Re: Terminal release ip command?

On 2007-04-18, Darrell Greenwood <darrell.usenet6@xxxxxxxxxxxxx> wrote:

In my case I have two dynamically assigned IP addresses from my ISP.

I can't get two *fixed* addresses without paying a lot more money, say
$50/more a month for a 'business' plan.

I can get a whole /48 of IPv6 address space allocated to me at no extra
charge by my ADSL supplier (who only charge me UKP 20 + VAT per month
for the connection). But that would be excessively geeky even for me
so I stick with the single static IPv4 address (for which I have full
control of the forward and reverse DNS entries).

I run without NAT, or firewall, everything works, and my configuration
is much easier. :-)

Apart from networking between the two machines right:-)

In a previous post you said that it is a problem when your two
DHCP addresses are on different netblocks so you need to keep
renewing a lease until they are on the same netblock.

So how are you routing between the two machines? Are you actually
sending packets out to your ISP's server room and waiting for
them to get back to you on the other line? That is OK at a pinch
but horribly laggy, low bandwidth, inefficient, insecure etc.
(analogus to two people sitting on a couch together and having
a conversation via cell phone instead of just talking directly).

The "standard" solution is to have a router make a connection and
pick up a single DHCP address from your ISP, then network your
two machines to the router via Ethernet with either static or
DHCP IP addresses on your own private network and NAT taking care
of talking to the Internet. That way they can talk to each other
direct. The configuration is easy and it works.

There is of course another possibility. Say for example you have
both machines independently connected to your ISP via dial-up
using their internal modems (you would need two phone lines).
Then you could *also* link the two machines directly via an Ethernet
cable (or perhaps even FireWire!), give them static IPs on any
bit of private IP space (eg 192.168.10.10 and 192.168.10.11)
and make sure they have sane routing tables (go via Ethernet
to get to 192.168.10.0 network, via modem to get anywhere else).
That way you would get fast networking between the machines which
works reliably regardless of whether your two ISP assigned
addresses are on the same netblock. This is not a common thing
to do but it should be relatively straightforward.

And just to return to the OP's original question, there is nothing
you can do to force your ISP's DHCP server to give you a new IP
address. It will give you whichever one it feels like and it will
normally be the same one you just had. Depending on whether you
are on dial-up, ADSL, cable, satellite etc there may be certain
things you can do to trick it into thinking you are someone else,
and then it *might* give you a different IP, but it might also
prevent you from connecting at all.

The general assumption is that, all other things being equal,
customers would prefer to have a static IP. There are two main
reasons why ISPs either don't provide them or charge more for them.
One is to conserve valuable IPv4 address space, particularly in
the case of free dial-up accounts where an ISP may create far more
accounts than they have IP addresses on the assumption that only a
fraction of accounts will be active at any one time. Clearly
then it is not possible to give static addresses but an account
will generally keep the same IP until such time as the lease is
given up and it gets allocated to another account. The second reason
is to discourage the running of public servers, but that does not
require the ISP to change IPs more frequently than is neccessary
to prevent people from assuming that they will never change.

So now you know.

Ian

PS to anyone who might be subject to an IP ban

Whilst changing IP address might evade a ban, your new IP could
be linked to your banned one through your ISP's logs so it is of
limited usefulness. You should contact whoever has banned you,
offer profuse apologies for your sins, promise not to be a naughty
boy again, and humbly ask to be unbanned. Either that or set up
TOR/privoxy before revisiting the site:-)

--
Ian Gregory
http://www.zenatode.org.uk/ian/
.

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