RE: [kNT] akamai

["Nick Bryant" <nick@xxxxxxxxxxxxx>]

> 
> Ok Nick,
> 
> you put some order in my mind but I still have some questions...


Thought you might ;)

> 
> >The root servers take the IP address of the
> >person that is trying to get to the content.
> 
> 1) How can the root servers know the client's IP address? I thought
that
> they knew the client's DNS server address (I read on an IETF draft
that
> one
> limit of the DNS RRS is the lack of knowledgement of the client
> position...)
> 

Yes you're right. It's not the client but client's DNS server. Some
might consider this a flaw of a DNS based system but others will argue
the DNS *should* be close to the user (usually in the same AS anyhow).

> 2) When I type on my browser "www.about.com", where do I get the
static
> page, from the origin server or from a surrogate (after the resolution
> process, obviously)?
> 

Static page comes off a normal static web server in most cases. However
after just looking at it about.com use the *special* Akamai service
where they actually host the whole site. The address for www.about.com
will change depending on where you look at it from.

For example from a level3 looking glass in san jose I get the address
208.185.127.40 but from one of my server hosted in the UK I get
209.143.212.20.

> 3) Why when I look the html code in www.about.com I see the same
> reference:
> "http://a1028.g.akamai.net/6/.../lego_wht.gif";?
> Is it a coincidence that we are served from the same server-farm or is
> this
> a "static" html code, identical for all people worldwide at a some
> instant?

Its static code - makes for an easier deployment. The a1028 is merely a
reference for Akamai to tell who the request is for and to make sure it
gets to the right servers. The actual IP address its self will obviously
change depending on where you look at it from.


> 
> >n0g.akamai.net.         30M IN A        62.41.114.7
> >n1g.akamai.net.         45M IN A        62.41.114.8
> >n6g.akamai.net.         30M IN A        198.31.3.20
> >n2g.akamai.net.         1H IN A         62.41.114.10
> >...
> 
> 4) What do 30M, 45M, 1H mean?
> 

They are the TTL (time to live) on the dns info. You will find top level
boxes (Akamai.net) have long lives as they wont change. The next level
down (g.akamai.net) seems to have between 30 - 60 mins. The actual host
records (a122 etc) have TTL's of 20 seconds.

This setup makes sense. If a box were to fall over then the max time you
would wait to get to content is 20 seconds. If there was a major
topology change you might have to wait upto an hour for the cached
record to expire.

Obviously, the *best* setup would be all having TTLs of 0. But this
would cause massive load on the DNS servers.

> Sorry for my "question-bombing" I thank you again...

No worries...

Nick