Each type has its own idea of addressing and protocols
Want to connect them all together and provide a unified view of the whole lot
4 The unifying effect of the network layer
Define a protocol that works in the same way with any underlying network
Call it the network layer
routers operate at the network layer
There are defined ways of using
protocol over ethernet ATM FDDI
protocol over serial lines (PPP)
protocol over almost anything
5 The 7 Layer OSI Model 6 Protocol Stacks
Applications TCP / UDP Transport layer IP Network layer atm x.25 hdlc ethernet token ring dialup frame relay 7 Layer Functions Mail Web etc. Application Presentation Session Transport TCP End to end reliability Forwarding best-effort IP Network Data Link Packet delivery Physical Raw signal 8 ISO seven layer model
1 Physical layer
moves bits using voltage current light etc.
2 Data Link layer
bundles bits into frames and moves frames between hosts on the same link
9 ISO seven layer model
3 Network layer (e.g. IP)
Makes routing decisions
uses destination address in packet
Forwards packet hop by hop
encapsulates network layer packet inside data link layer frame
different framing on different underlying network types
Single address space for the entire internetwork
10 ISO seven layer model
4 Transport layer (e.g. TCP)
end to end transport of datagrams
encapsulates datagrams in network layer packets
adds reliability by detecting and retransmitting lost packets
uses acknowledgements and sequence numbers to keep track
11 ISO seven layer model
5 Session layer
not used in the TCP/IP network model
6 Presentation layer
not used in the TCP/IP network model
7 Application layer
Uses the underlying layers to carry out work
12 Layer interaction Application Application Presentation Presentation Session Session Transport Transport Network Network Network Network Link Link Link Link Physical Physical Physical 13 INTERNET PROTOCOLS
can be used for communications between heterogeneous systems
can be used for communications between systems connected in a LAN
can be used for communications between systems connected in a WAN
can be used for communications between a set of interconnected networks
Documents called RFCs (Requests For Comments) which are reviewed and analyzed by the IETF community improvements additions and refinements of protocols are published in new RFCs (see ftp//ftp.rs.internic.net. ftp//ftp.ripe.net/).
Looking at all RFCs you can see the history of the development of Internet protocols people and companies that have contributed to this
TCP and IP are the best known of the Internet protocols and very often the term TCP/IP refers to the whole family of protocols.
14 TCP/IP Model Message Segment Datagram Frame Bit 5 4 3 2 1 15 TCP/IP is a 5 Layered model
Layers 1 and 2 are not actually defined by TCP/IP as TCP/IP was defined to be independent of physical media .
Layer 3 is the Internet Protocol (IP) layerThis provides a basic datagram service
ICMP (Internet Control Message Protocol) is normally provided in this layerICMP reports problems in transmission of datagrams
ARP (Adress Resolution Protocol)
RARP (Reverse Address Resolution Protocol)
In layer 4 are 2 possible protocols TCP (Transport Control Protocol) and UDP (User Datagram Protocol) .
TCP provides a reliable service with error correction and flow control .The cost of providing a reliable service is more overhead in connection setup and closedown processing power for correcting errors and data transmission but some applications need reliability irrespective of cost.
UDP just extends IPs connectionless datagram service to applications that do not require reliability .UDP datagrams can be sent to a network without the overhead of creating and maintaining a connection
Layer 5 is the Application layerThis layer provides services suitable for the different types of application that might wish to use the network .It does not provide the application itself .For example SMTP FTP Telnet ...
