Questions tagged [tcpdump]
a command line packet analyzer
234
questions
1
vote
0answers
12 views
tcpdump: why ack number greater than sack number?
I use tcpdump to troubleshot network problem, and found one record that ack number is greater than sack number:
Why ack number greater than sack number?
0
votes
1answer
35 views
What is Fedora doing in this TCPdump?
So I decided to have tcpdump listen on port 80 because I use HTTPS whenever possible, and thought there shouldn't be anything there. Well, there was. I can see that one of these connections is the ...
1
vote
1answer
82 views
How to use tcpdump safely (-Z option vs file capabilities / setcap)?
I am evaluating, how tcpdump can be used in a safer manner with as few as possible privileges. Two possibilities:
1. -Z option
If tcpdump is running as root, after opening the capture device or input ...
0
votes
0answers
38 views
Connection reset by peer errror when delaying network response packets
Client's side code written in redis-plus-plus
int main(){
auto redis = Redis("tcp://192.168.122.50:6379);
sleep(5);
int ep = 100;
while(true){
cout<<"==============...
0
votes
1answer
65 views
tcpdump -G option for rotation
I would like to rotate the tcp dump saving every 100mS.
Hence I am trying the following option:
tcpdump -i eth0 -G 0.1 -w '.pcap'
This dumps all the incoming data into file and do not rotate every ...
0
votes
0answers
84 views
tcpdump shows real local IP address instead of localhost IP (127.0.0.1)?
I have a small question about tcpdump. I have a laptop with Fedora31 and I wanted to check a network traffic on the local network interface. I run tcpdump -nni lo -vvv -s 0 -l port 88 and I was able ...
0
votes
0answers
32 views
ARP Response Is Being Ignored
I am having issues trying to set up bi-directional connectivity between a virtual machine and my host computer. I can connect via "console", but I would like to be able to connect to and ...
0
votes
0answers
15 views
Why is TCPDUMP unable to write in my android device?
I rooted the phone and use tcpdump from termux (the bin was already in android)
tcpdump -help
prints the normal options for tcpdump: basically the whole alphabet including the -w option.
When I do:
...
-1
votes
1answer
30 views
tcpdump displaying no output
I'm currently learning tcpdump and having trouble understanding it. When I type:
sudo tcpdump
It has all traffic going in and out of my machine. How would I apply this to listening to everything on my ...
0
votes
1answer
125 views
What is the filter expression to only sniff ICMP packets?
What is the filter expression to only sniff ICMP packets given the source IP address is 18.23.54.78 and the destination IP address is 12.67.24.89? The filter order must start with the protocol name ...
0
votes
2answers
102 views
Filter tcpdump output (PCAP)
The following is the output from my PCAP file.
20:02:52.306161 192.162.70.150.58078 > 192.179.91.61.1194: P 635362993:635363048(55) ack 2046024708 win 4373 <nop,nop,timestamp 52993632 1059054949&...
0
votes
1answer
92 views
filter by incoming ip v4 packets with tcpdump
I want to filter with TCPDUMP only incoming and ip v4 packets.
tcpdump -i eth0 inbound and ip -w res.pcap give me incoming packets with ipv4 and ipv6
How can I filter by ipv4 only?
1
vote
1answer
224 views
Using tcpdump to trace IP of strangers(predators) on omegle
I am using tcpdump to capture packets while being on omegle. However, I have been fairly unsuccessful to get strangers IP. All the IP I see are traced back to either 172...* which is for google 104....
0
votes
0answers
41 views
Why do my Send-Q keep getting loaded but nothing come out of it?
I'm currently diagnosing a issue related to packet forwarding. I forward link layer packets to B network namespace and I found that B network namespace didn't reply to them, but I could curl and view ...
1
vote
1answer
92 views
How to extract domains related to “Client Hello” in a pcap file
I have a tcpdump (pcap) capture file and want to extract all domains. I do it with the following command:
strings capture_file | grep -oiE '([a-zA-Z0-9][a-zA-Z0-9-]{1,61}\.){1,}(\.?[a-zA-Z]{2,}){1,}' |...
1
vote
0answers
89 views
non promiscuous option in tcpdump
Strangely, depending on the program in which it is included, the tcpdump command used with the -p option (which should say "don't use promiscuous mode") nevertheless switches it on during ...
0
votes
1answer
20 views
capturing and analyzing packages through Raspberry Pi 4
So I am a beginner to RP4.
