General :: Networking - Interface Stops Receiving Packets As Seen By Tcpdump
Mar 30, 2011
I have a linux box with two interfaces: eth0 is a builtin and eth1 is a USB-LAN.
There is an IP configured on eth1.
eth0 is up but no IP is configured. This interface is used for sniffing with tcpdump.
The problem is that eth0 frequently stops receiving packets -- my tcpdump captures are empty, and if I look at the interface stats with ifconfig, I can see that no packets are received.
If I bounce the interface (ifconfig eth0 down; ifconfig eth0 up), it starts receiving packets again.
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Nov 21, 2010
I am trying dump some packets using tcpdump and it does not seem to be working.
System is fedora12
TCPDUMP v4.1
Libpcap v1.0
I even rolled my own,
TCPDUMP v4.1.1
libpcap v1.1.1
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Mar 11, 2010
Does gzip have the capability to decode gzipped traffic? I have been beating my head against the wall with this issue. What I'm trying to do is capture traffic between a web server and clients, and I've got it set up where it's redirected to a file for ease of grepping, however it's seemingly incapable of decoding gzipped encoding. I know I can do this with tshark, I'm curious as to whether tcpdump has this capability (i.e. only using tcpdump, and not some additional tool like tcpshow or what-not).
I can't find much on this issue in the man page for tcpdump, but it is fairly lengthy, so it's possible that I missed something, but I don't see that as especially likely.
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Apr 11, 2010
I have a computer with two interfaces: a fixed connection (eth1) and a modem (ppp0). My goal is to receive UDP packets from both connections concurrently (using the recv() function). The problem is, that the received packets reach the application only when the default gateway is set to that interface's address. For example, if I set the default gw to be in the eth1 subnet, only packets from eth1 reach the application. Other packets are received in the interface (checked using tcpdump), but they seem to be blocked somewhere. The policy defined in iptables is "ACCEPT" for all incoming packets, with no rules at all. I would like to know how to overcome this problem, and anyway how is the default gateway related to incoming UDP?
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Apr 27, 2010
What is the syntax to capture packets from multiple host through tcpdumptcpdump ip host host1|host2|host3|host3
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Mar 6, 2010
I just installed Slackware 13 with xfce and everything went well (eventually). At first, my wireless didn't work, but then I found /etc/rc.d/rc.wireless.conf. Everything was working, and I was happily surfing and downloading packages.But then one day... It just stopped! I tried to ping google, and it could send packets but not receive them.I'm connecting through an unlocked network in my building, so I guess it's DHCP (thats what i set it up with the first time 'round
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Jan 28, 2011
I'm trying to capture traffic between two machines, A and B. I would like to make sure that the traffic I capture with tcpdump is between eth1 on the local machine and eth0 on the remote machine. As I understand it, the -i flag specifies the local machine interface - but how to set the remote one?
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Feb 20, 2010
For learning purposes i've set up a vpn between a laptop (running ubuntu) and a pc (running windows). The 2 computers are on the same lan. The VPN server is set on the laptop, and as a guide i used this tutorial:The problem is that the mtu on the ppp0 interface is 1396 and the mtu on the eth0 interface is 1492 so in order to pass packets from the et0 if to the ppp0 if, the laptop needs to fragment the packets, and here is where the problem appears: the packets come with the don't fragment bit set. I've tried lowering the mtu of the eth0 if but that didn't work. The only way i managed to make this work is setting the ppp0 mtu size to 1492. The thing is that setting the mtu and mru in the pptpd-options file to 1492 doesn't do anything (at least to solve this problem) and the only way to set the mtu of the ppp0 if is to manually set it using: Code:sudo ifconfig ppp0 mtu 1492 The issue with this is that every time the connection resets i have to enter the command.