19 TCP/IP 20 Internet Protocols NFS RPC FTP RFC 959 SNMP RIP RFC 1058 Routing protocols BGP OSPF IGRP EIGRP Telnet RFC 854 SMTP RFC 821 DNS RFC 1035 ICMP RFC 792 TCP RFC 793 UDP RFC 768 IP RFC 791 X.25 ARP RFC 826 PPP HDLC SLIP LAPB Ethernet/IEEE 802.3 LAN Public telephone network 21 SMTP mail exchange as an example
There is a protocol for mail that defines a set of commands and messages that one machine sends to the other for example a conversation between machines linkguide.ici.ro and mail.iob.ro
Different classes used to represent different sizes of network (small medium large)
Class A networks x.0.0.0 - 16.777.215 host addresses
8 bits network 24 bits host (/8 255.0.0.0)
First byte in range x1-127
Class B networks x.y.0.0 - 65.536 host addresses
16 bits network 16 bits host (/16 255.255.0.0)
First byte in range x128-191 y0-254
Class C networks x.y.z.0 - 256 host address
24 bits network 8 bits host (/24 255.255.255.0)
First byte in range x192-223 yz0-254
32 IP Address Structure - Class-full
Address format 32 bits Network address Host address Class A network8 bits 0 Class B network16 bits 1 0 Class C network24 bits 1 1 0 Class D (multicast) 1 1 1 0 Class E (reserved) 1 1 1 1 33 Special Addresses
All 0s in host part Represents Network
All 1s in host part Broadcast
e.g. 188.8.131.52 (184.108.40.206/16)
e.g. 220.127.116.11 (18.104.22.168/24)
e.g. 22.214.171.124 (126.96.36.199/17)
127.0.0.0/8 Loopback address (127.0.0.1)
0.0.0.0 Various special purposes
34 TCP/IP Basics Physical Datalink 35 The Physical and Datalink layer
IEEE and ISO
Network access protocol
The medium for communication between two machines directly connected can be coax twisted cable telephone link radio link satellite link etc. The lowest layer of protocols provides functions that manage the data transmission specific to a certain physical medium.
Classes of links
Point to point
Ethernet/IEEE 802.3 is a coaxial based bus cabling system developed by Digital Equipment Corporation Intel Xerox (DIX)
Ethernet was the technological basis for the IEEE 802.3 specification
Both of them specify the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) also referred as listen while talk (LWT)
Both are broadcast networks
37 Ethernet Topologies Fiber concentrator 10/100/1000 Base F Transceivers 38 The Ethernet frame
This Ethernet frame encapsulates the TCP/IP protocol and is responsible for transporting it across the cabling system to layer 2 of the destination device whether its a Router Gateway or end node .
39 MAC addressing
The ethernet frame uses addresses referred to as MAC (Medium Access Control)
MAC addresses identify the specific network cards
These are 48 bits long
Each network card has a unique address configured by its manufacturer
The LAN card will accept only 3 types of MAC address .
Unicast - Frames with destination to the exact MAC address .
Broadcast - Has all 48 bits set to binary 1 (or Hex FF FF FF FF FF FF) .This type of frame is used when the sender does not know the destination MAC address it tries to communicate so we broadcast to all .
Multicast - Addressing to groups of LAN cards that are related in some way .The LAN cards have to be configured to know they are part of a multicast group .
41 The type field
The Type field identifies different protocols .
A computer running multiple protocols can easily differentiate between them and path the contents to the relevant layer .
TCP/IP Generally uses 3 Ethernet types registered in IEEE .
42 CRC - Cyclic Redundancy Check
At the end of the frame is a CRC .
This is a 32 bit value that is calculated from all the bits of the Ethernet frame and its contents but ignoring the preamble and the CRC itself .
The remote node does the same calculation and compares the CRC .If the value is different the LAN card will not pass the Frame to the network layer .
43 The service provided by Ethernet
The medium access mechanism used by Ethernet is CSMA/CD (Carrier Sense Multiple Access with Collision Detection) .
This allows nodes on the network to manage shared access to the cable but it restricts the length of the cabling and the number of nodes that use it .
They are not specific to Protocol therefore for TCP/IP .
44 Ethernet Packet size
Minimum packet size - 64 octets
Maximum packet size - 1518 octets
The sizes above include all the frame apart from the preamble .
Because of the frame header fields the CRC and the overhead of the IP and TCP or UDP higher layer protocols the amount left for useful application data is less then 1518 .
To give an example The Ethernet frame overhead consists of 18 octets and the higher layer protocols often need 40 octets .That leaves 1460 (1518-40-181460) octets for application data .
46 IEEE and ISO systems
IEEE 802.3 uses CSMA/CD .
IEEE 802.4 uses a token mechanism on a bus .
IEEE 802.5 and FDDI (IS9314) use a token passing mechanism on a ring .
47 LLC (Logical Link Layer)
For LANs layer 2 is split to 2 sublayers .
The lower is MAC and above we have the LLC which has the standard number IEEE 802.2 .
