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Questions tagged [tcpdump]

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

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Cannot connect to exim4 SMTP server

I have the problem that I cannot connect to my exim4 SMTP server from my home network: $ telnet -4 example.com 25 Trying 1.2.3.4... telnet: connect to address 1.2.3.4: Connection refused telnet: Unable to connect to remote host netstat on the…
flyx
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How can I tunnel multicast traffic?

I am trying to receive multicast on 1 machine, forward it to another machine, and then replay it on that machine. test_env: the machine which has access to the original multicast stream mcast_sender: the machine which I'm trying to forward the…
Steve Lorimer
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Tcpdump works only the first time in a cron job

I have this cronjob that has the following two lines: /usr/sbin/tcpdump port 8086 -i any -l -e -n | /usr/bin/perl /root/netbps.pl > /root/bw/8086.txt /usr/sbin/tcpdump port 8085 -i any -l -e -n | /usr/bin/perl /root/netbps.pl >…
GuestThatNeedsHelp
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Taking tcpdump of data transmitting through tunnel

I have a service provider, who provides connection to his SMPP server only through a VPN. We setup a tunnel to connect to his VPN. Now there are some issues with the connectivity and I need to check the tcpdump. But I am not able to do so. I…
kadamb
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tcpdump gives encrypted results

If I run the following: tcpdump -A -w /tmp/apache_outgoing.pcap trigger an event and then look at the pcap file I see something like: �y�<�*�^L�cM9��^U^MK Is there any way to make the tool human readable output?
Antony
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Linux servers sometimes doesn't answer TCP connections or very delayed

I have Linux server (Ubuntu 16.04) where every serverce seems to be fine, except that it sometimes answers TCP connection very slowly (eg. 10 -20 sec) or not at all. The server is not under load and this happens accross all TCP services (HTTP, SMTP,…
Gene Vincent
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pings ignored across VPN with Centos 7

I'm trying to setup a CentOS 7 DNS server in a VPN. I can't get devices from the VPN subnet (different subnet) to ping servers. I can get pings to work between servers (same subnet) When I run tcpdump -nvi eth1 icmp I can see the following: When…
101010
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A process in LISTENING state is sending packets?

My TCPView shows that a process called winrdlv3.exe is in TCP LISTENING state while the count of its sent packets is keeping increasing (no received packets)? How can a process in LISTENING state send packets?
xiaokaoy
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How to display traffic information in a parsable format?

tcpdump is my go-to tool to analyze traffic (together with Wireshark when I want an easier review of the pcap file). This fantastic tool fails however to deliver a predictable and easy to parse output format ("predictable" as in "same on all Linux…
WoJ
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An odd-looking TCP-session script

I've faced a quite odd issue, which I'd like to share with you. Maybe you'd help me with some ideas on what's going on. There are 3 virtual machines on a KVM-powered host. Actually there are about 50 VMs, but they all are working fine, although…
Volodymyr Melnyk
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OpenVPN Routing to LAN Behind Server

I have a site-to-site VPN configured using OpenVPN. The tunnel seems to come up just fine (and I can ping from one end to another), but I cannot get the networks on the two ends to see each other. My topology is as follows: Net1 (192.168.13.0/24) …
Bogd
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http timing stats from tcp trace

I am trying to find a tool to extract HTTP timing stats from network traces; namely time to connect, time to first byte, total time to serve.I am talking about very large traces with millions of requests. Ideally I would like to generate Apache…
Azer H
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Zimbra/Postfix on ubuntu stoped receiving emails from outside. Help to confirm this is not ISP blocking incoming port 25

I'm using zimbra on ubuntu as an email server behind a zentyal firewall. Im having problem Zimbra stopped receiving email from outside. Internal emails or outgoing is fine. ISP blocks all outgoing 25, but we are using their SMTP server. I have…
lesmana
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In the output of Chaosreader, where are the source and destination port numbers and IP addresses for each packet?

I used this tutorial to use Chaosreader on an output file of WinDump. My purpose was to get the HTTP payload, which I got. But I'd also like to extract other information, like source IP and destination IP, source port and destination port, for each…
Jesss
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can tcpdump detect higher level protocols like wireshark?

Wireshark will guess what higher level protocols are being used in a packet, but how can I get tcpdump to do likewise (or any other linux command line tool)? For example, the following screenshot shows wireshark detecting "HTTP" as the protocol…
Alexander Bird
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