On Thu, 29 Mar 2001, Benjamin Scott wrote:
> On Thu, 29 Mar 2001, Tom Rauschenbach wrote:
> > I don't think it makes sense to talk about ppp over DHCP. What I want to
> > do is see the negoatiation between my ISP and my machine that assigns my
> > machine its IP address. Since this happens before interface ppp0 is up,
> > my packet sniffer can't see it. This may require either a kenel hack or
> > invasive hardware.
>
> Um, I think you have the wrong idea. A packet sniffer listens on the layer
> two network interface (e.g., your Ethernet driver). PPP does not really have
> such a thing; the "ppp?" interface springs into existence *after* the PPP link
> is setup, in order to give the IP layer something to work with. So there is
> nothing for a sniffer to sniff.
Right, when I started out on this I did have the wrong idea. IP packets are at
too high a level. The fact that the ppp? interface springs into existance AFTER
the link is set up is exactly the problem. Turning on the debug option of pppd
is by definition useless. If I have a pppd then it is too late. If I have an
IP address then it is too late. I want to watch the negotiation that occurs to
get the IP address.
My machine can have a different IP address everytime I dial into my ISP.
I want to watch the conversation that takes place between my machine and the ISP
before I have an IP address.
Once I have an IP address I can use tools I have to watch anything else.
>
> As I said before, what you want to do is turn on the "debug" option in pppd.
> To quote the man page, when pppd debugging is turned on, "pppd will log the
> contents of all control packets sent or received in a readable form".
>
> The only way to do for PPP what a packet sniffer does for Ethernet would be
> to intercept communications between pppd and the modem it is talking to. You
> could modify the kernel serial driver, setup a pseudo-tty capture, or -- if
> you have an external modem -- use an RS-232 serial debugger. Any of which
> would be overkill for what you're trying to do. :-)
No, sorry that's probably exactly what I have to do. I suspect that the
negotiation to determine things like line quality and baud rate take place in
an analog domain, two op-amps figuring out how to talk or something. Then, once
my ISP and I know how to trade bits, we talk about about things like IP
addresses and such. That's the part I'm curious about. Once I have an IP
address, I'm part of a network and I know how to watch the network. If I were
REALLY smart I'd be curious about the analog part too, but I know enough to
know that I can't do that kind of math. But there's a little bit of pre-IP
digital stuff that I'd like to watch.
I looked into the kernel source last night and I think I've found the
neighborhood of where I'd need to put my hacks, but it also looks to be timing
sensitive so I still may not get there from here.
>
> --
> Ben Scott <[EMAIL PROTECTED]>
> | The opinions expressed in this message are those of the author and do not |
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> | organization. All information is provided without warranty of any kind. |
>
>
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Tom Rauschenbach [EMAIL PROTECTED]
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