CS 480 M01 Lecture Notes 16 - Oct 31, 2022

Last Time

Ch 20. Storage Finished
Other hardware related commands
Ch 13: TCP/IP Networking
Managed by ... ICANN, ISOC , IETF ...
Network Standards and Documentation: RFCs, FYIs, BCPs, STDs
OSI Model
TCP/IP Protocol Suite and Network Model
Layers (Application, Transport, Network, Link, Physical)
Packets & encapsulation: Ethernet, IP, TCP, Application
Ethernet, TCP, UDP, and IP Headers

Ch 13: TCP/IP Networking Continued

1. textbook
2. TCP/IP Protocol Suite by Forouzan, McGraw Hill 2003, ISBN 0-07-246060-1
3. TCP/IP Illustrated, Vol 1 by Stevens, Addison-Wesley 2000 , ISBN 0-201-63346-9

Maximum Transfer Unit (MTU):

Size of packets limited by hardware specifications and protocol conventions
MTU - Size limit associated with link layer:
• IP layer splits packets to conform to MTU of a network link (at the source)
• May lead to fragmentation when a packet travels through several networks and an intermediate network/link may have smaller MTU
  -> router will fragment a packet if necessary or dumps it and sends ICMP err msg to the source (no fragmentation in IPv6 - required MTU discovery)

Ethernet

... CSMA/CD ... Aloha

Switches v. Hubs

Packet Addressing

• combination of several addressing schemes (by layer):
  • Hardware / MAC 00:07:E9:D7:2E:6E - one per interface
        first 3 bytes: manufacturer of the hardware
        last 3 bytes: unique serial number by manufacturer
        => in theory "Ethernet hardware addresses are permanently assigned and immutable" ...
  • IP (SW) - identifies network interface (machine) 192.168.8.1 - one interface may have more addresses
        ARP ( MAC <-> IP)
  • hostnames (people) lbc, www, ....
        /etc/hosts, DNS ( hostnames <-> IP)
  • Ports - 16bit number to specify a particular communication channel (to the application/service)
        /etc/services - well-known port numbers repo at Internet Assigned Numbers Authority
    port number < 1024 - restricted - only root can bind to (listen on) these

    # Network services, Internet style
    # Note that it is presently the policy of IANA to assign a single well-known
    # port number for both TCP and UDP; hence, most entries here have two entries
    # even if the protocol doesn't support UDP operations.
    #
    # This list could be found on:
    # http://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xml
    #
    # See also: services(5)
    #
    # SERVICE NAME AND TRANSPORT PROTOCOL PORT NUMBER REGISTRY
    # (last updated on 2017-03-03)
    #
    ....
    #
    # Service Name       Port/Proto   Description, Update Date, References
    # ------------       ----------   ------------------------------------
    ...
    ftp-data           20/tcp       # File Transfer [Default Data]  [Jon_Postel]
    ftp-data           20/udp       # File Transfer [Default Data]  [Jon_Postel]
    ftp-data           20/sctp      # FTP  [Randall_Stewart] [RFC4960]
    ftp                21/tcp       # File Transfer Protocol [Control]  [Jon_Postel] [RFC959]
    ftp                21/udp       # File Transfer Protocol [Control]  [Jon_Postel] [RFC959]
    ftp                21/sctp      # FTP  [Randall_Stewart] [RFC4960]
    ssh                22/tcp       # The Secure Shell (SSH) Protocol  [RFC4251]
    ssh                22/udp       # The Secure Shell (SSH) Protocol  [RFC4251]
    ssh                22/sctp      # SSH  [Randall_Stewart] [RFC4960]
    telnet             23/tcp       # Telnet  [Jon_Postel] [RFC854]
    telnet             23/udp       # Telnet  [Jon_Postel] [RFC854]
    #                  24/tcp       any private mail system  [Rick_Adams]
    #                  24/udp       any private mail system  [Rick_Adams]
    smtp               25/tcp       # Simple Mail Transfer  [Jon_Postel]
    smtp               25/udp       # Simple Mail Transfer  [Jon_Postel]
    ...
    finger             79/tcp       # Finger  [David_Zimmerman]
    finger             79/udp       # Finger  [David_Zimmerman]
    http               80/tcp       # World Wide Web HTTP
    http               80/udp       # World Wide Web HTTP
    www                80/tcp       # World Wide Web HTTP
    www                80/udp       # World Wide Web HTTP
    ...
    kerberos           88/tcp       # Kerberos  [B_Clifford_Neuman]
    kerberos           88/udp       # Kerberos  [B_Clifford_Neuman]
    ...
    sunrpc             111/tcp      rpcbind # SUN Remote Procedure Call  [Chuck_McManis]
    sunrpc             111/udp      rpcbind # SUN Remote Procedure Call  [Chuck_McManis]
    ...
    https              443/tcp      # http protocol over TLS/SSL  [Kipp_E_B_Hickman]
    https              443/udp      # http protocol over TLS/SSL  [Kipp_E_B_Hickman]
    ...
    login              513/tcp      # remote login a la telnet; automatic authentication performed based on priviledged port numbers and distributed data bases which identify "authentication domains"
    who                513/udp      # maintains data bases showing who's logged in to machines on a local net and the load average of the machine
    shell              514/tcp      # cmd like exec, but automatic authentication is performed as for login server
    syslog             514/udp
    printer            515/tcp      # spooler
    printer            515/udp      # spooler
    ...
    

