IP addressing Lecture 15
IP V4 AND IPV6
Addressing is a critical function of network layer protocols e.g. IP. Addressing enables data communication between hosts, regardless of whether the hosts are on the same network, or on different networks. Both Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6) provide hierarchical addressing for packets that carry data.
CONCLUSION
An IPV4 address is made up of 4 octets. Each octet holds 8 bits. A network address identifies one network from another. Subnet masks identify which part of the IP address is the network portion of the address and which portion identifies the unique host within that network. A subnet mask and IP address are ANDED together to get the network address.
LOGICAL ANDING TO IDENTIFY NETWORK ADDRESS!
Logical AND is the comparison of two bits. Note how only a 1 AND 1 produces a 1. To identify the network address of an IPv4 host, the IPv4 address is logically ANDed, bit by bit, with the subnet mask. ANDing between the address and the subnet mask yields a network address which identifies a specific network
PUBLIC OR PRIVATE
Network Address Translation (NAT) is used to translate between private IPv4 addresses and public IPv4 addresses. This is done on the organisation's router that connects the internal network to the ISP's network. Home routers provide the same capability. For instance, most home routers assign private IPv4 addresses to their wired and wireless hosts from the private addresses of 192.168.1.0 /24 range. The home router that connects to the (ISP) network is assigned a public IPv4 address to use over the Internet.
PUBLIC OR PRIVATE
Public IPv4 addresses (external IPs) are addresses which are globally routed between ISP (Internet Service Provider) routers. However, not all available IPv4 addresses can be used on the Internet. There are blocks of addresses called private addresses that are used by most organizations to assign IPv4 addresses to private internal hosts (internal IP addresses) Private IPv4 addresses are not unique and can be used by many internal networks.
PRIVATE ADDRESSES
Specifically, the private address blocks are: 10.0.0.0 to 10.255.255.255 172.16.0.0 to 172.31.255.255 192.168.0.0 to 192.168.255.255
SUBNET MASK - 255.255.255.0
Figure 4 displays the dotted decimal address and the 32-bit subnet mask. Notice how the subnet mask is essentially a sequence of 1 bits followed by a sequence of 0 bits. To identify the network and host portions of an IPv4 address, the subnet mask is compared to a given IPv4 address bit for bit, from left to right.
SUBNET MASK USING ANDING
The 'ones' in the subnet mask identify the network portion while the zer0s identify the host portion. Note that the subnet mask does not actually contain the network or host addresses, it just tells the computer where to look for these portions in a given IPv4 address. The actual process used to identify the network and host addresses is called ANDing.
SPECIAL USER IPV4 ADDRESS
There are certain addresses that cannot be assigned to hosts e.g. 127.0.0.1 There are also special addresses that can be assigned to hosts, but with restrictions on how those hosts can interact within the network. Loopback addresses (127.0.0.0 /8 or 127.0.0.1 to 127.255.255.254) - More commonly identified as only 127.0.0.1, these are special addresses used by a host to direct traffic to itself. For example, it can be used on a host to test if the TCP/IP configuration is operational. Link-Local addresses (169.254.0.0 to 169.254.255.254) - More commonly known as the Automatic Private IP Addressing (APIPA) addresses, they are used by a Windows DHCP client to self-configure in the event that there are no DHCP servers available. Useful in a peer-to-peer connection where there is no central server. TEST-NET addresses (192.0.2.0/24 or 192.0.2.0 to 192.0.2.255) - These addresses are set aside for experimentation, teaching and learning purposes and can be used in documentation and network examples.
WHAT ARE NAT TABLE ENTRIES?
For example, when the router receives a request from a device on the private network, each data packet's "Source IP" is changed from the private IP address (e.g. 192.168.0.100) to the router's public IP address (e.g. 68.202.151.70). The router then creates an entry in its NAT table. It records the destination address of the data packet and the private (source) IP address of the packet. Once the NAT entry is created, the router pushes the data packet to the public network, to its intended destination IP address. When an outside data packet comes from the public network to the private network, the router compares it with the NAT table entries to know to which private device it's meant to go. The "Destination IP" of the data packet coming in is changed to the target device's private IP address, then pushed to the private network.
THE SUBNET MASK
As shown, three dotted decimal IPv4 addresses must be configured when assigning an IPv4 configuration on a host computer. IPv4 address - Unique IPv4 address of the host Subnet mask- Used to identify the network/host portion of the IPv4 address Default Gateway - IP Address of router. From diagram, subnet mask is 255.255.255.0 This indicates that only the last octet of the address will represent the host and the rest will be a network address.
IP MASQUERADING
IP masquerading is a technique that hides an entire IP address space, usually consisting of private IP addresses, behind a single IP address in another, usually public address space. The hidden source address of outgoing packets are changed into a single public IP address. They appear as originating not from the hidden host but from the routing device itself. The majority of NATs map multiple private hosts to one publicly exposed IP address. The router on the network will have two IP addresses assigned, one private address and a public address assigned by an ISP.
STATIC IPV4 ADDRESS ASSIGNMENT TO A HOST
Devices can be assigned an IP address either statically or dynamically. In networks, some devices require a fixed IP address. For instance, printers, servers, and networking devices need an IP address that does not change. For this reason, these devices are typically assigned static IP addresses. Hosts on the other hand can obtain IP addressing information automatically or dynamically from a DHCP server.
STRUCTURE OF IP ADDRESS
Each address consists of a string of 32 bits, divided into four sections called octets. Each octet contains 8 bits (or 1 byte) separated with a dot. For example, PC1 in the Figure 1 is assigned IPv4 address 192.168.10.10
FIGURE 1 :IP ADDRESS IN DOTTED DECIMAL
Each address consists of a string of 32 bits, divided into four sections called octets. Each octet contains 8 bits (or 1 byte) separated with a dot. For example, PC1 in the Figure 1 is assigned IPv4 address 192.168.10.10
PRIVATE ADDRESSES
It is important to know that addresses within these address blocks are not allowed on the Internet and must be filtered (discarded) by Internet routers. Note: Private addresses are defined in RFC 1918. Most organizations use private IPv4 addresses for their internal hosts. These private addresses are not routable in the Internet and must be translated to a public IPv4 address.
NAT - NETWORK ADDRESS TRANSLATION
Network address translation (NAT) is a method of remapping one IP address space into another by modifying network address information in the IP header of packets while they are in transit across a traffic routing device [wikipedia.com, 2019] All data packets include header information which includes Destination IP address and Source IP address. As traffic passes from the local network to the Internet, the source address in each packet is translated on the fly from a private address to the public address by router software. The router has the ability to track and store information regarding each active connection. When a reply returns to the router, it uses the connection tracking data it stored during the outbound phase to determine the private address on the internal network to which to forward the reply.
NETWORK AND HOST PORTIONS
The bits within the network portion of the address must be identical for all devices that reside in the same network. The bits within the host portion of the address must be unique to identify a specific host within a network. If two hosts have the same bit-pattern in the specified network portion of the 32-bit stream, those two hosts will reside in the same network. But how do hosts know which portion of the 32-bits identifies the network and which identifies the host? That is the job of the subnet mask!!!.
NETWORK AND HOST PORTIONS
Understanding binary notation is important when determining if two hosts are in the same network. IPv4 are hierarchical addresses made up of a network portion and a host portion. When determining the network portion versus the host portion, it is necessary to look at the 32-bit stream. Within the 32-bit stream, a portion of the bits identify the network, and a portion of the bits identify the host as shown in the Figure 4.
