Bits and Bytes of Computer Networking (Week 2)

on many modern networks, you can connect a new device and an IP address will be assigned to it automatically through a technology known as ?

- Dynamic Host Configuration Protocol. (DHCP) - An IP address assigned this way is known as a dynamic IP address. - The opposite of this is known as a static IP address, which must be configured on a node manually. - In most cases, static IP addresses are reserved for servers and network devices, while dynamic IP addresses are reserved for clients

How is the address class system defined?

- The address class system is a way of defining how the global IP address space is split up. - address classes give us a way to break the total global IP space into discrete networks.

The Time to Live or TTL field.

- This field is an 8-bit field that indicates how many router hops a datagram can traverse before it's thrown away. - Every time a datagram reaches a new router, that router decrements the TTL field by one. Once this value reaches zero, a router knows it doesn't have to forward the datagram any further. - The main purpose of this field is to make sure that when there's a misconfiguration in routing that causes an endless loop, datagrams don't spend all eternity trying to reach their destination.

In our breakdown of an Ethernet frame, we mentioned a section we described as the data payload section how does it relate to IP datagram?

- We mentioned a section we described as the data payload section. This is exactly what the IP datagram is, and this process is known as encapsulation. - The entire contents of an IP datagram are encapsulated as the payload of an Ethernet frame.

a properly formatted IP header how many space do you need to fill yours data .

20 bytes is the minimum length of an IP header.

Address Resolution Protocol (ARP)

ARP is a protocol used to discover the hardware address of a node with a certain IP address. Once it IP datagram has been fully formed, it needs to be encapsulated inside an Ethernet frame. This means that the transmitting device needs a destination MAC address to complete the Ethernet frame header. - Almost all network-connected devices will retain a local ARP table. - An APR table is just a list of IP addresses and the Mac addresses associated with them. ARP table entries generally expire after a short amount of time to ensure changes in the network is accounted for.

this class system has mostly been replaced by a system known as?

CIDR or classless inter-domain routing

There are three primary types of address classes

Class A, Class B, and Class C. - Class A addresses are those where the first octet is used for the network ID and the last three are used for the host ID. - Class B addresses are where the first two octets are used for the network ID, and the second two are used for the host ID. - Class C addresses are those where the first three octets are used for the network ID, and only the final octet is used for the host ID. 123.456.780.00

An example of an IP address

For example, 12.30.56.78 is a valid IP address, but 123.456.789.100 would not be because it has numbers larger than could be represented by 8 bits. This format is known as dotted decimal notation.

How many numbers does an IP addresses have?

IP addresses are 32 bit long numbers made up of four octets, and each octet is normally described in decimal numbers. 8 bits of data or a single octet can represent all decimal numbers from 0 to 255.

So your laptop will always have the same MAC address no matter where you use it, but it will have a different IP address assigned to it at an Internet cafe than it would when you're at home, Why?

IP addresses belong to the networks, not the devices attached to those networks.

The maximum size of the 16-bits IP datagram is?

IP datagrams have a maximum size and this field indicates the size of an individual datagram, the maximum size of a single datagram is the largest number you can represent with 16 bits: 65,535. If the total amount of data that needs to be sent is larger than what can fit in a single datagram, the IP layer needs to split this data up into many individual packets. When this happens, the identification field is used so that the receiving end understands that every packet with the same value in that field is part of the same transmission.

IP options field.

IP options field. This is an optional field and is used to set special characteristics for datagrams primarily used for testing purposes.

The next after Header Length field is?

Service Type field. - These eight bits can be used to specify details about quality of service or QoS technologies. - The important takeaway about QoS is that there are services that allow routers to make decisions about which IP datagram may be more important than others.

Subnet IDs are calculated via what's known as a subnet mask.

Subnet IDs are calculated via what's known as a subnet mask.

padding field.

The IP options field is usually followed by a padding field. Since the IP options field is both optional and variable in length, the padding field is just a series of zeros used to ensure the header is the correct total size.

two closely related fields are?

The flag field and the Fragmentation Offset field.

Explain the flag field

The flag field is used to indicate if a datagram is allowed to be fragmented, or to indicate that the datagram has already been fragmented.

The fragmentation offset field

The fragmentation offset field contains values used by the receiving end to take all the parts of a fragmented packet and put them back together in the correct order.

The next field after 16-bit is?

The identification field is a 16-bit number that's used to group messages together.

What is the important thing to know about IP addresses

The important thing to know for now is that IP addresses are distributed in large sections to various organizations and companies instead of being determined by hardware vendors. This means that IP addresses are more hierarchical and easier to store data about than physical addresses are.

The next field is a

The next field is a 16-bit field, known as the Total Length field. It's used to indicate the total length of the IP datagram it's attached to.

Protocol field.

This is another 8-bit field that contains data about what transport layer protocol is being used.

how do both Mac addresses are used at the data link layer, and IP addresses are used at the network layer relate to each other.

Through the use of Address Resolution Protocol (ARP)

The first data in an IP datagram Header is?

Version Field The very first field is four bits, and indicates what version of an Internet protocol is being used. The most common version of IP is version four or IPv4.

The Class A network has millions of individual IPs, how does the gateway router connect to that many devices with the same router?

With subnets you can split your large network up into many smaller ones. These individual subnets will all have their own gateway routers serving as the ingress and egress point for each subnet.

Under the IP protocol, a packet is usually referred to as ?

an IP Datagram. Just like any Ethernet frame, an IP datagram is a highly structured series of fields that are strictly defined.

SUBNETTING

subnetting is the process of taking a large network and splitting it up into many individual smaller subnetworks or subnets.

After the version field, we have the?

the Header Length field. This is also a four-bit field that declares how long the entire header is.

The two primary sections of an IP datagram are?

the Header and the Payload.

two very important fields are?

the Source and Destination IP address fields. Remember that an IP address is a 32-bit number so, these fields are each 32 bits long.

the header checksum field.

the header checksum field. This field is a checksum of the contents of the entire IP datagram header.

IP addresses can be split into two sections namely?

the network ID and the host ID. an example IP address of 9.100.100.100, the network ID would be the first octet, and the host ID would be the second, third, and fourth octets.

How to communicate with IP address?

to communicate with the IP address 9.100.100.100, core routers on the Internet recognize the IP 9.0.0.0 as a Class A Network. They then route the message to the gateway router responsible for the network by looking at the network ID. A gateway router specifically serves as the entry and exit path to a certain network.