One of the major functions of LLC is to differentiate between the different types of network layer protocols in a similar way to the type field of Ethernet .
48 Ethernet 49 Token Ring 50 FDDI 51 Encapsulation
The type field specifies the upper-layer protocol to receive the data after Ethernet processing is complete
The CRC (Cyclic Redundancy check) is created by the sender and recalculated by the receiver
The frame length (header data and CRC) 64-1518 bytes
Application Application Data TCP TCP T Data T Data IP Data I T I T Data IP E I T Data Ethernet E I T Data C C Ethernet Ethernet 52 The IEEE 802.3 frame
The IEEE 802.3 frame has the same general format as DIX Ethernet (Ethernet_II) frame .
The Type field in Ethernet DIX is the Length field in IEEE 802.3
THE FCS (Frame Check Sequence) is instead of CRC
As there is no Type field it is not possible to detect which network layer protocol is carried in the MAC layerThe MAC frame consists of only addresses length and FCS.It is the function of LLC to separate the different network layer protocols .
Bridging between IEEE LANs is often promoted as transparent to any protocol above the MAC layer .This will bring expectations that there are no particular problems with TCP/IP .
There are 4 issues that need consideration
The length field for the 802.3 bus.
Encapsulation on bus networks.
The maximum frame sizes.
The representation of MAC addresses.
55 Length fields
The IEEE 802.3 CSMA/CD network has a length field immediately before the LLC .Other IEEE networks do not .
Bridging will at least involve changing the content of the frame and recalculating the FCS .This action will be totally transparent to the network planners .
56 Frame size
For TCP/IP the transmitted frame size is determined by the Maximum Transfer Unit (MTU) set in the driver software for the LAN interface .
It is possible on most TCP/IP implementations to modify the MTU to match the number of data octets carried by the Link Layer protocol .Setting the MTUs of each interface on a Token Ring to 1492 will prevent its frames from being to large for bridging to IEEE 802.3 .This reduction will limit Token Ring efficiency .
57 Representation of MAC addresses
The IEEE 802.1 committee defined how LANs should represent 48 bit MAC addresses as a bit stream on the cable .IEEE 802.3 and 802.5 committee chose to represent these addresses higher in the protocol .
IEEE 802.3 and 802.5 represent differently the MAC address .
Bridges now have to be wise and not only reverse the address but also to calculate the FCS .
58 Example of vendor-dependant Ethernet addresses
0000C0 Western Digital
59 TCP/IP Basics Serial Connections 60 SLIP - Serial Line Internet Protocol
In some situations it is advantageous to use asynchronous Serial lines to carry TCP/IP protocols either by
Modems on private wires
through an asynchronous network
Direct connection between 2 computers
61 SLIP functionality Asynchronous connections V.24/RS232C Direct connection Modem link LAN PCs with SLIP Host Dialup modem link 62 SLIP frame format
SLIP defines 2 special characters
SLIP END - 0xC0
SLIP ESC - 0xDB
Datagrams sent using SLIP are framed SLIP END characters .
63 SLIP frame format 64 PPP - Point to Point Protocol
PPP came to overcome a number of limitations of SLIP .
PPP has been designed to operate over both asynchronous (start/stop) connections and bit oriented synchronous systems .
PPP provides more then just a simple connection between hosts .It also defines several management and testing functions to deal with line quality option negotiation and the setup of IP addresses .
66 The service provided by PPP
PPP provides a Point to Point connection between 2 TCP/IP systems for the transfer of IP datagrams .
PPP can operate over virtually any serial link interface .
The only limitation is that it requires a full duplex connection .
It does not need serial interface control signals but the standard recommends it for performance improvements .
There is no restriction for the speed used for PPP .
68 The PPP frame
The address field is all 1s.
The control octet contains the value 0x03.
The protocol field defines the protocol carried by this frame
Link Control Protocol - 0xC021
Network Control Protocol - 0x8021
Internet Protocol - 0x0021
PPP can multiplex data from many sources which makes it practical for high speed connections between bridges or routers.
70 TCP/IP Basics Network Layer 71 Why do we need IP protocol layer
Although the services provided by TCP protocol are needed by many applications there are still some kind of applications that dont need them
However there are some services that every application needs.
