Routing Protocol and Concepts
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Routing Protocol and Concepts
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Routing Protocol and Concepts
 ลักษณะการส่ ง Packet ใน IP Network จะส่ งทีละ Hop จาก Network
หนึ่ง ไปยังอีก Network หนึ่ง
 Router จะทาหน้าที่ดงั กล่าว เนื่องจาก Router เป็ นตัวเชื่อมระหว่าง
Network
 การส่ งจะดูที่ส่วน Prefix ของ IP Address ดังนั้น Router จะต้อง Run
IP Protocol คือทางานในระดับ Layer 3
 ที่ Router จะมีตารางชื่อ Routing Table ที่กาหนด IP Address ของ
Next Hop
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Routing Protocol and Concepts
 Static Routing : หมายถึงตาราง Routing Table ของ Router แต่ละตัว
จะไม่เปลี่ยน ปกติตารางนี้จะถูกกาหนดจาก Network Administration
คือตารางนี้จะได้จากการทา Configuration ของ Router
 Dynamic Routing : หมายถึงตาราง Routing Table สามารถเปลี่ยนได้
ตามสภาวะความคับคัง่ ของ Network ขณะนั้นหรื อจากปัจจัยอื่นๆ
โดยมันจะมีการ Update ตลอดเวลา
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Routing Protocol and Concepts
หน้าที่หลักของ router
• การพิจารณาคัดเลือกเส้นทางในการส่ งผ่านข้อมูลไปยัง
เครื อข่ายคอมพิวเตอร์อื่น ๆ (Internetworking Device) การ
ส่ งผ่านข้อมูลของ Router จะใช้โปรโตคอล IP โดยทางานอยู่
บนระดับชั้นที่ 3 ของแบบจาลอง OSI Model
• Routers generally have 2 connections:
-WAN connection (Connection to ISP)
-LAN connection
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Routing Protocol and Concepts
 Data is sent in form of packets between 2 end devices
 Routers are used to direct packet to its destination
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Routing Protocol and Concepts
 Routers examine a packet’s destination IP address and
determine the best path by enlisting the aid of a routing
table
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Routing Protocol and Concepts
 ส่ วนประกอบของ router และ ฟังก์ชนั่ การทางาน
• CPU
• Random access memory (RAM)
• Read-only memory (ROM)
• Non-volatile RAM (NVRAM)
• Flash memory
• Interfaces
• -Ethernet / fast Ethernet interfaces
• -Serial interfaces
• -Management interfaces
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Routing Protocol and Concepts
 Router components
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Routing Protocol and Concepts
 กระบวนการทางานของ router
• Test router hardware
• Power-On Self Test
(POST)
• Execute bootstrap
loader
• Locate & load Cisco IOS
software
• -Locate IOS
• -Load IOS
• Locate & load startup
configuration file or enter
setup mode
• -Bootstrap program
looks for configuration
file
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Routing Protocol and Concepts
 การตรวจสอบข้อมูลของตัว router
-The show version command is used to view information about
the router during the bootup process. Information includes:
• Platform model number
• Image name & IOS version
• Bootstrap version stored in ROM
• Image file name & where it was loaded from
• Number & type of interfaces
• Amount of NVRAM
• Amount of flash
• Configuration register
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Routing Protocol and Concepts
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Routing Protocol and Concepts
• Router Interface is a physical connector that enables a
router to send or receive packets
• Each interface connects to a separate network
• Consist of socket or jack found on the outside of a router
• Types of router interfaces:
-Ethernet
-Fastethernet
-Serial
-DSL
-ISDN
-Cable
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Routing Protocol and Concepts
 Two major groups of Router Interfaces
LAN Interfaces:
Are used to connect router to LAN
network
Has a layer 2 MAC address
Can be assigned a Layer 3 IP
address
Usually consist of an RJ-45 jack
 WAN Interfaces
Are used to connect routers to external networks that
interconnect LANs.
Depending on the WAN technology, a layer 2 address
may be used.
Uses a layer 3 IP address
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Routing Protocol and Concepts
 Routers and the Network Layer
Routers use destination IP address to forward packets
The path a packet takes is determined after a router
consults information in the routing table.
