PPTP mtu

[Jay Hall]

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