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Bài giảng Computer Networks 1 (Mạng máy tính 1) - Lecture 7: Network Layer in the Internet - Phạm Trần Vũ

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Computer Networks 1  
(Mạng Máy Tính 1)  
Lectured by: Dr. Phạm Trần Vũ  
1
Lecture 7: Network Layer in the  
Internet  
Reference:  
Chapter 5 - “C
Andrew S. Tanenbaum, 4th Edition, Prentice Hall, 2003.  
2
The Network Layer in the Internet  
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The IP Protocol  
IP Addresses  
Internet Control Protocols  
OSPF – The Interior Gateway Routing Protocol  
BGP – The Exterior Gateway Routing Protocol  
IPv6  
3
Design Principles for Internet  
• Look for a good  
design; it need not be  
perfect.  
• Make sure it works.  
• Keep it simple.  
• Make clear choices.  
• Exploit modularity.  
• Expect heterogeneity.  
Be strict when  
sending and tolerant  
when receiving.  
• Think about  
scalability.  
• Avoid static options  
and paramet
• Consider performance  
and cost.  
4
Collection of Subnetworks  
The Internet is an interconnected collection of many  
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networks.  
The IP Protocol  
The IPv4 (Internet Protocol) header.  
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The IP Header  
ꢀ Version: version of the protocol used  
ꢀ IHL: header length (number of 32-bit words)  
ꢀ Type of service: combination of reliability and speed, commonly  
ignored by routers  
ꢀ Total length: length of the datagram  
ꢀ Identification: to identify a fragment within a datagram  
ꢀ DF: don’t fragment, tell the routers not to fragment  
ꢀ MF: more fragments  
ꢀ Time-to-live: a time counter to limit the message lifetime  
ꢀ Header checksum: of the header only  
ꢀ Source and destination addresses: address of the source and  
destination of the datagram  
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IP Options  
Some of the IP options.  
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IP Addresses  
IP address formats.  
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IP Address Classes  
ꢀ Class A: 128 networks, 16 mil hosts each  
ꢀ Class B: 16.384 networks, 64K hosts each  
ꢀ Class C: 2 mil networks, 256 hosts each  
ꢀ Class D: for multicast  
ꢀ Class E: Reserved  
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IP Addresses (2)  
Special IP addresses.  
11  
Subnets  
A campus network consisting of LANs for  
various departments.  
12  
Subnet and Subnet Mask  
•
•
Some bits of the host are used to create subnet  
number  
Subnet masks are used to indicate the splits  
between network, subnet number and host number  
A class B network subnetted into 64 subnets (6 bits).  
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Routing with Subnetting  
ꢀ Routing to destination to an outside network  
is done as usual  
ꢀ Routing table adds more entries for routing  
within the network  
ꢁ
(this-network, subnet, 0): to route message to  
another subnet  
ꢁ
(this-network, this-subnet, host): to route  
message to a host within this-subnet  
14  
CDR – Classless InterDomain  
Routing  
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Allocate IP addresses in variable size block without  
regard to classes  
If a site needs, it is provided with a block of  
addresses  
Routing process is more complicated  
A set of IP address assignments.  
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NAT – Network Address  
Translation  
Placement and operation of a NAT box.  
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NAT – Network Address Translation  
(2)  
ꢀ
ꢀ
ꢀ
Use TCP or UDP header (source port field) of a  
message to keep track of its outgoing  
connection  
A mapping table is used at the NAT box to  
keep track of the private IP + port the NAT  
index  
In coming miversed back  
to original private IP and source port using the  
index  
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Internet Control Message Protocol  
•
Used when unexpected events occurred in the  
network, also used to test the network  
The principal ICMP message types.  
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ARP– The Address Resolution  
Protocol  
•
Used to map an IP addresses to data link layer  
addresses, e.g. Ethernet addresses  
Three interconnected /24 networks: two Ethernets and  
an FDDI ring.  
19  
Dynamic Host Configuration  
Protocol – DHCP  
• A replacement for RARP (Reverse ARP)  
and BOOTP (Bootstrap protocol)  
20  
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