After router determines the best path
Packet is encapsulated into a frame
Frame is then placed on network medium in form of Bits
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Routing Protocol and Concepts
 Routers Operate at Layers 1, 2 & 3
Router receives a stream of encoded bits
Bits are decoded and passed to layer 2
Router de-encapsulates the frame
Remaining packet passed up to layer 3
-Routing decision made at this layer by examining
destination IP address
Packet is then re-encapsulated & sent out outbound interface
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Static Routing
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General Role of the Router
 Functions of a Router
Best Path Selections
Forwarding packets to destination
 Introducing the Topology
3 1800 series routers connected via WAN links
Each router connected to a LAN represented by a switch and a PC
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General Role of the Router
 Connections of a Router for WAN
-A router has a DB-60 port that can support 5 different cabling
standards
 Connections of a Router for Ethernet
-2 types of connectors can be used: Straight through and Cross-
over
Straight through used to connect:
-Switch-to-Router, Switch-to-PC, Router-to-Server, Hub-toPC, Hub-to-Server
Cross-over used to connect:
-Switch-to-Switch, PC-to-PC, Switch-to-Hub, Hub-to-Hub,
Router-to-Router
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Interfaces
 Examining Router Interfaces
-Show IP router command – used to view routing table
-Show Interfaces command – used to show status of an
interface
-Show IP Interface brief command – used to show a portion of
the interface information
-Show running-config command – used to show configuration
file in RAM
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Interfaces
 Configuring an Ethernet interface
-By default all serial and Ethernet interfaces are down
-To enable an interface use the No Shutdown command
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Interfaces
 Verifying Ethernet interface
-Show interfaces for fastEthernet 0/0 – command used to show
status of fast Ethernet
port
-Show ip interface brief
-Show running-config
 Ethernet interfaces participate in ARP
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Interfaces
 Configuring a Serial interface
-Enter interface configuration mode
-Enter in the ip address and subnet mask
-Enter in the no shutdown command
 Example:
-R1(config)#interface serial 0/0
-R1(config-if)#ip address 172.16.2.1 255.255.255.0
-R1(config-if)#no shutdown
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Interfaces
 Examining Router Interfaces
-Physically connecting a WAN Interface.
-A WAN Physical Layer connection has sides:
Data Circuit-terminating Equipment (DCE) – This is the
service provider. CSU/DSU is a DCE device.
Data Terminal Equipment (DTE) – Typically the router is the
DTE device.
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Interfaces
 Configuring serial links in a lab environment
One side of a serial connection must be considered a DCE
This requires placing a clocking signal – use the clock rate
command.
Example:
-R1(config)#interface serial 0/0
-R1(config-if)#clockrate 64000
Serial Interfaces require a clock signal to control the timing of
the communcations.
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Routing Table and CDP Protocol
 Purpose of the debug ip routing command
Allows you to view changes that the router performs when
adding or removing routes
Example:
-R2#debug ip routing
-IP routing debugging is on
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Routing Table and CDP Protocol
 To configure an Ethernet interface
Example:
-R2(config)#interface fastethernet 0/0
-R2(config-if)#ip address 172.16.1.1 255.255.255.0
-R2(config-if)#no shutdown
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Routing Table and CDP Protocol
 When a router only has its interfaces configured & no
other routing protocols are configured then:
-The routing table contains only the directly connected networks
-Only devices on the directly connected networks are reachable
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Routing Table and CDP Protocol
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Routing Table and CDP Protocol
 Checking each
route in turn
The ping
command is
used to check
end to end
connectivity
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Routing Table and CDP Protocol
 Purpose of CDP
A layer 2 cisco proprietary tool used to gather information about
other directly connected Cisco devices.
 Concept of neighbors
-2 types of neighbors
Layer 3 neighbors
Layer 2 neighbors
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Routing Table and CDP Protocol
 CDP show commands
Show cdp neighbors command
-Displays the following information:
Neighbor device ID
Local interface
Holdtime value, in seconds
Neighbor device capability code
Neighbor hardware platform
Neighbor remote port ID
Show cdp neighbors detail command
-Useful in determining if an IP address configuration error
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Routing Table and CDP Protocol
 Disabling CDP
To disable CDP globally use the following command
Router(config)#no cdp run
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Static Routes with Exit Interfaces
 Purpose of a static route
A manually configured route used when routing from a network
to a stub network
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Static Routes with Exit Interfaces
 IP route command
To configure a static route use the following command: ip route
Example:
-Router(config)# ip route network-address subnet-mask {ipaddress | exit-interface }
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Static Routes with Exit Interfaces
 Dissecting static route syntax
ip route - Static route command
172.16.1.0 – Destination network address
255.255.255.0 - Subnet mask of destination network
172.16.2.2 - Serial 0/0/0 interface IP address on R2, which is
the "next-hop" to this network
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Static Routes with Exit Interfaces
 Configuring routes to 2 or more remote networks
Use the following commands for R1
-R1(config)#ip route 192.168.1.0 255.255.255.0 172.16.2.2
-R1(config)#ip route 192.168.2.0 255.255.255.0 172.16.2.2
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Static Routes with Exit Interfaces
 Zinin’s 3 routing principles
Principle 1: "Every router makes its decision alone, based on
the information it has in its own routing table.“
Principle 2: "The fact that one router has certain information in
its routing table does not mean that other routers have the same
information.“
Principle 3: "Routing information about a path from one
network to another does not provide routing information about
the reverse, or return path."
