CCNA

Layer 2 Switching
Switching breaks up large collision domains into smaller ones

Collision domain is a network segment with two or more devices sharing the same bandwidth.

A hub network is a typical example of this type of technology

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
Switching Services
Unlike bridges that use software to create and manage a filter table, switches use Application Specific Integrated Circuits (ASICs)
Layer 2 switches and bridges are faster than routers because they don’t take up time looking at the Network layer header information.
They look at the frame’s hardware addresses before deciding to either forward the frame or drop it.
layer 2 switching so efficient is that no modification to the data packet takes place

How Switches and Bridges
Learn Addresses
Bridges and switches learn in the following ways:

Reading the source MAC address of each received frame or datagram

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.
Ethernet Access with Hubs
Ethernet Access with Switches
Address learning
Forward/filter decision
Loop avoidance
Ethernet Switches and Bridges
Switch Features
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



MAC Address Table
Initial MAC address table is empty.
Learning Addresses
Station A sends a frame to station C.
Switch caches the MAC address of station A 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).
Learning Addresses (Cont.)
Station D sends a frame to station C.
Switch caches the MAC address of station D to port E3 by learning the source address of data frames.
The frame from station D to station C is flooded out to all ports except port E3 (unknown unicasts are flooded).
Filtering Frames
Station A sends a frame to station C.
Destination is known; frame is not flooded.
Station D sends a broadcast or multicast frame.
Broadcast and multicast frames are flooded to all ports other than the originating port.

Broadcast and Multicast Frames
Forward/Filter Decision
When a frame arrives at a switch interface, the destination hardware address is compared to the forward/ filter MAC database.

If the destination hardware address is known and listed in the database, the frame is sent out only the correct exit interface

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.

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.
Learning Mac Address
Learning Mac Address
Learning Mac Address
Learning Mac Address
Learning Mac Address
Learning Mac Address
Learning Mac Address
Forward/Filter PC3 to PC1
Forward/Filter PC3 to PC2
Loop Avoidance
Redundant links between switches are a good idea because they help prevent complete network failures in the event one link stops working
However, they often cause more problems because frames can be flooded down all redundant links simultaneously
This creates network loops
Network Broadcast Loops
A manufacturing floor PC sent a network broadcast to request a boot loader
The broadcast was first received by switch sw1 on port 2/1
The topology is redundantly connected; therefore, switch sw2 receives the broadcast frame as well on port 2/1
Switch sw2 is also receiving a copy of the broadcast frame forwarded to the LAN segment from port 2/2 of switch sw1.
In a small fraction of the time, we have four packets. The problem grows exponentially until the network bandwidth is saturated
Multiple Frame Copies
Overview
Redundancy in a network is extremely important because redundancy allows networks to be fault tolerant.

Redundant topologies based on switches and bridges are subject to broadcast storms, multiple frame transmissions, and MAC address database instability.

Therefore network redundancy requires careful planning and monitoring to function properly.

The Spanning-Tree Protocol is used in switched networks to create a loop free network
Provides a loop-free redundant network topology by
placing certain ports in the blocking state.
Spanning-Tree Protocol
Spanning Tree Protocol
Spanning Tree Protocol resides in Data link Layer

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.


Spanning-tree transits each port through several different states:
Spanning-Tree Port States
Disabled
Selecting the Root Bridge
The first decision that all switches in the network make, is to identify the root bridge.

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).

The BID consists of a bridge priority that defaults to 32768 and the switch base MAC address.

When a switch first starts up, it assumes it is the root switch and sends BPDUs. These BPDUs contain BID.

All bridges see these and decide that the bridge with the smallest BID value will be the root bridge.

A network administrator may want to influence the decision by setting the switch priority to a smaller value than the default.
Spanning Tree Protocol Terms
BPDU Bridge Protocol Data Unit (BPDU) - All the switches exchange information to use in the selection of the root switch

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.

Root Bridge -The bridge with the lowest bridge ID becomes the root bridge in the network.

Nonroot bridge - These are all bridges that are not the root bridge.

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.

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

Nondesignated Port - A nondesignated port is one with a higher cost than the designated port. Nondesignated ports are put in blocking mode

Forwarding Port - A forwarding port forwards frames

Blocked Port - A blocked port is the port that will not forward frames, in order to prevent loops
Bpdu = Bridge Protocol Data Unit
(default = sent every two seconds)
Root bridge = Bridge with the lowest bridge ID
Bridge ID =

In the example, which switch has the lowest bridge ID?