The services that every application needs are put together into the IP protocol layer
IP protocol provides the basic service for the transmission of a datagram from one machine to another machine which do not need to be connected directly
As a result TCP calls on the services of IP
Like TCP IP protocol layer can be viewed as a library of routines that TCP calls on but which is also available to applications that dont use TCP
72 IP - Internet Protocol
IP is described as a connectionless datagram service .
Datagrams are packets of information that can be destined for one many or all stations (unique multicast or broadcast) - provide addressing.
There is no requirement for the intended recipient/s to acknowledge whether the datagram was received (no flow control no end-to-end data reliability).
As IP is connectionless no specific route is defined between 2 communicating nodes so datagrams traveling can travel through different routes and reach destination in a different order (no sequencing and allow for fragmentation).
One of the major roles of IP layer is to make it unnecessary for higher layer protocols to understand anything about the physical capabilities of the media supporting them .Note This is important for application developers writing programs on top of the transport layer with no variations because of the different kind of media used .
73 The IP Architecture Message Segment Datagram Frame Bit 5 4 3 2 1 ( ) 1 0800 ( ) ( ) ( ) 8035 0806 74 Encapsulation
Both the header and data of the IP datagram become the datalink frame of whichever network they happen to be on.This is called encapsulation .
Protocol number identifies the protocol in the layer above IP to which the data is passed (/etc/protocols)
0 IP pseudo protocol number
75 Fragmentation and Reassemble
IEEE 802.3 and Ethernet systems have maximum data sizes of 1492 and 1500 octets respectively .IEEE 802.5 frames is not defined but in practice it is usually no greater then 8192 octets .
This size limit seen by IP is known as the Maximum Transfer Unit (MTU) .
The MTU can be adjusted for each interface but its not necessary unless bridging different LAN technologies .
76 IP datagram Format 77
Version - 4 bitsVersion of the IP protocolCurrent version is 4
Internet Header Length - 4 bitsFor easy finding of beginning of data .Normally the value is 5 indicated no options are used .
Type Of Service - 8 bitsThe first of 3 bits are used to indicate 1 of 8 levels of priority .Some Routers Ignore these flags .
Total length - 16 bitsThe total length of the IP datagramThe size of data is computed from the total length field and IHL .
Identification - 16 bitsThis is an integer value used to help identify all fragments of a datagram .This field is unique for each new datagram .
Flags - 3 bitsThe 2 low order bits are used as flags to control fragmentation .The low order bit if 0 indicates the last fragment of a datagram - MF (More Flag) .The middle bit is used to indicate that the datagram should not be fragmented - DF (Do not Fragment) .
Fragment Offset - 13 bitsUsed in a fragmented datagram to indicate the position that the fragment occupies .
Time To Live (TTL) - 8 bitsThis prevents datagrams to get routed in a loop .If its set to 0 a router should discard the datagram .The recommended value is 32 but it can be set to a maximum of 255 too .
Protocol - 8 bitsThe transport layer protocol carried by this datagram .It tells the IP layer where to path the datagram .17 - UDP6 - TCP1 - ICMP
Header checksum - 16 bitsIt protects only the header and not the data .The reason is because the checksum must be recalculated every time it passes through a router .Other parameters change too .
Source IP address - 32 bits
Destination IP address - 32 bits
Data variableThis includes the headers of higher layer protocols and users data .
80 Routing IP Datagrams Target 81 IP Routing Subnet Default Gateway Direct Connection
82 IP algorithm
1. Search the routing table for an entry that matches the complete destination IP address (network ID or host ID). If found send the packet to the indicated next-hop router or to the directly connected interface. (second interface or ppp)
2. Search the routing table for an entry that matches just the destination network ID. If found send the packet to the indicated next-hop router or to the directly connected interface. (local networks)
3. Search the routing table for an entry labeled default. If found send the packet to the indicated next-hop router
83 ARP - Address Resolution Protocol
If we wish to connect to a remote computer we must know its IP address but we do not need to know its MAC address .
ARP was invented for this reason .It relates IPs to MAC addresses only on media that supports broadcasts .
Each node maintains a cache called the ARP cache which holds a table of IPs against MAC addresses .
