tags: ccna

IP Addressing

• layer 3 logical address assigned by an administrator(MAC built in NIC)
• used to identify specific devices on a network
• every device on the internet has a unique IP Address

Street Analogy

• network address portion
  • identifies a specific network
  • routers route traffic via routing tables, is based on network address(Network ID), not ip address
• host address portion
  • identifies a specific endpoint on a network
  • we can use a protocal such as ARP to find the host

Ipv4

• connectionless protocal: no sessions formd when transmitted, no status info
• packets treated independently
  • may take different paths: load balancing, bandwidth, hopcount
• hierarchical addressing sturture
• best effort delivery
• format
  • 32 bit with 4 octets
  • like DHL or FedEx routing parcel based on an address

Classes

• Unicast Traffic
  • A
    • start with binary 0
    • range from 0(00000000).0.0.0 to 127(01111111).255.255.255
    • exceptions:
      • 127 is reserved for loopback: 127.0.0.1
      • 0 network is reserved for default network: 0.1.1.1
    • actual range from 1.0.0.0 to 126.255.255.255
    • portions
      • first 1 octets: Networks
      • last 3 octests: Hosts
  • B
    • start with binary 10
    • range from 128(10000000).0.0.0 to 191(10111111).255.255.255
    • portions
      • first 2 octets: Networks
      • last 2 octests: Hosts
  • C
    • start with binary 110
    • range from 192(11000000).0.0.0 to 223(11011111).255.255.255
    • portions
      • first 3 octets: Networks
      • last 1 octests: Hosts
• Multicast
  • D
    • start with binary 111
• reserved for other purposes
  • E
    • start with binary 1111

These classes replaced by Classless Inter-Domain Routing(CIDR) in 1993

Special Address

• Directed Broadcast Address
  • host sends data to all device on a specific network
  • binarys 1s in the entire host portion
  • routers can route directed broadcast, disabled by default
  • Denial of service attack(DDoS)
• Local Broadcast Address
  • communicate with all device on local network
  • address is all binary 1 (255.255.255.255)
  • e.g. host requrest an IP address from an DHCP Server(Dynamic Host Configuration Protocal)
  • always dropped by routers, configuring DHCP forwarding or DHCP relay
• Local Loopback Address
  • let a system send a message to itself for testing
  • to make sure that the TCP/IP stack is correctly installed
  • typical use 127.0.0.1 with IPv4
    • class A
    • anything in 127 range is deemd as loopback address: 16 million ip wasted
  • also have IPv6 loopback suchas ::1, resolve the IPv4 wasted.
  • routers and switchers can also be configured with a IP address on a loopback interface, which are not the same as local loopback address

Private Address

See RFC1918

• 1 class A networks
• 16 class B networks
• 256 class C networks
• Microsoft IPv4 Link Local Address

See RFC3927

• Automactic Private IP Address (APIPA)
• PC automatically chooses an IP address in range 169.254.0.0/16 with no DHCP
• can immediately communicate using IP without configuration: only on LOCAL LINK
• non routable

Subnet Masks

• to determin the portion of address which is host and network
  • Remote: different sebnet, reached via a default gateway
  • Local: same subnet, communicate on local segment directly, does not require a default gateway

Class A, B and C have default masks:

• Class A: 255.0.0.0
• Class B: 255.255.0.0
• Class C: 255.255.255.0

Two simple rules, any address bits have corresponding mask bit:

• set to 1: represent the NETWORK ID
• set to 0: represent the HOST ID

To work out if another host is local or remote

• check network portion
• compare to the other host

Subnet mask need to be CONTIGUOUS:

CIDR Notation

• Replace classful IP Addressing
• Variable Length Subnet Mask(VLSM)
  • Use 10.0.0.0/8 notation rather than 10.0.0.0
• Vary Mask and allocate ip ranges dynamically instead of classful masks