PPTP MTU

[Jay Hall]

OK, I think I have an MTU negotiation problem.  The server side sets an 
MTU of 1458 and the client side sets an MTU of 1456.  Occassionally, the 
MTUs on the client and the server will be the same and then the 
connection comes up and runs like a champ as long as the MTU is 1456. 
Any other values, even if they are the same on the client and server end 
result in a connection that comes up and then drops.

Both the client and the server contain the line

set link mtu 1460

In order to use the PPTP connection, I connect to the Internet using a 
DSL connection.  I have tried using both MPD and ppp to establish the 
Internet connection.  And, while the Internet connection is always 
successful, the pptp connection is not.

I am using an Intel 10/100/1000 NIC in the server on the client end.  I 
am using a Westell 2100 DSL modem, in bridge mode, to establish the DSL 
connection.

Is it possible that this is a hardware issue?

Thanks for your help.


Jay

Date: Sat, 27 Mar 2004 08:08:34 -0600
From: Jay Hall <jhall at vandaliamo.net>
Subject: PPTP mtu
To: freebsd-net at freebsd.org
Message-ID: <40658AE2.2080506 at vandaliamo.net>
Content-Type: text/plain; charset=us-ascii; format=flowed

I am using mpd to establish a DSL connection and, once that connection
is established, I am brining up a PPTP connection.  However, I am having
problems keeping the PPTP connection up.



In the logs on the remote machine, I am seeing the following error message:

