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

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TCP stops sending weirdly

In case to find out the cause of TCP retransmits on my Linux (RHEL, kernel 2.6.18) servers connecting to the same switch. I had a client-server pair send "Hello" to each other every 200us and ...
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TCPDUMP - Capturing Packets on Multiple IP Address (FIlter)

What I need to do (via 'tcpdump' through Linux): • ECommerce App Servers: 192.168.1.2, 192.168.1.3, 192.168.1.4. - This is what I want to capture on (filtered on these exact IPs). Not an IP range ...
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Incoming packets to server

I have enabled iptables logging for packets coming from the outside -A INPUT ! -s 192.168.218.0/24 -j LOG Now i am seeing lots of incoming packets from unknown addresses Jun 5 14:54:56 localhost ...
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iptables logging packets coming from the outside world

I want to log all INPUT packets that do not originate in the LAN for audit purposes, I have a script with tcpdump basically appending to a file the result from this: tcpdump "(dst net 192.168.0.0/24 ...
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PPTP traffic logging

I am running pptpd on a Centos 5 machine but I didnt set up any logging. In case of an abuse, I need to determine which of my users did the bad things, meaning I need to log all the traffic. I may ...
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Daemon can't be started from fabric script or on boot - only interactively

I have a daemon script in /etc/init.d that performs some background packet logging using the tcpdump command. The script starts up fine using an interactive shell using sudo /etc/init.d/packetlog ...
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Network flooded with ARP requests

I am having networking problems on a virtual Debian server. The VPS provider I think may be the cause of these network problems as it's a fairly new/fairly standard Debian install. However, as their ...
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625 views

Port forwarding not working, tcpdump shows “reset connection”

I have an home web server that I use to serve a few pages for personal purposes. The server runs Ubuntu and is behind an ADSL connection, and it's working nicely. Recently I subscribed to a Hiperlan ...
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looking for multicast traffic

We have a j2ee webapp on tomcat which is using ehcache with multicast discovery. Except it's not discovering anything. There appears to to be no multicast traffic visible on the network but we're a ...
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tcpdump How do I use it to capture all traffic headers

I'm quite new to tcpdump. I've never used it except for very trivial tasks. Recently, I was asked to complete the following job. What I have: A server with a network interface connected to a switch. ...
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148 views

MySQL RESET [integer]

In an audit of queries running on our databases using tcpdump and Maatkit tools, the number one query is RESET [int] Running this statement from the MySQL command line results in an error as RESET ...
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Connecting to Samba share over the internet

I have been trying to connect a Linux box to a remote Samba share, with no success. The Samba share is a NAS, mapped to be accessible from the Internet, and to be used as a secondary backup box. The ...
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575 views

tcpdump over vpn/ssh

I'm redirecting tcpdump output from machine A to machine B. A and B must use a "secure" connection, using VPN or ssh tunnel. I only care about authentication, however: I don't need to protect from ...
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tcpdump unknown device

I am trying to run tcpdum on Solaris 10 as root user. I always get unknown device - even though I am using the name provided by ifconfig -a How can I find out the right device name?
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how to monitor traffic at port 53 (DNS)

I am a bit confused with the abundant tcpdump tutorials on internet. I am having a few of the virtual machines running on a virtualization server.Where I am debugging a problem.Port 53 is the one in ...
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tcpdump filter for tcp zero window messages

Is there a pcap filter for TCPDump that will allow be to filter zero window messages? I know how to filter these in a wireshark display filter (tcp.analysis.zero_window) but the amount of data I ...
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656 views

tcpdump output with iptables REJECT policy enabled

Quick question. I have a firewall with these simple rules: iptables -A INPUT -p tcp -s 127.0.0.1/32 --dport 6000 -j ACCEPT iptables -A INPUT -p tcp -s 192.168.16.20/32 --dport 6000 -j ACCEPT ...
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What is a RP Paket in a tcpdump log?

I have a tcpdump log with the following entry: 14:53:31.428570 IP 10.4.65.65.16666 > 192.168.201.10.80: RP 587:687(100) ack 48545454154 win 0 My Problem is that i have never seen an RP paket ...
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How to display interface in tcpdump output flow?

This seems to be quite a trivial problem, but after some searching I can't stil figure out the answer. One can run tcpdump using "any" as the interface description, ie: # tcpdump -i any -n host ...
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unable to sniff traffic despite network interface being in monitor or promiscuous mode

I'm trying to sniff out my network's wireless traffic but am having issues. I'm able to put the card in monitor mode, but am unable to see any traffic except broadcasts, multicasts and probe/beacon ...
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414 views

Sniff packets using tcpdump

I have a completely noob question. I want to see all packets that come to my computer from particular site (google.com). So I start tcpdump sudo tcpdump -i eth0 host google.com and enter google.com ...
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How to capture ack or syn packets by Tcpdump?

I want to know the filter rule , thanks!
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What program sent which packet to the network [duplicate]

I would like to have a tcpdump like program that shows which program sent a specific packet, instead of just getting the port number. This is a generic problem I've had on and off sometimes when you ...
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How to collect concise traffic statistics on linux?

I need to have statistics divided by time periods, like this: time_1 - time_1 + 5mins from_ip1 > to_ip2 total_packages_size1 from_ip3 > to_ip4 total_packages_size2 time_1 + 5mins - time_1 + ...
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Dropped packets in Linux

I'am using a machine as a router, it works sort of fine, however if I do a ping -t whatever.server it will always cause a 3-4% package loss, no matter what server. Looking at ifconfig or netstat -i ...
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How to see an application network protocol communication in real time

I would like to see the protocol used by client-server application in real-time. I'm not interested in any statistics. All I want to see is the message sent by server and the client. This is FreeBSD ...
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231 views

How to read and create this type of TCPDUMP

I am having an issue with my tcpdump command i have created. Chances are its wrong. What i want to do is this: Run this command: tc qdisc add dev eth0 root tbf rate 6kbit latency 50ms burst 1540 ...
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942 views

How to block packets after capturing?

