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

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Tcpdump says “Illegal instruction”

Following the tutorial on http://www.waitingforthefuture.org/2009/12/25/compiling-tcpdump-for-tomato-firmware/, I tried to compile tcpdump. I did the compilation on an Intel Pentium 4 2.26Ghz computer ...
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406 views

Can't see traffic in my guest OS with tcpdump

I've created a virtual machine (Centos 6.0) using QEMU/KVM, which is also running on a Centos 6.0. The virtual machine is configured to have two NICs. The first NIC is using a bridged network (eth0 of ...
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729 views

How to sniff request packet on VPN server?

With some safe reasons, I need to sniff pptp cleint request packets, then to get dst ip and src ip, for example 10.5.1.100 -> 218.100.211.100 , I want to know the correct rule in tcpdump
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Firewall blocks traffic - how to find out what ports / ip addresses are used by software?

Well I get a "host was not accessible" error when trying to use a software. I don't know which port they use nor which address they are trying to reach. Is there a more or less easy way to figure that ...
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5k views

how to calculate packet loss from a binary TCPDUMP file

Our connection to just one remote server on port 80 over the internet is not working properly. (From time to time it is working and sometimes not) It must be some kind of packet loss, because from ...
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180 views

Measuring delays between various components on a localhost

I need to profile a web application from a system performance standpoint and find out for typical user actions (accessing the home page, logging in...) where the delay comes from. The website uses the ...
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2answers
5k views

multicast tcpdump and subscriptions

From the multicast howto: IP_ADD_MEMBERSHIP. Recall that you need to tell the kernel which multicast groups you are interested in. If no process is interested in a group, packets ...
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227 views

Can tcpdump tell accessed port numbers?

I have a server with two NICs, and I would like to only have those ports open on eth1 that are being used. Question How do I get tcpdump to tell me the port numbers that is being accessed on eth1?
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112 views

I'm being asked to support mapping many SSL keys to one IP but I think it's a bad idea. Am I wrong?

At work, I've been asked to add support for mapping multiple keys to a single (or many even) IP to what is essentially a passive HTTP sniffer. It supports SSL decryption with user-uploaded keys. ...
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1answer
612 views

TCP Sessions Hanging with Debian and iptables

Up until now I have been using a CentOS 5.x PC with 2x NICs running iptables as a router for my network. It worked great but recently I decided to get a DreamPlug which runs Debian 5.0.3/kernel ...
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Extracting SSL certificates from the network or pcap files

I will appreciate if someone can point me to a tool or approach to extract SSL/TLS certificates from live HTTPS connections (directly from the network) or from a network trace file (pcap file). I ...
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86 views

How to save the packets received by a network interface or some port in a file and resend the packets received when needed?

I am doing my work on a server service program on Linux that processes the packets sent to the socket it listens.Their is already a old such service listening on the port doing its job,and I can't ...
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83 views

tcpdump strange udp line

I've found a strange line in the tcpdump output. Normally UDP packets are dumped in the following form: timestamp IP srcaddress.port > dstaddress.port: UDP, length packetlength but this is just: ...
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1answer
761 views

dhcp-server + iptables: Can't share ppp internet connection

I had this configuration before, and it used to work well, but now I got a new server and I can't setup it to share the internet connection from ppp0. I'm on Debian testing. The client connects ...
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1answer
1k views

How to reproduce http traffic of a real site in another environment (e.g. VM)

There is a bug in my web application which I cannot reproduce. All the logs look ok or at least I cannot see anything unusual. But it happens. So I thought I could record all the traffic to/from my ...
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1answer
617 views

TCPDUMP , SSL , Android, SSL dump

I run an application on Android phone. The application connects to a webservice via internet and I want to intercept the traffic between the application and the webservice. The connection is ...
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2answers
222 views

Solaris VM Experiencing Frequent Timeouts

We are having an issue with all of our Solaris VMs. The issue we're seeing is frequent timeouts when when connecting via SSH or HTTP. It only seems to affect initial connections... when I connect via ...
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2answers
563 views

tcpdump - just output the packet contents line by line

I'm trying to use tcpdump on the DEFCON packets. Here's the command I'm using: tcpdump -qns 0 -X -r ulogd.eth0.pcap And here's the output I'm getting: 10:39:12.356410 IP 192.168.103.2.3101 > ...
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Too many incorrect checksum errors in TCPDUMP

I find too many incorrect checksum errors from a TCPDUMP done on a GNU Linux 64bit server. There are close to 50% incorrect chekcsums in the export? cksum 0xe61f (incorrect (-> 0x8c37) How can we ...
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1answer
173 views

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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1answer
11k views

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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1answer
465 views

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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323 views

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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1k views

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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1k views

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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207 views

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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749 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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715 views

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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1answer
5k views

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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3answers
154 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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2answers
1k views

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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629 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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772 views

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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3answers
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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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1answer
2k views

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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757 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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338 views

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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796 views

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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494 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 use a filter rule to capture only ack or syn packets. How do I do this?
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3k views

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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278 views

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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3answers
541 views

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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251 views

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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240 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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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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723 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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1answer
629 views

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 ...