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

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4
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1answer
616 views

tcpdump and congestion window

Sniffing http traffic to my (linux) server it seems like it always responds advertising a window size of 14. It isn't affected if I change the default initcwnd size (with ip route), and it doesn't ...
5
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2answers
4k views

What do “Unknown SSAP” and “Unknown DSAP” mean in tcpdump?

While trying to fix a problem with intermittently losing internet connection on a machine with a wireless connection to a router, I ran tcpdump and noticed packets with "Unknown SSAP" and "Unknown ...
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2answers
2k views

TCPDUMP = How to detect and analyse “Suspicious” Traffic to 192.xxx Addresses?

I just played a little bit with tcpdump (as I wanted to check why my mails are not getting send) and thereby discovered very strange and a lot of traffic to the "Private IPs". Please See examples ...
5
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1answer
4k 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 ...
7
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4answers
6k views

Monitor number of bytes transferred to/from IP address on port

Can anyone recommend a linux command line tool to monitor the number of bytes transferred between the local server and a specified IP address/port. The equivalent tcpdump command would be: tcpdump ...
1
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1answer
180 views

tcpdump not giving details

Why does tcpdump not give my more details? Each time it only comes as - 16:22:26.128541 [|ether] # ./tcpdump -vv not port 22 tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size ...
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3answers
3k views

tcpdump filter according to http header content

using tcpdump i would like to filter the responses that comes back from a squid cache server to only the responses that came back from the cache. that means that i need to filter according to the ...
0
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3answers
3k views

tcpdump syntax for only capturing traffic coming to a specific virtual interface / local IP

CentOS 5.x Hello All, I need to collect a packet capture of https requests going to a specific IP address / virtual interface. Is there a specific switch/parameter for tcpdump that will allow ...
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2answers
1k views

Why Packet Loss AFTER tcpdump has logged the packet?

We encounter some strange packet loss and want to know the reason for this. We have an imageserver and a server for stressing the imageserver. Both are located in the same datacenter First we run a ...
1
vote
2answers
170 views

Question about tcpdump

On this link I found few informations about use of tcpdump. But, can you give me more information about example showed on that page: tcpdump -s 128 -vvv -T rtcp src orac and port 57393 ...
4
votes
2answers
919 views

Anyone can tell their experience with 10g Ethernet adapters on Linux

I wonder if any of you have an experience with 10g NICs (Intel, Myricom, SMC tiget, napatech, or by any other brand). Questions are: Was it easy to install, or a hassle, How does this adapter ...
2
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3answers
5k views

How can i sniff/dump HTTP protocol as ASCII for a port with tcpdump or altenative?

I need to view how an application is sending and is receiving traffic through a http protocol that it comunicates on localhost (it has an embeded port coded with .gz) I'm sure it's some XML that it ...
3
votes
1answer
2k views

Kill FINished sockets (using libpcap - tcpdump/tcpkill)

I'm trying to create a small service that monitors and kills sockets which have the FIN flag. I can get them with tcpdump (I also tried tcp[13] & 1): tcpdump "tcp[tcpflags] & tcp-fin != 0" ...
1
vote
2answers
3k views

How can I capture traffic with tcpdump and a sliding window or sort of “logrotate”?

I want to capture some traffic with tcpdump for troubleshooting. The problem is, the error is not reproducible. To not fill up the hole disks with captures, I would like to capture the traffic with ...
0
votes
2answers
593 views

Howto monitor traffic between IIS and MSSQL

I am trying to check how much traffic is flowing between MSSQL Server and IIS Server in different locations. There is 1 ipcop in every location and I download the tcpdump file from one firewall and ...
2
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0answers
1k views

How to know the source of certain TCP traffic on AIX

We have two AIX boxes, one for production system and another for testing. both systems are running ATM machine switches, where the ATM device is connected via TCP socket. we had an issue on ...
5
votes
4answers
6k views

Packet loss rate with iperf and tcpdump

I tested a line for its link quality with iperf. The measured speed (UDP port 9005) was 96Mbps, which is fine, because both servers are connected with 100Mbps to the internet. On the other hand the ...
0
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3answers
1k views

How can I log all traffic with its exact length?

