chapter 5 network layer
DESCRIPTION
Chapter 5 Network Layer. CIS 81 Networking Fundamentals Rick Graziani Cabrillo College [email protected] Spring 2010. This Presentation. For a copy of this presentation and access to my web site for other CCNA, CCNP, and Wireless resources please email me for a username and password. - PowerPoint PPT PresentationTRANSCRIPT
Chapter 5Network Layer
CIS 81 Networking Fundamentals
Rick Graziani
Cabrillo College
Spring 2010
2
This Presentation
For a copy of this presentation and access to my web site for other CCNA, CCNP, and Wireless resources please email me for a username and password. Email: [email protected] Web Site: www.cabrillo.edu/~rgraziani
3
Note
This presentation is not in the order of the book or online curriculum. This presentation also contains information beyond the curriculum.
Network Layer Overview
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Network Layer
IPv4
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Application Header + data
IP Header
0 15 16 31 4-bit
Version 4-bit
Header Length
8-bit Type Of Service (TOS)
16-bit Total Length (in bytes)
16-bit Identification
3-bit Flags
13-bit Fragment Offset
8 bit Time To Live
TTL
8-bit Protocol
16-bit Header Checksum
32-bit Source IP Address
32-bit Destination IP Address
Options (if any)
Data
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IP
IP
IP IP
8
Focus on Transport LayerIP
IP
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Network Layer
The Network layer (Layer 3) provides services to exchange the data over the network between identified end devices.
Layer 3 uses four basic processes: Addressing Encapsulation Routing Decapsulation
0 15 16 31 4-bit
Version 4-bit
Header Length
8-bit Type Of Service (TOS)
16-bit Total Length (in bytes)
16-bit Identification
3-bit Flags
13-bit Fragment Offset
8 bit Time To Live
TTL
8-bit Protocol
16-bit Header Checksum
32-bit Source IP Address
32-bit Destination IP Address
Options (if any)
Data
10
Addressing
0 15 16 31 4-bit
Version 4-bit
Header Length
8-bit Type Of Service (TOS)
16-bit Total Length (in bytes)
16-bit Identification
3-bit Flags
13-bit Fragment Offset
8 bit Time To Live
TTL
8-bit Protocol
16-bit Header Checksum
32-bit Source IP Address
32-bit Destination IP Address
Options (if any)
Data
172.16.3.10192.168.100.99 Source IP = 192.168.100.99
Destination IP = 172.16.3.10
Destination IP = 192.168.100.99
Source IP = 172.16.3.10
What would be the Source IP Address and Destination IP Address of a Packet from the client to the server?
What would be the Source IP Address and Destination IP Address of a Packet from the server to the client?
More later!
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DataHTTP Header
TCP Header
IP Header
Data Link Header
Data Link Trailer
IP PacketData Link Header
Data Link Trailer
IP PacketData Link Header
Data Link Trailer
IP PacketData Link Header
Data Link Trailer
IP PacketData Link Header
Data Link Trailer
IP PacketData Link Header
Data Link Trailer
IP PacketData Link Header
Data Link Trailer
DataHTTP Header
TCP Header
IP Header
Data Link Header
Data Link Trailer
Encapsulation and Decapsulation
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Decapsulation
Destination Arrival packet processed at Layer 3. Destination address examined. If the address is correct segment is passed up to the appropriate
service at Transport layer.
Is the Destination IP Address of this
packet my IP Address?
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Routing
Routers examine Layer 3 Destination IP addresses to forward packets. Search their routing tables. Send the packet to the next-hop router or host if on that network
0 15 16 31 4-bit
Version 4-bit
Header Length
8-bit Type Of Service (TOS)
16-bit Total Length (in bytes)
16-bit Identification
3-bit Flags
13-bit Fragment Offset
8 bit Time To Live
TTL
8-bit Protocol
16-bit Header Checksum
32-bit Source IP Address
32-bit Destination IP Address
Options (if any)
Data
172.16.3.10192.168.100.99
Source IP = 192.168.100.99
Destination IP = 172.16.3.10
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Network Layer Protocols
The Internet Protocol (IPv4 and IPv6) is the most widely-used Layer 3 data carrying protocol and will be the focus of this course.
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IPv4 basic characteristics…
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Connectionless
IP does not notify the destination host. Which layer 4 protocol on the sending host will establish a connection?
TCP: A connection-oriented protocol. Which layer 4 protocol on the sending host will not establish a connection?
UDP: A connectionless protocol.
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Best Effort Service (unreliable)
Layer 3 (IP) Speed over reliability
Unreliable: Does not have the capability or responsibility to manage, and recover from, undelivered or corrupt packets.
