IP help please. An IP datagram has arrived with the following information in the
ID: 3810875 • Letter: I
Question
IP help please.
An IP datagram has arrived with the following information in the header (in hex). All answers must be in DECIMAL.
45 00 00 54 00 03 00 00 20 06 00 00 7B 4E 03 02 B4 0E 0F 55
Are there any options?
Is the packet fragmented?
What is the size of the payload?
Is a checksum used?
How many more routers can the packet travel to?
What is the identification number of the packet?
What is the type of service?
Calculate the Checksum for the following IPv4 Header.
Note: The values given for each field are in decimal number format. The checksum value must be in HEX.
4
5
0
28
1
0
0
4
17
0
12.101.14.5
10.6.10.240
4
5
0
28
1
0
0
4
17
0
12.101.14.5
10.6.10.240
Explanation / Answer
4500 0054 0003 0000 2006 0000 7B4E 0302 B40E 0F55
Here, initial 4 corresponds to IP version and 5 to header length.
Actual header length is 5*4 =20 bytes (since it is described in 4 bytes words)
Next 00 -> type of service, this value indicates a normal operation
Next 0054 -> total length field of ip header. 84 (since in decimal)
0003 -> identification field
0000 -> divided into 3 bits flags and 13 bits as fragment offset
2006 -> first 20 gives TTL field (time to live) and 06 to protocol filed of header, which indicates protocol is TCP
0000 -> this is checksum which is set to zero while computing at destination end.
7B4E -> source ip address
Types of service used is TCP (since 06 is used in 2006)
45 00 00 54 00 03 00 00 20 06 00 00 7B 4E 03 02 B4 0E 0F 55
4500
+0054
----------
4554
+ 0003
-----------
4557
+ 0000
---------
4557
+2006
---------
6563
+0000
--------
6563
+7B4E
--------
e0b1
+ 0302
--------
E3B3
+B40E
---------
197C1 -> discard 1
97C1
+0F55
--------------
A716 checksum
--------------
Since TTL field is 20, so header can travel to 20 more router until final destination is reached.
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