Question

Show work please, this is the last problem for my homework and I cannot figure this out for the life of me

An IP4 datagram arrived with the following information in the header (in hexadecimal):

               0x4A 00 00 56 00 03 58 50 18 06 58 50 7C 4E 03 02 B4 0E OF 15 2f……….

1. Are there any options? How many bytes, if any?
2. How many more routers can the packet travel to? Explain.
3. What is the size of data only?
4. What is the destination IP address expressed in decimal notation?
5. What is the value of the checksum in hexadecimal?
6. What is the source IP address (in dotted decimal format)?

Answer 1

Let us first find the value of header fields before answering the questions:

Given-0x4A 00 00 56 00 03 58 50 18 06 58 50 7C 4E 03 02 B4 0E 0F 15 2f……….

VER = 0x4 = 4

HLEN =0xA = 10 * 4 = 40 bytes

Service =0x00 = 0 (Normal/routine)

Total Length = 0x0056 = 86 bytes

Identification = 0x0003 = 3

Flags and Fragmentation = 0x5850  D = 1 M= 0 offset = 6224

Time to live = 0x18 = 24

Protocol = 0x06 = 6

Checksum = 0x5850=(0101 1000 0101 0000) 1s complement(1010 0111 1010 1111)

Source Address: 0x7C4E0302 =7C:4E:03:02 =124.78.3.2

Destination Address: 0xB40E0F15 = B4:0E:0F:15=180.14.15.13

a. Are there any options? How many bytes, if any?

Yes

In an IPv4 packet, the value of HLEN is 1010 in binary The HLEN value is 10, which means the total number of bytes in the header is 10 × 4, or 40 bytes. The first 20 bytes are the base header, the next 20 bytes are the options.

b. How many more routers can the packet travel to? Explain.

Since the value of time to live = 24, the packet may visit up to 24 routers.

c. What is the size of data only?

Total Length= Length of header + Data (16 bits)

            Data=86-20

Data=66bytes

d. What is the destination IP address expressed in decimal notation?

180.14.15.13

e. What is the value of the checksum in hexadecimal?

Without 1s compliment 5850

With A7AF

f. What is the source IP address (in dotted decimal format)?

124.78.3.2