Spanning-Tree Protocol
Root Bridge Selection

One root bridge per network
One root port per nonroot bridge
One designated port per segment
Nondesignated ports are unused
Spanning-Tree Operation
Selecting the Root Port
The STP cost is an accumulated total path cost based on the rated bandwidth of each of the links
This information is then used internally to select the root port for that device

One root bridge per network
One root port per nonroot bridge
One designated port per segment
Nondesignated ports are unused
Spanning-Tree Operation
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.
Switching Methods
Physical Startup of the Catalyst Switch
Switches are dedicated, specialized computers, which contain a CPU, RAM, and an operating system.

Switches usually have several ports for the purpose of connecting hosts, as well as specialized ports for the purpose of management.

A switch can be managed by connecting to the console port to view and make changes to the configuration.

Switches typically have no power switch to turn them on and off. They simply connect or disconnect from a power source.

Switch LED Indicators
The front panel of a switch has several lights to help monitor system activity and performance. These lights are called light-emitting diodes (LEDs). The switch has the following LEDs:
System LED
Remote Power Supply (RPS) LED
Port Mode LED
Port Status LEDs

The System LED shows whether the system is receiving power and functioning correctly.

The RPS LED indicates whether or not the remote power supply is in use.

The Mode LEDs indicate the current state of the Mode button.

The Port Status LEDs have different meanings, depending on the current value of the Mode LED.
Verifying Port LEDs During Switch POST
Once the power cable is connected, the switch initiates a series of tests called the power-on self test (POST).

POST runs automatically to verify that the switch functions correctly.

The System LED indicates the success or failure of POST.
Switch Command Modes
Switches have several command modes.

The default mode is User EXEC mode, which ends in a greater-than character (>).

The commands available in User EXEC mode are limited to those that change terminal settings, perform basic tests, and display system information.

The enable command is used to change from User EXEC mode to Privileged EXEC mode, which ends in a pound-sign character (#).

The configure command allows other command modes to be accessed.   
Show Commands in User-Exec Mode
Tasks
Setting the passwords (Password must be between 4 and 8 characters)

Setting the hostname

Configuring the IP address and subnet mask

Erasing the switch configurations
Setting Switch Hostname
Setting Passwords on Lines
Switch Configuration
There are two reasons to set the IP address information on the switch:
To manage the switch via Telnet or other management software
To configure the switch with different VLANs and other network functions
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
Configuring Interface Descriptions
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)#

Setting Port Security
Sw1(config-if)#switchport port-security mac-address mac-address

Now only this one MAC address is allowed on this switch port


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
VLAN’s
A VLAN is a logical grouping of network users and resources connected to administratively defined ports on a switch.
Ability to create smaller broadcast domains within a layer 2 switched internetwork by assigning different ports on the switch to different subnetworks.
Frames broadcast onto the network are only switched between the ports logically grouped within the same VLAN
By default, no hosts in a specific VLAN can communicate with any other hosts that are members of another VLAN,
For Inter VLAN communication you need routers
VLANs
VLAN implementation combines Layer 2 switching and Layer 3 routing technologies to limit both collision domains and broadcast domains.

VLANs can also be used to provide security by creating the VLAN groups according to function and by using routers to communicate between VLANs.

A physical port association is used to implement VLAN assignment.

Communication between VLANs can occur only through the router.

This limits the size of the broadcast domains and uses the router to determine whether one VLAN can talk to another VLAN.

NOTE: This is the only way a switch can break up a broadcast domain!
A VLAN = A Broadcast Domain = Logical Network (Subnet)
VLAN Overview
Segmentation

Flexibility

Security

History
11 Hosts are connected to the switch
All From same Broadcast domain
Need to divide them in separate logical segment
High broadcast traffic reasons
ARP
DHCP
SAP
XWindows
NetBIOS

Definition
Logically Defined community of interest that limits a Broadcast domain
LAN are created on the software of Switch
All devices in a VLAN are members of the same broadcast domain and receive all broadcasts
The broadcasts, by default, are filtered from all ports on a switch that are not members of the same VLAN.


Security
A Flat internetwork’s security used to be tackled by connecting hubs and switches together with routers
This arrangement is ineffective because
Anyone connecting physical network could access network resources located on that physical LAN
Can observe the network traffic by plugging network analyzer into the HUB
Users could join a workgroup by just plugging their workstations into the existing hub
By creating VLAN’s administrators have control over each port and user

How VLANs Simplify Network Management
If we need to break the broadcast domain we need to connect a router

By using VLAN’s we can divide Broadcast domain at Layer-2

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.

