tcpdump is a CLI tool for capturing and displaying packets sent and received by network devices.

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1answer
114 views

can’t get any data from tcpdump from https server where i actually get the response

When i access https://xxx.xxx.xxx.xxx:5432/, i can get reseponse from the server. (https with 5432, for test purpose). But when i do tcpdump on server ‘xxx.xxx.xxx.xxx’, it doesn’t show me anything ...
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3answers
2k views

identifying vlan packets using tcpdump

I'm trying to figure out the vlan tagged packets that my host receives or sends to other hosts. I tried tcpdump -i eth1 vlan 0x0070 But it didnt work. Has anyone tried to view the vlan ...
2
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0answers
115 views

Suggestions on how to capture network connections/traffic for determining browser/SSL versions?

Note that I posted this Q to the StackExchange InfoSec site, but its not as populated as ServerFault and this is more on the technical side of network collection for web services. I've started ...
0
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1answer
118 views

Server sending packets every 5 minutes to 3 IPs

Been noticing in our firewall logs that three connections are being constantly established every 5 minutes from our web server and trying to send a packet to destination port 43 (whois port) cycling ...
0
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1answer
463 views

Routing traffic through a virtual machine [closed]

I have OpenWRT running in a virtual machine. It's network adapter is bridged to the host. Host ifconfig root@michael-VirtualBox:/home/michael/Scripts/python# ifconfig eth0 Link encap:Ethernet ...
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3answers
211 views

Recording network traffic on one linux box, transferring it to another in real time

I have a situation where I want to capture all of the network traffic on one Linux box (currently using tcpdump) but have that data transferred in real time to another Linux on a separate (but ...
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2answers
1k views

Tap0 not receiving traffic

I have created a tap device tap0 address 10.2.1.4 and added it to a host bridge br1 with address 10.2.1.1 I have "nc 10.2.1.4 -l 1234" running on the host and from another machine I do a "nc ...
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1answer
847 views

Random TCP Resets

We got randomly TCP "reset" error when we send request to remote server. Log from remote server Cisco TCP Connection Terminated,Nov 05 14:43:39 EST: %ASA-session-6-302014: Teardown TCP connection ...
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0answers
267 views

Tcpdump stops capturing wifi data while running in the background

I have a problem capturing wifi data using tcpdump while running in the background. OK, lets get some facts: my wifi-device is named wlan0 wlan0 is in monitor mode (that's what I want) I'm using ...
0
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1answer
311 views

pretty-printing IP packets [closed]

I'm receiving IP packets using the SLIP protocol, and I'd like to pretty-print them similarly to how tcpdump does it. My program is able to decode the SLIP protocol and create a single string ...
1
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1answer
256 views

tcpdump on a capture card

I have a server with a NT20E Capture Card (2x10Gb Packet Capture Card over PCI Express). I want to be able to dump the output to a pcap format but because this isn't listed as an ethX-interface ...
0
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1answer
18 views

Is there a way to explicitly set the maximum number of packets tcpdump will capture before terminating?

We have a small script that essentially does the following: A) Capture packets using tcpdump and pipe to output file. B) Run our own clean + sort script on output file. C) Display results using | ...
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1answer
1k views

What does tcpdump “BOOTP/DHCP, Request from …” mean?

I am seeing extreme amount of network traffic on a host despite it should be idle. When I do tcpdump -nni eth0 not net 10.10.10.10/32 I get lots of these 14:36:07.851048 IP 0.0.0.0.68 > ...
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1answer
5k views

Limit tcpdump capture files by time and size

I am having some problems getting tcpdump to log all internet traffic on an interface with the following limitations: I would like a new pcap file every hour with time and date tag in the name If ...
0
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1answer
746 views

tcpdump: can't create rx ring on packet socket: Cannot allocate memory

I've been using tcpdump without any issues before this error popped up. I use the following two commands with variations as soon as my server is attacked so the packets automatically get dumped if the ...
1
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2answers
70 views

Is it possible to capture transfered file to my apache server using tcpdump

I have web app installed on apache server(port 80, no ssl). This apps job is to gather some information via transferred from clients files. My goal is to check if my clients are sending proper files. ...
0
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1answer
425 views

How to install tcpdump on Cloud Linux

I am new on Linux, and I own a server with Cloud Linux installed. What I like to do is to install the tcpdump but I cannot. I have try to execute the following command from SSH: yum install ...
0
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1answer
2k views

Login my Linux with root ,executing command sshd、tcpdump failed

root# /usr/sbin/sshd Privilege separation user sshd does not exist root# tcpdump -i eth0 udp tcpdump : Couldn't find user 'tcpdump' but the users tcpdump and sshd are in the files ...
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2answers
2k views

Using tcpdump with iptables?

