I want to capture packets from other computers on my network. I have 3 computers in total on same SSID and I want to capture packets off these 2 other computer. How to?
I have tried using wireshark but it only shows packets that being sent to/from my computer not from other computers.
I am using backtrack5.
The 3 computers must be all connected to the same router. Hence, "sharin" packets. Use Wireshark and you'll be able to capture packets. Make sure you are connected through a cable to your router, and not via wireless.
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Network disconnect issue happens in a system of my company.
Here is the network topolgy:
PC1: two NICs, both static IP address. Data: 10.10.22.11, Control: 10.10.22.10
PC2: two NICs, both static IP address. Data: 10.10.22.101, Control: 10.10.22.100
Default Gateway 10.10.22.11 is set on both side. However I don't think this is necessary, as there is no router or gateway between the two PCs, there directly linked.
A consultant point out, since all the IPs are set in same segment 10.10.22, there could be broadcast storm, which might be the cause of network disconnect.
Is this true? Can broadcast storm happen in directly linked two PCs?
No it shouldn't be.
Broadcast storms happen when there is a loop in a network.
A packet is forwarded to all ports in a switch and if there is a loop the packets are again sent to the same switch on all ports, amplifying the storm, if there is no network loop there shouldn't be any storm.
I don't see any loop in your configuration so this shouldn't be any broadcast storm.
Identifying broadcast storm is not so hard, just sniff on an interface on the network, and if you see millions of times the same broadcast packet, it should be a broadcast storm.
When broadcasting in a wireless environment, does the packet spread through the AP? or directly from the device?
I installed an AP that was not connected to the Internet and connected the devices to the AP. And one device sent a broadcast packet.
The broadcast packets were successfully transmitted.
By the way, when I connected the lan line directly to the AP and watched nic with wireshark, I could see that the above packets were caught.
If the device connected to the AP sends a broadcast message, will this message be spilled directly from the device's nic, or is it going through the AP and messaging the AP?
Suppose we have a WiFi network with one AP, and two clients (A and B). If Client A wants to send a packet of any kind to Client B, that traffic goes through the AP first.
The AP is functionally equivalent to an Ethernet switch, where Client A and Client B are connected to different ports, even if they're located in the same room as each other. The data must flow to the switch first. There, the switch will inspect the destination MAC address and forward the packet on to whatever port(s) it should go to.
In the WiFi case, the client sends packets to the AP. The AP inspects the packet and sees that its destined for the BSSID (functionally equivalent to the Ethernet MAC address) of another client. So, the AP transmits that packet so that the other client can receive it. If the packet is addressed to something on the connected Ethernet, then the packet goes out as an Ethernet packet.
In the case of a UDP broadcast, the target MAC/BSSID address is FF:FF:FF:FF:FF:FF. It still goes through the AP though. The AP receives this packet from Client A and then reransmits it to all clients while also sending it out any connected Ethernet.
I have an RFID receiver that constantly sends UDP packets to port 5757. When connected over ethernet to my desktop, all packets are received and valid (confirmed with Wireshark), and there is no issue. When I connect the receiver via ethernet to my laptop, not one UDP packet is received.
Things I have tried:
I have connected the laptop to the desktop over ethernet, and have sent UDP packets via netcat in both directions. Netcat has no issues with sending/receiving the data.
I've also captured and saved the RFID UDP packets on the desktop, and played them back using bittwist, first on the desktop, and had no issues capturing them in Wireshark(desktop). Then I copied the saved packets over to the laptop, played them back using bittwist, and had zero UDP packets captured in Wireshark(laptop).
Finally, I updated the ethernet driver and had the same results.
Any help would be greatly appreciated.
Im new to the networking world and I'm trying to use wireshark to get a hang of how packets are sent from my machine etc. Hence this question might be a dumb one.
When I open the wireshark packet analyzer GUI (on windows 7) there is a source and destination column. It shows packets where source IP is not mine and the destination IP is not mine either. Why is this happening? My network interface card should be receiving and sending only packets addressed to/sent from my IP address, right?
(attaching a screenshot. My IP address is 10.177.255.186)
Thanks.
On a small LAN all packets are generally broadcast to everyone. By broadcast I mean that the data is physically sent to everyone. When received the network interface determines if the packet was sent to you by looking at the address.
Using Wireshark your network interface can be set into promiscuous mode which means that all packets are captured and sent from the network interface to the CPU. This allows programs like Wireshark to record all those packets and not just the ones addressed for your computer.
