Subject: NT RAS CCP oddity

From: Jonathan Goodchild <[email-masked]>
Date: Wed, 19 Jan 2000 16:25:27 -0000

I've recently been doing some testing with a PPP terminal (which happens to
be a mobile phone) connecting into Windows NT 4.0 RAS, and I've found
something rather odd that I thought I'd share with you all...

The connection proceeds as follows: LCP negotiation completes, then
Authentication occurs, and IPCP negotiation takes place (so far, so good).
During IPCP negotiation, RAS issues a CCP Configure Request, which the peer
attempts to Protocol Reject.

Now it so happens that the implementation of Protocol Rejects in the mobile
phone is broken: the format of the LCP Protocol Reject packet it transmits
is invalid (it doesn't contain the code for the rejected protocol, in this
case 0x80fd), so RAS quite properly ignores it, and eventually retransmits
the CCP Configure Request.  

In the meantime, IPCP negotiation completes, and the mobile attempts to
establish a TCP connection.  However, there is no response from RAS; the TCP
packet is retransmitted a couple of times, and then the mobile gives up.
(Before that happens, several more CCP Configure Requests are transmitted by
RAS, followed by invalid Protocol Rejects from the mobile.)

It appears that RAS is unable to deal with the incoming TCP packets until
the CCP negotiation completes.  If RAS is reconfigured to disable CCP (not a
straightforward change - you need to hack the RAS registry entry) then
everything works fine.

Now my interpretation is that it should be possible to transfer IP data as
soon as IPCP negotiation has completed, regardless of the state of CCP
negotiation.

Anyone have any views?
And does anyone know if Microsoft have fixed this problem in Windows 2000?

Jonathan Goodchild
Farsite Communications Ltd
email: [email-masked]
web: http://www.farsite.co.uk/

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From: Srinivasan Chakravarthy <[email-masked]>
Date: Wed, 19 Jan 2000 12:05:28 -0800

Win '98 uses CCP to negotiate MPPE as its option. In Win '98, only if you enable
the data encryption, it uses CCP. Having enabled the data encryption, if the CCP
negotiation fails (though the IPCP is UP), the windows station terminates the
connection which i feel is absolutely correct. So, the windows station behaves
correcly with the data encryption enabled.
Well, i dont know about how to configure CCP in the  Win NT RAS. But, even in
this case, if the data encryption is enabled, what NT does is correct.

Thanks & Regards,

Srinivasan.