I use iptables to block different kind of attacks on my server. We have a different set of rules along with different rate-limit rules. Now I also use a script that would observe the threshold if it ...
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0answers
176 views

Capturing on loopback device on Ubuntu LTS: 15 Mbit of traffic and “x dropped packets”

I am trying to capture about 15 Mbit of traffic on the loopback device on Ubuntu LTS using tcpdump, and I am seeing dropped packets. The CPU is a freaking i7, and i have yet to see CPU usage go above ...
0
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1answer
338 views

How can I dump nginx requests for a specific location while nginx is secured?

I want to dump all request that nginx is getting for a specific location so I can debug a strange problem that I have. Usually tcpdump would be the solution but remember that nginx is accessed using ...
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1answer
258 views

Why does OS X spend one more packet to establish and close a TCP connection?

Linux spends 3 packets to establish a TCP connection and 3 packets to close it, as shown by the tcpdump capture # establishing TCP connection 22:37:09.150456 IP 127.0.0.1.49327 > 127.0.0.1.8000: ...
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1answer
53 views

Check if traffic is gzipped

I have an application server running on port 80. How can I check if the incoming and outgoing traffic is gzipped? Also, the application communicates with another server (also HTTP requests). I'd like ...
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0answers
216 views

Apache logs or tcpdump slow loris

i know about the question : How can I detect Slowloris? but that does not apply. Now i have a big server that receives more then 10.000 events on the IDS per each 10 minutes, and i have suffered in ...
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1answer
482 views

How can I filter MongoDB Replica Set Heartbeats with tcpdump?

Occasionally, when troubleshooting the health of a replica set, I'd like to filter out the heartbeat packets specifically, track them going out, and the subsequent reply (or lack thereof) without all ...
0
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1answer
4k views

tcpdump - how to check rate of packets?

I'm using this script that actually checks for the rate of incoming packets and it gets triggered if the rate hits 5mbps or more. The packets are then logged to a tcpdump file. interface=eth0 ...
0
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2answers
184 views

How to run tcpdump on Centos right after reboot?

I see that my Amazon EC2 has a lot of traffic coming inbound after I reboot my Linux machine. I would like to find out what is going on right after the servers comes back after reboot. I thought ...
0
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1answer
76 views

missing network usage through iptables

I inserted a rule to iptables to track the input usage to a certain ip address. The vps server's IP is 192.168.1.5 and the guest os's IP is 192.168.1.115. I ran 'yum update' inside the guest OS to get ...
2
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1answer
1k views

How to parse OpenFlow packets using tcpdump capture file programmatically

I am working with OpenFlow packets and am analyzing the network via tcpdump. Currently, I use the WireShark GUI to parse the generated capture file and it does serve my need. However, I was ...
2
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1answer
4k views

tcpdump capturing tcp resets by host

I am trying to figure out where my tcp resets on my webserver happen. I have the following capture: tcpdump -fnni bond0:-nnvvS -w dump.pcap 'tcp[tcpflags] & (tcp-rst) !=0' When I look at the ...
4
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2answers
747 views

Packets only get forwarded when tcpdump running on bridge

I ran into the oddest thing when trying to debug a networking issue with OpenStack. I was doing a ping test between virtual machines. The ICMP request packets only made it to the destination host if I ...
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52 views

why tcpdump drop package for long running request?

I turn on tcpdump to capture requests going to my webserver. However, some of the requests are not captured by tcpdump but they showed up in apache access log. Those requests are usually long running ...
2
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1answer
2k views

Which are the possible reasons for an arp request that is not being solved/answered?

This weekend I was testing a new data link connection from a service provider, and I went through some address resolutions problems. I tested reachability to hosts at the far end using a laptop on my ...
3
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1answer
610 views

How to debug why WAN TCP/IP throughput is lower than expected?

