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May 2012

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Subject:
From:
Tam Nguyen <[log in to unmask]>
Reply To:
Tam Nguyen <[log in to unmask]>
Date:
Mon, 7 May 2012 22:48:42 -0400
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Btw, I just checked my old notes, which I copied and pasted below.
 Hopefully this will shed some light into your issue:


>    1. The server first checks its routing table to see which router
>    provides the next hop to the destination network.
>    2. If there is a valid router, let's say with an IP address of
>    192.168.1.1, the server checks its ARP table to see whether it has the MAC
>    address of the router's NIC. You could very loosely view this as the server
>    trying to find the Ethernet serial number of the next hop router on the
>    local network, thereby ensuring that the packet is sent to the correct
>    device.
>    3. If there is an ARP entry, the server sends the IP packet to its NIC
>    and tells the NIC to encapsulate the packet in a frame destined for the MAC
>    address of the router.
>    4. If there is no ARP entry, the server issues an ARP request asking
>    that router 192.168.1.1 respond with its MAC address so that the delivery
>    can be made. When a reply is received, the packet is sent and the ARP table
>    is subsequently updated with the new MAC address.
>    5. As each router in the path receives the packet, it plucks the IP
>    packet out of the Ethernet frame, leaving the MAC information behind. It
>    then inspects the destination IP address in the packet and use its routing
>    table to determine the IP address of the next router on the path to this
>    destination.
>    6. The router then uses the "ARP-ing" process to get the MAC address
>    of this next hop router. It then reencapsulates the packet in an Ethernet
>    frame with the new MAC address and sends the frame to the next hop router.
>    This relaying process continues until the packet reaches the target
>    computer.
>    7. If the target server is on the same network as the source server, a
>    similar process occurs. The ARP table is queried. If no entry is available,
>    an ARP request is made asking the target server for its MAC address. Once a
>    reply is received, the packet is sent and the ARP table is subsequently
>    updated with the new MAC address.
>    8. The server will not send the data to its intended destination
>    unless it has an entry in its ARP table for the next hop. If it doesn't,
>    the application needing to communicate will issue a timeout or time
>    exceeded error.
>    9. As can be expected, the ARP table contains only the MAC addresses
>    of devices on the locally connected network. ARP entries are not permanent
>    and will be erased after a fixed period of time depending on the operating
>    system used.
>
>


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