TCPIP

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TCP/IP

• EECE 542
• Brad Guenther

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History

• 1969 ARPANET (Defense Advanced Research Project
  Agency DARPA)
• Adopted as a military std in 1983, used with BSD
  UNIX
• ARPANET dissolved/evolved into the Internet

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TCP/IP Model vs. OSI
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IP Datagrams
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Datagram Headers

• Ver IPv4 0x0100
• HLEN Header Length 0-15x460 bytes max
• Serv Type priority, TOS, desired reliability,
  etc
• T. Length Length of entire datagram (2-bytes)
• ID Identify fragmented datagrams
• Flags fragmented or not, 1st , middle, or last
  frag.
• Frag. Offset pointer designating frag. offset
• TTL Time to live
• Protocol Encapsulated upper layer protocol
• Checksum Checks integrity of header only
• Src dst Addr 4 bytes each
• Options info on routing, timing, management,
  etc (variable length)
• Padding extra 0s to make header a multiple of
  32 bits.
• Data (Max 64 KB)

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IP addresses

• Network portion
• Host portion
• Network portion also identifies the class of
  network
• 0 in MSB -gt Class A, 10 -gt Class B, 110-gt Class
  C, 1110 -gt Multicast (Class D), 1111-gt Reserved
• Routing based on network portion (network number)
• Use Netmask (subnetmask) to identify Network and
  Host portion

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Netmasks

• Perform a logical AND between IP address and
  Netmask to obtain the network number
• Example 129.130.40.5/255.255.248.0 -gt Network
  number of 129.130.40.0

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Another Example

• 192.168.1.201/255.255.255.252
• Special Addresses Network Number Broadcast
  address.
• Routing based on Network Numbers
• How would the Network number broadcast address
  affect routing? (What do you lose?)

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Subnets

• Previous example of 192.168.1.201/255.255.255.252
• What class of network is this?
• What is different about this netmask?
• Rules on borrowing bits At least two, but must
  leave at least two for host bits. Why?

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Subnet Example

• I have a Class C network and I need at least 20
  hosts per subnet. (192.168.40.0)
• How many host bits will I need?
• What is the maximum number of subnets that I can
  have?
• What are my usable subnets?
• What is the usable IP range on each subnet?
• How many address have I lost?

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Another Subnet Problem

• 129.130.40.0/255.255.248.0
• I have 129.130.40.0/255.255.255.0
• Default gateway 129.130.47.224
• How can I subnet myself off and still talk to the
  rest of the world? Where is the main problem?

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CIDR

• Classless Interdomain Routing
• RFC 1519
• Variable Length Subnetting (any power of 2 rather
  than 28 blocks must have at least 2 subnet
  bits and two host bits)
• Supernetting Take contiguous blocks of class C
  and advertise a single route!

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Address Resolution

• 4 Problems
• IP -gt MAC
• MAC -gt IP
• Name -gt IP
• IP -gt Name

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IP -gt MAC Resolution (ARP)

• Address Resolution Protocol
• Layer 3
• Uses Broadcasts
• Proxy ARP
• How are duplicate IP addresses identified/dealt
  with?

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MAC -gt IP

• RARP
• BootP
• Used with diskless clients
• DHCP

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DHCP

• Dynamic Host Control Protocol
• Replaces RARP BOOTP
• Uses UDP. Why?
• Client broadcasts looking for DHCP servers
• Servers responds
• Server chosen, request broadcast sent
• Server sends acknowledgement
• Client sends release when done

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DHCP Messages

• DHCPDISCOVER Client broadcast to locate
  available servers
• DHCPOFFER Server -gt Client offer of config
  parameters
• DHCPREQUEST Client -gt Server a.) Requesting
  offered params from a particular server (implicit
  decline of other offers), b.) confirm correctness
  of previously allocated address, c.) extending of
  lease
• DHCPACK Server -gt Client confirmation of
  parameters and committed address
• DHCPNACK Server -gt Client address incorrect or
  expired
• DHCPDECLINE Client -gt Server address in use
• DHCPRELASE Client -gt Server relinquish address
• DHCPINFORM Client -gt Server asking for local
  config (already has address)

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Name -gt IP

• Host tables
• DNS (Domain Name Service)
• Fully Qualified Domain Name (FQDN)
• Hostname vs. Domain Name
• Distributed Hierarchical System
• Root Servers
• TLD Geographical Organizational

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IP -gt Name

• Similar to above, but in reverse
• Not guaranteed
• Searches local files and cache
• Caching controlled by TTL
• Secondary servers updated based on TTL and serial
  number differences

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Type of DNS Records

• NS Name servers
• A Addresses
• CNAME Aliases
• PTR Address To Name (reverse lookups)
• MX Mail Exchange

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ICMP

• Internet Control Message Protocol
• Sort of a subset of IP
• Flow Control similar to pause frames only at
  layer 3
• Error Reporting Destination Unreachable (may be
  sent by router or host itself)
• Route Redirection
• Troubleshooting