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Oct 13, 2010
I want to build a topology of this kind:
|eth0 (a.a.a.a) |
Linux PC |<----------------> | ROUTER
|eth1 (b.b.b.b) |
|<----------------->|
the linux machine has two interfaces eth0 (a.a.a.a) and eth1 (b.b.b.b) connnected to two interfaces of a router. Now that if I send any packet destined to b.b.b.b from a.a.a.a interface on the linux machine, it should take the folowing path: eth0->router->eth1 . and it should be the same for vice versa.
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Aug 13, 2011
I want to capture all packets from site "www.examplesite.com" so I checked its ip address in an ip address look up and it was 123.456.abc.def.So I set my filter to "dst host 23.456.abc.def"However I then realised that multiple ip address point to ww.examplesite.com, for example say the following ips also go to987.654.321.000111.222.333.444So is there a filter that will automatically capture all traffic going to www.examplesite.com or do I have to go and manually find all it's ip addresses and pass them all to the filter?
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Nov 23, 2010
If I am sniffing with TCPDUMP or tshark, I have an issue. If I specify a host to watch, I get no packets back, but if I don't specify a host, I get all traffic, including the host traffic I was filtering for the first time. ?? IE: If I: tcpdump -vnnXs 1514 -i bond0 I see all traffic and traffic to x.x.x.x But if I: tcpdump -vnnXs 1514 -i bond0 host x.x.x.x I see no traffic.
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Feb 9, 2011
I'm a student who is working on a wireless research project. I have a madwifi driver for Atheros chipset on Debian Linux. With having the wireless interface get into monitor mode, I want to forward the captured packets from the wireless interface to the other Ethernet interface so that a different computer which is connected to this machine via Ethernet receives those packets. I checked that alll packets are received in the wireless interface using TCPDUMP. I tried to forward those packets with IPTABLES like 'iptables -p FORWARD -i ath0 -o eth2 -j ACCEPT' However, I couldn't see any packets forwarded to eth2 using TCPDUMP.
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Mar 22, 2010
I am trying to do something outlandish with iptables (or so I think!).I have a source sending udp packets to a destination (say dst11). Using port mirroring I am able to get all these packets to a different machine (say dst22). I am able to see these packets on dst22 interface using tcpdump.I want to analyze the packets on dst22. So what I do is put dst22 interface in promiscuous mode (using ifconfig eth0 promisc). This in theory should get the packet through the MAC layer. Now using iptables I am trying to DNAT the packets in nat prerouting to change the packets destination IP to dst22's interface and change the destination port.
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Feb 8, 2010
i have a linux server runnig oracle applications. i need to access this server from putty using ssh through internet. i did by registering my static ip with the dnydns.org and i am able to connect to the server. but now there is no security to authenticate any user as any one knowing the password can login to it.
i thought of configuring the firewall of linux server but the client ip`s are not static and they change continiously. so thought of keeping one more pc between the server and the router which will do the work of authenticating. but i am confuse as how to configure it to allow the packets coming from the internet after authenticating and to by pass the packets generated from internal LAN?
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Aug 30, 2010
i need to write a program in c that can sniff packets from Ethernet and distinguish RTP packets from Non-RTP packets, i have no idea what should i do
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Sep 27, 2010
I have a hardware device with two ethernet ports, eth0 and eth1 running Centos 5. Basically my goal is to forward packets from eth0->eth1 and eth1->eth0 as well as get a copy of these packets for analysis. If I set IP routing to do the forwarding then I won't get a copy of the packets for analysis.
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Dec 7, 2010
I am trying to create a dump log using tcpdump. I want display the top 10 ip addresses sorted numerically showing how many times the ips are hitting the server. I'm getting frustrated because It's not working how I'd like it to.
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Feb 16, 2011
Is there a way to do multiple interfaces in tcpdump? I have found that when using "-i any", not all packets are captured (compared to "-i eth0" on a machine with only one interface). I need to monitor traffic on some machines with as many as 6 interfaces, and get these packets that "-i any" misses. When I give the "-i" option multiple times, it seems to only use the last one.
