Given that I'm on a local network, if I can capture a ICMP echo request packet, and considering that I want to spoof a echo reply, what part of the original packet would I need to change supposing I make a copy of the original before i send it back? I'm guessing the IP header would need to change, (the destination IP of the original would become the source, and vice versa) as well as the ICMP header (the type would need to change to ECHO_REPLYPACKET). But besides those 2 are there any others?
Quoting RFC 792 :
Echo or Echo Reply Message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+-
To form an echo reply message, the source and destination addresses
are simply reversed, the type code changed to 0, and the checksum
recomputed.
Identifier and Sequence Number must be 0 as well.
RFC 1071 shows you how to calculate the Checksum
Related
I have data in Stata regarding the feeling of the current situation. There are seven types of feeling. The data is stored in the following format (note that the data type is a string, and one person can respond to more than 1 answer)
feeling
4,7
1,3,4
2,5,6,7
1,2,3,4,5,6,7
Since the data is a string, I tried to separate it by
split feeling, parse (,)
and I got the result
feeling1
feeling2
feeling3
feeling4
feeling5
feeling6
feeling7
4
7
1
3
4
2
5
6
7
1
2
3
4
5
6
7
However, this is not the result I want. which is that the representative number of feelings should go into the correct variable. For instance.
feeling1
feeling2
feeling3
feeling4
feeling5
feeling6
feeling7
4
7
1
3
4
2
5
6
7
1
2
3
4
5
6
7
I am not sure if there is any built-in command or function for this kind of problem. I am thinking about using forval in looping through every value in each variable and try to juggle it around into the correct variable.
A loop over the distinct values would be enough here. I give your example in a form explained in the Stata tag wiki as more helpful and then give code to get the variables you want as numeric variables.
* Example generated by -dataex-. For more info, type help dataex
clear
input str13 feeling
"4,7"
"1,3,4"
"2,5,6,7"
"1,2,3,4,5,6,7"
end
forval j = 1/7 {
gen wanted`j' = `j' if strpos(feeling, "`j'")
gen better`j' = strpos(feeling, "`j'") > 0
}
l feeling wanted1-better3
+---------------------------------------------------------------------------+
| feeling wanted1 better1 wanted2 better2 wanted3 better3 |
|---------------------------------------------------------------------------|
1. | 4,7 . 0 . 0 . 0 |
2. | 1,3,4 1 1 . 0 3 1 |
3. | 2,5,6,7 . 0 2 1 . 0 |
4. | 1,2,3,4,5,6,7 1 1 2 1 3 1 |
+---------------------------------------------------------------------------+
If you wanted a string result that would be yielded by
gen wanted`j' = "`j'" if strpos(feeling, "`j'")
Had the number of feelings been 10 or more you would have needed more careful code as for example a search for "1" would find it within "10".
Indicator (some say dummy) variables with distinct values 1 or 0 are immensely more valuable for most analysis of this kind of data.
Note Stata-related sources such as
this FAQ
this paper
and this paper.
I'm studying about dns and would like to understand about this information, because I could not fully understand.
The header contains the following fields:
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR| Opcode |AA|TC|RD|RA| Z | RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| QDCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ANCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| NSCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ARCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
I would to know what mean this numbers on top.
The numbers across the top are simply the bit numbers within the 16 bit word, although as is common with the RFC series of documents they're ordered from most significant bit to least, instead of the (more intuitive) other way around.
So, for example, given an array data of octets containing that header, the ID would be:
(data[0] << 8) | data[1]
and the QR bit would be the most significant bit of data[2]
everyone. I have some questions about sorting in bash. I am working with Ubuntu 14.04 .
The first question is: why if I have file some.txt with this content:
b 8
b 9
a 8
a 9
And when I type this :
sort -n -k 2 some.txt
the result will be:
a 8
b 8
a 9
b 9
which means that the file is sorted first to the second field and after that to the first field, but I thought that is will stay stable i.e.
b 8
a 8
...
...
Maybe if two rows are equal it is applied lexicographical sort or what ?
The second question is: why the following doesn`t working:
sort -n -k 1,2 try.txt
The file try.txt is like this:
8 2
8 11
8 0
8 5
9 2
9 0
The third question is not actally for sorting, but it appears when I try to do this:
sort blank.txt > blank.txt
After this the blank.txt file is empty. Why is that ?
Apparently GNU sort is not stable by default: add the -s option
Finally, as a last resort when all keys compare equal, sort compares entire lines as if no ordering options other than --reverse (-r) were specified. The --stable (-s) option disables this last-resort comparison so that lines in which all fields compare equal are left in their original relative order.
(https://www.gnu.org/software/coreutils/manual/html_node/sort-invocation.html)
There's no way to answer your question if you don't show the text file
Redirections are handled by the shell before handing off control to the program. The > redirection will truncate the file if it exists. After that, you are giving an empty file to sort
for #2, you don't actually explain what's not working. Expanding your sample data, this happens
$ cat try.txt
8 2
8 11
9 2
9 0
11 11
11 2
$ cat try.txt
8 2
8 11
9 2
9 0
11 11
11 2
I assume you want to know why the 2nd column is not sorted numerically. Let's go back to the sed manual:
‘-n’
‘--numeric-sort’
‘--sort=numeric’
Sort numerically. The number begins each line and consists of ...
Looks like using -n only sorts the first column numerically. After some trial and error, I found this combination that sorts each column numerically:
$ sort -k1,1n -k2,2n try.txt
8 2
8 11
9 0
9 2
11 2
11 11
I have a following shell script
RETVAL=`sqlplus -silent user/password <<EOF
SET PAGESIZE 9990
SELECT id, type, count(*) "count" FROM event
EXIT;
EOF`
echo $RETVAL
it output like
ID TYPE count ------------- ---------- ----------- 2 11 2 1 4 1 2 10 29 1 1 35 2 1 6 2 18 1 2 2 3 7 rows selected
But i want output like
ID TYPE count
------------- ---------- -----------
2 11 2
1 4 1
2 10 29
1 1 35
2 1 6
2 18 1
2 2 3
7 rows selected.
I tried to figure out if i get some new line character but couldnt find it.
Regards,
Your variable contains the newlines, but the way you're displaying it removes them.
Replace the echo statement with:
echo "$RETVAL"
The shell won't mess with the newlines then. You should pretty much always quote variables that can contain any form of whitespace that needs to be preserved.
I'm implementing a DNS(multicast DNS in fact) in c#.
I just want to know if I must encode my uint/int/ushort/... with the LSB on the left or the MSB on the left. And more globally how I could know this? One of this is standard?
Because I didn't found anything in the IETF description. I found a lot of things(each header field length, position), but I didn't found this.
Thank you!
The answer is in RFC 1035 (2.3.2. Data Transmission Order)
Here is the link: http://www.ietf.org/rfc/rfc1035.txt
And the interesting part
2.3.2. Data Transmission Order
The order of transmission of the header and data described in this
document is resolved to the octet level. Whenever a diagram shows a
group of octets, the order of transmission of those octets is the
normal order in which they are read in English. For example, in the
following diagram, the octets are transmitted in the order they are
numbered.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 3 | 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | 6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Whenever an octet represents a numeric quantity, the left most bit in
the diagram is the high order or most significant bit. That is, the
bit labeled 0 is the most significant bit. For example, the following
diagram represents the value 170 (decimal).
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|1 0 1 0 1 0 1 0|
+-+-+-+-+-+-+-+-+
Similarly, whenever a multi-octet field represents a numeric quantity
the left most bit of the whole field is the most significant bit.
When a multi-octet quantity is transmitted the most significant octet
is transmitted first.