Who does? TCP at the end-to-end hosts
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Responsibility of the OSI Data Link layer to take an IP packet and prepare it for transmission over the communications medium.
Transport of IP packets is not limited to any particular medium. May need to fragment the packet if it is too many bits (later).
Media Independent
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IP Header
IP Destination Address 32-bit binary value that represents the packet destination
Network layer host address. IP Source Address
32-bit binary value that represents the packet source Network layer host address.
Where I am going.
Where I came from.
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Sending hosts generates the value for TTL. Common operating system TTL values are:
UNIX: 255 Linux: 64 or 255 depending upon vendor and version Microsoft Windows 95: 32 Microsoft Vista: 128
IP’s TTL – Time To Live field
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IP’s TTL – Time To Live field
Decremented by each router. If the router decrements the TTL field to 0, it will then drop the packet. What is the advantage to decrementing the TTL by each router and dropping
the packet if it is 0? So IP packets can not travel around the Internet forever, from router to
router.
Decrement by 1, if 0 drop the packet.
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IP’s Protocol Field
Protocol field enables the Network layer to pass the data to the appropriate upper-layer protocol.
Example values are: 01 ICMP 06 TCP 17 UDP
Protocol = 06 TCP
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IP’s ToS Field
Type-of-Service is used to determine the priority of each packet. Enables Quality-of-Service (QoS) mechanism for high priority traffic. What types of traffic might a network administrator need to give priority to?
Traffic that cannot accept any delays. VoIP Streaming video
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TCP MSS = 1460Data = 1460 bytes
20 bytes 20 bytes 1460 bytes
1500 bytes
Determining TCP MTU The default Ethernet MTU value
for a PC is 1500 bytes. (curriculum says MSS)
Typical Maximum Segment Size (MSS) of a TCP segment is 1460 bytes. The number of bytes of data.
TCP MSS defines the maximum size of the data in the TCP segment.
Ethernet MTU defines the maximum size of the data in the Ethernet frame.
The host using Ethernet, MTU of 1500 octets so I will set my MSS to 1460.
IP Fragmentation
How much is enough?
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IP Fragmentation
A router may have to fragment a packet when forwarding it from one medium to another medium that has a smaller MTU. If Don’t Fragment flag set, it will not fragment packet, but discard it.
Data = 1480 bytesIP
Data = 500IP
Data = 480IP
IP Packet Fragments
Original IP Packet
IP Header = 20 bytes
Data = 500IP
Data = 520L2 L2This packet is too big to go over my serial link all at once. I need to break it
into smaller fragmentsData = 520L2 L2
Data = 500L2 L2
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IP Fragmentation
When fragmentation occurs, it does not get reconstructed until it reaches the host. This takes processing time. Fragment Offset field identifies the order
IP Packet
IP Packet
IP Packet
IP Packet
IP Packet
IP Packet
IP Packet
IP Packet
IP Packet
IP PacketIP Packet
Network link with larger MTU
Network link with smaller MTU
Network link with larger MTU
The outgoing link has a smaller MTU so I have to
fragment the packets.
The outgoing link has a large enough MTU but I
don’t reconstruct packets.
It is my job to reconstruct the packets.
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Path MTU Discovery
Path MTU Discovery (Not discussed here, but is important) RFC 1191 (RFC1191) Path MTU Discovery and Filtering ICMP
Marc Slemko Link on CIS 81 web page
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Other IPv4 fields
Version - Contains the IP version number (4) Header Length (IHL) - Specifies the size of the packet header. Packet Length - This field gives the entire packet size, including header and
data, in bytes. Identification - This field is primarily used for uniquely identifying fragments
of an original IP packet Header Checksum - The checksum field is used for error checking the
packet header. Options - There is provision for additional fields in the IPv4 header to
provide other services but these are rarely used.
Host and Network Addresses
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IP Addresses – First look
Host IP addresses are IP addresses assigned to end devices such as: Client computers Server computers Network Printers Router interfaces
Note: the /16 refers to the subnet mask, which will be discussed later. Note: Intermediary devices such as a switch may have an IP address to allow
the network administrator to Telnet to the device for remote management.
Kiwi Airliners - Network Address 172.16.0.0/16
172.16.10.100/16
172.16.10.55/16
172.16.10.3/16
172.16.20.77/16
172.16.20.96/16
172.16.20.103/16
172.16.30.39/16
172.16.30.10/16
172.16.30.111/16
172.16.40.123/16
172.16.40.51/16
172.16.40.29/16
172.16.1.1/16
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IP Addresses – First look
Host IP addresses are members of a group of addresses call the Network Address
IANA (Internet Assigned Numbers Authority) have the responsibility to allocate network addresses.
