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Questions tagged [packet-capture]

Packet capture is the act of capturing data packets crossing a computer network. Packet capture can be: Deep packet capture (headers & payload), or partial packet capture (headers only).

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tcpdump -vvv is not verbose enough

For tcpdump, I use this command to see the packet details: tcpdump -vvv -i interface and to save the packets into a pcap file: tcpdump -i interface -w output The details from the first command are ...
shadow's user avatar
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0 answers
30 views

How to capture GOAWAY from a Linux VM (Centos)

Objective: I'm troubleshooting integration between two service fleets proxied by Envoy (AWS AppMesh) using GRPC. My GRPC clients never send traffic to the new GRPC servers (after scale-out). Context: ...
Alcaneo's user avatar
0 votes
1 answer
381 views

Understanding TCP RST Network Capture

I only really need help understand the following image, but I will give the background for context. We have an app that is configured to use a proxy on port 8080 and requires Internet access. At ...
Mucker's user avatar
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0 answers
130 views

Method of streaming a packet capture from a Windows machine

I have a Windows 10 VM on Hyper-V. It is a production system (yeah I know) that is running multiple critical services that I need to analyse so I can migrate it off to something better. I need to ...
RoyT's user avatar
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0 answers
65 views

[Send mail with attachment]: TCP Retransmission, Duplicate ACK => TCP Reset

So, we have a linux box with postfix running on LAN site A which sends emails to an Microsoft exchange server sitting on site B. This runs perfectly when there is no attachment to the mail. But as ...
Michael Muller's user avatar
1 vote
0 answers
60 views

Ifconfig result on the server running PF_RING with zerocopy

I have an application which uses PF_Ring zero copy as a part of its packet sniffing capability. When this application is running would it be possible to find out the amount of RX/TX traffic using ...
user2714795's user avatar
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0 answers
292 views

Traffic capture at boot

I'm trying to figure out what packets a linux host sends at boot in order to debug it. Is there a way to start packet capture during boot time to not miss any packets? What is your way of going about ...
lolz's user avatar
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1 vote
0 answers
377 views

Disabled all TCP Offloading and still get 65Kb packets

I'm capturing packets in a Tensorflow two-node training. I want to capture the packet sizes over the wire (< MTU) from the hosts. Because of that, I turned off all of the offloading with ethtool. ...
morteza hosseini's user avatar
1 vote
0 answers
128 views

How to see contents of output queue of NIC in Linux and introspect frame delay

I am experimenting with tc tool to implement prioritization of specific data coming from my computer and would like to see exatly how the frames are scheduled and how much time they spend in the qdisc ...
Hadarelv's user avatar
0 votes
1 answer
882 views

Capture filter filter with tcpdump/tshark

I'd like to filter ip messages which are constructed as follow (see picture below): GRE on top of IP GRE contains IP with UDP on port 1234 (in the picture below port 80). How can I filter such ...
user1977050's user avatar
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252 views

How to identify source, destination ip using STUN and DTLS protocols?

enter image description here Given image i'm not able to identify which is source and destination ip address ( client or server). From STUN protocol 1st packet it's user request so i thought 131.202....
David Roonie's user avatar
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Where is the ACK to the packet in frame 76? [closed]

I am working through Kurose's book as part of a class and this particular exercise involves submitting a .txt file to the server and capturing this transfer and the server's response. In one exercise ...
Segmentation fault's user avatar
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1 answer
1k views

Is there a way to disable TCP segmentation offloading to prevent packets greater than the MTU from being captured from the loopback interface?

I'm trying to create some captures on my linux box. The problem I have is that any captures I take from the loopback interface will contain massive packets that are much larger than the MTU. This ...
kansas_bulldog382's user avatar
0 votes
1 answer
810 views

Pcap (tcpdump) filter to match against local port

I'm trying to write a libpcap (tcpdump, iftop) filter that would match packets having a specific local port. That is, I'm interested in traffic that either goes out of port 12345 on the local machine ...
intelfx's user avatar
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1 vote
1 answer
1k views

Forwarded Packets are received by namespace's veth0 but not received by application

I use libtins (It uses Pcap) to capture link layer packets and forward to a network namespace where the actual application runs on. Client(Browser) -> Server -> Pcap -> Pcap Send -> br0 (...
sqlbie's user avatar
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1 vote
0 answers
312 views

Drawbacks of having pruned and collapsed packets

I am a newbie in networking field, I come across a note that we should not have pruned packets and collapsed packets, if we have, we should have to optimize the system. But the note (neither the ...
smc's user avatar
  • 133
3 votes
1 answer
3k views

TCP Duplicate Ack without Packet Loss

edit: there were actually 2 problems, a buggy TCP implementation on the device running the RTOS and an issue causing the Linux network stack to receive the TCP fragments out of order when more than 1 ...
Mathieu Borderé's user avatar
1 vote
0 answers
217 views

How can I capture traffic for a daemon listening on a cloned loopback IP address?