I want to process all packets with their size going through our gateway server (running Debian 4.0). My idea is to use tcpdump, but I have two questions. The command I'm currently thinking of is ...
22
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3answers
26k views

how to split a pcap file into a set of smaller ones

I have a huge pcap file (generated by tcpdump). When I try to open it in wireshark, the program just gets unresponsive. Is there a way to split a file in set of smaller ones to open them one by one? ...
3
votes
3answers
10k views

wireshark http POST

I would like to have a http POST request method CAPTURE filter. I know it is easy to do it by display filter http.request.method==POST but I need tcpdump compatible. I wrote tcp dst port 80 and ...
7
votes
5answers
5k views

How to Break Up Large tcpdump Files

Is there something that can break up tcpdump file after the captuure and make sure the breaks are on the border of packet data? Like -C but after the fact.
4
votes
2answers
4k views

tcpdump filter that excludes private ip traffic

For a generic filter to exclude all traffic in my dump that is between private IP address, I came up with the following: sudo tcpdump -n ' (not ( (src net 172.16.0.0/20 or src net ...
1
vote
1answer
44 views

Running Job and Paused Job Writing to the same File

So I ran tcpdump twice overnight by accident, both outputting to the same file. However, I ran them as jobs and one of them has been paused the whole time. Anyone have a recommendations on how to ...
1
vote
2answers
641 views

pcap stream rotation and pruning

Some of my servers collect a lot of packet data. Is there a utility (or patch to tcpdump(1)) to log a pcap stream to disk which: Rotates based on size of data written Prunes written files, keeping ...
0
votes
1answer
545 views

openvpn dual install (client and server) routing problem

I have the following install: PROD net (10.88.88.0/24) OFFICE net (192.168.2.0/24) on PROD I have openvpn server (vpnprod), so OFFICE can connect. on OFFICE I have openvpn machine (vpnoffice) ...
2
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4answers
2k views

tcpdump and dynamic dns update

So here we have an example of why google is scared.... asking google to find the specific recipe for "what is the tcpdump incantation to sniff / filter only for ddns update packets" winds up with a ...
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6answers
69k views

Monitoring HTTP traffic using tcpdump

To monitor HTTP traffic between a server and a web server, I'm currently using tcpdump. This works fine, but I'd like to get rid of some superfluous data in the output (I know about tcpflow and ...
2
votes
1answer
9k views

Unknown tcpdump packets

I was just doing tcpdump on a linux server connected directly to a provider, and about every second and a half there is a line like this: 00:19:49.926700 00:15:c6:::** (oui Unknown) > ...
1
vote
4answers
489 views

Change protocol associated with port in tcpdump?

Following on from this question, how can I tell tcpdump to use a specific protocol analyzer for a particular port? I'm doing some DNS development using a test server running on port 5053, but I can't ...
1
vote
2answers
3k views

(D)DOS - tcpdump established connections analysis (too many established connections)

¿How can I debug this problem? (I've got full tcpdump captures) I have a TCP server into which many clients establish persistent connections. Normally all these clients behave, and I never reach ...
45
votes
8answers
159k views

How can I read pcap files in a friendly format?

a simple cat on the pcap file looks terrible: $cat tcp_dump.pcap ?ò????YVJ? JJ ?@@.?E<??@@ ?CA??qe?U????иh? .Ceh?YVJ?? JJ ?@@.?E<??@@ ...
3
votes
6answers
3k views

Dumping rawdata for a host on a proxy using tcpdump

Im trying to save the rawdata that is beeing sent throu our proxy to a specific url. A friend of mine gave me the tip to use tcpdump, so I started reading about it on their page. But for some reason I ...