A company or individual needing a network addresses typically goes to their ISP
ISPs then allocate network addresses to their customers. More detail in the next chapter.
Kiwi Airliners - Network Address 172.16.0.0/16
172.16.10.100/16
172.16.10.55/16
172.16.10.3/16
172.16.20.77/16
172.16.20.96/16
172.16.20.103/16
172.16.30.39/16
172.16.30.10/16
172.16.30.111/16
172.16.40.123/16
172.16.40.51/16
172.16.40.29/16
172.16.1.1/16
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IP Addresses – First look
Host IP Address Unique host IP address
Default Gateway A router which is used to forward packets out of the network. This is a host IP address on the router. Host IP address on the same network as the host.
The host only has to be aware of: Its own network address Default gateway IP address to reach all devices outside its own network
Network Address 172.16.0.0
172.16.10.100/16
172.16.10.55/16
172.16.10.3/16172.16.1.1/16
ISP
Internet
Network Address 192.168.1.0/30
192.168.1.2/30
192.168.1.1/30
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IP Addresses – First look
All hosts in the same network will typically have the same default gateway IP address.
Network Address 172.16.0.0
172.16.10.100/16
172.16.10.55/16
172.16.10.3/16172.16.1.1/16
ISP
Internet
Network Address 192.168.1.0/30
Gateway: 172.16.1.1
Gateway: 172.16.1.1
Gateway: 172.16.1.1
192.168.1.2/30
192.168.1.1/30
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Confirming IP Address, Default GatewayC:\> ipconfig
Windows IP ConfigurationEthernet adapter Local Area Connection: Connection-specific DNS Suffix . : IP Address. . . . . . . . . . . . : 172.16.10.100 Subnet Mask . . . . . . . . . . . : 255.255.0.0 Default Gateway . . . . . . . . . : 172.16.1.1
Root# ifconfigeth0 Link encap:Ethernet HWaddr 00:0F:20:CF:8B:42 inet addr:172.16.1.100 Bcast:172.16.255.255 Mask:255.255.0.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:2472694671 errors:1 dropped:0 overruns:0 frame:0 TX packets:44641779 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:1761467179 (1679.8 Mb) TX bytes:2870928587 (2737.9 Mb) Interrupt:28
Linux: netstat –rn for default gateway information.
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Subnets
Networks can be subdivided into subnets. This provides for several benefits which we will discuss later. Networks can be grouped based on factors that include:
Geographic location, Purpose, Ownership
Kiwi Airliners - Network Address 172.16.0.0/16
172.16.10.100/24
172.16.10.55/24
172.16.10.3/24
172.16.20.77/24
172.16.20.96/24
172.16.20.103/24
172.16.30.39/24
172.16.30.10/24
172.16.30.111/24
172.16.40.123/24
172.16.40.51/24
172.16.40.29/24172.16.1.1/24
172.16.10.1/24 172.16.20.1/24 172.16.30.1/24 172.16.40.1/24
172.16.10.0/24 172.16.20.0/24 172.16.30.0/24 172.16.40.0/24
A Quick Look at Routing
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Routing – First Look
Routers know about: Directly connected networks (C):
Network addresses of its interfaces Remote networks
192.168.1.254/24
C 192.168.2.0/24 is direction connected, FastEthernet0/1
Network 192.168.2.0/24
Network 192.168.1.0/24
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Routers know about: Directly connected networks (C):
Network addresses of its interfaces When a router is configured with the IP address/mask on an interface the
router knows that it has an interface which is part of that network. This is just like a host that is configured with an IP address/mask. (coming)
192.168.1.254/24
C 192.168.2.0/24 is direction connected, FastEthernet0/1
Network 192.168.2.0/24
Network 192.168.1.0/24
Routing – First Look
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Routers learn about remote networks using: Static routes Dynamic Routing Protocol (R = RIP)
Routes in a routing table have three main features: Destination network Next-hop Metric
192.168.1.254/24
C 192.168.2.0/24 is direction connected, FastEthernet0/1
Network 192.168.2.0/24
Network 192.168.1.0/24
Routing – First Look
40
Static routes Manually entered by the administrator
Dynamic Routing protocols Routers automatically learn about remote networks Ex: RIP, EIGRP, OSPF, IS-IS, BGP
192.168.1.254/24
C 192.168.2.0/24 is direction connected, FastEthernet0/1
Network 192.168.2.0/24
Network 192.168.1.0/24
Routing – First Look
41
Host Routing Table
Hosts also have a local routing table. Usually only contains:
Its own network address (directly connected network) Default gateway IP address
Hosts usually do not have remote networks in their routing tables
netstat –r
or
route print
Chapter 5Network Layer
CIS 81 Networking Fundamentals
Rick Graziani
Cabrillo College