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  • Does libpcap get a copy of the packet ?

    - by ShaChris23
    Does libpcap get a copy of the packet or the actual packet? By copy, I mean: the application using libpcap gets packet A, and the kernel also gets packet A. By actual, I mean: only the application using libpcap gets packet A, but the kernel didn't get it.

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  • Confusion about TCP packet analysis terms

    - by Berkay
    I'm analyzing our network and have some confusion about the terms: this is the 2-packet output from source to destination. from these i have to get some features as describe, pls make me clear... packets with at least a bytes of TCP data payload: it seems tcp.len0; The minimum segment size (confusion is headers are included or or not) The average segment size observed during the lifetime of the connection, the definition: is calculated as the value reported in the actual data bytes divided by the actual data pkts reported. Total bytes in IP packets, should be ip_len value. Total bytes in (Ethernet) The total number of bytes sent probably related to frame.len and frame.cap_len these two terms are describes as, also make me clear about these two terms. frame.cap_len: Frame length stored into the capture file frame.len: Frame length on the wire

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  • On an unencrypted public wi-fi hotspot, what exactly is a packet sniffer doing to get another computer's packet?

    - by hal10001
    I get mixed results when reading information security articles, some of them stating that in order to do something similar you need to also setup some sort of honeypot with a running access point and local Web server to intercept traffic. Then other articles seem to indicate you don't need that, and you can just run Wireshark, and it will detect all packets being sent on the network. How could that be, and what exactly is a packet sniffer doing to get those packets? Does this involve intercepting wireless signals transmitted over the wireless protocol and frequency via the NIC on the computer running a program like Wireshark?

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  • Web server connection to SQL Server: Response Packet [Malformed Packet]

    - by John Murdoch
    I am seeing very, very sluggish performance between my web server (which handles HTTP web services connections) and a separate server running Microsoft SQL Server 2008. I have been capturing packet traffic on the web server trying to understand why things are running so slowly. I am using Wireshark to capture the packet traffic. The apparent problem is that the web server is sending TDS packets to the data server--each packet followed by a response from the data server with Response Packet [Malformed Packet] in the Info field. The packet sent from the web server appears to have an invalid checksum. Has anyone seen this type of problem before? Any ideas?

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  • Where does traffic shaping typically take place?

    - by eekmeter
    As part of upgrading our network infrastructure we are looking to traffic shape our bandwidth since we only have about 3Mb down / 1 Mb up. We're looking to prioritize it so that web browsing gets priority and in the future some VOIP might be added in as well. Internal LAN traffic doesn't need to be controlled just our outbound connection. I've been looking at Cisco hardware and it seems that several of their products do shaping at the core switch, firewall, and router level. I'm wondering where does shaping normally take place? Is it normally done at the router, core switch, or firewall?

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  • Packet drop measured by ethtool, tcpdump and ifconfig

    - by Rayne
    Hi all, 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? Thank you. Regards, Rayne

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  • Networking Client Server Packet logic (How they communicate)

    - by Trixmix
    I want to know what is the logic behind server client communication through packets for a real time game. for example the server sends x packets then the client receives x packets and processes them.. Basically what is the process to keep the client and server in sync and able to receive and send packets. more in depth example of what I want to know: client step 1 wait for a packet step 2 read x packets step 3 process x packets step 4 send x packets and so on... I need to know the very basic outline of the communication. Big questions are: 1) do I send and read packets all at one time? i.e for loop though the incoming packets array list and read them all or one every server loop or what... 2) what order should I do things i.e first receive then read then process then send etc.. 3) what I asked above a step by step of what the server / client should do.. Thanks!

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  • Java: Reflection Packet Builder using getField()

    - by Matchlighter
    So I just finished writing a packet builder that dynamically loads data into a data stream which is then sent out. Each builder operates by finding fields in its class (and its superclasses) that are marked with an @data annotation. Upon finishing the builder, I remembered that getFields() does not return in "any specific order". I quite like my builder because it allows for quite simple, yet hard-typed packets. Could this implementation be a problem? What would be the best next step to keep the simplicity - do alphabetical sorting of fields?

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  • Localhost packet analyzer for Mac

    - by kingjeffrey
    Packet sniffers generally do not capture localhost traffic. I need to inspect some post data in a localhost environment (being generated from a Ruby on Rails development). Do you know of any programs that expose localhost packets?