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Oct 18, 2010
I'm trying to capture packets to a file with the -w option but the file is empty yet if I use the '-w -' option to put data on stdout I see plenty of captured packets.I'm using CentOS 5.5 x86
Code:
[root@server ~]# tcpdump -v -i eth0 -w dump -s0
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
[code]....
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Apr 6, 2010
I would like to set up tcpdump to rotate log file every 1 hour and retain files for the lat 14 days but I don't think any combination of -C and -W would allow me to do that (Atleast I haven't been able to figure it out), so I am trying to rotate the files every X number of MB and retain the last 20 files. This seems to be fairly simple with the '-C X -W 20' option but I am having some trouble in customizing the names of the log files. I have tried '-w capture-$(date +%Y-%M-%d-%H:%M-)' thinking that each file would start with the current date and time but all files are using the date and time when the capture was started so the only difference is the number at the end (which is done by -W). if I can customize the names of the file so that it has the date and time when the capture in started. In fact if I can do that, I dont need the numbers that '-W' appends at the end but I dont know how to get rid of them.
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May 27, 2010
I'm running NetWare SLES 10 sp3 with OES2 sp2. I was working with the folks at Novell to resolve an iPrint Print Manager problem.
During the process they wanted to perform a packet capture using tcpdump. While logged in as the root user the error no suitable device was found, and I received no data at all. This server is running on a VMWare Center. On other SLES 10 sp3 systems (residing on that same VMWre Center), tcpdump captures packets just fine. I inherited all of these servers, so I wasn't here during the initial build, but I'd make the guess that they were configured similarly. On a Server that I built recently, tcpdump works fine. On two of my Servers it does not, and gives the mentioned error.
It's not that big a deal, otherwise the Servers are communicating and working just fine. But, I'd like to get it working just because it's supposed to work. Students are off for the summer, so I have time to play.
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Jan 24, 2011
The only window that's open is the terminal running this command, no pidgin, skype, samba, torrent or anything I can think of is using the network yet there is ***** load of output from tcpdump. I was hoping to use this to check where certain applications connect to and what messages they send but when I'm doing nothing there is already more output than I can go through. Running tcpdump for less than 10 seconds gives me the following output:
Code:
16:13:22.015683 IP ns.hihkptt.net.cn.domain > desk.local.56598: 46887 1/2/2 (166)
16:13:22.016251 IP ns.hihkptt.net.cn.domain > desk.local.60099: 21168 1/2/2 (166)
16:13:22.016743 IP ns.hihkptt.net.cn.domain > desk.local.42325: 50346 1/2/2 (166)
16:13:22.034733 IP ns.hihkptt.net.cn.domain > desk.local.41441: 63658 1/2/0 (134)
16:13:22.035215 IP ns.hihkptt.net.cn.domain > desk.local.42865: 37537 1/2/0 (134)
16:13:22.036124 IP ns.hihkptt.net.cn.domain > desk.local.35006: 7520 1/2/0 (134)
16:13:22.036569 IP ns.hihkptt.net.cn.domain > desk.local.38480: 51322 1/2/0 (134)
16:13:22.066006 ARP, Reply 192.168.0.1 is-at 00:b0:0c:02:60:9c (oui Unknown), length 46 .....
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Feb 16, 2010
I have configured NFS Server on CentOS 5.2 with IBM Web Server,which is having AIX 5.3 The IBM Web Server can upload all data onto NFS Server. Now, Today i was having slow response on IBM Web Server & by measuring the NFS, i found below error while running "tcpdump" command on CentOS Server.
tcpdump -n -i eth1 | grep 2049
18:36:37.237451 IP 10.100.19.241.2049 > 10.100.19.88.1758143293: reply ok 1448 read [|nfs]
18:36:37.237476 IP 10.100.19.241.2049 > 10.100.19.88.539981409: reply ERR 1448
18:36:37.237481 IP 10.100.19.241.2049 > 10.100.19.88.796287348: reply ERR 1448
[code]....
