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

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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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50 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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166 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
334 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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2k 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
150 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
74 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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624 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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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
408 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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46 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
505 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
3k 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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596 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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4answers
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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372 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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310 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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4k 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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265 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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2answers
1k views

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
380 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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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
507 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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418 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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131 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
157 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
702 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
60 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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126 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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239 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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95 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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263 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
797 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
831 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
2k 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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195 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)
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125 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 ...
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1answer
351 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 ...
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1answer
177 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 ...
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2answers
621 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?
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1answer
102 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
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1answer
56 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 ...
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1answer
488 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 ...
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1answer
39 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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1answer
343 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.
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2answers
3k 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 ...
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1answer
368 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] ...