Re: DSL and static IP addresses

"tom" <wolfemet@ameritech.net> wrote in message
news:2tVQa.21248$BM.6040115@newssrv26.news.prodigy .com...
> I was told by the telco that if we get a static
> ip address for the DSL line, we would need two.
> One for the modem and one for the switch.
>
Actually, there is no need (and no way) to attach
static IP to a switch. They are however right,
you need at least two usable static IP's untill
the modem has NAT capability (in which case 1 could be enough).
I haven't cleared the subject, have I? ;-) Ok, here is how it works:

ISP
|
modem
|
computer

now, both modem and the computer need to have public (static) IPs
since modem needs its IP to be able to receive traffic from the ISP,
while computer needs an IP from the same class to be able to talk
to the modem and send/receive information via it.
the computer may have a routing and NAT (network address translation)
or MASQUERADE capability in which case you can connect more
machines to it and have all of them acces the internet via the modem.
Some modems have the MASQUERADE functionality built
in, in which case you can connect a local network right to the modem.

hope this helps,
Marek




> I am confused. How does this work?
>
>

Marek Zachara wrote:

> Actually, there is no need (and no way) to attach
> static IP to a switch. They are however right,
> you need at least two usable static IP's untill
> the modem has NAT capability (in which case 1 could be enough).
> I haven't cleared the subject, have I? ;-) Ok, here is how it works:
>
> ISP
> |
> modem
> |
> computer
>
> now, both modem and the computer need to have public (static) IPs
> since modem needs its IP to be able to receive traffic from the ISP,
> while computer needs an IP from the same class to be able to talk
> to the modem and send/receive information via it.

The modem can be on a "private" address (RFC1918) and should be transparent
to the user. There's no reason why a static customer needs one more
address than dhcp.

--

Fundamentalism is fundamentally wrong.

To reply to this message, replace everything to the left of "@" with
james.knott.

>
> The modem can be on a "private" address (RFC1918) and should be
transparent
> to the user. There's no reason why a static customer needs one more
> address than dhcp.
>

Well, any DSL modem I have seen so far required an assigment of a public IP.
And the minimal subnet assigned was 4 IP subnet : 2 for network/broadcast,
1 for modem and the last one for single host or router. The solution
you have mentioned with transparent modem does not allow any
routing to be implemented.

Marek

> >
> > Well, any DSL modem I have seen so far required an assigment of a public
> > IP. And the minimal subnet assigned was 4 IP subnet : 2 for
> > network/broadcast, 1 for modem and the last one for single host or router.
> > The solution you have mentioned with transparent modem does not allow any
> > routing to be implemented.
>
> Someone seems to be missing something about how IP works. The method for
> assigning an IP address to a computer has nothing to do with routing. No
> matter if an address is static or dhcp, it behaves exactly the same way
> through routers etc. The 2 functions are entirely separate. The main
> difference, is that the dhcp client has to obtain an address from a server,
> instead of it being manually configured. Beyond that, there's no practical
> difference.
>
Someone seems to be reading something that was never written ...
I never said one can't use dhcp for that purpose. The way the IPs
are assigned (whether it is input by hand, dhcp or other) is irrelevant.
I was refering to the number of IPs needed for the task
which was the question in the initial post. Since dhcp has nothing to
do with that why bringing this issue again?

Marek

Marek Zachara wrote:

> Someone seems to be reading something that was never written ...
> I never said one can't use dhcp for that purpose. The way the IPs
> are assigned (whether it is input by hand, dhcp or other) is irrelevant.
> I was refering to the number of IPs needed for the task
> which was the question in the initial post. Since dhcp has nothing to
> do with that why bringing this issue again?
>

The OP was told he needed 2 addresses, if he wanted a static address. I
haven't seen anything to indicate a valid need for 2.

--

Fundamentalism is fundamentally wrong.

To reply to this message, replace everything to the left of "@" with
james.knott.