Re: PPP for accessing an embedded device (routing problem)

"James Carlson" <james.d.carlson@xxxxxxx> a écrit dans le message de news:
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"Gingko" <nospam@xxxxxxxxxxxxxxxxxxxxxxxx> writes:

By default, PPP with IPCP provides just a point-to-point IP link. It
does *NOT* provide access to the Internet or any other such thing.
That's a matter of IP routing configuration.

Some PPP implementations have a feature that allows them to change
routing configuration. This has nothing to do with PPP itself; it's a
convenience feature. If yours does that and isn't configurable as you
need, then complain to the vendor of that software, or get a better
implementation.

I am wondering if there is any way to have it differently configured, by
asking the dialing computer to not set the default route, and instead
having
it to just set a host or a network route to the device's IP or to the
device
network, so the client machine would be able to access simultaneously the
embedded server machine and any Internet access that it had before
establishing the connection.

Sure. You'll need to mention what platform you're using and what
software.


Very simple.
The dialed server is made by myself (actually derived from Zilog's ZTP), and
the dialing clients should be any Internet enabled computer, but very likely
a vast majority of Windows XP, 2000, NT or 98 systems.

Even if it is not part of the PPP specifications, it looks like that almost
all common implementations use to build a default route to the dialed peer
after establishing the connection, and this is certainly necessary for this
very common use of PPP : creating an Internet connection through a telephone
line. I understand that this is not part of PPP, but it is certainly very
commonly associated to it.

I just expect having my users to use their common (if not standard)
installations for accessing my devices like if they have to connect to
Internet through (in most of the cases) a telephone line. These users will
be using the computer that they already own, and will not buy another one
(and should not have to install some particular extension) just for making
these specific connections. I expect them to use the resources they already
have.


So my question is basically : is there any way to configure the dialup
server for telling the dialing machine that he is NOT an ISP and that
only a
very small segment of the global network will be handled by the dialup
server ?

No. The server side does not control the client's routing table. The
client does that. (In fact, PPP is peer-to-peer, so there is no
"client" or "server.")


Ok ... But when establishing a PPP connection, there is at least one end
initiating the connection and the other receiving the request.
Thus I call them (maybe improperly) "client" for the first one, and "server"
for the second one.


But the client system _may_ opt to use suitable protocols over the PPP
link to set up the local routing (forwarding) tables as needed, and
those protocols can in fact gather the necessary information from the
other end of each link. One way to do this is to run DHCP over the
link. Another way is to run a routing protocol (such as RIP-2) to
receive the appropriate routes. Both of those mechanisms work on
links other than PPP -- this is another intentional design decision in
these protocols; they're intentionally layered so that the same
feature doesn't have to be redesigned each time a new link layer is
developed.


Ok ... Is it possible to do this on a basic Windows XP machine with no
specific extensions ?


Again, if the client system isn't behaving as you want, then you need
to complain to that software vendor. What you're talking about isn't
really related to PPP at all.


Do you really think that I could complain to Microsoft for having them
changing all of their already sold Windows PPP implementations in order to
met my very tiny needs ? :-) :-) :-)

By the way, the IPCP extensions (see RFC 1877) seem to have mostly been
added in order to allow the settings for the DNS servers needed on the
established links. I am wondering if this really had to be included in the
PPP specifications if PPP was only intended to establish a simple TCP/IP
link ....

Thank you anyway for having answered my message.

Gingko


.

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