I have changed Network Card in CentOS. All LAN is on Gigabit Network. Also I have changed the Network Cable(Patch Cord). But,still no response.
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Feb 14, 2010
I just had an ATT Uverse RG installed. However my Smoothwall router that previously worked fine with the ADSL SpeedStream is no longer accepting an address assignment DHCP ip address from this new gateway. (3800HGV-B)Any thoughts ideas or experience working with this hardware? ATT only supports Windows and Mac
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Jul 18, 2011
I have a ppp0 entry with post-up options like this
mapping ppp0
map none photon-plus motorola
map timeout: 12
[code]...
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May 20, 2010
I am running a test to determine when packet drops occur. I'm using a Spirent TestCenter through a switch (necessary to aggregate Ethernet traffic from 5 ports to one optical link) to a server using a Myricom card.While running my test, if the input rate is below a certain value, ethtool does not report any drop (except dropped_multicast_filtered which is incrementing at a very slow rate). However, tcpdump reports X number of packets "dropped by kernel". Then if I increase the input rate, ethtool reports drops but "ifconfig eth2" does not. In fact, ifconfig doesn't seem to report any packet drops at all. Do they all measure packet drops at different "levels", i.e. ethtool at the NIC level, tcpdump at the kernel level etc?nd am I right to say that in the journey of an incoming packet, the NIC level is the "so-called" first level, then the kernel, then the user application? So any packet drop is likely to happen first at the NIC, then the kernel, then the user application? So if there is no packet drop at the NIC, but packet drop at the kernel, then the bottleneck is not at the NIC?
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May 6, 2010
I have a need to make a rather odd filter in tcpdump- I would like to capture only all those packages on interface eth0, that are outgoing(in other words from IP 192.168.1.1, which is IP for eth0 in this computer) and doesn't have src MAC address 11:22:33:44:55:66. However, fallowing command says, that syntax is wrong:
Code:
tcpdump -n -p -i eth0 src host 192.168.1.1 ether src not 11:22:33:44:55:66
Is this possible? If yes, then what is the correct command?
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Feb 21, 2011
How to convert Tcpdump output file to a Pcap format? Is there such way?
This is what i mean:
tcpdump -i eth0 >> test.out
Now i want to convert test.out to Pcap so It's readable via Wireshark.
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Jan 11, 2011
I have a WAN network that i need to do some analysis on, for the traffic flows. I did lots of googling to figure out what useful tool to collect the packet informations.I found this site [URL]..witch i made great use of to recognize the tcpdum tool. I also have a network simulator on windows platform wich is Opnet Guru, (by the way.. is there a linux version for this simulator?).
MY QUESTION IS: How can i feed the Opnet Guru with the flows data collected with the
Code:
tcpdump
with its different options?
NOTE: in the Opnet Guru invironment there is an object called the profile that is beeing used to customize and genarate data flows with the desired characteristics to simulate the real flows. So i need to feed the Opnet with the fresh data collected with the tcpdump tool (command) instead of using the built-in profile.. i hope i was clear enough..
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May 19, 2010
I have a question regarding packet drops. I am running a test to determine when packet drops occur. I'm using a Spirent TestCenter through a switch (necessary to aggregate Ethernet traffic from 5 ports to one optical link) to a server using a Myricom card. While running my test, if the input rate is below a certain value, ethtool does not report any drop (except dropped_multicast_filtered which is incrementing at a very slow rate). However, tcpdump reports X number of packets "dropped by kernel". Then if I increase the input rate, ethtool reports drops but "ifconfig eth2" does not.
In fact, ifconfig doesn't seem to report any packet drops at all. Do they all measure packet drops at different "levels", i.e. ethtool at the NIC level, tcpdump at the kernel level etc? And am I right to say that in the journey of an incoming packet, the NIC level is the "so-called" first level, then the kernel, then the user application? So any packet drop is likely to happen first at the NIC, then the kernel, then the user application? So if there is no packet drop at the NIC, but packet drop at the kernel, then the bottleneck is not at the NIC?
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