[Gllug] ADSL2 router help / recomendation

[Mike Brodbelt]

t.clarke wrote:
> My understanding is that the Router DOES require an IP address on its
> 'external' interface.

If it's a *router*, its a layer 3 device, and requires an IP address. It
will in fact have an address for each routed interface it presents,
though of course the internal interface is likely to use an RFC 1918
address in a NAT configuration.

The external interface must be reachable by traffic coming to you. It's
theoretically possible for a further layer of NAT to happen at your ISP,
but of course any ISP that implements this sort of thing does so at the
cost of degrading your IP connectivity, as many protocols you might want
to use require a publicly accessible IP address (or specialist
handling). There will always be stuff that would need special handling
that won't get it, so any ISP that does not provide you with a routable
address on your external interface is one to avoid, in my book.

> Our ISP actually provides two IP addresses for the line  (which sort of
> alias to each other it seems).
> Offhand I think the router uses one of those addresses on its external
> interface and the Linux box uses the other address on its external interface
> (to the router).
> 
> Maybe some routers work differently ?

No, they don't. They do if you use a mix of layer 2 and layer 3
functionality, but for a plain router, you get one address (or more) per
interface.

Mike
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