• Address Types IP (network) layer and some in link layer:
  • Unicast - single host
  • Multicast - group of hosts (to help with routing of multimedia streaming , video conferencing, tv, gaming, ...)
  • Broadcast - all hosts on local (sub)net
  • Anycast - any host in a group (delivered to the closest in terms of routing - load balancing) - IPv6 related mainly

IP Addresses:

... have network portion and a host portion (except for multicast addresses).
IPv4 - 4 bytes similar to 98.138.219.231, IPv6 - 16 bytes (128 bits) long
1st byte 127 (127.x.y.z) - loopback
set by ifconfig - obsoleted by ip , ip-address, ip-maddress,...
• IPv4 address classes:A,B,C,D - 1st few bits determine which bytes are in network part and which are in host portion
  

  

  Today - explicit mask identifies the network option, can be in between any adjacent bits (not just the bytes boundary)
• IP subnetting and netmask
  reassigning part of the host portion to the network portion
  1s - network portion (at least 8 bits), 0s - host portion (at least 2 bits)
  /26 or 255.255.255.192 splits class B network into 1024 subnets each supporting 62 (2⁶ - 2 ) hosts
  
  

  # ipcalc 192.168.8.9/26
  Address:   192.168.8.9          11000000.10101000.00001000.00 001001
  Netmask:   255.255.255.192 = 26 11111111.11111111.11111111.11 000000
  Wildcard:  0.0.0.63             00000000.00000000.00000000.00 111111
  =>
  Network:   192.168.8.0/26       11000000.10101000.00001000.00 000000
  HostMin:   192.168.8.1          11000000.10101000.00001000.00 000001
  HostMax:   192.168.8.62         11000000.10101000.00001000.00 111110
  Broadcast: 192.168.8.63         11000000.10101000.00001000.00 111111
  Hosts/Net: 62                    Class C, Private Internet
  
  # ipcalc 128.123.64.173/24
  Address:   128.123.64.173       10000000.01111011.01000000. 10101101
  Netmask:   255.255.255.0 = 24   11111111.11111111.11111111. 00000000
  Wildcard:  0.0.0.255            00000000.00000000.00000000. 11111111
  =>
  Network:   128.123.64.0/24      10000000.01111011.01000000. 00000000
  HostMin:   128.123.64.1         10000000.01111011.01000000. 00000001
  HostMax:   128.123.64.254       10000000.01111011.01000000. 11111110
  Broadcast: 128.123.64.255       10000000.01111011.01000000. 11111111
  Hosts/Net: 254                   Class B
  	

  Local (destination directly reachable on the same ethernet segment)
    or
  Not ( packet has to travel through a router to reach its destination)

  Read about the topics below in the book !

  IP address crisis
  CIDR: Classless Inter-Domain Routing
  CIDR allows the network portion to be made smaller than would be implied by an address’s implicit class. Aggregating several networks for purposes of routing => "supernetting"
  Private Addresses and NAT
  Private Addresses that will never be globally allocated and can be used internally by any site:
  

  A	10.0.0.0	10.255.255.255	10.0.0.0/8	(1x)
  B	172.16.0.0	172.31.255.255	172.16.0.0/12	(16x)
  C	192.168.0.0	192.168.255.255	192.168.0.0/12	(256x)

  NAT - network address translation on the border router (sharing single external address)
  IPv6

next ... Routing