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  • Why would a server not send a SYN/ACK packet in response to a SYN packet

    - by codemonkey
    Lately, we've become aware of a TCP connection issue that is mostly limited to mac and Linux users who browse our websites. From the user perspective, it presents itself as a really long connection time to our websites (11 seconds). We've managed to track down the technical signature of this problem, but can't figure out why it is happening or how to fix it. Basically, what is happening is that the client's machine is sending the SYN packet to establish the TCP connection and the web server receives it, but does not respond with the SYN/ACK packet. After the client has sent many SYN packets, the server finally responds with a SYN/ACK packet and everything is fine for the remainder of the connection. And, of course, the kicker to the problem: it is intermittent and does not happen all the time (though it does happen between 10-30% of the time) We are using Fedora 12 Linux as the OS and Nginx as the web server.

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  • printing sequence number of a sniffed packet

    - by scatman
    i am using pcap to create a packet sniffer. i have this tcp structure: typedef struct TSP_header{ unsigned short int sport; unsigned short int dport; unsigned int seqnum; unsigned int acknum; unsigned char reserved:4, offset:4; unsigned int tcp_res1:4, //little-endian tcph_hlen:4, //length of tcp header in 32-bit words tcph_fin:1, //Finish flag "fin" tcph_syn:1, //Synchronize sequence numbers to start a connection tcph_rst:1, //Reset flag tcph_psh:1, //Push, sends data to the application tcph_ack:1, //acknowledge tcph_urg:1, //urgent pointer tcph_res2:2; unsigned short int tcph_win; unsigned short int tcph_chksum; unsigned short int tcph_urgptr; }TSP_header; how can i print the sequence number? shou i use htons(sequence_number)?? coz it isn't working this way!!

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  • Shaping outbound Traffic to Control Download Speeds with Linux

    - by Kyle Brandt
    I have a situation where a server makes lots of requests from big webservers all at the same time. Currently, I have not control over the amount of requests or the rate of the requests from the application that does this. The responses from these webservers is more than the internet line can handle. (Basically, we are launching a DoS on ourselves). I am going to get push to get this fixed at the application level, but for the time being, is there anyway I can use traffic shaping on the Linux server to control this? I know I can only shape outbound traffic, but maybe there is a way I can slow the TCP responses so the other side will detect congestion and this will help my situation? If there is anything like this with tc, what might the configuration look like? The idea is that the traffic control might help me control which packets get dropped before they reach my router.

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  • Port based bandwidth shaping

    - by nixnotwin
    I have an interent connection with the speed of 4000k bits up and down. I want to do port based traffic shaping on a ubuntu machine, which acts as router. eth0 is the WAN interface. This is how I would like to allocate bandwidth: For ports 80 and 445 the bandwidth usage can go upto 90% For ports above 1024 upto 65535 the bandwidth usage can go upto 10% For remaining ports the bandwidth usage can go upto 40% The easiest way for achieving the above is using a router with tomato firmware. I have used it and it is very efficient. I want to try if it can be done on a Ubuntu or any GNU/Linux machine. I have googled extensively about the topic and I feel there isn't much information.

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  • Traffic shaping L2TP/IPsec VPN (via accounts not connection)

    - by Cromulent
    I need to be able to control the amount of bandwidth a specific user account can use on a VPN connection. One account I want to be able to use the VPN with no restrictions and another account I want to limit to a reasonable amount of bandwidth (say 10GB or so a month). I'm aware that you can traffic shape individual connections but that does not quite solve the problem as the limited account can just disconnect and reconnect to get a new connection. I need to be able to limit bandwidth on a login basis for a given period of time (monthly limit). I'm really not that familiar with traffic shaping in general so any advice would be appreciated. Thank you.

