IP addressing

An IP address is a numeric identifier assigned to each machine on an IP network

• logical address, not hardware.
  • Hardware is hard-coded on the NIC and used to find machines on a network
• IP addr designed to allow a host on one network to communication with a host on another network, regardless of LAN design

Terminology

Bit

One binary digit, either 0 or 1

Byte

7 or 8 bits, depending on whether parity is used.

Octet

Ordinary 8-bit binary number, typically displayed in decimal up to 255. Same as octet.

Network address

Designation used in routing to send packets to a remote network. For example, 10.0.0.0 or 172.16.0.0.

IP address

Logical address that defines a single host, but can also reference many or all hosts.

Broadcast address

Used by applications and hosts to send information to all hosts on a network. For example:

• 255.255.255.255: all netowrks and all hosts
• 172.16.255.255: all subnets and hosts on 172.16.0.0
• 10.255.255.255: all subnets and hosts on network 10.0.0.0

IP addressing scheme

IP address is 32 bits long, divided into 4 sections of 1 octet each in one of the following formats:

• dotted-decimal: 172.16.30.56
• binary: 10101100.00010000.00011110.00111000
• hexadecimal: AC.10.IE.38

32-bit address is called structured, which means hierarchical address.

• hierarchical address can created 4.3 billion addresses
• hierarchical as opposed to flat, where each machine has its own address. This would mean that a router needs to store the IP address for every machine on the planet.
• hierarchical is structured by network and host, or network, subnet, and host

Network addressing

Also called network number, and uniquely identifies each network

• host address uniquely identifies each machine on a network
• there are classes of networks based on size:
  • Class A: large number of hosts
  • Class B: between large and small number of hsots
  • Class C: small number of hosts

            8 bits      8 bits      8 bits      8 bits
Class A:  ----------- ----------- ----------- -----------
          | network | |   host  | |   host  | |   host  |
          ----------- ----------- ----------- -----------

Class B:  ----------- ----------- ----------- -----------
          | network | | network | |   host  | |   host  |
          ----------- ----------- ----------- -----------

Class C:  ----------- ----------- ----------- -----------
          | network | | network | | network | |   host  |
          ----------- ----------- ----------- -----------

Class D: Multicast

Class E: Research

Reserved addresses

Address space

Class A

Uses the following format:

network.host.host.host

Network address is 1 byte long:

• first bit is reserved and remaining 7 bits can be used for addressing
• first bit must always be “off”, or 0
  • Class A address must be between 0 and 127 in the first byte, inclusive:
    • 00000000 = 0
    • 01111111 = 127
  • All 0s is the default route
  • 127 is reserved for diagnostics
  • actual number of usable Class A network addresses is 126
• 3 bytes for the host address of the machine
• Network address - all host bits off: 10.0.0.0
• Broadcast address - all host bits on: 10.255.255.255

Class B

Uses the following format:

network.network.host.host

All CLass B network addresses start with 10. First bit on, second bit off. This gives the following range:

• 10000000 = 128
• 10111111 = 191
• Uses 2 bytes for host addresses
• Network address - all host bits off: 176.16.0.0
• Broadcast address - all host bits on: 176.16.255.255

Class C

Uses the following format:

network.network.network.host

All Class C network addresses start with 110. First and second bits on, third bit off. This gives the following range:

• 11000000 = 192
• 11011111 = 223
• Network address - all host bits off: 192.168.100.0
• Broadcast address - all host bits on: 192.168.100.255

Class D and E

First octet 224 - 255 are reserved for D and E:

• Class D multicast: 224-239
  • Multicast range is 244.0.0.0 through 239.255.255.255
• Class E scientific: 240-255

Private IPs

Private IP addresses can be used on a private network, but they’re not routable through the internet

• provides security but also saves address space
• This requires Network Address Translation (NAT)
  • takes a private IP address and converts it for use on the internet
  • provides security in that these IP addresses cannot be seen by external users - external users only see the public IP addr that the private IP is mapped to
  • multiple devices in a private network can be mapped to a single external, public IP address

Reserved private address space

Virtual IP (VIP)

Virtual IPs do not correspond to an actual physical network interface. For example:

• when a public IP address is substituted for the actual private IP address that was assigned to the network interface of the device, the public IP address is the virtual address.
• a subinterface configured on a physical router interface that allows you to create multiple IPs or subnets on one interface
• Whena web proxy server substitutes its IP address for the sender’s IP address before sending a packet to the internet

APIPA

Automatic Private IP Addressing.

When a DHCP server isn’t avaialable, clients can automatically self-configure an IP address and subnet mask

• APIPA IP address range is 169.254.0.1 - 169.254.255.254
• Client uses Class B subnet mask of 255.255.0.0
• Hosts that use APIPA can communicate with each other, but not addresses that were statically configured
• Used as a fallback to DHCP
  • If your computer has an address in the APIPA range, then there is a DHCP issue

IPv4 address types

Four IPv4 address types.

Layer 2 broadcasts

Sent to all nodes on a LAN.

