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

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5
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28 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. ------- ...
2
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0answers
128 views

Suggestions on how to capture network connections/traffic for determining browser/SSL versions?

Note that I posted this Q to the StackExchange InfoSec site, but its not as populated as ServerFault and this is more on the technical side of network collection for web services. I've started ...
1
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1answer
44 views

Tcpdump/Iptables on bridge interface without assigned IP address

I have set up a bridge interface without an ip on it. $ brctl addbr br0 $ brctl addif tap0 $ brctl addif tap1 $ ifconfig br0 up As seen above, this bridge is connecting 2 TAP interfaces setup ...
2
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0answers
30 views

Wireshark only capturing broadcast packages [closed]

I've ran Wireshark multiple times on my notebook for wireless networks verifying mobile packages for my devices and it used to work most of the time. I haven't been able to monitor my traffic today ...
12
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4answers
240 views

tcpdump increases udp performance

I'm running a set of load tests to determine the performance of the following setup: Node.js test suite (client) --> StatsD (server) --> Graphite (server) In short, the node.js test suite ...
4
votes
4answers
80 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 ...
1
vote
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 ...
0
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0answers
56 views

Nginx TCP Fast Open Issue

I have configured Nginx and Apache on one of my servers. The nginx server listens on port 80 and Apache on port 81. Nginx works as a reverse proxy. In nginx I configured TCP Fast Open: server { ...
0
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3answers
457 views

shell record UDP stream from a specific address

I'm trying to record an incoming UDP stream (stream the sense that it's a stream of consecutive datagrams). I tried netcat but unfortunately multiple sources send data on the same port address and nc ...
0
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0answers
82 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 > ...
0
votes
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 ...
0
votes
1answer
25 views

tcpdump capture destined to other server

I´d like to ask for help in understanding this tcpdump capture. Tcpdump is running on server 10.13.255.27 and received the packet: root@server27 ~]# tcpdump -i eth0 dst host 10.13.255.26 and not src ...
5
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1answer
5k 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 ...
0
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2answers
755 views

tcpdump Server Hello Certificate Filter

On a devices located between my local network and a router, (all the traffic pass through) I need to read the common name from Hello Server Certificate packet. So I'm trying to figure out how to get ...
21
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6answers
34k views

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?
1
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1answer
48 views

How to strip TCP headers from tcpdump (with hexadecimal output of non-printable data)

tcpdump don't know how to strip TCP headers from packed data. tcpflow print's only packet data, nice, but it supports only ASCII characters, no hexadecimal output possible. Did I overlooked some ...
0
votes
1answer
80 views

how to determine client side or server side retransmission from a pcap

I am trying to get some clarification on something I read here: how to calculate packet loss from a binary TCPDUMP file The first answer says that the sequence number will be the same from client to ...
3
votes
1answer
102 views

Tcpdump maximum split file size

I refer to this thread : how to split a pcap file into a set of smaller ones I have tried to use the command tcpdump -r old_file -w new_files -C 4096 and tcpdump returns tcpdump: invalid file size ...
2
votes
1answer
76 views

How to filter for the most common problems with tcpdump/tshark

I am currently using the following command in Linux to get specifics on network problems. tshark -r file.pcap -q -z io,stat,1,\ "COUNT(tcp.analysis.retransmission) tcp.analysis.retransmission",\ ...
7
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2answers
2k views

TCP Dump, cannot understand these 4 lines?

I need support understanding these 4 lines. looks like tcp dump but im actully not understanding what exactly is happening here. 13:13:22.407445 IP 192.168.246.128.54955 > 192.168.246.13.80: S ...
3
votes
1answer
620 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 ...
0
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0answers
38 views

How to manage overload of ICMP with PF?

I would like to make a basic managment of ICMP overload with packet filter on FreeBSD. The function I would like to realise is:     if target receive too many ICMP from a given source IP address,   ...
4
votes
6answers
5k 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
68 views

server is not responding on SYN packets

On the attached tcp dump, the first two SYN packets (#21800 and 21801) came to the server, however SYN ACK was sent for the second SYN. Is that correct behaviour? My understanding is that the client ...
0
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3answers
75 views

how to use tcpdump to log only certain data in real time

I'd like to monitor network interfaces but only log things likes errors, collisions and dropped packets. The send that to stdout. – Can tcpdump be configured to do this?
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2answers
88 views

How to use tshark or tcpdump to calculate bytes transmitted

I am using this command with tshark: tshark -r pcapfile "tcp and ip.src==192.168.1.1" -T text -V -x | grep 'Total Length' This essentially parses the pcap for only connections from the source ip ...
0
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0answers
60 views

What conditions can account for incorrect inbound TCP checksums?

