What is IHL field of an IP packet, and how is it specified? How many bits are in

Question

What is IHL field of an IP packet, and how is it specified?

How many bits are in a IP address?

What is the TTL field of a IP packet? How is it modified and what happens when it is 0?

How many octets are in a header of an IP packet that has no options?

What is the protocol field going to be if the layer 4 payload of an IP packet is UDP?

If the protocol field is set to 1 in an IP datagram, what is the protocol of the payload of the IP datagram?

What part of the IP datagram is the checksum calculated for?

If you are told a host has an address of 64.17.33.2, but no other information, can you determine the network number and netmask of the network it is on?

If you are told a host has an address of 81.245.17.30/24, what is that hosts:

Network?

Netmask in dotted quad format?

If you are told a host has an address of 131.94.133.86/26, what is that hosts:

Network?

Netmask in dotted quad format?

If you are told a host has an address of 199.66.128.15/16, what is that hosts:

Network?

Netmask in dotted quad format?

If you are told a host has an address of 204.77.144.9/30, what is that hosts:

Network?

Netmask in dotted quad format?

If you are told a host has an address of 198.32.252.201/28, what is that hosts:

Network?

Netmask in dotted quad format?

A host has and address of 131.91.161.12 and a netmask of 255.255.255.128. What is the network the host is on, and the directed broadcast address for the network?

What IP addresses are available to assign to hosts on the network 128.227.116.0/24?

What IP addresses are available to assign to hosts on the network 129.171.160.0/19?

If you have been assigned a network of 66.88.64.0/20 and you want to divide it into subnets of 128 address (126 hosts), what would the new netmask be? What would be an example of one of the subnets addresses, including the new netmask.

Explanation / Answer

1.Talking about IPv4 this is the 4th version of internet protocol and it is represented in 32-bit integer value. It basically consists of 4 octets of address.

So for example

69.81.31.226

So writing it the binary form this comes out to be a 32-bit number:

01000101.01010001.00011111.11100010

So there are basically 4 octets:

1st octet- 01000101

2nd octet- 01010001

3rd octet- 00011111

4rth octet- 11100010

So the last 4 bits of the 1st octet is called IHL or Internet Header Length. This field specifies the size of the header and its minimum value is 5

2. An IPv4 address consists of 32 bits for example :

69.81.31.226 - 01000101.01010001.00011111.11100010 (4 Octets and 8 bit in each of them == 32 Bits)

An IPv6 address consists of 128 bits:

2001:0db8:0a0b:12f0:0000:0000:0000:0001

3.Again using the above IPv4 Example:

69.81.31.226 - 01000101.01010001.00011111.11100010

1st octet- 01000101

2nd octet- 01010001

3rd octet- 00011111

4rth octet- 11100010

The 1st 8 bits specify time to live(TTL) it is an 8-bit number. This field indicates the maximum time the datagram is allowed to remain in the internet system The time is measured in units of seconds. If this TTL field contains the value 0, then the datagram must be destroyed.

4. If the Internet Header Length is less than 5 then there is no option in the IP Packet.

5. In case the 4 layer payload is UPD or User Datagram Protocol which helps in transmitting Voice and video traffic than the Protocol number used is 17. It is a transport layer protocol.

6. If the protocol field is set to 1 in IP Adress then ICMP Protocol is followed. It is used by network devices, including routers, to send error messages and operational information.

7. Header checksum is calculated for the last 16-bits of an IP address. It is basically used at the router end to verify the packet if the checksum doesn't match the packet is discarded.

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