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ICMP Troubleshooting

• Ping Check base layer 3 connectivity
• Traceroute Uses TTL field to determine where
  communications break down
• When the TTL reaches zero the router sends an
  ICMP TIME_EXCEEDED back to sender
• Example

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IGMP

• Internet Group Management Protocol
• Like ICMP somewhat of a subset of IP part of
  the IP implementation on a device
• Used to report multicast group membership to
  immediately neighboring multicast enabled routers
• Two main types of messages Membership Query and
  Membership Report

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Layer 4

• TCP Connection Oriented
• UDP Connectionless
• Both use port numbers to allow Layer 5 to track
  different conversations (sessions) going on at
  the same time
• Port number IP address gt Socket

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TCP and UDP Port Numbers

• Ports lt 1024 considered privileged ports
  (controlled by IANA)
• Ex 20ftp data, 21ftp, 22ssh, 23telnet,
  25smtp, 80http, 53dns, 69tftp, 123ntp
• Ports lt 255 gt Public applications
• Ports 255-1023 gt Commercial apps
• 1024 and up unregulated (max 65535) these are
  also usually used by the client
• 1024-49,151 may be registered with IANA

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UDP

• User Datagram Protocol
• Unreliable Best Effort Delivery Relies on
  upper layer protocols to do error detection and
  recovery
• Where is this usefull?

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Scenarios Suited to UDP

• Small amounts of data lower overhead
• Query-Response applications (response considered
  an ACK)
• Need fastest possible transfers over reliable
  links

UDP Segment Format
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TCP

• Transmission Control Protocol
• Reliable, Connection-Oriented protocol
• Uses a 3-way handshake to establish connections
• Uses sliding windows
• May require keepalives to keep connection up
• Connection terminations should be acknowledged by
  both stations FIN flag

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TCP Segment Format
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TCP 3-Way Handshake

• Used to establish connection and synchronize ISNs

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TCP Sliding Window

• Provides positive acknowledgement and flow
  control
• Window sizes are dynamically negotiated between
  hosts and represent the number of BYTES that can
  be sent before an acknowledgement is received
• Sequence numbers reflect cumulative number of
  bytes of user data sent (but ISN may not be 0).

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TCP Sliding Window

• Best Case Send X bytes, receive ACK X1
• Send X bytes, receive ACK X-Y?
• Send X bytes, receive nada?
• Receive X5, but expecting X?
• Error Detection based on timers

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TCP Sliding Window

• Error correction gt Retransmission
• Timer too short too many unnecessary
  retransmissions
• Timer too long must wait a long time before
  retransmitting
• Retransmission can be handled with a back-off
  algorithm allows timers to be dynamic
• Many retransmissions may result in smaller window
  size

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Silly Window Syndrome

• Sender sending too slowly Nagles Algorithm
• 1. Send first chunk of data (even if only a byte)
• 2. Accumulate data and wait for either and ACK or
  until enough data is accumulated to fill max.
  sized segment.
• Receiver receiving/processing too slowly
• Can advertise 0 window size OR
• Delay ACK until ready (shouldnt be more than
  500ms).

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Congestion Control

• Pause Frames revisited (Layer 2)
• Congestion Windows (use smaller of two window
  sizes advertised vs. congestion).
• Slow Start start sending max segment size with
  congestion window of 1 segment.
• Each successful ACK up it by 1 more until ½
  window size (ACKs may be combined)
• Then increase only for each ACK
• Lost segment knock it down to ½ current size

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IP Fragmentation

• How/Why does it happen?
• Who does it?
• Who puts it back together?
• Role of dont fragment flag!?
• What happens if fragments are received out of
  order?
• What happens if a fragment is lost?
• Optimizing with MTU (Ethernet1500 1460 data)

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IPv6

• Problems with IPv4 32-bit address space, only
  two layers (network and host), address allocation
  dependent on single organization
• IPv6 128 bit addresses allocated in
  variable-size segments which can be allocated by
  a combination of ISPs, large enterprises, and
  other entities along the way

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IPv6 Addresses

• 123456789ABCDEF0000000000000FEDC
• 123456789ABCDEF0FEDC
• IPv4 with IPv6
• Right justify the IPv4 address
• Set the preceding 16 bits MSB of IPv4 address
• 00000FFFF129.130.40.5
• 00000010.1.2.1

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IPv6 Address Types

• Unicast one host
• Multicast all hosts in multicast group
• Anycast All or SOME hosts in group
• Anycasts look like unicasts, but participating
  nodes must advertise their participation. This
  seems to be aimed at routers for table
  maintenance.

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IPv6 Goals

• Larger Address Space
• Better Efficiency Header boundaries, fewer
  headers to process, fragmentation done by sender
  NOT routers
• Better Security Packet signing, encryption,
• WORK IN PROGRESS

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