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

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Identify local IP address in tcp dump [on hold]

I have a tcp dump file with 4100 connection details. How can i filter the data to identify the local IP address and the number of host?
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2answers
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How do I see absolute time stamps in Wireshark?

There is an example of pcap file opened in wireshark The second column is time. Is it possible to see absolute timestamps here instead of relative?
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2answers
8k views

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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1answer
17 views

Is it possible to specify tcpdump that I want it to interpret packet differently before printing it to STDOUT?

I am using iperf to pinpoint packet reordering issue. Unfortunately, tcpdump does not know how to parse iperf's UDP payload that I could use to pinpoint the issue. I know that iperf stores packet ...
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1answer
36 views

Why are ICMP packets not captured on the target interface?

I have a network setup as in the picture: The central box is a gateway (Ubuntu 15.10) which relays the packets betwen the various networks (only one is shown on the picture - lan0) and Internet. ...
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2answers
20 views

tcpdump http containing non expected payload bytes

I am monitoring an openvpn link with tcpdump a la tcpdump -i tun5 -w capture.dump -W 100 -C 100M -s 0 -n There is http/xml traffic going over that link which is basically caputered just fine. However, ...
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5answers
2k views

Determine originating process for outbound traffic

I can see that my server is sending out a lot of traffic. If I go to netstat -apln | grep httpd I can see that all the traffic is going to one IP. Is there a way I can see what script / file is ...
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1answer
25 views

PCAP filter for first few packets, and packets related to disconnection, TCP-only

I'd like to use tcpdump with a filter for some long-running debugging. Specifically, I only want to capture packets with the following conditions: First 10 packets or so of a new TCP connection ...
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1answer
60 views

Use tcpdump to capture an ICMP destination unreachable message

I am new in this area. I am asked to use tcpdump to capture an ICMP destination unreachable message in my network course. So I am trying to capture one message that is an ICMP destination unreachable ...
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1answer
90 views

Is it possible to run 2 concurrent tcpdump with different options?

I need to run 2 concurrent tcpdump commands with different arguments/options. Why ? Because we wrote some long long scripts compatible with following options : tcpdump -ixenbr0 -s 400 -n -A 'port sip ...
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35 views

NATted host cannot talk to itself unless virbr0 is in promiscuous mode

We have the following situation: A hypervisor using KVM-Qemu/libvirt with a single VM. The VM has the internal IP 192.168.122.151 on the default network pool using virbr0 on the hypervisor. We've ...
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1answer
26 views

tcpdump - filter applies after some time?

I have a strange problem with tcpdump - it's like the filter I want to be applied to captured packets doesn't work instantly. Maybe it's perfectly normal but to be honest I've never seen this before. ...
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30 views

Analyzing SSL Encryption Alerts

I have captured the traffic between my machine and my server using Wireshark, trying to find why some SSL requests fail. I've read this and this post about debugging SSL entries, and I'm able to find ...
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2answers
747 views

user agent in http or https request

Is there any way that I can differentiate, the HTTP or HTTPS packets are coming from browser or not ? specially for https request.There is User-Agent field in packet in Http,but I could not found ...
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0answers
33 views

Duplicate SYN package forwarded by Docker?

I'm experiencing a strange interaction between a CISCO firewall and my Docker host connected to it: the CISCO periodically marks my host as a SYN attacker and shuts my ethernet port down. I've been ...
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2answers
28 views

Ubuntu server - packets from different networks not coming through (flushed iptables)

I have set up a brand new Ubuntu server, and I'm encountering a very strange network related issue - the processes running on the server cannot 'see' packets originating from external networks, but ...
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1answer
105 views

Server send TCP ACK with wrong number after receiving SYN

I have a client establish new TCP connection then sends request to a server per second. Both client and server are on the same linux box (via loopback interface). The client periodically reports ...
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2answers
6k 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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2answers
3k views

Filtering GRE enacpsulated packets with tcpdump

I can ask tcpdump to show me GRE encapsulated packets quite simply with tcpdump -ni any proto gre: 15:02:57.209082 IP 10.14.0.3 > 10.14.0.2: GREv0, key=0x1, length 106: IP 10.10.10.11 > ...
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2answers
34 views

Monitor networking between two interfaces

I need to monitor TCP networking between two hosts which does not have tcpdump installed, and I cannot install on them. Is it possible to do so with tcpdump using some known rule ?
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3answers
33k 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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63 views

Xen networking - dom0 receives ARP requests but no reachability

Both dom0 and domU are Debian 8. Dom0 network configuration is: auto xenbr0 iface xenbr0 inet manual bridge_ports eth1 bridge_stp off bridge_waitport 0 bridge_fd 0 auto xenbr0.4 ...
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2answers
3k views

TCP Messages Merged?

I have an application that sends 100 of 186-byte (excluding headers) TCP messages back to back without gap from host A to host B. I ran tcpdump to capture the packets on host A (where the sender is), ...
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2answers
48 views

How to send captured packets to a different destination?

I have some data packets captured using tcpdump in a pcap file. Now I want to send those packets to a another destination. how I can achieve this?
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114 views

tcpdump on bridge interface (virbr) does not receive any packets destined for one of its addresses

Here's the configuration for the interface: # ifconfig virbr0 virbr0: flags=4355 mtu 1500 inet 192.168.11.1 netmask 255.255.255.255 broadcast 255.255.255.255 ether ...
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45 views

How can tcpdump monitor TCP disconnect and log timedate stamp?