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Static Routes with Exit Interfaces

Using Zinin’s 3 routing principles, how would you
answer the following?
-Would packets from PC1 reach their destination?
Yes, packets destined for 172.16.1.0/24 and 192.168.1.0/24
networks would reach their destination.
-Does this mean that any packets from these networks destined
for 172.16.3.0/24 network will reach their destination?
No, because neither R2 nor R3 router has a route to the
172.16.3.0/24 network.
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Static Routes with Exit Interfaces
 Modifying Static routes
Existing static routes cannot be modified. The old static route
must be deleted by placing no in front of the ip route
Example:
-no ip route 192.168.2.0 255.255.255.0 172.16.2.2
A new static route must be rewritten in the configuration
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Static Routes with Exit Interfaces
 Verifying the Static Route Configuration
-Use the following commands
Step 1 show running-config
Step 2 verify static route has been entered correctly
Step 3 show ip route
Step 4 verify route was configured in routing table
Step 5 issue ping command to verify packets can reach
destination and that Return path is working
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Static Routes with Exit Interfaces
 Ethernet interfaces and ARP.
– If a static route is configured on an Ethernet link
-If the packet is sent to the next-hop router then…
the destination MAC address will be the
address of the next hop’s Ethernet interface
This is found by the router consulting the
ARP table.
If an entry isn’t found then an ARP
request will be sent out
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Summary and Default Route
 Summarizing routes reduces the size of the routing
table.
 Route summarization is the process of combining a
number of static routes into a single static route.
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Summary and Default Route
 Configuring a summary route
Step 1: Delete the current static route
Step 2: Configure the summary static route
Step 3: Verify the new static route
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Summary and Default Route
 Default Static Route
This is a route that will match all packets. Stub routers that
have a number of static routes all exiting the same interface are
good candidates for a default route.
-Like route summarization this will help reduce the size of the
routing table
 Configuring a default static route
Similar to configuring a static route. Except that destination IP
address and subnet mask are all zeros
Example:
-Router(config)#ip route 0.0.0.0 0.0.0.0 [exit-interface | ipaddress ]
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Summary and Default Route
 Static routes and subnet masks
The routing table lookup process will use the most specific
match when comparing destination IP address and subnet
mask
 Default static routes and subnet masks
Since the subnet mask used on a default static route is 0.0.0.0
all packets will match.
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Summary
 ข้อดีของ Static Routing คือง่าย และไม่ตอ้ งใช้ Routing Software(Router
จะทางานน้อยลง) นอกจากนี้จะไม่ใช้ Resource ของ Network เพราะ
Router ไม่ตอ้ งแลกเปลี่ยนข้อมูลกัน
 ข้อเสี ยคือ ตารางเปลี่ยนไม่ได้ ถ้ามี Link Down หรื อ Router Down เส้นทาง
นั้นจะใช้ไม่ได้ ทาให้การส่ งข้อมูลที่กาหนดเส้นทางนั้นหยุดชะงักหรื อใช้
กาหนดสาหรับ Host ที่เชื่อมต่อกับ Network ที่มีทางออกผ่าน Router ตัว
เดียว(คือค่า Gateway)
 การใช้ Static Route ควรมีการกาหนด Default Route เสมอ
 การทา Static Route ต้องตรวจสอบให้ดีวา่ จะไม่มี Route Loop
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Basic Static Route
(LAB 2.8.1)
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Dynamic Routing Protocol
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Dynamic Routing Protocols
 Function(s) of Dynamic Routing Protocols:
-Dynamically share information between routers.
-Automatically update routing table when topology changes.
-Determine best path to a destination.
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Dynamic Routing Protocols
 The purpose of a dynamic routing protocol is to:
-Discover remote networks
-Maintaining up-to-date routing information
-Choosing the best path to destination networks
-Ability to find a new best path if the current path is no longer
available
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Dynamic Routing Protocols
 Components of a routing protocol
Algorithm
In the case of a routing protocol algorithms are used for
facilitating routing information and best path determination
Routing protocol messages
These are messages for discovering neighbors and
exchange of routing information
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Dynamic Routing Protocols
 Advantages of static routing
-It can backup multiple interfaces/networks on a router
-Easy to configure
-No extra resources are needed
-More secure
 Disadvantages of static routing
-Network changes require manual reconfiguration
-Does not scale well in large topologies
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Classifying Routing Protocols
 Dynamic routing protocols are grouped according to
characteristics. Examples include:
-RIP
-IGRP
-EIGRP
-OSPF
-IS-IS
-BGP
 Autonomous System is a group of routers under the control of
a single authority.
