Review the key networking concepts

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• Review the key networking concepts
• TCP/IP reference model
• Ethernet
• Switched Ethernet
• IP, ARP
• TCP
• DNS

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FTP data can be infinitely large, when do we chop
it into smaller Units?
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• Internetworking devices
• Repeaters PHY device that restores data and
  collision signals
• Hub Multiport repeater
• Bridge Datalink layer device connecting two or
  more collision domains (extended LAN). MAC
  multicasts are propagated throughout the extended
  LAN
• Switch Multiport bridge with parallel paths
• Router Network layer device.
• Network address translator (NAT) Transport layer
  device.
• Gateways Transport layer or application layer
  devices

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• Ethernet
• Shared medium LAN technology
• Need medium access control
• CSMA/CD binary exponential backoff
• Frame format
• PreambleStartDst AddrSrc Addrlength Data
  Pad Checksum 7 1 6
  6 2 0-1500 0-46 4
• Minimum data pad length 46 bytes
• Maximum data length 1500 bytes

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• Fast Ethernet (100Mbps)
• Reduce cable length and keep everything else
• Duplex mode
• Gigabit Ethernet (1000Mbps)
• Reduce cable length and increase minimum frame
  size
• Duplex mode

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• Switched Ethernet
• Get dedicated link in Ethernet in a transparent
  manner.
• Issue the switch needs to know where to forward
  a packet
• How is it accomplished?
• Self-learning algorithm to obtain the location of
  each machine
• Forwarding algorithm
• Can switched Ethernet take advantage of the dense
  connectivity in the network topology?
• Spanning tree algorithm

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• IP
• Addressing
• (type, network number, host number)
• Class A, Class B, Class C
• Classless inter-domain routing
• IP address prefix length
• e.g. 192.168.0.3/22

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• IP header format
• Version (4 bits) IPv4, IPv6
• Header length (4 bits) in 32-bit words, min
  header is 5 words or 20 bytes
• Type of service (8 bits) reliability,
  precedence, delay, and throughput. Used in
  DiffServ (IP QoS support)
• Total length (16 bits) header data in bytes,
  total must less than 64 KB.
• Identifier (16 bits) uniquely identify the
  datagram during its life for a given source and
  destination addess.

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• IP header format
• Flags (3 bits) more flag, no-fragmentation
• Fragment offset (13 bits) in units of 8 bytes
• Time to live (TTL) specified in router hops
• Protocol next level protocol to receive the data
• Header checksum 1s complement sum of all 16 bit
  words in the header
• Source/destination address original
  source/destination
• Options (variable) Security, source route,
  record route, timestamp recording
• Padding (variable) makes header length a
  multiple of 4
• Data (variable) data header lt 65535 bytes.

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• IP functionality
• Framentation
• Addressing
• Routing is done by other protocols
• IP router
• Routing computes the next hop for each
  destination.
• Forwarding based on the destination address in
  an IP packet, forward the packet to the right
  next hop
• Longest prefix matching

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• Internet Routing protocols
• RIP distance vector algorithm
• OSPF link state algorithm
• BGP path vector algorithm that supports policy
  based routing

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TCP segment structure
URG urgent data (generally not used)
counting by bytes of data (not segments!)
ACK ACK valid
PSH push data now (generally not used)
bytes rcvr willing to accept
RST, SYN, FIN connection estab (setup,
teardown commands)
Internet checksum (as in UDP)
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• TCP header
• Source port (16 bits) identifies the source
  process. 20FTP, 23Telnet, 80HTTP.
• Destination port (16 bits)
• Sequence Number (32 bits) Sequence number of the
  first byte in the segment. If SYN is present,
  this is the initial sequence number (ISN) and the
  first data byte is ISN1
• ACK number (32 bits) Next byte expected
• Data offset (4 bits) number of 32-bit words in
  header
• Reserved (6 bits)

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• TCP header
• Control (6 bits)
• URG urgent pointer field significant
• ACK ACK field significant
• PSH push function
• RST reset the connection
• SYN synchronize the sequence number
• FIN no more data from sender
• Window (16 bits) wil accept ack to
  ackwindow
• Checksum (16 bits) cover the header plus a
  pseudo header.

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• TCP header
• Urgent pointer (16 bits) points to the byte
  following urgent data.
• Options (variable) max segment size, window
  scale factor, etc.

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• Each computer has a name resolver routine
  (gethostbyname in UNIX)
• Each resolver knows the name of a local DNS
  server
• Resolver sends a DNS request to the server
• DNS server either gives the answer, forwards the
  request to another server, or gives a referral
• Recursive query / iterative query
• Referral next server to whom the request should
  be sent