I have two servers each running a Java application that creates two separate TCP connections, one from HostA -> HostB and one from HostB -> HostA on separate ports. I am told the TCP connection is ...
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How does TCP PSH and HTTPS works?

Right now I monitor traffic on my VPN server. I'm using tcpdump for it and it works pretty good. sudo tcpdump -n host SENDER_IP In this example you can see one HTTPS request from SENDER_IP to ...
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43 views

Server socket sitting in FIN_WAIT_1 whilst network doesn't see its traffic

We've been trying to get a grip on a really weird problem where we can wget a page from Apache 2.2.19 on solaris 10 and some permutations of requests reliably take various fixed lengths of time to ...
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51 views

Monitor outgoing web traffic sources on CentOS [duplicate]

I received a report today that a server I manage (Centos + Apache) is launching a bruteforce attack against wordpress websites: hacked-joomla/brobot The requests sent look like this: x.x.x.x - - ...
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24 views

Not getting TCP Update Window packet after TCP Zero Window begins

Once I get TCP Zero Window during data transmission, I can't send data anymore in that desktop sharing session. Even I stopped the data sending to check if it can resume but no benefit! In my test ...
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4answers
262 views

Monitor and collect statistics on TCP connection to src or dst host

I would like to collect stats on TCP/UDP packets sent between two hosts (A and B). I am looking for a tool to install on A and B to get the following information: kb/seconds packets/seconds ...
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1answer
164 views

Wireshark shows “TCP Dup Ack” on SACK after each regular ACK

I have a TCP session captured via switch port mirroring and tcpdump. When viewing it (in Wireshark), I see the same pattern whenever I send a message; here's an excerpt of the outbound packets (I ...
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2answers
57 views

wget only works when tcpdump is listening

I am running two Virtual Machines over the XEN hypervisor both with Ubuntu trusty (Linaro-Developer version) with the following simple bridge networking setup: Backend domain (dom0): br0 ...
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55 views

“Filtered” port when accessing server

I'm having periodic trouble accessing one of my DigitalOcean servers from Azure machines. I have isolated a test that - I believe - demonstrates the issue and captured a tcpdump from the server for ...
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244 views

Capturing on loopback device on Ubuntu LTS: 15 Mbit of traffic and “x dropped packets”

I am trying to capture about 15 Mbit of traffic on the loopback device on Ubuntu LTS using tcpdump, and I am seeing dropped packets. The CPU is a freaking i7, and i have yet to see CPU usage go above ...
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1answer
75 views

On-the-fly decoding HTTP bodies on Linux?

My wish is to monitor HTTP exchanges between my server and a browser. At present time, I use the localhost because I'm developping the app. I installed and used tcpflow and found it quite useful but ...
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1answer
24 views

What does “-tnn” mean in “tcpdump -i eth0 -tnn dst port 80 -c 1000”

What does -tnn mean in tcpdump -i eth0 -tnn dst port 80 -c 1000. I didn't find -tnn on the man page, and I didn't find it on the Internet. Can anyone explain it to me?
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1answer
186 views

Finding google unusual traffic

We are a small Internet provider. In order to get Internet access we are using NAT (10-20 users per one public IP). And lately we've met with Google blocking services (captcha and full block) and we ...
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1answer
1k views

Will tcpdump see packets that are being dropped by iptables?

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 iptables -A INPUT -p tcp ...
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45 views

Packet capture on ESXi host

I have an issue I am trying to track down and I believe the problem is with physical networking hardware. I have read the VMWare documentation on the pktcap-uw command and I know I can use it to dump ...
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87 views

Wireshark RST against TCP Zero Window

During application sharing with Microsoft Lync Client (Mac OS X), TCP ACK with RST flag is sent from my application end to Lync end against TCP Zero Window packets and call gets dropped. Image Link. ...
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293 views

Sometimes unable to tune Linux TCP stack for improved high-latency performance

I have been unsuccessfully trying to apply the TCP Tuning techniques discussed at http://fasterdata.es.net/host-tuning/ As you'll see when you read through the entire question, sometimes the es.net ...
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45 views

pfsend does not send a pcap file at specified rate

I'm replaying traffic using pfsend application that comes from PF_RING. I'm using SMIA pcap file to evaluate Bro and Snort on a multi-core machine. Using pfsend, we can specify at which rate the pcap ...
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2answers
1k 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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3answers
464 views

How would a PCAP filter look like to capture all DHCP related traffic?

As I understand it, for IPv4 I would need to capture UDP port 67 and 68, ARP, ICMP echo request and reply, and for IPv6 I would need UDP port 546 and 547, all DHCP-related multicast addresses, ...
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7answers
10k 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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OOM Killer when tcpdump is run in system with low memory

I am working on an embedded system with limited memory. Here is the dump from my vmstat: procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu----- r b swpd free buff ...
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1answer
408 views

SynProxy can not return syn ack packets with asymmetric dual bridge topology

I have a asymmetric dual bridge topology as shown below when i connect from 172.16.11.5 and 172.16.10.6 with ssh but i can not connect because of SynProxy. ------- ...
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2answers
2k 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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87 views

Capture all mysql requests/responses and caculate the response time using tcpdump

I need to capture all mysql requests/responses using tcpdump and after that need to find out which response related to which request in order to caculate the response time of each request. I used the ...