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Network Layer (Responsible for routing packets from one node to another…
Network Layer
(Responsible for routing packets from one node to another between networks.)
Primary jobs of the network layer include
-Logical Addressing
-Routing
-Encapsulation
-Fragmentation and Reassembly
-Error Handling
Common Network Layer Protocols
Internet Protocol version 4 (IPv4)
Internet Protocol version 6
(IPv6)
Legacy Network Layer Protocols
Novell Internetwork Packet Exchange (IPX)
AppleTalk
Connectionless Network Service (CLNS/DECNet)
Characteristics of the IP protocol
TCP Segments encapsulated into IP Packets.
| IP Header | Segment |
Connectionless - No connection is established before sending data packets.
Best Effort (unreliable) - No overhead is used to guarantee packet delivery.
Media Independent - Operates independently of the medium carrying the data.
Connectionless Communication
The sender doesn't know :
If the receiver is present
if the letter arrived
if the receiver can read the letter
The receiver doesn't know :
when it is coming
Packet
Sender -> Receiver
Best Effort Delivery (Unreliable)
Unreliable means simply that IP does not have the capability to manage and recover from undelivered or corrupt packets.
Since protocols at other layers can manage reliability, IP is allowed to function very efficiently at the Network layer
Media Independent
Not concerned with the physical medium.
Operates independent of the layers that handle the physical medium that carries the packet.
Is concerned with the size of the packet or Maximum Transmission Unit (MTU)
The MTU is established as part of the communication between the Data Link and Network Layers.
Fragmentation:
At times, an intermediary device (router) will need to split up a packet when forwarding it from one media to a media with a smaller MTU.
Copper Ethernet : MTU = 1518 bytes
Copper Serial : Frame Relay MTU = 512 bytes.
Optical Fiber : ATM MTU = 17,966 bytes.
Wireless : 802.11 MTU = 2272 bytes
IPv4 Packet Header Byte 1
Version, IP Header Length
Identifcation
Time to Live(Maximum "hops" before undeliverable)
Source IP Address (32 Bits binary value. Source of the packet)
Destination IP Address (32 Bits binary value. Destination of the Packet)
Options (Optional)
IPv4 Packet Header Byte 2
Differentiated Services (8-bit fields - Throughput Priority)
DSCP, ECN
Identifcation
Protocol (Upper Layer Protocol TCP/UDP)
Source IP Address
Destination IP Address
Options(optional)
IPv4 Packet Header Byte 3
Total Length
Flag, Fragment Offset
(Used in reconstruction of any fragments).
Header Checksum
Source IP Address
Destination IP Address
Options(optional)
IPv4 Packet Header Byte 4
Total Length
Fragment Offset
Header Checksum
Source IP Address
Destination IP Address
Padding
IPv6
128 Bit Addresses
8 Groups of 4 hex digits
Increased address space
Improved packet handling
Eliminates the need for NAT
Integrated security
340 undecillion IPv6 addresses
340,000,000,000,000,000,000,000,000,000,000,000,000
Ipv4 is the most commonly used.
32 Bit Addresses
4 OCTETS (8 bit groups)
Uses Dotted Decimal Notation (For humans to read)
Up to 4 billion addresses available.
Limitations of IPv4
IP Address depletion
Internet routing table expansion
Lack of end-to-end connectivity
Routing/ Encapsulation
Router appends layer 4 data to layer 3
Then sends data down to layer 2 (Encapsulation)
Layer 3 Header contains IP Addressing information
Network Layer must be able to route data
Routing information determines best path
Path between networks are hops
Logical Addressing.
Each node must have a logical address in order to communicate, using IPv4 or IPv6.
Addresses are assigned statiscally or dynamically via DHCP server.
Layer 3 uses Logical IP Addresses
Layer 2 uses MAC Addresses (Hardware Address)
Fragmentation and Reassembly
Network Layer delivers data between networks
Data is passed to the data link layer
If the message is too large, it is fragmented
Fragments are reassembled at arrival
Maximum payload for ethernet : 1500 bytes
Error Handling
ICMP is used to send error messages
ICMP is a layer 3 protocol
Used only for feedback purposes
Utilizezd by ping and traceroute