I have a daemon listening on a virtual IP address attached to a cloned loopback interface (lo1) on FreeBSD 11.x. Inbound traffic for that daemon could arrive on several different physical interfaces, ...
Alnitak's user avatar
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1 answer
1k views

Send duplicate UDP packets to another computer

We have a production server where we receive a continuous stream of UDP packets (~ 15 Mbps). We have a small research team which wants to process this same exact stream for some research purposes on ...
Azeem Khan's user avatar
0 votes
1 answer
2k views

How do I capture packets on a Linux VM in a VMware environment?

I've got a Linux server that is a VM running on ESXi 6.7. We're running into some network trouble with it, and I'm trying to use tcpdump to capture traffic on the VM itself, but I'm getting only the ...
le_jawa's user avatar
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0 votes
1 answer
2k views

OpenVPN log connections per user

I'm trying to set up a VPN solution where I can log packet captures of individual connections. I've been focusing on using OpenVPN but I am amenable to other solutions. It is important to note that I ...
ahjohnston25's user avatar
1 vote
1 answer
253 views

how to man-in-the-middle blocking/intercepting/editing all network traffic going to a single cabled device and a server

I need to completely block and intercept and alter all packets going between two devices. possibly i need to isolate one device and block/intercept/edit ALL traffic going to and from it if i cannot ...
Ya Guy Godzilla's user avatar
0 votes
0 answers
524 views

Loopback interfaces is not pinging on both pcs for packet tracer

I am trying to ping my isp ip address (aka loopback 1) and loopback 10 to PC1 and PC2. Whenever I ping both ip addresses and default gateway from pc1 to pc2 it works. However, when I'm trying to ping ...
Kevin 's user avatar
0 votes
1 answer
2k views

How can I gathering Network Traffic on AWS?

I am building packet mirroring using the Linux type's iptables tee module. In the case of instances(EC2), we confirmed that promiscuous mode can be set on AWS console configuration. than, I wonder if ...
scott's user avatar
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0 votes
1 answer
68 views

CentOS 6 - Find KVM VM with HW addr

We are running KVM VM's (Linux & Windows) on our CentOS 6 & 7 hypervisors. Sometimes we are noticing a lot of packets going in or out. Now I want to see which IP address or network adapter ...
Pinkman's user avatar
1 vote
2 answers
4k views

What are the numbers preceeding a DNS packets flags for?

What does the Flags: 0x0500 section of this DNS query packet mean? Domain Name System (query) Transaction ID: 0x4242 Flags: 0x0500 Standard query 0... .... .... .... = Response: ...
Justin's user avatar
  • 13
0 votes
1 answer
126 views

Tips for working with very large pcaps?

What is the best approach for working with very large collections of network traffic (500GB+)? Specifically, I'd like to be able to filter packets which match various payload and protocol criteria (...
pavja2's user avatar
  • 101
0 votes
1 answer
307 views

Network sniffer that work as windows service

We need to log the traffic of incoming traffic for some application on our server. The first instinct is to use Wireshark and of course, as soon our remote session end Wireshark also shutdown. Since ...
Lishi's user avatar
  • 101
0 votes
1 answer
581 views

Are TCP RTO value and RTT value influenced by the packet size?

I am doing troubleshooting in my network. I found some re-transmission by using wireshark. The segment 1400 bytes are well transmitted but The segment 800 bytes are lost and re-transmitted. I know ...
nimdrak's user avatar
  • 139
1 vote
2 answers
1k views

What should be the next sequence number after a packet with the FIN containing payload?

I was capturing some HTTP traffics and I observed a packet with the FIN flag set and also containing payload data. I searched for this topic and I found some similar questions but none of them ...
mrazimi's user avatar
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2 votes
2 answers
3k views

Get network data transfer rate / throughput for use in Wireshark

I'm trying to get the ethernet NIC throughput rate / data transfer rate on a VPS in order to start a capture on Wireshark during DOS/DDOS attacks so I can analyze the nature of the packets. I'm ...
I'm Root James's user avatar
1 vote
1 answer
297 views

How does LDAP Authentication Work at the TCP Layer?

Specifically, how does an LDAP server distinguish a TCP packet containing a SearchRequestOp from an authenticated user, from a TCP packet containing a SearchRequestOp from an unauthenticated user? I ...
Tikiyetti's user avatar
  • 113
1 vote
1 answer
642 views

Can user credentials from HTTP session be seen through Wireshark? [duplicate]

Can we get that info the same way we do for FTP since HTTP is a plain text protocol?
Yoane Maior's user avatar
2 votes
1 answer
2k views

Can I verify failure of port forwarding using wireshark / packet capture

I've recently configured a Debian 9 server (Debian 4.9.130-2) to run as a lightweight server, running a series of Docker containers (nextcloud, sync, etc.) alongside basic services like ssh. Services ...
Jeremy Kidwell's user avatar
1 vote
1 answer
4k views

Can I capture full TCP packet content with haproxy without knowing length of the packet?

