[ubuntu-za] Problem with my understanding of archive.ubuntu.com

[Alf Stockton]

If, in my 12.04, I try sudo apt-get update I get:-
Connecting to 172.27.30.6 (172.27.30.6)
which fails with
Err http://archive.ubuntu.com precise-updates/main i386 Packages
   Unable to connect to 172.27.30.6:3128:
http://security.ubuntu.com precise-security/main Translation-en_GB
   Unable to connect to 172.27.30.6:3128:
etc, etc
but now if I ping archive.ubuntu.com
I get a whole bunch of
64 bytes from kraken.canonical.com (91.189.88.29): icmp_req=33 ttl=53 
time=211 ms
if on the other hand I ping security.ubuntu.com I get
64 bytes from cursa.canonical.com (91.189.92.181)
if I look in my /etc/apt/sources.list I see entries like
deb http://archive.ubuntu.com/ubuntu/ precise main restricted

Now please explain to me what I am misunderstanding and why 
archive.ubuntu.com when I try apt-get translates to 172.27.30.6 but when 
I do a ping it translates to 91.189.88.29 or 91.189.92.181

-- 
Regards,
Alf Stockton                 www.stockton.co.za