Mar 27 00:22:52 ST_CHARLES mpd: [vpn] CCP: rec'd Configure Nak #1 link 0
(Req-Sent)
Mar 27 00:22:52 ST_CHARLES mpd:  MPPC
Mar 27 00:22:52 ST_CHARLES mpd:    0x01000040: MPPE, 128 bit, stateless
Mar 27 00:22:52 ST_CHARLES mpd: [vpn] CCP: SendConfigReq #2
Mar 27 00:22:52 ST_CHARLES mpd:  MPPC
Mar 27 00:22:52 ST_CHARLES mpd:    0x01000040: MPPE, 128 bit, stateless
Mar 27 00:22:52 ST_CHARLES mpd: [vpn] error writing len 14 frame to
bypass: No route to host
Mar 27 00:22:54 ST_CHARLES mpd: [vpn] CCP: rec'd Configure Request #56
link 0 (Req-Sent)
Mar 27 00:22:54 ST_CHARLES mpd:  MPPC
Mar 27 00:22:54 ST_CHARLES mpd:    0x01000060: MPPE, 40 bit, 128 bit,
stateless
Mar 27 00:22:54 ST_CHARLES mpd: [vpn] CCP: SendConfigNak #56
Mar 27 00:22:54 ST_CHARLES mpd:  MPPC
Mar 27 00:22:54 ST_CHARLES mpd:    0x01000040: MPPE, 128 bit, stateless
Mar 27 00:22:54 ST_CHARLES mpd: [vpn] error writing len 14 frame to
bypass: No route to host
Mar 27 00:22:54 ST_CHARLES mpd: [vpn] CCP: SendConfigReq #3
Mar 27 00:22:54 ST_CHARLES mpd:  MPPC
Mar 27 00:22:54 ST_CHARLES mpd:    0x01000040: MPPE, 128 bit, stateless
Mar 27 00:22:54 ST_CHARLES mpd: [vpn] error writing len 14 frame to
bypass: No route to host
Mar 27 00:22:56 ST_CHARLES mpd: [vpn] CCP: rec'd Configure Request #57
link 0 (Req-Sent)
Mar 27 00:22:56 ST_CHARLES mpd:  MPPC
Mar 27 00:22:56 ST_CHARLES mpd:    0x01000060: MPPE, 40 bit, 128 bit,
stateless
Mar 27 00:22:56 ST_CHARLES mpd: [vpn] CCP: SendConfigNak #57
Mar 27 00:22:56 ST_CHARLES mpd:  MPPC
Mar 27 00:22:56 ST_CHARLES mpd:    0x01000040: MPPE, 128 bit, stateless
Mar 27 00:22:56 ST_CHARLES mpd: [vpn] error writing len 14 frame to
bypass: No route to host
Mar 27 00:22:56 ST_CHARLES mpd: [vpn] CCP: SendConfigReq #4
Mar 27 00:22:56 ST_CHARLES mpd:  MPPC
Mar 27 00:22:56 ST_CHARLES mpd:    0x01000040: MPPE, 128 bit, stateless
Mar 27 00:22:58 ST_CHARLES mpd: [vpn] CCP: rec'd Configure Request #58
link 0 (Req-Sent)
Mar 27 00:22:58 ST_CHARLES mpd:  MPPC
Mar 27 00:22:58 ST_CHARLES mpd:    0x01000060: MPPE, 40 bit, 128 bit,
stateless
Mar 27 00:22:58 ST_CHARLES mpd: [vpn] CCP: SendConfigNak #58
Mar 27 00:22:58 ST_CHARLES mpd:  MPPC
Mar 27 00:22:58 ST_CHARLES mpd:    0x01000040: MPPE, 128 bit, stateless
Mar 27 00:22:58 ST_CHARLES mpd: [vpn] CCP: SendConfigReq #5
Mar 27 00:22:58 ST_CHARLES mpd:  MPPC
Mar 27 00:22:58 ST_CHARLES mpd:    0x01000040: MPPE, 128 bit, stateless
Mar 27 00:23:00 ST_CHARLES mpd: [vpn] CCP: rec'd Configure Request #59
link 0 (Req-Sent)
Mar 27 00:23:00 ST_CHARLES mpd:  MPPC
Mar 27 00:23:00 ST_CHARLES mpd:    0x01000060: MPPE, 40 bit, 128 bit,
stateless
Mar 27 00:23:00 ST_CHARLES mpd: [vpn] CCP: SendConfigNak #59
Mar 27 00:23:00 ST_CHARLES mpd:  MPPC
Mar 27 00:23:00 ST_CHARLES mpd:    0x01000040: MPPE, 128 bit, stateless
Mar 27 00:23:00 ST_CHARLES mpd: [vpn] CCP: SendConfigReq #6
Mar 27 00:23:00 ST_CHARLES mpd:  MPPC
Mar 27 00:23:00 ST_CHARLES mpd:    0x01000040: MPPE, 128 bit, stateless
Mar 27 00:23:02 ST_CHARLES mpd: [vpn] CCP: rec'd Configure Request #60
link 0 (Req-Sent)
Mar 27 00:23:02 ST_CHARLES mpd:  MPPC
Mar 27 00:23:02 ST_CHARLES mpd:    0x01000060: MPPE, 40 bit, 128 bit,
stateless
Mar 27 00:23:02 ST_CHARLES mpd: [vpn] CCP: SendConfigNak #60
Mar 27 00:23:02 ST_CHARLES mpd:  MPPC
Mar 27 00:23:02 ST_CHARLES mpd:    0x01000040: MPPE, 128 bit, stateless
Mar 27 00:23:02 ST_CHARLES mpd: [vpn] CCP: SendConfigReq #7
Mar 27 00:23:02 ST_CHARLES mpd:  MPPC
Mar 27 00:23:02 ST_CHARLES mpd:    0x01000040: MPPE, 128 bit, stateless
Mar 27 00:23:04 ST_CHARLES mpd: [vpn] CCP: rec'd Configure Request #61
link 0 (Req-Sent)
Mar 27 00:23:04 ST_CHARLES mpd:  MPPC
Mar 27 00:23:04 ST_CHARLES mpd:    0x01000060: MPPE, 40 bit, 128 bit,
stateless
Mar 27 00:23:04 ST_CHARLES mpd: [vpn] CCP: SendConfigNak #61
Mar 27 00:23:04 ST_CHARLES mpd:  MPPC
Mar 27 00:23:04 ST_CHARLES mpd:    0x01000040: MPPE, 128 bit, stateless
Mar 27 00:23:04 ST_CHARLES mpd: [vpn] CCP: SendConfigReq #8
Mar 27 00:23:04 ST_CHARLES mpd:  MPPC
Mar 27 00:23:04 ST_CHARLES mpd:    0x01000040: MPPE, 128 bit, stateless
Mar 27 00:23:06 ST_CHARLES mpd: [vpn] CCP: SendConfigReq #9
Mar 27 00:23:06 ST_CHARLES mpd:  MPPC
Mar 27 00:23:06 ST_CHARLES mpd:    0x01000040: MPPE, 128 bit, stateless
Mar 27 00:23:08 ST_CHARLES mpd: [vpn] CCP: rec'd Configure Request #63
link 0 (Req-Sent)
Mar 27 00:23:08 ST_CHARLES mpd:  MPPC
Mar 27 00:23:08 ST_CHARLES mpd:    0x01000060: MPPE, 40 bit, 128 bit,
stateless
Mar 27 00:23:08 ST_CHARLES mpd: [vpn] CCP: not converging
Mar 27 00:23:08 ST_CHARLES mpd: [vpn] CCP: parameter negotiation failed
Mar 27 00:23:08 ST_CHARLES mpd: [vpn] CCP: Close event
Mar 27 00:23:08 ST_CHARLES mpd: [vpn] CCP: state change Req-Sent -->
Closing
Mar 27 00:23:08 ST_CHARLES mpd: [vpn] CCP: SendTerminateReq #10
Mar 27 00:23:08 ST_CHARLES mpd: [vpn] CCP: encryption required, but MPPE
was not negotiated in both directions
Mar 27 00:23:08 ST_CHARLES mpd: [vpn] CCP: failed to negotiate required
encryption
Mar 27 00:23:08 ST_CHARLES mpd: [vpn] CCP: Close event
Mar 27 00:23:08 ST_CHARLES mpd: [vpn] CCP: state change Closing --> Closed
Mar 27 00:23:08 ST_CHARLES mpd: [vpn] CCP: LayerFinish
Mar 27 00:23:08 ST_CHARLES mpd: [vpn] IPCP: failed to negotiate required
encryption
Mar 27 00:23:08 ST_CHARLES mpd: [vpn] IPCP: LayerFinish
Mar 27 00:23:08 ST_CHARLES mpd: [vpn] IPCP: LayerStart


On the server I am seeing the following messages:

[pptp1] CCP:  parameter negotiation failed

I think this might be an MTU problem.  When the MTU is negotiated at
1456, the connection runs fine.  However, at values higher or lower, the
connection does not work, and will drop after a few seconds.

I am using mpd-3.15 on both ends of the connection.

Any suggestions would be greatly appreciated.  Thank in advance for your
assistance.


Jay