As a logical grouping of users by function, VLANs can be considered independent from their physical locations.

VLAN Memberships
VLAN created based on port is known as Static VLAN.


VLAN assigned based on hardware addresses into a database, is called a dynamic VLAN
VLAN Membership Modes
Static VLANs
Most secure

Easy to set up and monitor

Works well in a network where the movement of users within the network is controlled
Dynamic VLANs
A dynamic VLAN determines a node’s VLAN assignment automatically

Using intelligent management software, you can base VLAN assignments on hardware (MAC) addresses.

Dynamic VLAN need VLAN Management Policy Server (VMPS) server

LAB – Creating VLAN
Connect two computers on a switch
Ping and see both are able to communicate
Create two vlans and configure static VLAN’s so both ports are on separate VLAN’s
Test the communication between PC’s

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
LAB – 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
VLANs can span across multiple switches.
Trunks carry traffic for multiple VLANs.
Trunks use special encapsulation to distinguish between different VLANs.

VLAN Operation
Types of Links
Access links
This type of link is only part of one VLAN
It’s referred to as the native VLAN of the port.
Any device attached to an access link is unaware of a VLAN
Switches remove any VLAN information from the frame before it’s sent to an access-link device.

Trunk links
Trunks can carry multiple VLANs
These carry the traffic of multiple VLANs
A trunk link is a 100- or 1000Mbps point-to-point link between two switches, between a switch and router.
Access links
Trunk links
Frame Tagging
Can create VLANs to span more than one connected switch
Hosts are unaware of VLAN
When host A Create a data unit and reaches switch, the switch adds a Frame tagging to identify the VLAN
Frame tagging is a method to identify the packet belongs to a particular VLAN
Each switch that the frame reaches must first identify the VLAN ID from the frame tag
It finds out what to do with the frame by looking at the information in the filter table
Once the frame reaches an exit to an access link matching the frame’s VLAN ID, the switch removes the VLAN identifier
Frame Tagging Methods
There are two frame tagging methods
Inter-Switch Link (ISL)
IEEE 802.1Q
Inter-Switch Link (ISL)
proprietary to Cisco switches
used for Fast Ethernet and Gigabit Ethernet links only
IEEE 802.1Q
Created by the IEEE as a standard method of frame tagging
it actually inserts a field into the frame to identify the VLAN
If you’re trunking between a Cisco switched link and a different brand of switch, you have to use 802.1Q for the trunk to work.
Performed with ASIC
ISL header not seen by client
Effective between switches, and between routers and switches
ISL trunks enable VLANs across a backbone.
ISL Tagging
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
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
Assigning Access Ports to a VLAN
Switch(config)#interface gigabitethernet 1/1
Enters interface configuration mode
Switch(config-if)#switchport mode access
Configures the interface as an access port
Switch(config-if)#switchport access vlan 3
Assigns the access port to a VLAN
Verifying the VLAN Configuration
Switch#show vlan [id | name] [vlan_num | vlan_name]
VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Fa0/1, Fa0/2, Fa0/5, Fa0/7
Fa0/8, Fa0/9, Fa0/11, Fa0/12
Gi0/1, Gi0/2
2 VLAN0002 active
51 VLAN0051 active
52 VLAN0052 active
…

VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
1 enet 100001 1500 - - - - - 1002 1003
2 enet 100002 1500 - - - - - 0 0
51 enet 100051 1500 - - - - - 0 0
52 enet 100052 1500 - - - - - 0 0
…

Remote SPAN VLANs
------------------------------------------------------------------------------
Primary Secondary Type Ports
------- --------- ----------------- ------------------------------------------

Verifying the VLAN Port Configuration
Switch#show running-config interface {fastethernet | gigabitethernet} slot/port
Displays the running configuration of the interface
Switch#show interfaces [{fastethernet | gigabitethernet} slot/port] switchport
Displays the switch port configuration of the interface
Switch#show mac-address-table interface interface-id [vlan vlan-id] [ | {begin | exclude | include} expression]
Displays the MAC address table information for the specified interface in the specified VLAN
A messaging system that advertises VLAN configuration information
Maintains VLAN configuration consistency throughout a common administrative domain
Sends advertisements on trunk ports only
VTP Protocol Features
VLAN Trunking Protocol (VTP)
Benefits of VTP
Consistent VLAN configuration across all switches in the network
Accurate tracking and monitoring of VLANs
Dynamic reporting of added VLANs to all switches in the VTP domain
Forwards
advertisements
Synchronizes
Not saved in
NVRAM
Creates VLANs
Modifies VLANs
Deletes VLANs
Sends/forwards
advertisements
Synchronizes
Saved in NVRAM
Creates VLANs
Modifies VLANs
Deletes VLANs
Forwards
advertisements
Does not
synchronize
Saved in NVRAM

