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

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2answers
205 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 ...
-2
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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
85 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 ...
0
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2answers
258 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 ...
3
votes
1answer
297 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
119 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
0
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2answers
363 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 ...
3
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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
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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 ...
4
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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
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1answer
268 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
160 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
493 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
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1answer
209 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
110 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
70 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
606 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 ...
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votes
1answer
650 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.
4
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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
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1answer
396 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
152 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
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1answer
539 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 ...
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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
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1answer
468 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
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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
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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
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2answers
348 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
209 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
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2answers
2k 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
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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 ...
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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 ...
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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
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2answers
357 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 ...
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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
609 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 ...
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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 ...
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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
700 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 ...
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votes
2answers
279 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
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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 ...