According to The Wireshark FAQ TCP checksum offloading causes checksums for outbound traffic to be calculated incorrectly. On some Linux hosts I see some inbound TCP traffic that is flagged with ...
6
votes
5answers
7k views

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 ...
0
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1answer
102 views

Capturing LDAPS traffic with tcpdump

I have an app server that authenticates against Active Directory using LDAPS. I am connecting to the AD server over port 636. I'm trying to troubleshoot/debug some performance issues and am beginning ...
0
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0answers
62 views

Analyzing TCPDUMP results for failed request

I'm making http POST calls to a database every 30 seconds, both the server and database are on the same host. Every 5 minutes or so, I get an error back from the endpoint indicating that the request ...
0
votes
1answer
108 views

How to trace TIME_WAIT sessions using tcpdump (or similar tool)

I have a server with large number of TIME_WAIT sessions. These are sessions that the server closed, but the client didn't close. I want to analyze a sample session, to understand what happens there. ...
2
votes
5answers
414 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 ...
0
votes
1answer
226 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 ...
3
votes
2answers
348 views

tcpdump truncates to 1472 bytes useful data in UDP packets during the capture

I am writing an application which work with network. To perform some tests I need to reproduce the flow which I had a day before. But at the same time it is not allowed to stop the current working ...
1
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0answers
746 views

Only capture HTTP post requests through tcpdump

For security purposes we want to list all POST requests URI's that are used in our applications (so we would disable POST through mod_security except for those URI's). The idea is to use tcpdump to ...
0
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0answers
71 views

multicast packets: when are they received with the receivers ip and when with a multicast ip

I am trying to connect 2 computers running jack for audio re-routing. Jack communicates through multicast packets on address 225.3.19.154 (port 19000) by default. I have successfully connected linux ...
1
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0answers
35 views

An already acknowledged data sequence number is coming back as null byte repeatedly

There is a transaction processing server (TP-Server) to which my application (Client) connects to. We are seeing a strange packet sequence where in the TP-Server is sending a PUSH packet with a null ...
0
votes
1answer
103 views

Tcpdump advanced filters

i want ask for command can Get only the IPs have more then 1 connection with different source port xxx.xxx.xxx.xxx:X | xxx.xxx.xxx.xxx:Y (example) if IP1 has connection to server with Src Port X ...
-1
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1answer
77 views

Is it Possible to Capture All HTTP Packets to a Target IP on a subnet?

I've been trying to use tcpdump to capture packets to a target IP on my subnet, but am unable to do so successfully. I've tried: tcpdump -i eth0 net network-ip-address/27 -A and tcp port 80 But it ...
7
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3answers
12k 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 ...
0
votes
1answer
115 views

What can possibly prevent tcpdump from showing request packets?

I am trying to debug a little SOAP issue. I am using a java web app to consume an API over a VPN. ping and telnet on the webservice server are fine.The Environment is aws ec2 for my app. I have no ...
8
votes
2answers
547 views

Packet captures: filtering on RX vs TX

I have a network problem where frames with a source MAC which matches with one of my host's source MACs are arriving at the host - an apparent duplicate MAC, or loop, or other L2 problem. I believe ...
0
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0answers
81 views

amazon ec2 ftp RETR hangs

The problem is with an Amazon ec2 instance "Red Hat Enterprise Linux Server 7.0 (Maipo)" (kernel 3.10.0-123.6.3.el7.x86_64) When attempting to RETR a remote file the FTP client hangs indefinitely. I ...
2
votes
1answer
2k 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 ...
0
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0answers
92 views

Use tcpdump to find interface errors

I looking for what's causing dropped packets on an interface: RX packets:9064457 errors:0 dropped:4736 overruns:0 frame:0 TX packets:6388938 errors:0 dropped:0 overruns:0 carrier:0 I ...
0
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0answers
216 views

tcpdump on any interface does not support VLAN

I have tried the following command: tcpdump -i any vlan , on both Ubuntu 10.04 (kernel 2.6.32-36) and Ubuntu 12.04 (kernel 3.8.0-39) and got the following output: tcpdump: no VLAN support for data ...
0
votes
1answer
110 views

Need help examining tcpdump file to block attack

I need some help, my game server has been under fire with DoS attacks for 2 days now. Bandwidth attacks are no problem since I host with OVH and they are filtered out but my game server ports are ...
3
votes
1answer
70 views

tcpdump: decode packet starting at non-zero offset

I'm debugging a Linux embedded platform which has an interface where regular ethernet frames have an additional 82-octet platform header tacked on the front. I am able to sniff from this interface ...
1
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2answers
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 ...
0
votes
1answer
775 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 ...