84 How ARP works
When IP is requested to send a datagram to another IP address it first looks in the ARP cache to find the corresponding MAC address .If there is no entry it then attempts to look for it using ARP .
In order to do this ARP sends an ARP request datagram to all LAN cards using a broadcast address .
ARP uses its own Ethernet type 0x0806 for these requests so they are passed to the ARP software in all nodes within the broadcast area .
All cards on a network read this request datagram and any that discover a match between their IP and the requested IP reply with an ARP response .
If a response is received the answer is entered to the ARP cache for future use .If none is received the request is repeated .
ARP datagrams are not passed through routers as a router operates at the IP layer and will not relay MAC broadcast traffic .This makes routers a good buffer between broadcast domains and prevent flooding networks .
86 ARP commands
arp command can be used to display the content of the ARP table
arp -a ! displays all the entries in the ARP table
arp lthostnamegt ! displays the entry for lthostnamegt specified
arp -d lthostnamegt ! deletes an entry for lthostnamegt
arp -s lthastnamegt ltether-addressgt ! adds a new entry
87 RARP - Reverse ARP
RARP is intended for use with devices that cannot store their IP address usually diskless workstations.
RARP like ARP operates directly over the datalink layer and has an Ethernet type 0x8035 .
Nodes acting as RARP servers that find a match for the MAC address in their RARP tables will reply with the corresponding IP address in a RARP response .
This system requires that at least one server is present and that the server has a table defining which IP addresses should be used by each MAC address .
89 ICMP - Internet Control Message Protocol
Even though IP is a datagram service and there is no delivery guarantee ICMP is provided within IP and can generate error messages regarding datagram delivery .
ICMP uses IP datagrams to carry its messages back and forth between relevant nodes .
ICMP error messages are generated by a node recognizing there is a transmission problem and they are sent back to the originating address of the datagram that caused the problem .
91 (No Transcript) 92 General format of ICMP message
Type (8) specifies the type of ICMP message
Code (8) used to specify parameters of the message that can be encoded in a few bits
Checksum (16) checksum of the entire ICMP message
Parameters (32) used to specify more lengthy parameters
Information (variable)provides additional information related to the message
ECHO and ECHO REPLY - mechanism for testing if communication is possible between two entities. A host can send the ICMP ECHO message to see if a remote IP is up and operational. When a system receives an echo message it send the same packet back to the source host in an ICMP ECHO REPLY message. The ping command uses this message.
A TIME EXCEEDED message is sent by a gateway if the ttl value of a datagram expires (becomes zero). This facility is used by the traceroute command.
Type (8 bits) Code (8 bits) Checksum (16 bits) Parameters (32 bits) Information (variable) 93 Type field Message Type
Echo reply Destination unreachable Source quench Redirect Echo request Time exceeded for datagram Parameter problem on datagram Time stamp request Time stamp reply Information request Information reply Address mask request Address mask response 94 The ping command
it is a simple function extremely useful for testing the network connection
it allows the network administrator to determine whether further testing should be directed toward the network (the lower layers) or the application (the upper layers)
if ping shows that packets can travel to the destination system and back the problem is probably in the upper layers
If packets cant make the round-trip lower protocol layers are probably at fault
ping lthostgt ltpacketsizegt ltcountgt
lthostgt The host name or IP address of the remote host being testyed.
ltpacketsizegt Defines the size in bytes of the test packets. This field is only required if the count field is going to be used. Default packet size is 56 bytes.
ltcountgt The number of packets to be sent in the test. Default number is usually 5.
95 ping example
info.ripe.net is alive
ping -s ftp.ripe.net 100 10
PING info.ripe.net 100 data bytes
108 bytes from info.ripe.net (188.8.131.52) icmp_seq0. time1070. ms
108 bytes from info.ripe.net (184.108.40.206) icmp_seq1. time990. ms
108 bytes from info.ripe.net (220.127.116.11) icmp_seq2. time990. ms
108 bytes from info.ripe.net (18.104.22.168) icmp_seq3. time990. ms
108 bytes from info.ripe.net (22.214.171.124) icmp_seq4. time990. ms
108 bytes from info.ripe.net (126.96.36.199) icmp_seq5. time990. ms
108 bytes from info.ripe.net (188.8.131.52) icmp_seq6. time990. ms
108 bytes from info.ripe.net (184.108.40.206) icmp_seq7. time980. ms
----info.ripe.net PING Statistics----
8 packets transmitted 8 packets received 0 packet loss
round-trip (ms) min/avg/max 980/998/1070
96 traceroute - Tracing routes
is the program that can help the network administrator locate the problem when something is down between the local host and a remote destination
traces the route of UDP packets from the local host to a remote host
prints the name (if it can be determined) and IP address of each gateway along the route to the remote host
uses two techniques small ttl values and invalid port number
97 traceroute - Tracing routes
traceroute sends out 3 UDP packets with ttl value set to one
the first gateway decrement ttl and gets the value zero.