I use tcpdump to capture output packets for one server, but I also need to block these packets. If I use iptables to block them, then I also can not capture anything. Can I block packets with ...
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618 views

Log network traffic with process ID on Mac OS X?

I want to log all network traffic on a Mac OS X server (like tcpdump does), but including the ID of the process that is responsible. Using lsof only gives me the current connections, not the past ...
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How do I make tcpdump not print the tcp headers?

I tried this: tcpdump -s 1500 -A -l -i eth0 '(port 6667) and (length > 74)' I need only the ascii part of it. How do I remove the rest?
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tcpdump and congestion window

Sniffing http traffic to my (linux) server it seems like it always responds advertising a window size of 14. It isn't affected if I change the default initcwnd size (with ip route), and it doesn't ...
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What do “Unknown SSAP” and “Unknown DSAP” mean in tcpdump?

While trying to fix a problem with intermittently losing internet connection on a machine with a wireless connection to a router, I ran tcpdump and noticed packets with "Unknown SSAP" and "Unknown ...
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TCPDUMP = How to detect and analyse “Suspicious” Traffic to 192.xxx Addresses?

I just played a little bit with tcpdump (as I wanted to check why my mails are not getting send) and thereby discovered very strange and a lot of traffic to the "Private IPs". Please See examples ...
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tcpdump: capture one of several vlans

I want tcpdump to capture VLAN 1000 or VLAN 501. man pcap-filter says: The vlan [vlan_id] expression may be used more than once, to filter on VLAN hierarchies. Each use of that expression ...
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Monitor number of bytes transferred to/from IP address on port

Can anyone recommend a linux command line tool to monitor the number of bytes transferred between the local server and a specified IP address/port. The equivalent tcpdump command would be: tcpdump ...
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tcpdump not giving details

Why does tcpdump not give my more details? Each time it only comes as - 16:22:26.128541 [|ether] # ./tcpdump -vv not port 22 tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size ...
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tcpdump filter according to http header content

using tcpdump i would like to filter the responses that comes back from a squid cache server to only the responses that came back from the cache. that means that i need to filter according to the ...
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tcpdump syntax for only capturing traffic coming to a specific virtual interface / local IP

CentOS 5.x Hello All, I need to collect a packet capture of https requests going to a specific IP address / virtual interface. Is there a specific switch/parameter for tcpdump that will allow ...
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Why Packet Loss AFTER tcpdump has logged the packet?

We encounter some strange packet loss and want to know the reason for this. We have an imageserver and a server for stressing the imageserver. Both are located in the same datacenter First we run a ...
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Question about tcpdump

On this link I found few informations about use of tcpdump. But, can you give me more information about example showed on that page: tcpdump -s 128 -vvv -T rtcp src orac and port 57393 ...
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Anyone can tell their experience with 10g Ethernet adapters on Linux

I wonder if any of you have an experience with 10g NICs (Intel, Myricom, SMC tiget, napatech, or by any other brand). Questions are: Was it easy to install, or a hassle, How does this adapter ...
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How to understand the output of tcpdump? [on hold]

15:24:27.156744 IP 192.168.1.106.ssh > 192.168.1.105.1128: P 2327968:2328112(144) ack 30721 win 182 15:24:27.156827 IP 192.168.1.106.ssh > 192.168.1.105.1128: P 2328112:2328256(144) ack 30721 ...
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How can i sniff/dump HTTP protocol as ASCII for a port with tcpdump or altenative?

I need to view how an application is sending and is receiving traffic through a http protocol that it comunicates on localhost (it has an embeded port coded with .gz) I'm sure it's some XML that it ...
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Kill FINished sockets (using libpcap - tcpdump/tcpkill)

I'm trying to create a small service that monitors and kills sockets which have the FIN flag. I can get them with tcpdump (I also tried tcp[13] & 1): tcpdump "tcp[tcpflags] & tcp-fin != 0" ...
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How can I capture traffic with tcpdump and a sliding window or sort of “logrotate”?

I want to capture some traffic with tcpdump for troubleshooting. The problem is, the error is not reproducible. To not fill up the hole disks with captures, I would like to capture the traffic with ...
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Howto monitor traffic between IIS and MSSQL

I am trying to check how much traffic is flowing between MSSQL Server and IIS Server in different locations. There is 1 ipcop in every location and I download the tcpdump file from one firewall and ...
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How to know the source of certain TCP traffic on AIX

We have two AIX boxes, one for production system and another for testing. both systems are running ATM machine switches, where the ATM device is connected via TCP socket. we had an issue on ...
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Packet loss rate with iperf and tcpdump

I tested a line for its link quality with iperf. The measured speed (UDP port 9005) was 96Mbps, which is fine, because both servers are connected with 100Mbps to the internet. On the other hand the ...
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How can I log all traffic with its exact length?

I want to process all packets with their size going through our gateway server (running Debian 4.0). My idea is to use tcpdump, but I have two questions. The command I'm currently thinking of is ...
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how to split a pcap file into a set of smaller ones

I have a huge pcap file (generated by tcpdump). When I try to open it in wireshark, the program just gets unresponsive. Is there a way to split a file in set of smaller ones to open them one by one? ...