I am trying to learn more about network security using the Raspberry Pi 4.
I managed to set up the raspberry pi 4 as an access point. I am able to connect my personal laptop ...
1
vote
2answers
36 views
How can I forward output from one terminal to another server where I can use grep?
I need to run tcpdump on some switch and pass it through grep with advanced regexp. That switch shell ist quite stupid and there is no grep with regexp but there is a tcpdump with the options I need.
...
0
votes
0answers
87 views
Diagnosing packets dropped by bond0 interface
I recently setup Netdata on my home server, and observed the following behaviour on bond0:
It would seem that, rather consistently, about 60 inbound packets are dropped every 10 minutes. This ...
3
votes
1answer
655 views
I installed tcpdump, but it is showing command not found while using it
Also I used whereis & which command to check if the package exists
and it does exist.
0
votes
1answer
96 views
Timed tcpdump: pipe is slow
What I actually want to do is measure tcpdump for 10s.
$ timeout 10s tcpdump > my.log
but I found there has only a short period actually being logged, instead of whole 10s.
therefore I did this ...
0
votes
0answers
56 views
Incoming packet was garbled on decryption
I'm using Mobaxterm (SSH to a local VM), and I'm always disconnected with the following error :
Incoming packet was garbled on decryption
How can I fix that ?
Note : It happened when I was using ...
0
votes
0answers
6 views
In tcpdump how do I know if I'm using a port-type or port-expression type?
I came across an example of using tcpdump see below:
tcpdump port 3398
tcpdump src port 1025
And I don't know how to tell if I'm using a port-type or a port-expression-type
I know what tcpdump does,...
0
votes
2answers
92 views
Why there are a lot of packets not related to my IP been captured with tcpdump ? (Centos 7)
Tcpdump running by :
/usr/sbin/tcpdump -U -n -i eth0 icmp or tcp dst port 22 or tcp dst port
When I review the captured data , it shows :
132.132.211.221.40372 > 89.31.125.17.ssh: Flags [S], ...
-1
votes
1answer
50 views
Can “dumb” ethernet hub device be used for breaking security on Ethernet cable connection? [closed]
Many people will still know about those old ethernet "hub"-devices - also called "dumb" device or "Ethernet signal concentrator". Did anyone ever try to "listen to ANY traffic" on such port through an ...
0
votes
1answer
269 views
Get the user-agent from tcpdump
I'm working on a monitoring application for my home gateway and I want to know the device type of all connected clients. For that purpose I'm using tcpdump to extract the user-agent of all devices
...
0
votes
1answer
100 views
tcpd, inetd/rinetd and iptables
What is the correlation between these programs?
tcpd and inted/rinetd are very old but despite this they are still present in many distributions ... why?
And there is also a correlation between hosts....
1
vote
1answer
765 views
tcpdump traffic in network namespaces in `net=host` dockercontainer
I am trying to capture a tcpdump of a set of processes running in the mininet network emulation framework.
Mininet works by putting each process/set of processes into its own network namespace and ...
1
vote
5answers
139 views
sed/awk: replace numbers in a line after last occurance of '.'
I have the following tcpdump stream:
Current:
07:36:03.848461 IP 172.17.3.41.33101 > 172.17.3.43.17408: UDP, length 44
07:36:03.848463 IP 172.17.3.42.33101 > 172.17.3.43.17409: UDP, length 44
...
0
votes
1answer
112 views
Determine program responsible for periodic short-lived network connections
I am interested in learning the proper procedure to determine which Linux program / process is responsible for a given short-lived network connection which repeats periodically.
Without making any ...
0
votes
1answer
79 views
Traffic into lo vs eth, why might I be seeing only half the traffic on lo compared to eth?
I am forwarding traffic to ports on eth0 and lo.
For the same traffic at the same ports and different ports, when I do a tcpdump and count the packets, for time t, I only see about half the number of ...
0
votes
1answer
109 views
network behaviour with tcpdump
We are developing communication interface converter which is running Linux.
The unit may receive unicast or multicast IP and converts it to some other physical layer. On the other hand, the unit ...
3
votes
1answer
17k views
How can I capture all the UDP packets using tcpdump?
I have to capture all the UDP packets sent from host A to any UDP port of host B. The following, if run on host B, doesn't work.
$ sudo tcpdump -i eth0 -SX udp src <hostA>
tcpdump: 'udp' ...