VTP Modes
VTP Operation
VTP advertisements are sent as multicast frames.
VTP servers and clients are synchronized to the latest update identified revision number.
VTP advertisements are sent every 5 minutes or when there is a change.
VTP Pruning
VTP pruning provides a way for you to preserve bandwidth by configuring it to reduce the amount of broadcasts, multicasts, and unicast packets.

If Switch A doesn’t 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.

By default, VTP pruning is disabled on all switches.

Pruning is enabled for the entire domain
Increases available bandwidth by reducing unnecessary flooded traffic
Example: Station A sends broadcast, and broadcast is flooded only toward any switch with ports assigned to the red VLAN
VTP Pruning
VTP Configuration Guidelines
Configure the following:
VTP domain name
VTP mode (server mode is the default)
VTP pruning
VTP password


Switch(config)#vtp mode server
Switch(config)#vtp domain gates
SwitchA#sh vtp status

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

Verifying the VTP Configuration
Switch#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#
Verifying the VTP Configuration (Cont.)
Switch#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
VLAN to VLAN
If you want to connect between two VLANs you need a layer 3 device
Router on Stick
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
Fig. 3 NAT (TI1332EU02TI_0003 New Address Concepts, 7)
New Addressing Concepts
Fig. 2 Address shortage and possible solutions (TI1332EU02TI_0003 New Address Concepts, 5)
NAT: Network Address Translator
Fig. 4 How does NAT work? (TI1332EU02TI_0003 New Address Concepts, 9)
NAT Addressing Terms
Inside Local

The term “inside” 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.

Inside Global

NAT uses an inside global address to represent the inside host as the packet is sent through the outside network, typically the Internet.
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.
Inside/Outside
Inside/Outside
NAT Addressing Terms

Outside Global

The term “outside” refers to an address used for a host outside an enterprise, the Internet.
An outside global is the actual IP address assigned to a host that resides in the outside network, typically the Internet.

Outside Local

NAT uses an outside local address to represent the outside host as the packet is sent through the private network.
This address is outside private, outside host with a private address
Network Address Translation
An IP address is either local or global.
Local IP addresses are seen in the inside network.
Types Of NAT
There are different types of NAT that can be used, which are
Static NAT
Dynamic NAT
Overloading NAT with PAT (NAPT)
Static NAT
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.

In static NAT, the computer with the IP address of 192.168.32.10 will always translate to 213.18.123.110.


Dynamic NAT
Dynamic NAT - Maps an unregistered IP address to a registered IP address from a group of registered IP addresses.

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.

Overloading NAT with PAT (NAPT)
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.

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..
Static NAT Configuration
For each interface you need to configure INSIDE or OUTSIDE

Fig. 2 Address shortage and possible solutions (TI1332EU02TI_0003 New Address Concepts, 5)
E0
10.0.0.1
S0
200.0.0.1
Internet
10.0.0.2
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
INSIDE/OUTSIDE
Dynamic NAT
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.

The dynamic entry in the NAT table stays in there as long as traffic flows occasionally.

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)
Dynamic NAT
Instead of creating static IP, create a pool of IP Address, Specify a range
Create an access list and permit hosts
Link Access list to the Pool
Fig. 2 Address shortage and possible solutions (TI1332EU02TI_0003 New Address Concepts, 5)
Dynamic NAT Configuration
For each interface you need to configure INSIDE or OUTSIDE

S0
200.0.0.1/200.0.0.254
Internet
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
PAT
Overloading an inside global address
NAT overload only one global IP shared among all hosts
Fig. 2 Address shortage and possible solutions (TI1332EU02TI_0003 New Address Concepts, 5)
200.0.0.1
Internet
Shared Global IP
200.0.0.1:1025
200.0.0.1:1026
200.0.0.1:1027
PAT
PAT
PAT
PAT
PAT
PAT
PAT
Configuration
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

To see host to host ping configure static or dynamic routing

To check translation
#sh ip nat translations
S0
S0
E0
E0
192.168.10.2
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

To see host to host ping configure static or dynamic routing

To check translation
#sh ip nat translations