I know I can capture 6 bytes length packet using this config: global log /dev/log local0 debug log /dev/log local1 notice chroot /var/lib/haproxy stats socket /...
Defozo's user avatar
  • 153
0 votes
1 answer
1k views

How to turn an ethernet port into a passive listener?

I want to capture ethernet packets with my raspberry pi's ethernet port. I know I could create an ethernet bridge between two ethernet ports on the raspberry and analyze the packets internally with ...
guerlando's user avatar
1 vote
1 answer
602 views

rpcapd behind a firewall

I have a remote server with rpcapd installed that follows strict security policy rules. Any client can access to the server only via firewall that follows same security policy (please, don't blame me, ...
enzo's user avatar
  • 11
0 votes
2 answers
135 views

Port forwarding for 100K+ IP's

I need to do port forwarding on my Linux (Debian 8) to intercept packets going through the machine. It needs to be based on source IP, so different ports for different IPs. I've though of using ...
Alfred Balle's user avatar
0 votes
2 answers
2k views

Who can issue a RST?

I have a client connecting to a server via a VPN tunnel. The connectivity is in place, I can ping the server and requests some other services (a curl request on an API for instance) through that ...
WoJ's user avatar
  • 3,657
-5 votes
1 answer
61 views

How packet is transmitted over the network? [closed]

I am writing discrete event-driven simulator to measure time between sending datasets over network. If multiple processes sends n packets through network they (packets) will go one after one through ...
Kenenbek Arzymatov's user avatar
0 votes
1 answer
81 views

Cisco 877 doesn't respond to IP determined through ARP

I have just obtained an old Cisco 877. I made sure to first push the reset button in the back. I then plugged into one of the LAN ports. The device gave me an IPv4 address (169.254.14.65/16) and an ...
Stringers's user avatar
7 votes
2 answers
7k views

How can I decrypt STARTTLS communication over SMTP in a packet capture (if I have the private key)?

For the purpose of troubleshooting, I need to see what an email looks like when it's sent to my sendmail server via SMTP. The upstream server requires the SMTP connection to use STARTTLS so a packet ...
Mike B's user avatar
  • 12k
2 votes
1 answer
5k views

How can NETSH be used to sniff and collate network traffic?

I am trying to capture all network traffic and view it in a human-readable way. To begin packet capture with netsh, I am running the following command. netsh trace start scenario=NetConnection ...
jsc's user avatar
  • 145
2 votes
1 answer
16k views

Client sends RST after FIN,ACK

While doing a file transfer using secure file transfer protocol, I am seeing the behaviour as given in the below image. Instead accepting packets from server, it simply sends a RST. Found a similar ...
Joemon Emmatty's user avatar
0 votes
1 answer
965 views

How can I identify the cause of packet loss in DNS?

We have upgraded some of our routers to Ubuntu 16.04 and are now getting some performance problems with DNS. It seems that packets are sometimes truncated, but I have no clue what else I can do: This ...
Thomas's user avatar
  • 187
6 votes
2 answers
8k views

How to determine which process is sending UDP packets once per hour?

I was doing a packet capture as part of a development project and saw some odd traffic coming from my machine in the capture file. About every 3600 seconds, a NAT-PMP request is being sent to the IP "...
fdmillion's user avatar
  • 419
1 vote
1 answer
3k views

Packet Captures saved in bin file format

Does anyone know of a tool to open a packet capture saved as a .bin file? That or how to convert it to pcap or something wireshark can open. I took a packet capture from a thin client and when I ...
veel84's user avatar
  • 288
0 votes
1 answer
690 views

How do I generate a source of netflow data for nfcapd?

I am trying to use nfcapd to save netflow files for use by a network analysis tool. How do I capture network traffic on my host and send it into nfcapd? Can I use wireshark/tshark or something ...
aaa90210's user avatar
  • 351
1 vote
0 answers
455 views

Netsh trace vs PEF trace cmdlets vs NetEvent cmdlets

I am playing with capturing my network traffic and came across two different MS commandline tools that allow doing this: a well-known netsh tool, recently equipped with powerful capture switch a ...
Suncatcher's user avatar
2 votes
2 answers
2k views

Process names in MS Message Analyzer

I am trying to set up the Message Analyzer viewer exactly like it is explained in this reference, but instead of steady process names I got some weird numbers, both in ProcessName and ProcessID ...
Suncatcher's user avatar