-1
votes
1answer
262 views
Supress TCPDump output and show only the unique entries
I am trying to execute a tcpdump command which to show me only the unique entries. This is my command and the output:
$ sudo tcpdump -c 5 -q -i eno1 -nn -vvv tcp | sort | uniq
tcpdump: listening on ...
1
vote
0answers
186 views
How to measure software + hardware latency using tcpdump? ( Hw Timestamp)
I have an low latency application.But it's performance is unstable. So i want to find the bottleneck if it's related to network or related to my server ( software , os etc.)
So first i tried tcpdump ...
1
vote
1answer
170 views
What does it mean if requests from a blocked IP do not show up on tcpdump?
I have a VPS with Ubuntu 16.0.4 installed on it. Every time I connected to it through SSH, the next times I attempted to connect would end up in time out errors along with any other kind of connection ...
2
votes
1answer
182 views
How to know the interface from which we received a ping request
I know how to ping to a specific interface using the -I option. I want to know the interface through which I received the ping. I tried to use tcpdump for this but I cannot get any details. I can ...
3
votes
2answers
792 views
Tc qdisc delay not seen in tcpdump recording
I have two linux containers connected with a veth-pair. At veth-interface of one container I set up tc qdisc netem delay and send traffic from it to the other container. If I watch traffic on both ...
1
vote
1answer
1k views
tcpdump -z postrotate-command with shell script
I'm struggling to see where I am going wrong on trying to run a shell script with the -z flag for tcpdump. There does not seem to be a lot of/any examples of this flag being used. In the man page they ...
0
votes
2answers
5k views
How to record only the header info when using `tcpdump`
When running the following command
tcpdump -i deviceName 'host 1.2.3.4' -q -w /mypath/dump.pcap
the dump file contains a huge amount of data because there's a lot of traffic. However, I only need ...
2
votes
2answers
4k views
How to capture WOL packets?
I used
sudo tcpdump -v -i eth0 ether proto 0x0842 or udp port 9
but didn't see anything when WakeMeOnLan from NirSoft wakes the computer.
The same with Wireshark
0
votes
1answer
402 views
tcpdump usbmon module output explained
Running the command:
tcpdump -qAXni usbmon3 -s 0
I am getting this output:
02:32:04.781964 BULK SUBMIT to 3:16:4
What does the last number after the colon (4) represent?
How can I identify it in ...
-1
votes
1answer
116 views
Tcpdump to usb drive
Packets are being generated at 750 packets/second and I am using tcpdump to capture these packets and write them to file stored in a usb drive. Due to write speed limitations, the overall process of ...
2
votes
1answer
894 views
Stop CTRL+C Exiting Local Script Which is Running tcpdump in Remote Machine
I have setup a simple script like the below:
sshpass -p $password ssh -T $username@$ip_address -p 30007 <<- EOF > $save_file.pcap
sh
tcpdump -i eth5.1 -s 0 -n -v -U -w -
EOF
sed -i '...
0
votes
1answer
152 views
How to Pipe Segment of Heredoc Output to Local File
I am issuing a command to a remote device in order to run a tcpdump on one of it's interfaces, but capture the output to a local .pcap file on my Ubuntu VM. The command that I'm issuing is as follows:
...
0
votes
1answer
937 views
How to Pass Multiple Commands to Remote Device via SSHPass [duplicate]
I'm trying to setup a method in which I can run remote tcpdumps on some of my devices, and save the file to my local machine for analysis (I don't want to save the file on the remote device and then ...
2
votes
1answer
2k views
Capture http token with tcpdump
My server runs curl commands to some API using a token. For example:
curl --header "Private-Token: aaaaaaaaaaaaaa" http://mysite.example.com/api/v4/any
Can i capture with tcpdump all of the requests ...
5
votes
2answers
971 views
'ping' uses localhost instead of public IP address
Let's say my server has IP address 11.22.33.44 and hostname server1.mydomain.com.
When I ping server1.mydomain.com, it looks as if ping is actually using the public IP address:
# ping server1....
0
votes
1answer
797 views
Ping responses missing but can see them in tcpdump
Redhat 2.6.32-754.el6.x86_64
I have an FPGA card acting as a NIC with an associated driver.
On my RH host, if I run ping through the FPGA NIC I see lots of missing responses. However, if I also run ...
3
votes
2answers
3k views
What and how length is determined in tcpdump
What my application does is read data from kafka and hit another service via HTTP. I was seeing outgoing traffic slower in one box compare to others. I analysed tcpdump to that outgoing IP, logs from ...