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  • FreeBSD Traffic Shaping

    - by alexus
    Hi I'm trying to do traffic shaping with FreeBSD, here are my rules su-3.2# ipfw show | grep pipe 08380 1514852 125523804 pipe 1 tcp from any to any dst-port 80 su-3.2# ipfw pipe 1 show 00001: 2.000 Mbit/s 0 ms 50 sl. 1 queues (1 buckets) droptail mask: 0x00 0x00000000/0x0000 - 0x00000000/0x0000 BKT Prot ___Source IP/port____ ____Dest. IP/port____ Tot_pkt/bytes Pkt/Byte Drp 0 tcp 64.237.55.83/60598 72.21.81.133/80 6520267 1204533020 0 0 1216 su-3.2# first of all why when I run ipfw pipe 1 show i get same source and destination ip, that doesnt seem like ever change yet total packets/bytes increasing and most important question, after donig all that I'm looking at my MRTG stats and I see i'm very well over 2Mbit/s limit. what am I doing wrong? here is config file flush pipe flush pipe 1 config bw 2Mbit/s add 100 allow ip from any to any via lo0 add 200 deny ip from any to 127.0.0.0/8 add 300 deny ip from 127.0.0.0/8 to any add 8380 pipe 1 tcp from any to any src-port www uid daemon add 8380 pipe 1 tcp from any to any dst-port www uid daemon add 65000 pass all from any to any

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  • Flow of packet in network

    - by user58859
    I can't visualize in my mind the network traffic flow. eg. If there are 15 pc's in a LAN. When packet goes from router to local LAN, do it passes all the computers? Means did it goes to ehernet card of every computer and those computers accept the packet based on their physical address. To which pc the packet will go first? To the nearest to the router? What happen if that first pc captures that packet(though it is not for it)? What happens when a pc broadcast a message? Do it have to generate 14 packets for all the pc's or only one packet reach to all pc's? If it is one packet and captured by first pc, how other pc's can get that? I can't imagine how this traffic is exactly flows? May be my analogy is completely wrong. Can anybody explain me this? Thanks in advance.

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  • Server not sending a SYN/ACK packet in response to a SYN packet

    - by jeff
    Using iptraf, tcpdump and wireshark I can see a SYN packet coming in but only the ACK FLAG is set in reply packet. I'm running Debian 5 with kernel 2.6.36 I've turned off window_scaling and tcp_timestamps, tcp_tw_recycle and tcp_tw_reuse: cat /etc/sysctl.conf net.ipv4.tcp_tw_recycle = 0 net.ipv4.tcp_tw_reuse = 0 net.ipv4.tcp_window_scaling = 0 net.ipv4.tcp_timestamps = 0 I've attached an image of the wireshark output. http://imgur.com/pECG0.png Output to netstat netstat -natu | grep '72.23.130.104' tcp 0 0 97.107.134.212:18000 72.23.130.104:42905 SYN_RECV I've been doing everything possible to find a solution and have yet to figure out the problem, so any help/suggestions are much appreciated. UPDATE 1: I've set tcp_syncookies = 0 and noticed I am now replying with 1 SYN+ACK for every 50 SYN requests. The host trying to connect is sending a SYN request about once every second. PCAP FILE

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  • libpcap read packet size

    - by spicyramen
    I started to write an application which will read RTP/H.264 video packets from an existing .pcap file, I need to read the packet size. I tried to use packet-len or header-len, but it never displays the right number of bytes for packets (I'm using wireshark to verify packet size - under Length column). How to do it? This is part of my code: while (packet = pcap_next(handle,&header)) { u_char *pkt_ptr = (u_char *)packet; struct ip *ip_hdr = (struct ip *)pkt_ptr; //point to an IP header structure struct pcap_pkthdr *pkt_hdr =(struct pcap_pkthdr *)packet; unsigned int packet_length = pkt_hdr->len; unsigned int ip_length = ntohs(ip_hdr->ip_len); printf("Packet # %i IP Header length: %d bytes, Packet length: %d bytes\n",pkt_counter,ip_length,packet_length); Packet # 0 IP Header length: 180 bytes, Packet length: 104857664 bytes Packet # 1 IP Header length: 52 bytes, Packet length: 104857600 bytes Packet # 2 IP Header length: 100 bytes, Packet length: 104857600 bytes Packet # 3 IP Header length: 100 bytes, Packet length: 104857664 bytes Packet # 4 IP Header length: 52 bytes, Packet length: 104857600 bytes Packet # 5 IP Header length: 100 bytes, Packet length: 104857600 bytes Another option I tried is to use: pkt_ptr- I get: read_pcapfile.c:67:43: error: request for member ‘len’ in something not a structure or union

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  • GUI tool for packet replay

    - by superuser
    Is there a freeware Windows/Linux GUI packet replay tool that has the advanced features of tcpreplay (http://tcpreplay.synfin.net/) or bittwist (http://bittwist.sourceforge.net)? I'm particularly interested in the following features: Open pcap files for editing and injecting into arbitrary network Change source and destination addresses/ports of UDP packets Change packet timing (with millisecond resolution) Edit packet contents, including modifying its length Has graphical front end for Windows or Linux (or Mac OS X) I've scanned a couple lists of potential tools (here and here), but nothing really fits my requirements. The closest tool might be Ostinato (http://code.google.com/p/ostinato/), but it doesn't appear to open packet capture files. Thanks for any help!

