Explaining IPv4 Addressing

# Explain IPv4 Addressing Schemes How does layer 3 prepare a packet to go through layer 2 ## IPv4 Datagram Header (layer 3) & routing ![[Pasted image 20230518081856.png]] - version - length - Protocol - Protocol type in datagram payload - Transmission Control Protocol (TCP) - User data gram protocol (UDP) - Internet Control message protocol (ICMP) - TCP - tranmission control protocol - each packet is checked and then reciever tells sender it has been received and verified - retransmits corrupt packets - file transfers - UDP - no handshakes - used for broadcasting - no retransmit ## IPv4 Address Format the network ID is the first 3 octets **192.168.1**.3 The host ID is the last number 192.168.1.**3** - 32-bit IPv4 - `11000110001010010001000000001001` (32 numbers) - Divide into octets (8 bits) - `11000110 00101001 00010000 00001001` - Convert each octet to dotted decimal notation - 192.51.100.1 for example for the IP 192.168.1.3 - `11000000 10101000 00000001 00000011` - convert each octet to binary decimal - `11000110001010010001000000001001` - 32 bit IP encoded https://www.browserling.com/tools/ip-to-bin | __ | __ | __ | __ | __ | __ | __ | __ | | --- | --- | --- | --- | --- | --- | --- | --- | | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 | ## Subnet Mask the subnet mask represents the network ID (255) . The host ID is represented by a 0 - accompanies IP address to reveal the network ID part - Binary 1 in the mask indicates corresponding bit is part of the network ID - Dotted Decimal mask or network prefix (slash notation) - Default masks align to octet boundaries - divide an IP network into multiple IP subnets - Designate some host bits as subnet ID bits - Subnet masks only used within the IP network ## Host address ranges The number of host bits determins available addresses - The first address is reserved for the network - the last address is reserved for broadcast **192.168.1**.10 /24 - the network ID - the /24 says on the last octet (.10) there are 254 possible addresses (different hosts) - /24 also denotes that the first 24 bits are the subnet mask The subnet design fits requirements for number of subnets and hosts per subnet ![[IPv4CIDR.png]] # Explain IPv4 Forwarding ## Layer 2 vs Layer 3 addressing and Forwarding ![[Pasted image 20230518085243.png]] ## IPv4 Default Gateways - Compare destination and source address against mask - Local delivery over ethernet uses Address Resolution Protocol (ARP) - Remote delivery sent to the default gaetway for forwarding - configured as entry in host's local routing table - host uses ARP to locate gateway host on local network - Default gateway is a router - routers hold paths to multiple networks - paths configured statically or learned using a dynamic routing protocol ## Address resolution protocol works at layer 2. it works with switches. Finds / locates DHCP server. - when 2 hosts communicate over ethernet using TCP/IP an IP is used at the network layer to identify each interface. - if the destination address is on a remote network, then the local host must use the default gateway to forward the packet ## Unicast and Broadcast addressing - unicast is when packets are directed to a single destination IP address 1-1 - Broadcast packet is directed to all interfaces in the local IP network. it will fill all the ports on the switch - layer 3 broadcast domain - each broadcast domain is isolated to its own port on a switch - Delivered at layer 2 by broadcast MAC - Map layer 3 broadcast domains to layer 2 broadcast domains - routers do not typically for ward broadcasts ## Multicast and Anycast Addressing - Multicast (almost like broadcast, but instead of going everywhere it goes to the group) - hosts join a multicast group - Internet group management protocol (IGMP) - IPv4 multicast delivery uses special address ranges - Delivery at layer 2 - Anycast (almost like a unicast) - Group of hosts configured with the same IP address - Router forwards to one node only based on prioritization algorithm - used for load balancing and service failover - randomizes who that one person its sent to is examples of where each of these are used # Configure IP Networks and Subnets ## Virtual LANs and Subnets - they limit the number of hosts within broadcast domain to improve performance. - In its default config every port on a switch is on the same local segment. (you can see each other) - any host within the same local segment (same network ID, subnet etc...) can see/talk to each other if too many hosts attached are attached to the same switch, broadcast traffic can become excessive and reduce performance. - VLANs at layer 2 are a means of addressing this issue... - each VLAN is a separate broadcast domain apart from breaking up broadcast domains, subnets can be used to achieve other network design goals: - many organizations have more then 1 site with WAN links between them. The WAN link normally forms a separate subnet - useful to divide a network into logically distinct zones for security and admin control - networks that use different physical and data link technologies, such as Token ring and ethernet, should be logically separated as different subnets. ## Classful addressing IP network and subnet IDs using masks or network prefixes -- this is classless addressing.... (what we have been previously talking about) **CLASSFUL** addressing scheme allocates a network ID based on the first octet of the IP address. This is the old way. Classless is the better way. ![[Pasted image 20230518095429.png]] FIRST OCTET CLASS CIDR 1–126 Class A /8 128–191 Class B /16 192–223 Class C /24 ## Public Vs Private Addressing **These below are private ranges and cannot route over the internet** - 10.0.0.0 to 10.255.255.255 (Class A private address range). - 172.16.0.0 to 172.31.255.255 (Class B private address range). - 192.168.0.0 to 192.168.255.255 (Class C private address range). This is governed by IANA and assigned by regional registries and ISPs Hosts on the private network use NAT to access the internet - **Automatic private IP addressing (APIPA)** - means for clients that could not connect to a DHCP server to commuinicate on the local network anyway. - If a windows host does not receive a response from DHCP within a specific amount of time it selects an IP from the below range - **169.254.1.1 thru 169.254.254.254** ## Other reserved address ranges - Class D multicast range - 224.0.0.0 through 239.255.255.255 - Class E experimental range - 240.0.0.0 through 255.255.255.255 - Loopback range - 127.0.0.0 to 127.255.255.255 - Other - 0.0.0.0/8 (address unknown) - 100.64.0.0/10, 192.0.0.0/24, 192.88.99.0/24, 198.18.0.0/15 (special usage) - 192.0.2.0/24, 198.51.100.0/24, 203.0.113.0/24 (documentation and examples) - 255.255.255.255 (subnets, CANT USE AS IP) ## IPv4 Address Scheme Design - Consider - Whether you need a public or private addressing scheme - how many networks and subnets you need - how many hosts per subnet - Addressing rules - network ID must be from valid range - network and/or host IDs cannot be all 1s or 0s - Host ID must be unique in the subnet - Network ID must be unique - on the internet (in a public addressing scheme) - on your internal system of networks (in a private addressing scheme) - Calculate how many subnets are needed - Round up to nearest power of 2 - Exponent (the value of n in 2n) is how many bits to add to the default network prefix - Check subnets allow sufficient hosts (2n-2 where n is host bits) - Calculate the subnets - For the first subnet ID, deduct the least significant octet in the mask from 256 - For the next subnet ID, find the lowest subnet value higher than the previous one - Calculate the host ranges for each subnet - For the first host, add a binary 1 to the subnet address - For the last host, deduct two binary digits from the next subnet’s ID ## Math problem to find the subnet 2n-2