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

learn more… | top users | synonyms

3
votes
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 ...
3
votes
1answer
1k 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 ...
2
votes
1answer
38 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 ...
0
votes
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 ...
4
votes
6answers
4k 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 ...
0
votes
1answer
253 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)
0
votes
1answer
155 views

Application traffic classification with tcpdump

I have a trace file from my network. I would like to identify the top 10 applications used by us . Does tcpdump provide any application based filtering options ? Any details regarding this would be ...
1
vote
1answer
444 views

Counting the number of flows in a tcpdump file

I have a large tcpdump file which I need to parse to identify the number of flows in the capture based on the ( source ip + source port , destination ip + destination port ) pairs. Does tcpdump / any ...
0
votes
1answer
202 views

Filtering inbound traffic without knowing the destination subnet

I have a linux machine configured as a router with two interfaces facing LAN A and LAN B. I want to filter traffic passing from LAN A to LAN B (inbound traffic) using tcpdump, but I don't have the ...
3
votes
2answers
1k views

Filter tcpdump file AFTER capturing

I captured a really big tcpdump file which now always crashes my wireshark. It was captured with no filters and I need to apply some afterwards to make the file smaller. Is this somehow possible?
3
votes
1answer
105 views

How do I get the network usage of a server per-IP?

I'd like to know a tool to programmatically measure, in KB/s, the load that each IP applies to a server. So far, tcpdump does a good job at telling me the amount of packets sent per second, but I ...
2
votes
1answer
67 views

In tcpdump filtering is “port” redundant with “tcp”?

Why would one want to force "tcp" in a "tcpdump" filter when using "port", given port numbers are defined in TCP Headers (as opposed to IP) In other words, is tcpdump tcp and port 10000 synonym to ...
2
votes
1answer
565 views

Using darkstat to monitor bandwidth — how to exclude my dynamically assigned IP address?

I am using darkstat to collect data about bandwidth usage on my local box. My internet connection is provided by a 3G USB stick, connecting to a mobile network. Each time I connect to the internet I ...
1
vote
1answer
43 views

How can I print only tcpsequence number with tcpdump

I search for a way to limit or change the output format of tcpdump to print only tcp sequnce number, but i didnt find a way to do this. Can you please advice? Running on Ubuntu. If there is no way to ...
-3
votes
1answer
587 views

Filter tcpdump capture to gather info on DNS/URL/URI [closed]

I'm looking to extract the DNS/URL/URI information from packets and produce a CSV output which I can then feed into flowtag.
3
votes
2answers
4k views

How filter only keep-alive packet with tcpdump

I need to analyze a traffic-dump on my network to check if all the PCs have enabled tcp keep-live features. I'm using tcpdump for that purpose. What I need to know is if there is a possibility to ...
0
votes
1answer
389 views

find common string to block IPs

Currently I have all these IPs coming in. Is there a way to find a common string in the content of the packets and then block the attack via IPTables? Oct 24 16:28:52 host kernel: [ 823.255566] ...
3
votes
1answer
149 views

Why isn't 'ether proto \ip host host' a legal tcpdump expression?

In its description of valid tcpdump expressions, the pcap-filter man pages state: The filter expression consists of one or more primitives. Primitives usually consist of an id (name or number) ...
0
votes
1answer
493 views

IPv6 DNS Lookup

I am trying to prevent a webserver to do IPv6 lookups (AAAA) to the DNS-server. The webserver has no IPv6 addresses set-up on the interfaces. Disabling IPv6 in sysctl.conf had no impact either, the ...
0
votes
1answer
1k views

using tcpdump to display XML API requests without headers or ack packets

I need assistance, I am trying to use tcpdump in order to capture API requests and responses between two servers, so far I have the following command: tcpdump -iany -tpnAXs0 host xxx.xxx.xxx.xxx and ...
1
vote
1answer
431 views