The first gateway will send back to the source host an ICMP TIME EXCEEDED message as error message
traceroute displays one line of output for each gateway from which it receives an ICMP TIME EXCEEDED message
traceroute will then increment by one the ttl value and sends again 3 UDP packets
the flow of packets tracing to a host three hops away is illustrated below
When the destination host receives a packet from traceroute it returns back an ICMP Unreachable Port message. This happens because traceroute intentionally uses an invalid port number (33434) to force this error.
When traceroute receives the Unreachable Port message it knows that it has reached the destination host and it terminates the trace.
In this way traceroute is able to develop a list of the gateways starting at one hop away and increasing one hop at a time until the remote host is reached.
98 traceroute example
traceroute to info.ripe.net (220.127.116.11) 30 hops max 40 byte packets
1 agsici1.ici.ro (18.104.22.168) 20 ms 10 ms 0 ms
2 Vienna-EBS1.Ebone.NET (22.214.171.124) 870 ms 870 ms 870 ms
3 Paris-EBS2.Ebone.net (126.96.36.199) 900 ms 890 ms 890 ms
4 Stockholm-ebs.ebone.net (188.8.131.52) 920 ms 930 ms 960 ms
5 Amsterdam-ebs.Ebone.NET (184.108.40.206) 970 ms 990 ms 970 ms
6 Amsterdam.ripe.net (220.127.116.11) 1000 ms 970 ms 970 ms
7 info.ripe.net (18.104.22.168) 1040 ms 970 ms 990 ms
99 Flow of traceroute packets ping program First router Second router Third router ttl1 decrements ttl to 0 return error TIME EXCEEDED decrements ttl to 1 forward ttl2 decrements ttl to 0 return error TIME EXCEEDED ttl3 decrements ttl to 2 forward decrements ttl to 1 forward received at destination port unreachable Return error port unreachable 100
ICMP has its own IP protocol number (1) so the IP layer knows when it receives them.
Even though ICMP uses the IP layer it is considered as being within IP because it does not necessarily provide any service to the layers above.
101 ICMP types 0 and 8 - echo
The most common ICMP messages used for diagnostics are type 0 and 8.
These are generated by Ping.Ping sends ICMP type 8 datagrams to a node and expects an ICMP type 0 reply returning the data sent in the request.
102 ICMP echo datagram (0 or 8) 103 Note
How can Ping generate ICMP echo requests if ICMP does not provide a service to Ping
A Ping implementation does not use ICMP to generate the request.It merely mimics what ICMP would do as a program that operates over the IP layer.Ping generates an IP datagram with a data field that equates to ICMP echo request (protocol number 1 and the first octet of data is 8 - ICMP echo request).It then adds the rest of the fields including the data pattern that it expects to be echoed.
104 ICMP type 3 - destination unreachable
If a router is unable to deliver a datagram it can return the destination unreachable ICMP datagram to indicate why.
The code field is used to identify the cause of failure.
The values in the code field help to pinpoint the reason for the datagram failure to arrive its destination.
105 ICMP type 3 - Destination Unreachable 106 Code value Meaning
0 Network unreachable
1 Host unreachable
2 Protocol unreachable
3 Port unreachable
4 Fragmentation needed and the do not fragment bit set
5 Source route failed
If a router is unable to deliver a datagram it can return the destination unreachable ICMP datagram to indicate why .
Network unreachable - The network specified in the IP address cannot be found .
The IP address and routing tables should be checked .
This error message is only generated by a router .
We can find where the error occurred from the source address in IP header that carried the ICMP message .
