[LINK] RFI: Dynamic IP-Addresses on Consumer Broadband

[Craig Sanders]

On Fri, Oct 19, 2007 at 04:09:25PM +0800, Roger Clarke wrote:
> Maybe someone can help with an oddity that's arisen with my MSc(ECOM) 
> candidates up here in Hong Kong.
>
> One of the slides in the session on IP distinguishes static and dynamic 
> IP-addresses.  I referred to dial-up as one extreme, major servers as the 
> other;  and consumer ADSL/cable as in-between, but increasingly static.

the form of connection doesn't determine whether an IP address is static
or dynamic. dialup and adsl and cable can be either static or dynamic
(in practice, they tend to be dynamically assigned for most residential
services and static for many business services. not always, though).

even fixed ethernet connections can be static (fixed/hard-coded config)
or dynamic (e.g. IP is picked from a pool by a bootp or DHCP server).

even DHCP doesn't always mean dynamic - it's easy enough to configure
DHCP to always give the same IP address to a particular MAC address
(aka ethernet hardware addr)....that's static allocation but with the
convenience/ease of DHCP for network configuration.



many ISPs in AU will allocate a static IP to adsl customers on request.
some for no extra cost, some for a once-off fee, some for an additional
monthly fee.


> (Since the bad old days of ADSL instability, mine lasts months at a
> time without either end falling over and having to be re-initialised
> with, pretty inevitably, a different IP-address from before).

unless you're 100% guaranteed to get the same IP address every time you
connect, it's still a dynamic IP.

static means that the IP address is assigned to a specific customer (or
computer)

dynamic means that the IP is allocated to customers or computers from a
pool of IP addresses - even if specific machines are highly likely (as
distinct from guaranteed) to get the same IP when they connect, e.g.
with a very long lease time in DHCP.


> Several candidates (these are mostly 26-40 year-olds, many with
> at least one postgrad qual, half in CS/IT) suggest that the main
> factor is to prevent people signing consumer contracts and running
> servers. (We went through that phase 3-4 years ago in Oz!).

it's not much of an obstable. most servers (except for mail servers
- which do run but the dynamic IP results in several undesirable
failure modes and opportunities for either mail bouncing or mail being
intercepted by the next person to get your IP) run fine with a dynamic
IP address and one of the dynamic DNS services.

if ISPs really want to block residential users from running servers,
they block the common ports (e.g. port 80 for web, port 25 for mail, and
so on).

craig

-- 
craig sanders <cas at taz.net.au>

"We owe it to ourselves as respectable human beings, as thinking human
 beings, to do what we can to make humanity more rational...Humanists
 recognize that it is only when people feel free to think for themselves,
 using reason as their guide, that they are best capable of developing
 values that succeed in satisfying human needs and serving human interests."
                         [Isaac Asimov]