Connection Failure with D Router as the User When L2TP Is Enabled in Coordination with an LNS

Publication Date:  2012-07-27 Views:  81 Downloads:  0
Issue Description
The MA5200F adopts L2TP in coordination with an LNS. The VPDN is test normally on a PC, but the connection fails with the D router (The PPPoE dialing is available) as the user.
Alarm Information
1) The debugging information on the MA5200F (see the detailed process): * [0.60759870-] L2TP-8-02023000: L2TP::RcvStopCCN 2) The debugging information on the LNS (see the detailed process): *Mar 1 20:26:21.282: Vi1 VPDN: PPP LCP not accepting sent CONFACK
Handling Process
1) Because the test on the PC is normally, there should be no problem about the L2TP configuration between the MA5200 and the LNS, and the tunnel should be established normally. 2) Through the trace of debugging packets on the MA5200F, it is found that the sent information is rejected by the LNS. So it is necessary to find reasons on the LNS. * [0.60759870-] L2TP-8-02023000: L2TP::RcvStopCCN 3) The debugging information on the LNS indicates that the packets from the MA5200F are normally received by the LNS until ICCN packets, and the L2TP session is normally established. But the LNS rejects the LCP CONFACK packets, as shown in the following information: *Mar 1 20:26:21.114: Tnl/Cl 13380/29 L2TP: I ICCN from MA5200F tnl 24, cl 1 *Mar 1 20:26:21.114: Vi1 PPP: Phase is DOWN, Setup *Mar 1 20:26:21.278: %LINK-3-UPDOWN: Interface Virtual-Access1, changed state to up *Mar 1 20:26:21.278: Vi1 PPP: Using set call direction *Mar 1 20:26:21.278: Vi1 PPP: Treating connection as a callin *Mar 1 20:26:21.278: Vi1 PPP: Phase is ESTABLISHING, Passive Open *Mar 1 20:26:21.278: Vi1 PPP: No remote authentication for call-in *Mar 1 20:26:21.278: Vi1 LCP: State is Listen *Mar 1 20:26:21.282: Vi1 LCP: I FORCED CONFREQ len 14 *Mar 1 20:26:21.282: Vi1 LCP: MRU 1492 (0x010405D4) *Mar 1 20:26:21.282: Vi1 LCP: AuthProto PAP (0x0304C023) *Mar 1 20:26:21.282: Vi1 LCP: MagicNumber 0x0463AE06 (0x05060463AE06) *Mar 1 20:26:21.282: Vi1 LCP: I FORCED CONFACK len 10 *Mar 1 20:26:21.282: Vi1 LCP: MRU 1492 (0x010405D4) *Mar 1 20:26:21.282: Vi1 LCP: MagicNumber 0x9E670900 (0x05069E670900) *Mar 1 20:26:21.282: Vi1 VPDN: PPP LCP not accepting sent CONFACK 4) It can be seen that the LNS does not receive the LCP parameter (PAP or MRU) negotiated by the MA5200F and D router. The largest possibility is that the MRU value is too large. Solution: The LNS forces the LCP renegotiation. Modify the configuration at the client to the MRU non-negotiation or a smaller value. Configure the MTU under the VT on the MA5200 to a smaller value (1460 or so), and modify the MRU at the client to a smaller value. At last, the problem is solved by using solution a.
Root Cause
The LNS does not receive the LCP parameter (PAP or MRU) negotiated by the MA5200F and D router. The largest possibility is that the MRU value is too large.

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