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    <p>There's no guaranteed always-correct answer, but there are a few likely possibilities.</p> <p>If the client is configured for <a href="http://www.freesoft.org/CIE/RFC/1035/45.htm" rel="nofollow">DNS over UDP</a>, then the first packet will be a UDP datagram containing a <a href="http://www.freesoft.org/CIE/RFC/1035/39.htm" rel="nofollow">DNS query</a> to resolve <code>www.google.com</code> to an IP address. </p> <p>If the client is configured for <a href="http://www.freesoft.org/CIE/RFC/1035/46.htm" rel="nofollow">DNS over TCP</a> and the browser hasn't already got an established TCP connection to the DNS server, the first packet will be part of the connection handshake to DNS, and therefore the answer will be that a <code>SYN</code> packet is first out of the gate.</p> <p>If the browser has been coded to maintain a long-lived TCP connection to the DNS server and assuming the DNS server has allowed the connection to stay alive, the first packet will be a DNS query, sent across the existing connection to that DNS server.</p> <p>Finally, if the browser had recently visited <code>www.google.com</code> recently and is built to do some smart local caching of DNS query results then the first packet will be a SYN to establish a new connection to Google's web server. </p> <p>If you want to be glib but absolutely precise about it, drop down a layer for your answer and say, <em>"The first packet out will be an Ethernet frame containing a payload which supports whatever higher-level protocol is needed for the browser to serve up www.google.com".</em> In fairness, the question is about the Ethernet layer...</p>
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    1. CObrowsers don't maintain long lived TCP connections to DNS servers. And going down to layer 2 isn't glib, it's the _right answer_. L3 packets can't be exchanged until L2->L3 mappings have been established.
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    2. COI'd bet money that the interviewer wasn't asking about the Ethernet layer, though. I'm certain they were testing knowledge of TCP and/or UDP instead.
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    3. COHow can you possibly second guess that? FWIW, if I were asking this question of a potential network admin or network app programmer, I _would_ expect them to go down to L2.
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