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

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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 ...
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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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993 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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4k 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 ...
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612 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 ...
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2answers
68 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. ...
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341 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 ...
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1k 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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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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166 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 ...
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1answer
293 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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249 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
51 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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189 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
401 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 ...
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1answer
3k 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 ...
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2answers
165 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 ...
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1answer
75 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 ...
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1answer
796 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 ...
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1answer
3k 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 ...
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2answers
575 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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49 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 ...
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1answer
1k 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 ...
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1answer
563 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 ...
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2answers
4k 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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742 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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1k 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 ...
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436 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 ...
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1answer
361 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 ...
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3answers
6k 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 ...
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1answer
317 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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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
513 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 ...
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1answer
1k 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
590 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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493 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 ...
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1answer
157 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 ...
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2answers
182 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
843 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 ...
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1answer
71 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 ...
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182 views

Tcpdump packet-PID correspondence

So I've installed winpcap and use windump: E:\>windump -i 2 -B 5000 -n -s 0 -l -C 1 -W 10 -e -q -X windump: listening on \Device\NPF_{9718B3B1-6C96-4431-889B-2B1A37BED06E} 01:25:23.029278 ...
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1answer
259 views

How to use a switch as a network tap?

I would like to tcpdump all traffic that my router does when it makes a firmware update. So I have taken a HP ProCurve 1800-8G switch and mirrored port 7 to port 8. I have connected: Internet ...
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1answer
106 views

how to use tcpdump to capture packets with “ACK” flag set [closed]

I want to capture packets with ACK flag set using tcpdump including SYN/ACK, data packet and ACK packets thanks
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296 views

How to diagnose large number of TIME_WAIT connections

We have a production issue with only one of our servers and have correlated slow performance to an abundance of sockets in the TIME_WAIT state. Without drawing this question into a huge backstory, we ...
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2answers
1k views

How to use Linux to capture packets on eth0 and send everything to eth1?

Today I got an enterprise Internet connection together with a Sagemcom router. The first time it is connected to the Internet, it will spend 20 minutes upgrading the firmware. I would really like to ...
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1answer
992 views

tcpdump shows traffic until I use a filter

I have a server that is receiving traffic from a mirror port on a switch. The interface that is connected to this mirror port is in promisc mode. When I use just a plain catch all tcpdump on the ...
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1answer
37 views

Network interface reading traffic from 2 different hosts

Situation: Server A is receiving network traffic sent from server B to server C. Server B & C send over MySQL dumps. Quite some traffic. For some reason the interface on server A is measuring this ...
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3answers
1k views

logging HTTP traffic with tcpdump on a router

I have a linux box acting as a router between many clients and the internet, and i need to pull some statistics on usage: I need to log which internal IPs access which addresses externally. I use ...
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5answers
3k views

tcpdump: out.pcap: Permission denied

[root@localhost ~]# cat /etc/issue Fedora release 17 (Beefy Miracle) Kernel \r on an \m (\l) [root@localhost ~]# uname -a Linux localhost.localdomain 3.6.10-2.fc17.i686 #1 SMP Tue Dec 11 18:33:15 UTC ...
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223 views

tell tcpdump to not include the port numbers in the output

how can tell tcpdump to not include the port numbers in the output? Right now it includes the resolved IP + resolved port. I just need the resolved IP address (hostnames)