checks a lookup table that matches your name with your extension. The receptionist knows that you requested this call, and therefore forwards the caller to your extension.
Like static NAT, the NAT router creates a one-to-one mapping between an inside local and inside global address and changes the IP addresses in packets as they exit and enter the inside network.
However, the mapping of an inside local address to an inside global address happens dynamically.
<number>
There should be router 2600 configured
To verify whether router supports IP NAT static go to config and
# IP NAT inside source ? (there should be a static Entry)
Configure router 2600 with an IP address on Fastethernet port 10.0.0.254 and Serial 0/0 200.0.0.1, need not to connect any cables, configure IP and no shut then see the above commands
<number>
There should be router 2600 configured
Configure router 2600 with an IP address on Fastethernet port 10.0.0.254 and Serial 0/0 200.0.0.1, need not to connect any cables, configure IP and no shut then see the above commands
Can have 65000 concurrent connection sharing one connection