• Also called hardware broadcasts
• Only go out on a LAN and don’t go past the LAN boundary (router)

Typical hardware address is 6 bytes and looks like this: 0c.43.a4.f3.12.c2

Broadcast is all 1s in binary, which is all Fs in hex: FF.FF.FF.FF.FF.FF

Broadcasts (Layer 3)

Sent to all nodes on the network. Its the address with all host bits on. For example:

• ARP request
  • When a host has a packet it has the logical IP address of the dest
  • Sends to default gateway if IP address is not on local network
  • If on local network, needs MAC address, so sends out a broadcast message that says ‘if you are owner of IP address X, please forward your MAC address’

Unicast

Address for a single interface, used to send packets to a single destination.

Multicast (Class D)

Packets sent from a single source to many devices on different networks, referred to as one-to-many.

• Multicast allows point-to-multipoint communication, which is similar to broadcasts but lets multiple recipients receive messages without flooding messages to all hosts on a broadcast domain
• packets are sent to only hosts that subscribe to a group address
• Multicast addresses are 244.0.0.0 - 239.255.255.255 (Class D)

1. Sends messages or data to IP multicast group addresses
2. Routers forward copies of the packet out every interface that has hosts subscribed to a particular group address

IPv6

We need IPv6 because we are running out of IP addresses. By default, IPv6 has the following features:

• IPSec for e2e security
• mobility, which means that a device can roam from one network to another without dropping connection
• packet header has 1/2 the fields at 64 bits
• 128 bits in length
• routing is more efficient
• doesn’t use broadcast, uses multicast
  • also has unicast and anycast, which allows the same address to be placed on more than one device so that when the traffic is sent to one device addressed in this way, it is routed to the nearest host that shares the same address

IPv6 addressing and expressions

• Eight groups of hex numbers and the groups are separated by colons
• 16-bit colon-delimited blocks

              subnet
               /  \
2001:0db8:2a3b:0016:0000:0000:1234:5678
|_____________|____|__________________|
 \ global prefix  /\  interface ID    /
  \-- 64-bits ---/  \---- 64-bits ---/

When you want to use IPv6 in a browser, you have to wrap it in brackets:

https://[2001:0db8:2a3b:0016:0000:0000:1234:5678]/page-name.html

Shortened expression

You can leave out parts of the address to abbreviate it:

• drop any leading zeroes in each individual block: 2001:db8:2a3b:16:0:0:1234:5678
• remove two blocks of zeroes by replacing them with double colons: 2001:db8:2a3b:16::1234:5678
  • You CANNOT use double colons twice in the same address. When the router comes to the double colon, it replaces it with enough zeroes to reach 128 bits. It would not know how many zeros go in the first set or second.

Address types

A single interface can have multiple types of IPv6 addresses assigned:

Unicast

Packets addressed to unicast are delivered to a single interface. For load balancing, multiple addresses can use the same address.

Global unicast address

These are your typical publicly routable addresses, same as in IPv4.

Link-local address

Like APIPA addresses in IPv4, not meant to be routed and are unique for each LAN. For example, you can create a small LAN that does not need to be routed but still needs to share and access files and services locally.

Link-local address is an FE80::/10 address.

Unique local address

Nonrouting purposes, nearly globally unique. Designed to replace site-local addresses, so very similar to private IPv4 addresses: allow communication throughout a site while being routable to multiple local networks. Unique local can be routed within your organization or company.

Multicast

Same as IPv4, packets addressed to multicast address are delivered to all interfaces identified by the multicast address.

Anycast

identifies multiple intefaces, but the anycast packet is delivered to only one address–the first IPv6 address it finds in terms of routing distance. Could be called one-to-one-of-many addresses, or one-to-nearest.

Special addresses

Stateless Address Autoconfiguration (SLAAC)

Autoconfig is useful bc it lets devices on a network address themselves with a link-local and global unicast address. Creates an Extended Unique Identifier (EUI-64) address:

• Takes the prefix info from the router, adds 16-bits of padding, and then appends the devices own interface (MAC) address as the interface ID
• Padded bc it must be 128-bits long, and the
  • IPv6 address = 64 bits
  • padding = 16 bits
  • MAC address = 64 bits
• 7th bit in the first byte is the Universal/Local bit (U/L) that signifies a locally unique or global address.

Read into this more, not clear in the book

DHCPv6 (stateful)

Works the same as in IPv4, except that it addresses using IPv6 format.

Autoconfiguration does not provide the following, which makes DHCP more useful:

• no DNS servers
• no domain names

Migrating to IPv6

Dual stacking

Lets both IPv4 and IPv6 protocol stacks run simultaneously so that its capable of continuing on with its existing communications and running newer IPv6 communications as they’re introduced.

• Easiest migration strategy
• Upgrade devices and apps on network one at a time
• Remove old IPv4 protocol stacks as needed

6to4 tunneling

Carries IPv6 packets over a network that runs IPv4:

• Ex: IPv6 subnets that need to communicate with a WAN that you do not control
• Grabs IPv6 packet that is traveling across the network and attach an IPv4 header on the front of it
  • Requires dual-stacked routers
  • Create a tunnel, which means tell routers where the tunnel begins and ends
• NAT translation points would break the tunnel encapsulation
  • Can use Teredo, which places all tunneled traffic in UDP packets, which NAT does not inspect
  • Miredo is a very rare tunneling technique on native IPv6 linux and BSD unix machines to communicate on IPv4 internet directly without a dual-stack router or 6to4 tunnel.