user58859 - Developer IT

Why my laptop sends ARP request to itself ?

- by user58859

I have just started to learn about protocols. While studying the packets in wireshark, I came across a ARP request sent by my machine to my own IP. Here is the details of the packet : No. Time Source Destination Protocol Info 15 1.463563 IntelCor_aa:aa:aa Broadcast ARP Who has 192.168.1.34? Tell 0.0.0.0 Frame 15: 42 bytes on wire (336 bits), 42 bytes captured (336 bits) Arrival Time: Jan 7, 2011 18:51:43.886089000 India Standard Time Epoch Time: 1294406503.886089000 seconds [Time delta from previous captured frame: 0.123389000 seconds] [Time delta from previous displayed frame: 0.123389000 seconds] [Time since reference or first frame: 1.463563000 seconds] Frame Number: 15 Frame Length: 42 bytes (336 bits) Capture Length: 42 bytes (336 bits) [Frame is marked: False] [Frame is ignored: False] [Protocols in frame: eth:arp] [Coloring Rule Name: ARP] [Coloring Rule String: arp] Ethernet II, Src: IntelCor_aa:aa:aa (aa:aa:aa:aa:aa:aa), Dst: Broadcast (ff:ff:ff:ff:ff:ff) Destination: Broadcast (ff:ff:ff:ff:ff:ff) Address: Broadcast (ff:ff:ff:ff:ff:ff) .... ...1 .... .... .... .... = IG bit: Group address (multicast/broadcast) .... ..1. .... .... .... .... = LG bit: Locally administered address (this is NOT the factory default) Source: IntelCor_aa:aa:aa (aa:aa:aa:aa:aa:aa) Address: IntelCor_aa:aa:aa (aa:aa:aa:aa:aa:aa) .... ...0 .... .... .... .... = IG bit: Individual address (unicast) .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default) Type: ARP (0x0806) Address Resolution Protocol (request) Hardware type: Ethernet (0x0001) Protocol type: IP (0x0800) Hardware size: 6 Protocol size: 4 Opcode: request (0x0001) [Is gratuitous: False] Sender MAC address: IntelCor_aa:aa:aa (aa:aa:aa:aa:aa:aa) Sender IP address: 0.0.0.0 (0.0.0.0) Target MAC address: 00:00:00_00:00:00 (00:00:00:00:00:00) Target IP address: 192.168.1.34 (192.168.1.34) Here the sender's mac address is mine(Here I have hiden my mac address). target IP is mine. Why my machine is sending ARP request to itself? I found 3 packets of this type. There was no ARP reply for these packets. Can anybody explain me why it is? (My operating system is windows-7. I am directly connected to a wifi modem. I got these packets as soon as I started my connection.) I want one suggestion also. many places I read that RFC's are enough for study about protocols. I studied the RFC 826 on ARP. I personally feel that is not enough at all. Any suggestion regarding this? Is there more then 1 RFC for a protocol? I want to study about the protocols in very detail. Can anybody guide me for this? Thanks in advance.

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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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Flow of packets 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? Does it go to the ethernet 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 happens 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?

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How a router decides destination of packet?

- by user58859

I have basic networking question. Scenario : Two pc's are communicating on a wan. Both the pc's ate behind routers or modems. My question : Both the pc's have public IP of each other. That public IP is most of the time is either of the router or of the modem. There can be more then one pc's behind those routers and modems. Then how the pc's are communicating. I can understand the packets can reach upto those routers or modems. But what after that. In the packet , destination IP is public IP. Then how the router or modem decides where to send the packet? Can anybody explain me this please. Thanks in advance.

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Why configuring manual IP do not work for me in DHCP?

- by user58859

I have broadband connection in my laptop. It's getting the IP by protocol. configuration is : ip : 192.168.1.2 subnet : 255.255.255.0 gateway : 192.168.1.1 Now I am curious, In IPV4 properties when instead of choosing "Obtain an IP address automatically", I choose "Use the following IP address" and configure everything same, why it do not work? Do DHCP do not work when we configure the IP manually? (operating system : windows-7) EDIT : After configuring the ip manually, when I used ipconfig/all , it's showing dhcp enabled : NO. I am not doing it. Why it got disabled automatically? and how to enable it? DHCP Enabled. . . . . . . . . . . : No Autoconfiguration Enabled . . . . : Yes IPv4 Address. . . . . . . . . . . : 192.168.1.2(Preferred) Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : 192.168.1.1 NetBIOS over Tcpip. . . . . . . . : Enabled

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