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  • Traffic Shaping using tc

    - by Simon
    Hi guys, I have a 1.5 Mbit/s link that i want to share with 150 users. My setup is the following: Linux box with 3 NICs eth0 - public ip eth1 - subnet A - 50 users (static ips) eth2 - subnet B - 100 users (via dhcp) I am using squid as a transparent proxy on port 3128. dhcp server using ports 67 and 68. I was creating, but I think packets are not going to the right queues #!/bin/bash DEV=eth0 RATE_MAIN=2048kbit CEIL_MAIN=2048kbit BURST=1b CBURST=1b RATE_DEFAULT=1024kbit CEIL_DEFAULT=$CEIL_MAIN PRIO_DEFAULT=3 RATE_P2P=1024Kbit CEIL_P2P=$CEIL_MAIN PRIO_P2P=4 RATE_IND=32kbit CEIL_IND=$CEIL_DEFAULT tc qdisc del dev $DEV root tc qdisc add dev $DEV root handle 1: htb default 30 tc class add dev $DEV parent 1: classid 1:1 htb rate $RATE_MAIN ceil $CEIL_MAIN tc class add dev $DEV parent 1:1 classid 1:10 htb rate $RATE_DEFAULT ceil $CEIL_MAIN burst $BURST cburst $CBURST prio $PRIO_WEB ## some other sub class for p2p other traffic tc class add dev $DEV parent 1:1 classid 1:20 htb rate $RATE_P2P ceil $CEIL_P2P burst $BURST cburst $CBURST prio $PRIO_P2P $IPS_NET1=50 $IPS_NET2=100 let $IPS=$IPS_NET1+$IPS_NET2 for ((i=1; i<= $IPS; i++)) do let CLASSID=($i+100) let HANDLE=($i+100) tc class add dev $DEV parent 1:10 classid 1:$CLASSID htb rate $RATE_IND ceil $CEIL_IND tc qdisc add dev $DEV parent 1:$CLASSID handle $HANDLE: sfq perturb 10 done ## Generate IP addresses ## IP_ADDRESSES="" # Subnet A BASE_IP=10.10.10. for ((i=2; i<=$IPS_NET1+1; i++)) do TEMP="$BASE_IP$i" IP=ADDRESSES="$IP_ADDRESSES $TEMP" done # Subnet B BASE_IP=192.168.0. for ((i=2; i<=$IPS_NET2+1; i++)) do TEMP="$BASE_IP$i" IP_ADDRESSES="$IP_ADDRESSES $TEMP" done ## FILTERS ## j=1 U32="tc filter add dev $DEV protocol ip parent 1:0 prio $PRIO_DEFAULT u32" for NET in $IP_ADDRESSES; do let CLASSID=($j+100) $U32_DEFAULT match ip src $NET/32 flowid 1:$CLASSID $U32_DEFAULT match ip dst $NET/32 flowid 1:$CLASSID let j=j+1 done Can you guys help me figure out what's wrong with it? basically I want my classes to be 1:1 (1.5 Mbit ) 1:10 (1024 Kbit) 1:20 (1024 Kbit) (200 ips each with 32 kbit)

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  • traffic shaping for certain (local) users

    - by JMW
    Hello, i'm using ubuntu 10.10 i've a local backup user called "backup". :) i would like to give this user just a bandwidth of 1Mbit. No matter which software wants to connect to the network. this solution doesn't work: iptables -t mangle -A OUTPUT -p tcp -m owner --uid-owner 1001 -j MARK --set-mark 12 iptables -t mangle -A POSTROUTING -p tcp -m owner --uid-owner 1001 -j MARK --set-mark 12 tc qdisc del dev eth0 root tc qdisc add dev eth0 root handle 2 htb default 1 tc filter add dev eth0 parent 2: protocol ip pref 2 handle 50 fw classid 2:6 tc class add dev eth0 parent 2: classid 2:6 htb rate 10Kbit ceil 1Mbit tc qdisc show dev eth0 tc class show dev eth0 tc filter show dev eth0 does anyone know how to do it? thanks a lot in advance

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