Host unreachable - The datagram reached the router which is directly connected to the destination network but failed to communicate with the host.This message is generated by a router only .
Protocol unreachable - The datagram reached the destination host but the particular protocol carried in the datagram is not available .
Port unreachable - A host sends the message that the particular application layer service is not available .
Fragmentation needed and the do not fragment bit set - Normally comes from a router indicating that it needs to fragment the datagram but is instructed not to by the do not fragment (DF) bit in the flags field of the IP header .This fault is uncommon DF is normally used on diskless workstations booting via TFTP .
TFTP has only 512 octets of user data .
Check MTU size .
Source route failed - If we specified a route and the datagram failed to complete the route we will get this error .The point of failure will be the router that generated the ICMP message .
110 ICMP type 4 code 0 - Source Quench
The format of the datagram is the same as destination unreachable but with a type of 4 and a code of 0 .
Source quench gives a router or a host the ability to request that a source of datagrams will slow down .
Source quench will occur if a node is running low on buffer resources and is unable to process datagrams quickly enough .
111 (No Transcript) 112 ICMP type 5 - route change request
It is used only by routers .
A router that knows that it is not the optimum router for a particular destination uses the relevant field of a route change request to suggest a more suitable router .
113 ICMP type 11 - time exceeded for datagram
The format is the same as destination unreachable .
It can be sent in 2 situations
From a router - Indicating that the TTL in the IP header has been decremented to 0 .It indicates that the original Time To Live was not suitable to the number of hops needed .
From a node - An attempt to recreate the original datagram by reassembly of fragments failed .The code value is 1 .
114 ICMP type 12 - Parameter problem message
Indicates that a wrong argument has been used with an option field in the IP header .It can also indicate an error in the implementation of IP .
Its sent only if the datagram has been discarded .
The pointer field indicates the position of the octet position of the suspect field .
115 ICMP types 1314 - Time stamp request reply
This message is used to obtain the time from a clock in a distant machine .
It is rarely used today .
116 ICMP types 1516 - information request
This message is used to obtain the network number of the requesting host if its unknown .
It can be used in dial in systems using SLIP as a method for allocating the appropriate network addresses for each end of the link .
117 ICMP types 1718 - Address mask request
Used to allow a node to discover the subnet mask of the network it is connected to .
The node can send the request to a known address or to broadcast .
118 Transport Protocol Ports The address of an application within a host
Port 0 - Special use
Ports 1 - 255 - Well-known ports
Ports 256 - 1023 - Reserved ports
Ports 1024 - 4999 - Dynamic client ports
Ports 5000 - 65535 - Fixed server ports
119 User Datagram Protocol
Connectionless delivery service
Uses the IP layer service
Does not add reliability to the IP protocol
Enables distinguishing among multiple destinations within a host computer
End point 120 UDP Protocol Header Format
What if the packet size is larger then 1500
It is divided to 1500xN frames.
fragmentation flags are set
121 Flow using Datagrams (UDP) Server Client socket() socket() bind() sendto()/recvfrom() sendto()/recvfrom() closesocket() closesocket() 122 Transmission Control Protocol
Connection based communication
Uses the IP layer service
Provides reliable service
Enables distinguishing among multiple destinations within a host computer
123 TCP - Transmission Control Protocol
TCP is the protocol layer responsible for making sure that the commands and messages are transmitted reliably from one application program running on a machine to another one on the other machine
A message is transmitted and then a positive acknowledgement is being waited for
If the positive acknowledgement does not arrive in a certain period of time the message is retransmitted
Messages are numbered in sequence so that no one is being lost or duplicated
Messages are delivered at the destination in the same order they were sent by the source
If the text of a mail is too large the TCP protocol will split it into several fragments called datagrams and it makes sure that all the datagrams arrive correctly at the other end where they are reassembled into the original message
The TCP protocol layer provides all the functions that are needed for many applications and it is better to put them together on a separate protocol rather than being part of each application
TCP can be viewed as forming a library of routines that many applications can use when they need reliable network communication with an application on another computer
TCP provides also flow control and congestion control
124 TCP Protocol Format Source Port Destination Port Sequence Number Acknowledgment Number Offset Reserv Flags(6) Window (16 bits) Checksum (16) Urgent Pointer Options(If any) Padding Data (variable length) 0 4 10 16 24 31 125 Establishing and closing TCP Connections FIN SYN time ACK SYNACK FIN ACK ACK Close Open Three-way handshake 126 Sliding Windows segment 1 ack1 time segment 2 ack2 Positive acknowledgment with retransmission Sliding window transmission 127 Application Addresses Sockets
On a network server normally several application programs are running at the same time FTP server telnet server mail server www server gopher server etc.