How to Monitor Aborted Connections on Port 80 With tcpdump

Can I use tcpdump to detect Aborted connections on port 80 (Apache) originating from a specific IP (my remote IP). I can reproduce the Aborted connection in my web browser, but I have no way to verify ...
1
vote
1answer
2k views

tcpdump failed withi permission denied on centos when using with rotated file option

When I use tcpdump on centos 6, I got a permission denied error even when I was root. My command is like this: sudo tcpdump -i eth0 -G 10 -w test.dmp port 80 i have tried with -Z root or -Z ...
6
votes
2answers
7k views

Lots of dropped packages when tcpdumping on busy interface

My challenge I need to do tcpdumping of a lot of data - actually from 2 interfaces left in promiscuous mode that are able to see a lot of traffic. To sum it up Log all traffic in promiscuous mode ...
2
votes
1answer
2k views

Capture network traffic simultaneously on three interfaces

I need to capture traffic on a CentOS 5 server which acts as a web proxy with 2 wan interfaces and 1 LAN. In order to troubleshoot a weird proxy problem, I would like to have a capture of a full ...
0
votes
1answer
4k views

PPPoE Connection : “Generic-Error ”RP-PPPoE: Child pppd process terminated"

I have 2 Ubuntu 64-bit Virtual Machines installed on Virtual Box.Their name and ip addresses are given below.I am trying to establish PPPoE connection between the two machines. nas ...
3
votes
2answers
341 views

tcpdump file size == traffic size?

I created a tcpdump file: tcpdump -i eth0 host xxx.208.xxx.59 -n -s 0 -vvv -w /tmp/dump.dmp duration was about 3 hours. This file now has 450 MB. Can I say now that the IP xxx.208.xxx.59 generated ...
1
vote
1answer
202 views

Validate send packet against recived packets?

Running Ubuntu. I have machine A -> machine B (one-way connection from A to B) . Machine A goal is to forward tcp packets to machine B (it dosnt has tcp connection with machine B. it just forward tcp ...
7
votes
2answers
3k views

tcpdump: snaplen set to 0 but still get “Packet size limited during capture”?

Due to this problem, I'm going to sniff some packets on the MySQL server backend to see what happens: # tcpdump -vv -s0 -c 100 -i bond0 tcp port 3306 and host 192.168.3.87 -w ...
1
vote
1answer
1k views

DNS resolve timeout on RHEL 6.3 behind firewall

I have a server running Red Hat 6.3 Enterprise inside a VMWare virtual machine. There's a Juniper SSG 5 firewall sitting between the server and the Internet. I'm trying to diagnose what it looks like ...
-1
votes
1answer
2k views

How can I make tcpdump stop the capture after a certain number of packets captured?

I am debugging a problem where two servers get stuck in a loop when communicates with each other. After a server restart the problem will start at some point, it can be in an hour or in a day. I want ...
3
votes
2answers
1k views

Cheap way to detect client round trip times for http

I am trying to figure out a way to detect round trip times for each IP that connects to port 80 on my server. What is a good way to do this? There are far to many connections, and pinging each ip is ...
1
vote
4answers
2k views

Sniffing packets of specific binaries / apps / process id?

Is there a way to associate packets with executing binaries? I would be open to traditional sniffing methods or even dtrace for that matter. I have a specific issue on a system with very high ...
5
votes
2answers
348 views

Ubuntu 12 crashed and took down network

We recently set up a new Ubuntu 12.04LTS server on our network. It's not fully configured so it's not doing much beyond sshd and a default apache2 install. But this evening it appears to have ...
4
votes
1answer
3k views

iptables drop packet by hex string match

I got this packet captured with tcpdump but I'm not sure how to use the --hex-string param to match the packet. Can someone show me how to do it? 11:18:26.614537 IP (tos 0x0, ttl 17, id 19245, offset ...
3
votes
3answers
1k views