Edit: However the packets don't have to be sent to all computers. A hub can be used to connect multiple computers together and acts as just a repeater meaning all packets are always sent everywhere (except on the wire where the packet came from). A switch however is similar but smarter.
If three computers A, B and C are connected to a switch and A sends a packet to B then the packet will first arrive at the switch. If the switch knows what wire B is connected to then it will only send it down that wire. If it doesn't know it sends it everywhere and later if B replies to A the switch will figure out what wire B is on. This means that C will generally never get to see any of the messages sent between A and B once the switch knows what wires A and B are on.
I am familiar with the basic OSI model but I always get confused how does a packet travel from one machine to another over the Internet and what OSI layers do come into picture? For example, for the following topology:
Machine A<----->Switch<---->Router<---->Router<---->Router<---->Switch<---->Machine B
where the multiple routers are shown to represent the Internet, what happens at the OSI layer level, when Machine A send a packet (say a simple "ls" command over FTP) to Machine B.
The above is just a suggested example, but if any one can explain with any other network topology, that is fine too. All I am looking a very basic explanation of how the packet gets transformed to different OSI layers at each nodes (Machine, Switch, Router, etc.).
Routers use the IP layer (layer 3) and switches use the data-link layer (layer 2). Layer 1 is the physical 1s and 0s that go over a wire, Layer 2 is the data-link layer, which is protocols like Ethernet and Point-To-Point Protocol (PPP), which carries information between adjacent nodes about MAC address from and to and allows for error detection and retransmission. Layer 3 is the IP layer, which carries information about where in the whole network the packet is from and to, not just the current hop.
The transmission would go like this:
Machine A wants to send a packet to Machine B. Machine A knows Machine B's IP address, so it places that in the layer 3 packet. Machine A needs to place the MAC Address of the next hop in the layer 2 packet, however. If it does not know, then it will send something called an ARP request (Address Resolution Protocol, read here: http://www.tildefrugal.net/tech/arp.php ) to the network, with the destination IP. One of a few things will happen here:
The IP is local. The machine with that IP will reply back to the sender with its MAC address.
The IP is non-local. The gateway router will detect this and send its MAC address.
The IP is non-local and Machine A's default gateway and subnet mask are set. Using this information Machine A can determine the non-locality of the IP address and send it to the router's MAC address (ARPing if not known yet).
(If Machine A found this out earlier, it will be in the ARP cache and Machine A will just use that.) Now that the MAC address is sent, the packet can be transferred (the physical layer 1 performing the actual transfer of data on the wire). The next stop will be the switch. The switch knows which outbound port the MAC address listed as the layer 2 destination is on, because it tracks every MAC address it's seen a packet come from and which port it came on - if it does not know, then it will flood it out every single port, guaranteeing it'll arrive.
As such, the packet arrives at the router. The cool thing about the IP model is that it divides every single IP address in the network/world into a hierarchy - Subnets by definition cannot overlap subnets partially, they either wholly contain them or are wholly contained by them. So as long as subnets follow this hierarchy, the router can unambiguously determine where each of the 4 billion possible IP addresses are on the network just by looking at what subnet the IP will fall under in its table! The packet is then sent out that port.
As the packet travels through interconnected ISPs' routers, backbone infrastructure and so on, it arrives at Machine B's router, where the opposite process happens - router B sees that its destined for Machine B and sends it inbound. (Similarly, Router B will have to use a process like ARP to find Machine B's MAC address if not known.) The rest should be trivial from here.
good references:
https://web.archive.org/web/20120129120350/http://www.tildefrugal.net/tech/arp.php
http://en.wikipedia.org/wiki/Data_link_layer
http://en.wikipedia.org/wiki/Network_switch
http://en.wikipedia.org/wiki/Network_layer
http://en.wikipedia.org/wiki/Routing
http://en.wikipedia.org/wiki/Router_(computing)
http://en.wikipedia.org/wiki/Address_Resolution_Protocol
The only thing that can travel over a copper wire are pulses of electricity.
The binary number 1 is represented by a pulse of electricity or no pulse of electricity for 0.
Just keep in mind that real data of any kind cannot be sent over copper wire, fibre optic, or through the air ...only a representation of the data which has previously been converted to a 1 or a 0 and then is reconverted back at the receiving end.
Network layer protocol supervises the transmission of packets from a source machine to a destination. Data is broken down into packets, or datagrams, up to 64 kb long before it is transmitted, with a stamp of destination IP address, and forwarded to the network gateway. A gateway can be router to interconnect networks.