Journey of a Web Request

Question

I was just curious about how a "web request packets" travels from my browser (as soon as I type www.google.com) to the Google server and back.

Please answer me in the two possible scenarios; one being when I type in www.google.com from my home (which has nothing but a wireless router) and the other being when I use my office network, where there are Switches, DNS Servers, Default Gateways and stuff.

As far as my understanding in a office network, the request flows from my machine -> switch -> default gateways (are routers ,I presume) -> DNS Servers -> Data Centres -> the Web Server .. am I correct ?

Answer 1

the request flows from my machine -> switch -> default gateways (are routers ,I presume) -> DNS Servers -> Data Centres -> the Web Server .. am I correct ?

No.

PC -> Ethernet broadcast: ARP-request: 
    "what is ethernet address for IP-address of DNS server?"
DNS-Server: ARP-response: "My Ethernet address is a:b:c:d:e:f"
PC -> DNS: "What is the IP-address of www.google.com?"
DNS-Server -> ISP DNS: "What is the IP-address of www.google.com?"
ISP-DNS -> DNS server 
    "I don't do recursive, do your own work, google.com DNS at 2.3.4.5, 4.5.6.7"
DNS-Server -> 2.3.4.5 "What is the IP-address of www.google.com?"
2.3.4.5 -> DNS-Server "I refuse your connection attempt!"
DNS-Server -> 4.5.6.7 "What is the IP-address of www.google.com?"
4.5.6.7 -> DNS Server 
    "www.google.com is 1.2.3.4; google.com DNS at 4.5.6.7, 3.2.1.3"
DNS-server -> PC "www.google.com is 1.2.3.4"
PC -> Ethernet broadcast: ARP request: 
    "what is ethernet address for IP-address of router?"
Router -> PC: "my ethernet address is d:e:a:d:b:e"
PC -> Router: IP to 1.2.3.4 "get / HTTP1.1; host: www.google.com"
Router -> PC: ICMP redirect: "for 1.2.3.x use router2.internal at 192.168.0.253"
PC -> Ethernet broadcast: ARP-Request: 
    "what is ethernet address for 192.168.0.253?"
Router2 -> PC: "my ethernet address is b:e:e:f:f:o"
PC -> Router2: IP packet for 1.2.3.4 ("get / HTTP1.1; host: www.google.com")
Router2 -> Router3 "1 IP packet  for 1.2.3.4 (...)"
Router3 -> Router4 "3 IP packets for 1.2.3.4 (...)" (he split em)
Router4 -> Router5 "3 IP packets  for 1.2.3.4 (...)"
Router3 -> Router2 "Routing change, line to Router 4 outage, find new route!"
Router5 -> Akamai mirror 
    "{external IP of Router2} sent you 'get / HTTP1.1; host: www.google.com'"
...
etc etc etc etc etc etc etc
(thousands of packets later)
PC .... { hmm, I still need 4 images and two CSS files, can't display page yet ... }
(hundreds of packets later)

I've omitted switch details, collisions, backoffs, throttling, re-transmits, spanning-tree, timeouts, NAT, three way-handshakes, concurrent persistent HTTP connections, and hundreds of other things that happen all the time. Filling in all the steps would take thousands of lines (if not tens or hundreds of thousands) like the above.

Answer 2

You are throwing many things together:

No matter if you are at home or at work, a packet travels between your computer and the server over switches and routers. Of course, at home those switches etc might not be located within your own walls.

A default gateway is just an information about which router to use if no other route is explicitly given.

A DNS server responds to an additional request to lookup the servers address, none of your other traffic flows through DNS.

A datacenter is just a place where servers and networking equipment live. So yes, factually you are going through datacenters but they could as well be set up in a tent in the deep forrest.

That's all for packets. A web request is built on top of pure networking. See the HTTP standard for that.

Answer 3

Try a traceroute from command prompt (although this is only 1 direction, so will hit the destination but not return). This isn't guaranteed to work or provide detail about each step, but it may give you an idea.

From command prompt (assuming Windows), type in

tracert 8.8.8.8 

8.8.8.8 is the Google DNS

More details about traceroute