TCP segments of an HTTP Request in wrong order

My web-services server sometimes does not receive correct HTTP requests and returns "500 - Internal Server Error". Using tcpdump and Wireshark on the server, I found out that HTTP requests are ...
4
votes
2answers
2k views

tcpdump dns output codes

Captured on the nameserver: 21:54:35.391126 IP resolver.7538 > server.domain: 57385% [1au] A? www.domain.de. (42) What das the percent sign in 57385% mean? As far as I can see 57385 is the ...
-1
votes
3answers
2k views

ping: unknown host google.com

Relevant output: /etc/hosts 127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 ...
1
vote
1answer
563 views

How to filter out “bad-len 0” packets with tcpdump?

When I listen internal network interface of router on freebsd, I get outputs like this 10:36:02.372026 IP 192.168.1.11.8888 > 192.168.1.2.49831: Flags [.], ack 1097, win 65050, length 0 ...
4
votes
6answers
3k views

Log tcpdump Output

What I basically want is to to write all tcpdump captured packets to a file every 3 days. So basically tcpdump should run for 24 hours on day 1 and write the output to Day1.log and similar for Day2 ...
6
votes
2answers
6k views

Clarification about Linux TCP window size and delays

I have delays when sending data through a TCP channel I am not able to understand. The link is a 1Gb link with a end to end latency of roughly 40ms. In my current setup, latency (the time from one ...
0
votes
1answer
669 views

Cannot get a TCPdump from MySQL

I am having quite a few problems on a tricky server. One of my main problems at the moment is that tcpdump cannot seem to get the packets sent to mysql, unless I tinker with MySQL a bit. This is ...
-2
votes
2answers
269 views

TCP dump used for and how can it be used [closed]

What are the advantages and benifits of TCP dump and how can this be used and in which environments it can be used
1
vote
2answers
6k views

How to get http requests details in a tcpdump?

I am trying to get a tcpdump trace of some http requests. Here is what I got so far (I replaced the real IP addresses with REMOTE and LOCAL): C:\>Windump -na -i 3 ip host REMOTE and ip src LOCAL ...
5
votes
2answers
7k views

Pings from VPN network to VPN client work; pings into from VPN client to VPN network fail - why?

We are in the process of setting up an OpenVPN server for some servers running in a cloud. We are stumped with a connectivity problem whereby the hosts on the VPN server's LAN can ping te VPN client, ...
0
votes
1answer
773 views

tcpdump/Wireshark on restricted virtual server

When I try to dump some traffic on my vserver's network interface, I get an error that I'm not allowed to do that: # tcpdump -p -i eth0 tcpdump: eth0: You don't have permission to capture on that ...
4
votes
1answer
523 views

how to view hostnames in traffic entering my webserver (Apache)?

Is there any way I can view the hostnames used by incoming traffic that is accepted by my apache webserver? For example, say the webserver is set up to process incoming traffic for an IP address, ...
1
vote
1answer
290 views

PCAP to Syslog utility

I am looking for a tool which sniff all the traffic on an interface and produce a syslog like Cisco log in real time. Example : Feb 16 10:19:05 tcp S.S.S.S(6083) -> D.D.D.D(80), 1 packet Feb 16 ...
8
votes
3answers
5k views

Why won't tcpdump write a pcap file?

In the process of debugging a python irc bot that can't seem to connect, I thought "I know, I'll just tcpdump it and see what it's doing." So I ran tcpdump like I usually do and it says it's captured ...
3
votes
1answer
1k views

tcpdump udp data capture latency

I am using tcpdump to capture UDP packets and analyze network latency between a UDP broadcaster and my server. To calculate latency I compare the source host timestamps reported in UDP application ...
4
votes
1answer
14k views

tcpdump filter on network and subnet mask

I'm using the following tcpdump command: tcpdump -w net75.out -s 0 host 65.207.95.222 I want to change the filter on the single host to be all addresses in the following subnet: 65.192.0.0/10 I ...