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I was trying the other day to do a traceroute on www.nasa.gov.

I tried doing this from a couple of different sites (found @ www.traceroute.org) and they all exhibit similar behaviour: when connecting to www.nasa.gov, instead of connecting to one of nasa.org's cannonical names, it tries to connect to another IP address, generally from the same country the traceroute site I'm using is from. Even worse, it seems that for each country there are a couple of different IPs associated with www.nasa.gov.

Example:

  traceroute to www.nasa.gov (203.106.85.57), 30 hops max, 40 byte packets
 1  gx-kmi-e1-a.mdn.nusa.net.id (202.162.192.254)  0.266 ms  0.265 ms  0.432 ms
 2  gw-kmi.mdn.nusa.net.id (202.162.199.238)  1.430 ms  1.433 ms  1.416 ms
 3  112.215.16.1 (112.215.16.1)  32.137 ms  32.143 ms  32.149 ms
 4  112.215.5.249 (112.215.5.249)  32.155 ms  33.083 ms  33.069 ms
 5  icore-sgp.ge-1-3-0.bb.xl.net.id (202.152.254.62)  130.189 ms 202.152.245.186 (202.152.245.186)  130.134 ms icore-sgp.ge-1-3-0.bb.xl.net.id (202.152.254.62)  130.178 ms
 6  tm.net.my (58.26.179.213)  65.494 ms  66.277 ms  66.039 ms
 7  203.106.85.57 (203.106.85.57)  64.707 ms  64.693 ms  65.792 ms  

where 203.106.85.57 is an IP from malasya.

At first I thought this could be related with mirrors, but I am not so sure now. Even for trace sites of small countries, it seems there are several IPs, and I have my doubts that a site such as www.nasa.gov generates that much traffic to need to be replicated on so many places, even for small countries.

What is the reason of this? Is my racionale wrong?

Thanks

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Here nasa.gov resolves to an Akamai mirror. –  Heandel Apr 28 '11 at 12:58
    
Here too. My question is what happens between my computer and www.nasa.gov such that Akamai gets in the way. Why when I'm doing a dig it shows up nasa's true canonical names and why when I'm tracing it gets to Akamai? –  devoured elysium Apr 28 '11 at 13:03
    
Akamai runs the DNS for these sites, and their code chooses a geographically appropriate mirror based on your location, latency, etc. –  Joe Apr 28 '11 at 13:21
    
nasa.gov resolves to Akamai because NASA uses Akamai DNS (nameservers), check NS records. –  osgx Apr 28 '11 at 13:54
    
If you're interested, you can do a ping/nslookup on 'whoami.akamai.com'. This will show you the IP of the name server that queried for that name - this is what akamai will use to figure out what cluster to serve you the content with. –  Aaron Aug 4 '11 at 16:01

1 Answer 1

up vote 14 down vote accepted

This is an effect of Content delivery network (CDN)

http://en.wikipedia.org/wiki/Content_delivery_network

Akamai is one of the biggest CDN.

Explain: CDN have a lot of servers around the world, which serves as caching reverse proxy (this is not a proxy for user; but a proxy just before to server, to lower number of request). To make access to site faster, CDN should connect each user with nearest server.

To select a nearest server, a special DNS server is used. When you want to connect some webserver, e.g. www.abc.com, your browser must find an IP address of server with DNS. Normally, DNS should return some fixed address for any client, but akamai and other CDN DNS will act differently.

They will return different server IPs based on IP of client (IP from which DNS request is sent). Such special DNS have a database of geolocation for any IP and database of akamai servers with needed content. DNS reply will redirect your browser to nearest server.

Another technique is Anycast - the IP of server is the same for any client; but IP packets will be routed differently to some set of servers (to any of some server group).

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Yes. But it doesn't quite explain what is happening at the low level. –  devoured elysium Apr 28 '11 at 13:12
    
I'll expand the answer –  osgx Apr 28 '11 at 13:46
    
In this presentation some aspects of DNS-based load-balancing are shown (slide Geographical DNS and below) nedworks.org/~mark/presentations/hd2006 –  osgx Apr 28 '11 at 14:02

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