I'm trying to figure out why tcp/ip throughput between two hosts I control is much lower than expected. Host A: internet connectivity provided by Comcast (Residential) in Boston Metro -- can ...
0
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2answers
5k views

Fragmentation and packet size,using tcpdump

i am trying to understand concept of fragmentation: i have two virtual machines with public ip connected to a switch. tracepath shows packet not going through gateway from vm1: Trying to send ...
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0answers
864 views

PPTP refusing to connect when client is windows

I have a PPTP server running and I can connect to it from linux. When I try from windows 7 (2 instances tested) it fails. Here's the syslog for such a conn: pptpd[540]: CTRL: Client 109.xxx.158.201 ...
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4answers
2k views

Rsyslog not logging from remote server

I am trying to set up a centralized log server. I have central server (A) receiving logs via a remote server (B) on port 514. I know it is receiving these. Here are a few entries from a tcpdump on ...
0
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1answer
485 views

syn flood attack — packet hits on shared ip

How can I dump the TCP packets to get a better idea to know which website is being attacked? Here is what I have in my logs: May 4 23:10:26 host kernel: [2130002.635000] Firewall: *SYNFLOOD ...
1
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1answer
388 views

openvpn (tun0 + bridge) : Comunication bridge --> tun0 works but not the opposite direction

My network is composed as follows: Host A with ip 9.x.x.x and vpn ip 192.15.206.x (openvpn client) Host B with ip 9.x.x.x and vpn ip 192.15.206.1 (openvpn server) this host has a bridge br0 with ip ...
4
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3answers
10k views

Human readable format for http headers with tcpdump

I would like to view the HTTP headers sent from Apache (listening on port 80) to Tomcat (on port 4080) in a Linux machine. According to Wikipedia, Header fields are colon-separated name-value ...
0
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1answer
398 views

How to debug SSH “connection timeout”

I'm getting error (sometimes) while connecting from host1 to host2 Errno::ETIMEDOUT: Connection timed out - connect(2) TCP dump on host1 while trying to connect (tcpdump -vv -i eth0 -s 0 'port 22 ...
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2answers
1k views

TCPDump and IPTables DROP by string

by using tcpdump -nlASX -s 0 -vvv port 80 I get something like: 14:58:55.121160 IP (tos 0x0, ttl 64, id 49764, offset 0, flags [DF], proto TCP (6), length 1480) 206.72.206.58.http > ...
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4answers
642 views

Locally examine network traffic of remote machine

I have root access to my dd-wrt router at 192.168.0.1 and computer at 192.168.0.100. I need to get the traffic comming through the router(in the Internet and out) from some other ...
2
votes
1answer
2k views

tcpdump not picking up traffic redirected by iptables

The following iptables rule is used to redirect all internet traffic coming in from eth1 to port 3000 at localhost (interface lo with ip 127.0.0.1): iptables -t nat -A PREROUTING -i eth1 -p tcp ...
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3answers
719 views

Monitor traffic between two network switches using a transparent firewall

For debugging reasons i need to see what network traffic especially TCP is transmitted or not. I thought about using an Endian firewall for this, but it doesn't support 2 network interfaces with the ...
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0answers
612 views

How to interpret findings on TCP Send/Recv Buffers

I have an application running on a CentOS machine that connects to a remote DB server on another CentOS machine. Every once in a while, without any discernable warning signs, the application seems to ...
0
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1answer
183 views

Getting packet rate with tcpdump or iptables

I need to get the rate at which certain packets (i.e. LDAP) arrive on a interface in a linux environment. I was thinking of using tcpdump to filter the wanted packets and subsequently monitor the ...
2
votes
2answers
201 views

Is TCP RWIN set by application or OS?

I have a situation where an application is listening on a TCP port and every once in a while, as seen in tcp dumps, gets its Receiving Window (RWIN) set to zero. When this happens, its Recv-Q stops ...
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2answers
1k views

Using tcpdump to find strings [closed]

I need to block certain TCP packets by trying to find a string match in and on them. Is there a way to do that with TCPDump? Or do I need wireshare install on my linux server? One I have the string ...
1
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1answer
82 views

How to diagnose why a port is broadcasting a “ZeroWindow” status

I have two CentOS servers (one is an app server, the other is a DB) communicating over a port. Every once in a while, the application server starts broadcasting that the port connected to the DB has a ...