Network Layer

Layer Addressing

• Ports
• IP (Internet Protocol) Addresses
• MAC

MAC

84:18:88:9e:20:a6

IPv4 and IPv6

• IPv4: 32-bits
• IPv6: 128-bits

IP address ->        172  .    16  .    31  .      46
Bit format ->     10101100.00010000.00011111.00101110
netmask    ->        255  .    255 .   254  .      0
CID form   ->       172.16.31.46/23

2001:da8:100a:43::2a/64

IP Address Allocation

• static/Manual
• Automatic
  • DHCP or DHCPv6
  • stateless autoconfiguration
• link local
  • 169.254.0.0/16
  • fe80::/64

Name Resolution

• Domain Name to IP address
• Domain Name System (DNS)
• Client utils: host and dig; /etc/resolv.conf

Network Interfaces

• List network interface card (NIC) info: ifconfig
• Linux ip utilties: ip link; ip addr; ip route ...
• ping
• route; traceroute
• netstat

Network Applications

• wget; curl
• ssh; scp

Hash function

• Function to map any size data to data of fixed size
• Return hashes/hash values/hash sums
• Search; Data integrity; Cryptography
• checksums, fingerprints

Cryptographic hash function

• one-way Hash functions
• Practically impossible to invert, get input data from hashes
• Hashes uniquely identifies original data: fingerprint

Common hash functions

• MD5
• SHA-1
• SHA-256; SHA-512
• SHA-224; SHA-384

ls [OPTION]... [FILE]...
host [-aCdlnrsTwv] [-c class] [-N ndots] [-R number] [-t type]
        [-W wait] [-m flag] [-4] [-6] {name} [server]
stone [-C <file>] [-P <command>] [-Q <options>] [-N] [-d] [-p] [-n]
      [-u <max>] [-f <n>] [-l] [-L <file>] [-a <file>] [-i <file>]
      [-X <n>] [-T <n>] [-A <n>] [-r]
      [-x <port>[,<port>][-<port>]... <xhost>... --]
      [-s <send> <expect>... --]
      [-b [<var>=<val>]... <n> <master>:<port> <backup>:<port>]
      [-B <host>:<port> <host1>:<port1>... --]
      [-I <host>]
      [-o <n>] [-g <n>] [-t <dir>] [-D] [-c <dir>]
      [-q <SSL>] [-z <SSL>]
      [-M install <name>] [-M remove <name>]
      <st> [-- <st>]...   

BNF

• Notation techniques to describe syntax
• Extended Backus-Naur Form (EBNF), ISO/IEC 14977
• BNF and EBNF

Regular Expression

Sequence of characters define a search pattern, string matching.

Found in text editors, text processing utilities and programming languages.

• ^[ \t]+|[ \t]+$
• ^[+-]?(\d+(\.\d+)?|\.\d+)([eE][+-]?\d+)?$
• IEEE POSIX standard: BRE (Basic), ERE (Extended)
• PCRE (Perl Compatible Regular Expressions)
• Regular Expressions