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Classifying Routing Protocols
 Types of routing protocols:
-Interior Gateway Protocols (IGP)
-Exterior Gateway Protocols (EGP)
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Classifying Routing Protocols
 Interior Gateway Routing Protocols (IGP)
-Used for routing inside an autonomous system & used to route
within the individual networks themselves.
-Examples: RIP, EIGRP, OSPF
 Exterior Routing Protocols (EGP)
-Used for routing between autonomous systems
-Example: BGPv4
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Classifying Routing Protocols
 IGP: Comparison of Distance Vector & Link State
Routing Protocols
Distance vector
– routes are advertised as vectors
of distance & direction.
– incomplete view of network
topology.
–Generally, periodic
updates.
Link state
– complete view of network
topology is created.
– updates are not
periodic.
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Classifying Routing Protocols
Distance-vector algorithms (Bellman-Ford algorithms) แต่ละ
router ส่ งข้อมูลทั้งหมดหรื อบางส่ วนของ routing table ของตัวเองแต่ส่งให้
เฉพาะ router ที่อยูต่ ิดกัน จุดสาคัญ link-state algorithms ส่ ง small update
ไปทุก ๆ ที่ขณะที่ distance-vector algorithms ส่ ง large update ไปเฉพาะ
router ที่อยูต่ ิดกัน Distance-vector algorithms จะทราบข้อมูลเกี่ยวกับ
router ที่อยูต่ ิดกันเท่านั้น
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Classifying Routing Protocols
Link-state algorithms (shortest path first algorithms) จะส่ ง routing
information ถึงทุก node ใน internetwork แต่ละ router ส่ งบางส่ วนของ
routing table ที่อธิบายสถานะของการเชื่อมโยงของตัวเอง ใน link-state
algorithms แต่ละ router สร้างภาพของเครื อข่ายทั้งหมดใน routing tables
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Classifying Routing Protocols
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Classifying Routing Protocols
 Classful routing
protocols
Do NOT send subnet mask in
routing updates
 Classless routing
protocols
Do send subnet mask in
routing updates.
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Classifying Routing Protocols
 Convergence is defined as when all routers’ routing
tables are at a state of consistency
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Routing Protocols Metrics
 Metric
A value used by a routing protocol to determine which
routes are better than others.
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Routing Protocols Metrics
 Metrics used in IP routing protocols
-Bandwidth
-Cost
-Delay
-Hop count
-Load
-Reliability
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Routing Protocols Metrics
 The Metric Field in the
Routing Table
 Metric used for each
routing protocol
-RIP - hop count
-IGRP & EIGRP Bandwidth (used by
default), Delay (used by
default), Load, Reliability
-IS-IS & OSPF – Cost,
Bandwidth (Cisco’s
implementation)
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Routing Protocols Metrics
 Load balancing
This is the ability of a router to distribute packets among
multiple same cost paths
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Administrative Distance of a Route
 Purpose of a metric
It’s a calculated value used to determine the best path to a
destination
 Purpose of Administrative Distance
It’s a numeric value that specifies the preference of a particular
route
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Administrative Distance of a Route
 Identifying the Administrative Distance (AD) in a
routing table
It is the first number in the brackets in the routing table
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Administrative Distance of a Route
 Dynamic Routing Protocols
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Administrative Distance of a Route
 Directly connected routes
Have a default AD of 0
 Static Routes
Administrative distance of a static route has a default value of
1
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Administrative Distance of a Route
 Directly connected routes
-Immediately appear in the routing table as soon as the
interface is configured
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Summary
 Dynamic routing protocols fulfill the following functions
-Dynamically share information between routers
-Automatically update routing table when topology changes
-Determine best path to a destination
 Routing protocols are grouped as either
-Interior gateway protocols (IGP)Or
-Exterior gateway protocols(EGP)
 Types of IGPs include
-Classless routing protocols - these protocols include subnet mask
in routing updates
-Classful routing protocols - these protocols do not include subnet
mask in routing update
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Summary
 Metrics are used by dynamic routing protocols to calculate the
best path to a destination.
 Administrative distance is an integer value that is used to
indicate a router’s “trustworthiness”
 Components of a routing table include:
-Route source
-Administrative distance
-Metric
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Basic RIP Configuration
(Lab 7.5.1)
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74
Basic EIGRP Configuration
(Lab 9.6.1)
หลักสู ตรผูเ้ ชี่ยวชาญระบบโครงข่ายการศึกษาขั้นพื้นฐาน (OBEC Network)
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
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© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
76