TCP must know to which program to deliver the received message
If you want to connect to the FTP server it is not enough to know the IP address of the server you have to specify that you want to talk to the FTP server program
This is done by having the well-known sockets - TCP ports - (see the file /etc/services on a UNIX machine)
In a file server session e.g. two different applications are involved FTP server and FTP client
The client program gets commands from the user and passes them to the FTP server program
There is no need for the client FTP program to use a well know socket number because nobody is trying to find it as opposed to the FTP server program which have to have a well-known socket number so that people can open connections to it and start sending commands
The client FTP program asks the network software to assign it a port number that is guarantee to be unique for example 1236 if that number was free
A connection is identified by four numbers
connection 1 22.214.171.124 1236 126.96.36.199 21
connection 2 188.8.131.52 1237 184.108.40.206 21
Two connections are different if at least one number is different
128 Application Addresses Sockets Socket IP address port Message Segment Datagram Frame 129 Well-known TCP ports 21 - FTP server 23 - telnet server 25 - SMTP mail server 53 - domain nameserver 109 - POP2 server 110 - POP3 server 130 Flow using Streams (TCP) Server Client socket() bind() socket() listen() connect() accept() send()/recv() send()/recv() closesocket() closesocket() 131 ROUTING
The source and the destination hosts are on the same LAN
There is no decisions for routing
The packet is transmitted on the cable (coax twisted cable optical fiber)
Every computer connected to the LAN will receive it.
That computer which finds that the destination Ethernet address in the header is equal to his Ethernet address will get the message the others will discard it.
Note that the address of each computer on the LAN begins with the same network number
Routing table for host A
132 Example of complex configuration A .1 G .4 ec0 eth0 .4 .1 Routing tables net gw int. M 193.230.5 none eth0 220.127.116.11 sl0 193.230.4 18.104.22.168 eth0 193.230.3 22.214.171.124 eth0 192.162.16 126.96.36.199 eth0 default 188.8.131.52 sl0 I 193.230.5 none eth0 184.108.40.206 sl0 193.230.3 220.127.116.11 sl0 192.162.16 18.104.22.168 sl0 default 22.214.171.124 eth0 H 193.230.3 none ec0 193230.4.2 sl0 192.162.16 193.230.1 ec0 default 126.96.36.199 sl0 A 192.162.16 none eth0 default 188.8.131.52 eth0 D 193.230.3. eth0 ec0 ec1 H .2 .1 192.162.16. sl0 193.230.4. sl0 .2 .1 J .2 K .3 L .4 I eth0 193.230.5. .5 .1 M sl0 193.230.6. backbone network with Internet connectivity sl0 .2 N 133 Routing table initialization and updating
Initialization of routing table
Normally at startup time by executing script command files
IPv4 Header Total Length IHL Type of Service Version Identification Flags Fragment Offset Protocol Time to Live Header Checksum Source Address Destination Address Padding Options IPv6 Header Priority Flow Label Version Payload Length Next Header Hop Limit Source Address Destination Address 141 IPv6 Autoconfiguration
Host autonomously configures
its own address
Link Local Addressing
(single subnet scope formed from reserved prefix and link layer address)
Facilitates graceful renumbering
Addresses defined as valid deprecated or invalid
142 IPv6 Real Time/Premium Services support
Flow based defines flow label and priority
Can be combined with Source Routing header options
Instrumental in building existing 6-Bone (http//www.6bone.net)
Network Address Translation IPv4 IPv6
146 IPv6 Routing
Hierarchy is key
Test address space allocation available- (RFC 1897)
Existing routing protocols extensions for IPv6
RIPv6 - Same destination/mask/metric information as RIPv2
Multiprotocol BGP4 - Currently Draft
Integrated IS-IS - 20 byte NSAP support
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