RE: PPTP MTU

From: Jay Hall (jhall_at_vandaliamo.net)
Date: 03/29/04

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    Date: Sun, 28 Mar 2004 21:21:10 -0600
To: freebsd-net@freebsd.org

    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@vandaliamo.net>
    Subject: PPTP mtu
    To: freebsd-net@freebsd.org
    Message-ID: <40658AE2.2080506@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
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