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aimensaimens Member Posts: 14 ■□□□□□□□□□
in Network+
when the device want to connect to any network he will send message say i want ip address in this network
in layer 3 he will be put the ip source and disit what he will put int the source if he doesn't have ip ?
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    OctalDumpOctalDump Member Posts: 1,722
    Are you talking about DHCP? In the case of the DHCP discover request, the source IP is set to 0.0.0.0 and the destination set to 255.255.255.255. At layer 2, the source MAC is used and the destination MAC is the broadcast.

    The Offer segment has the destination IP set to the offered IP, and the source IP is the DHCP server

    The Request segment still uses 0.0.0.0 as the source IP and 255.255.255.255 as the destination

    Finally the Acknowledge segment uses the 'acknowledge' IP (same as the offered) as the destination.

    Once the client has the Acknowledge reply, it will then start using the IP.
    2017 Goals - Something Cisco, Something Linux, Agile PM
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    aimensaimens Member Posts: 14 ■□□□□□□□□□
    Thank you , yes i talking about DHCP ?
    i have question why we put 0.0.0.0 ?
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    YanioYanio Member Posts: 37 ■■□□□□□□□□
    As OctalDump says, until the client receives the acknowledgement from the DHCP server it won't start using the IP address it's being leased. Therefore it uses 0.0.0.0 as a placeholder until that time.

    Also, it might be an idea to put more then just 'help' in the subject of a new threadicon_thumright.gif.
    "That's what" -She
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    aimensaimens Member Posts: 14 ■□□□□□□□□□
    Thanks , what you want me make the subject ?
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    OctalDumpOctalDump Member Posts: 1,722
    aimens wrote: »
    Thank you , yes i talking about DHCP ?
    i have question why we put 0.0.0.0 ?

    Because that's how DHCP works :)

    Actually, it's because the client doesn't have an IP and can't just pick one at random in case it is already in use. This means that the communication needs to happen at Layer 2 (with MAC address). Which will work as long the DHCP server (or relay) is in the same broadcast zone. The 0.0.0.0 address is used as a place holder, which signals also that it has no "proper" address. It has to use an address because it is still using Layer 3 and Layer 4 and higher to communicate, so it still needs to form proper packets which means including a source address.
    2017 Goals - Something Cisco, Something Linux, Agile PM
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